29.4D: Modern Reptiles
- Differentiate among the types of modern reptiles
Modern Reptiles
Class Reptilia includes many diverse species that are classified into four living clades. These are the 25 species of Crocodilia, 2 species of Sphenodontia, approximately 9,200 Squamata species, and the Testudines, with about 325 species. A reptile is any amniote (a tetrapod whose egg has an additional membrane, originally to allow them to lay eggs on land) that is neither a mammal nor a bird. Unlike mammals, birds, and certain extinct reptiles, living reptiles have scales or scutes (rather than fur or feathers) and are cold-blooded. Modern reptiles inhabit every continent with the exception of Antarctica.
Crocodilia
Crocodilia (“small lizard”) arose with a distinct lineage by the middle Triassic; extant species include alligators, crocodiles, and caimans. Crocodilians are large, solidly built lizard-like reptiles with long flattened snouts and laterally-compressed tails, and eyes, ears, and nostrils at the top of the head. Their skin is thick and covered in non-overlapping scales. They have conical, peg-like teeth and a powerful bite. As with birds, they have a four-chambered heart and a unidirectional system of air flow around the lungs; however, in contrast to birds, they are ectotherms, as are all other reptiles. Crocodilians live throughout the tropics and subtropics of Africa, South America, Southern Florida, Asia, and Australia. They are found in freshwater, saltwater, and brackish habitats, such as rivers and lakes; they spend most of their time in water. Some species are able to move on land due to their semi-erect posture.
Sphenodontia
Sphenodontia (“wedge tooth”) arose in the Mesozoic era and includes only one living genus, Tuatara, which comprises two species that are found in New Zealand. Tuataras measure up to 80 centimeters and weigh about 1 kilogram. Although quite lizard-like in gross appearance, several unique features of the skull and jaws clearly define them and distinguish the group from the squamates. Their dentition, in which two rows of teeth in the upper jaw overlap one row on the lower jaw, is unique among living species. They are also unusual in having a pronounced photoreceptive eye, dubbed the “third eye”, whose current function is a subject of ongoing research, but is thought to be involved in setting circadian and seasonal cycles.
Squamata
Squamata (“scaly”) arose in the late Permian; extant species include lizards and snakes. They are most closely-related to tuataras; both groups evolved from a lepidosaurian ancestor. Squamata is the largest extant clade of reptiles. Most lizards differ from snakes by having four limbs, although these have been variously lost or significantly reduced in at least 60 lineages. Snakes lack eyelids and external ears, which are present in lizards. Lizard species range in size from chameleons and geckos, which are a few centimeters in length, to the Komodo dragon, which is about 3 meters in length. Most lizards are carnivorous, but some large species, such as iguanas, are herbivores.
Snakes are thought to have descended from either burrowing lizards or aquatic lizards over 100 million years ago. Snakes comprise about 3,000 species and range in size from 10 centimeter-long thread snakes to 10 meter-long pythons and anacondas. All snakes are carnivorous, eating small animals, birds, eggs, fish, and insects. Although variations exist, most snakes have a skull that is very flexible, involving eight rotational joints. They also differ from other squamates by having mandibles (lower jaws) without either bony or ligamentous attachment anteriorly. Having this connection via skin and muscle allows for great expansion of the gape and independent motion of the two sides; both advantages in swallowing big items.
Testudines
Turtles are members of the clade Testudines (“having a shell”). Turtles are characterized by a bony or cartilaginous shell. The shell consists of the ventral surface called the plastron and the dorsal surface called the carapace, which develops from the ribs. The plastron is made of scutes or plates; the scutes can be used to differentiate species of turtles. The two clades of turtles are most easily recognized by how they retract their necks. The dominant group, which includes all North American species, retracts its neck in a vertical S-curve. Turtles in the less speciose clade retract the neck with a horizontal curve.
Turtles arose approximately 200 million years ago, predating crocodiles, lizards, and snakes. Similar to other reptiles, turtles are ectotherms. They lay eggs on land, although many species live in or near water. None exhibit parental care. Turtles range in size from the speckled padloper tortoise at 8 centimeters (3.1 inches) to the leatherback sea turtle at 200 centimeters (over 6 feet). The term “turtle” is sometimes used to describe only those species of Testudines that live in the sea, with the terms “tortoise” and “terrapin” used to refer to species that live on land and in fresh water, respectively.
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Key Points
- Reptile are amniotes that lay their eggs on land; they have scales or scutes and are ectothermic.
- Crocodilia includes the alligators, crocodiles, and caimans; they are mostly aquatic species, but some are able to move on land because of their semi-erect posture.
- Tuataras are classified as the only group under Sphenodontia; they may be lizard-like, but skull and jaw differences set them apart from true lizards.
- Squamata, the largest group of reptiles, includes the lizards and snakes.
- Snakes, which lack the eyelids and external ears present in lizards, are believed to have evolved from burrowing or aquatic lizards.
- Turtles are grouped under the Testudines; species in this group all have bony or cartilaginous shells.
Key Terms
- scute : a horny, chitinous, or bony external plate or scale, as on the shell of a turtle or the skin of crocodiles
- plastron : the nearly flat part of the shell structure of a tortoise or other animal, similar in composition to the carapace
- amniote : a group of vertebrates having an amnion during the development of the embryo; mammals, birds, and reptiles


8.3: Educational Environment, Access, and Quality
By the end of this section, you should be able to:
- Describe the association between health indicators and educational level.
- Explain the implications of poverty, disabilities, and discrimination on learning and access to quality education.
- Discuss the intersection between the social determinants of health and health literacy.
The evidence is clear: individuals with higher levels of educational attainment are more likely to live longer and healthier lives (ODPHP, 2020c). Higher levels of educational attainment refer to the education a person completes after receiving a high school diploma, such as earning an associate or baccalaureate degree. Education is one of the most important modifiable SDOH, as higher education is associated with increased healthy lifestyle behaviors and improved health outcomes. Those with higher educational attainment have greater economic resources and better access to health care (RHIhub, 2020a).
In contrast, a person is said to have low educational attainment if they have not completed high school. This is associated with economic insecurity and can result in overall worse health outcomes. The cycle of poverty and economic insecurity affects both educational access and the quality of education. Individuals in impoverished neighborhoods often have less access to community resources and wield less effective political influence, rendering them less able to demand higher-quality schools. Lower-quality schools lack the resources to support students, resulting in significant educational opportunity gaps based on neighborhood and school district. For example, children from low-income families are more likely to struggle with math and reading. They are less likely to graduate from high school and go to college than children from higher-income families (ODPHP, 2020c). Academically gifted children attending public schools in low-income areas are also less likely to have access to gifted and talented programs if their schools do not offer these resources or if their families cannot afford to access them elsewhere (Yaluma & Tyner, 2021). The stress of living in poverty can adversely affect a child’s brain development, making it harder for them to do well in school (ODPHP, 2020c). This can have a domino effect, as a college education is associated with safer and higher-paying jobs; individuals who do not graduate from high school or go to college are more likely to have chronic health problems (ODPHP, 2020c).
The educational roots of health inequities result from institutional and systemic biases in policies that separate individuals into either resource-rich or resource-poor neighborhoods, as these neighborhoods dictate school access. This separation into resource-rich or resource-poor neighborhoods is principally based on socioeconomic position and race, resulting in wide health disparities in life expectancy and health outcomes, as education is a major factor in shaping the course of an individual’s life.
(See Weinstein et al., 2017.)
Early Childhood Development and Education
A child’s first 5 years of life are critical for cognitive, emotional, and physical growth and development. A healthy, safe, and stable early childhood helps determine if a child will have a healthy, happy life. A variety of social, environmental, and economic factors greatly affect early childhood development. Risk factors for potential developmental delays and future poor health outcomes include early life stressors, low income, and lack of access to quality early educational programs. In contrast, protective factors include higher socioeconomic status (SES), stable relationships with caregivers, and access to quality early education programs (ODPHP, 2020m).
As mentioned previously, early life stressors and ACEs impact a child’s health. Early life stressors such as physical abuse, family instability, poverty, and unsafe environments contribute to developmental delays and poor health outcomes later in life. These children may lack adequate coping skills and have difficulty regulating their emotions and behaviors, thereby struggling in early childhood education programs (ODPHP, 2020m). Inadequate social functioning skills like lack of impulse control, difficulty forming relationships, and trouble regulating behaviors can negatively impact a child’s ability to learn or connect with peers in early elementary school programs.
Poverty, by itself, negatively impacts children’s academic achievement. Research has demonstrated that children from disadvantaged backgrounds are more likely than other children to repeat grades and drop out of high school (ODPHP, 2020m). Children from communities with higher SES and more resources have been shown to experience safer and more supportive environments and better early education programs. Quality early childhood programs help foster the mental and physical development of children. They are linked to increased earning potential and higher educational attainment (ODPHP, 2020m).
Early childhood education programs can help reduce educational gaps. Head Start is a federally funded early childhood program that supports children from low-income families. It provides comprehensive services and strives to improve health, increase learning and social skills, and prepare young children for kindergarten. Studies have demonstrated that children who experience quality early education programs like Head Start that are comprehensive and include health care and nutritional components partake in less risky health behaviors such as binge drinking alcohol, smoking cigarettes, and using illegal substances and have lower risks for heart disease, obesity, hypertension, hyperglycemia, and hypercholesterolemia (ODPHP, 2020m). Quality comprehensive early childhood development and education programs reduce risky heath behaviors and prevent or delay the onset of chronic disease in adulthood.
The quality of education in elementary schools is an important determinant in the health and well-being of children. Receiving a high-quality elementary school education reduces educational disparities in children. Children attending a school with safety concerns, limited health resources, and low teacher support are more likely to experience adverse physical and mental health. Until disparities in access to quality early childhood development programs and quality school systems are addressed, children without access will suffer worse health outcomes (ODPHP, 2020m).
In this University of Minnesota Center for Early Education and Development video, Dr. Megan Gunnar discusses the impact of early childhood development on the future abilities and health outcomes of children.
Watch the video, and then respond to the following questions.
- How does early childhood development affect learning later in life?
- List five ways families and communities can help build a strong and proper brain foundation in early childhood.
- How does a strong brain foundation impact health outcomes?
High School Graduation
Most jobs require at least a high school (secondary) education. Individuals who do not complete high school have limited employment opportunities, earn lower wages, and are more likely to live in poverty. Disparities in high school completion rates exist by racial and ethnic groups with Black and American Indian/Alaska Native students having the lowest graduation rates (ODPHP, 2020o). Students’ home and school environments impact their chances of graduating from high school. High school graduation can be affected by family support, the school district, resources within the school, and the greater community.
Lack of parental involvement in school is linked to lower graduation rates. Teacher quality is also a critical factor; students who believe their teachers are of high quality and that they care are more likely to graduate, whereas students who feel their teachers are uninterested in teaching are more likely to drop out (ODPHP, 2020o). Violence and safety concerns also affect high school dropout rates. Low-income families often live in neighborhoods where schools lack resources and underperform. These factors contribute to higher dropout rates and lower academic achievement. In 2016, low-income families were almost four times more likely than high-income families to have a student not complete high school (ODPHP, 2020o). Economically insecure BIPOC communities are disproportionately represented with lower educational attainment in comparison to economically insecure White individuals. Approximately 85 percent of economically insecure White adults have at least a high school diploma, whereas only about 50 percent of economically insecure adults who identify as Latina/Latino have attained their diploma (Langston, 2018).
Reading skill level in third grade is linked to high school completion rates. One Annie E. Casey Foundation study found that almost a quarter of students with below-basic reading skill level in the third grade failed to finish high school compared with 4 percent of students with third-grade proficient reading skills who failed to finish high school (ODPHP, 2020o). Twenty-six percent of students who were not reading at the proficient level in third grade and who had lived in poverty for at least one year during their school years did not finish high school on time or at all (ODPHP, 2020o). Teen pregnancy and parenthood are also risk factors for dropping out of high school, as only half of teens who have given birth earn a high school diploma.
Many positive outcomes come with graduating from high school. Individuals with a high school diploma have a decreased risk of premature death, more employment opportunities, and a higher lifetime earning potential (ODPHP, 2020o). Lacking a high school diploma is associated with self-reported overall poor health and chronic health issues such as asthma, diabetes, heart disease, hypertension, and hepatitis. Additionally, individuals with a high school diploma who are employed full-time earn almost 25 percent more than those who are employed full-time without a high school diploma (ODPHP, 2020o). Supporting individuals to graduate high school is an important public health intervention.
Enrollment in Higher Education
Higher education refers to any education after high school, including community colleges, vocational and technical schools, colleges, and universities. Many higher-paying jobs require a college degree; less than one in five economically insecure individuals have a college degree, whereas half of economically secure individuals do (Langston, 2018). College graduates have more employment options than individuals without college degrees. On average, lifetime earnings for individuals with a bachelor’s degree are double those of individuals without a degree (ODPHP, 2020n). Higher education is associated with better-paying, less hazardous jobs. This all supports an individual’s health, as the higher their income, the greater their ability to secure material and social resources like higher-quality housing and social status (ODPHP, 2020n). Overall, higher education is associated with improved health and a decreased risk of premature death. Individuals with more education are more likely to partake in healthy behaviors, such as drinking less alcohol, exercising regularly, and seeking preventive health care when needed (ODPHP, 2020n).
How well an individual’s middle and high schools prepare them for college greatly influences their likelihood of graduating. Students who attend high schools that do not provide honors or advanced courses may be less academically prepared for college-level work than students who attend high schools that provide these courses (ODPHP, 2020n). Students without access to a consistent guidance counselor may not receive help navigating the college application and admissions process. In many low-income neighborhoods, schools lack the financial resources necessary to offer these courses and dedicated guidance counselors, potentially lowering college admissions rates for their students (ODPHP, 2020n).
While the diversity of undergraduate college students is increasing, BIPOC individuals still demonstrate lower levels of academic persistence in college compared to their White counterparts (ODPHP, 2020n). Black and Hispanic individuals also have lower college enrollment and graduation rates. These lower enrollment and graduation rates may be affected by the discrimination, social isolation, and stress of debt accumulation that these students face (ODPHP, 2020n). BIPOC students experience discrimination at rates two to four times higher than White students, and in a study up to a quarter of these students reported feeling that the discrimination they experienced adversely affected their academic outcomes (Stevens et al., 2018). Barriers to higher education exist, but strengthening the curriculum in school districts in lower-income communities and offering more teacher and guidance counselor support can help to better prepare students for the admissions process and the rigors of college (ODPHP, 2020n).
The Role of the Nurse in Addressing Educational Disparities
Community and public health nurses play an important role in early childhood, primary, and secondary education. Partnering with school nurses and administrators, community and public health nurses can use their assessment data as a foundation to influence policy development at the local level. By analyzing trends in the data and presenting this information to the local school committee and city officials, nurses can advocate for meaningful change, such as creating or expanding Head Start programs to ensure equal access to evidence-based successful early childhood education programs. Community and public health nurses can also advocate for increased funding for school districts to create high-quality primary education. Community and public health nurses can advocate for and support transition programs to support students moving from middle to high school. Additionally, nurses can advocate for advanced courses and other programs that better prepare students for the future. These types of programs can encourage students to continue with their studies.
In this video, Harvard University’s Director of the Achievement Gap Initiative, Ronald Ferguson, discusses educational inequality and encouraging efforts that are being made in Boston to address these gaps. This is an example of a community-level approach to addressing educational inequalities that a community and population health nurse can spearhead and lead.
Watch the video, and then respond to the following questions.
- Why do you think educational gaps exist?
- How do you think the Boston Basics program can help address these educational gaps?
- What is the community health nurse’s role in addressing and responding to these educational gaps?
Language and Literacy
Literacy refers to listening and speaking skills, reading and writing skills, and cultural and conceptual knowledge. Health literacy refers to an individual’s ability to find, understand, and use health-related information (ODPHP, 2020t). Low literacy skills are linked with lower educational attainment, poorer health outcomes, and chronic diseases like diabetes and cancer (ODPHP, 2020l).
Limited English proficiency (LEP) can be a barrier to accessing health care services. Individuals with limited English proficiency tend to be immigrant s to the United States who may speak another language at home. In 2019, almost 22 percent of the U.S. population ages five and above spoke a language other than English at home, and among these individuals, 39 percent reported speaking English less than very well (ODPHP, 2020l). Individuals who identify as having limited English proficiency are less likely to have a primary care provider and, therefore, less likely to have preventive health care (ODPHP, 2020l). These individuals also encounter difficulty following medication instructions and communicating with health care providers.
Many barriers impede individuals with limited English proficiency from receiving appropriate health services. A lack of trained interpreters and culturally responsive health care providers adversely affects their health. Cultural barriers, language barriers, and financial difficulties create significant obstacles for immigrants trying to access health information (ODPHP, 2020l). Language barriers create a quality-of-care issue, especially if the provider is not linguistically competent, and a lack of quality trained interpreters impedes access to mental health services for individuals with limited English proficiency (ODPHP, 2020l). See Culturally and Linguistically Responsive Nursing Care for more information on this topic.
Read the scenario, and then respond to the questions that follow.
Serena and her children attend the local community center’s biannual fair. Twice a year, the community center hosts this one-day event for the community’s residents, where they have food, games, health screenings, health promotion education events, yoga, senior center representatives, and sign-up sheets for various community groups. Serena decides to have her blood pressure (BP) taken at the screening tent. Her BP reading is 162/92. The nurse takes it manually and repeats it two times, but the readings are similar. The nurse asks Serena about any medical history of daily medications, but Serena shakes her head no. She feels lucky to be healthy overall and does not take any medications except for ibuprofen for headaches occasionally.
- What factors could be contributing to Serena’s elevated blood pressure?
- What lifestyle questions could the nurse ask Serena to develop a health teaching plan for her?


5: Electric Charges and Fields
In this chapter, we begin the study of the electric force, which acts on all objects with a property called charge. The electric force is much stronger than gravity (in most systems where both appear), but it can be a force of attraction or a force of repulsion, which leads to very different effects on objects. The electric force helps keep atoms together, so it is of fundamental importance in matter. But it also governs most everyday interactions we deal with, from chemical interactions to biological processes.
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- 5.1: Prelude to Electric Charges and Fields
- Back when we were studying Newton’s laws, we identified several physical phenomena as forces. We did so based on the effect they had on a physical object: Specifically, they caused the object to accelerate. Later, when we studied impulse and momentum, we expanded this idea to identify a force as any physical phenomenon that changed the momentum of an object. In either case, the result is the same: We recognize a force by the effect that it has on an object.
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- 5.2: Electric Charge
- You are certainly familiar with electronic devices that you activate with the click of a switch, from computers to cell phones to television. And you have certainly seen electricity in a flash of lightning during a heavy thunderstorm. But you have also most likely experienced electrical effects in other ways, maybe without realizing that an electric force was involved. Let’s take a look at some of these activities and see what we can learn from them about electric charges and forces.
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- 5.3: Conductors, Insulators, and Charging by Induction
- In the preceding section, we said that scientists were able to create electric charge only on nonmetallic materials and never on metals. To understand why this is the case, you have to understand more about the nature and structure of atoms. In this section, we discuss how and why electric charges do—or do not—move through materials. A more complete description is given in a later chapter.
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- 5.4: Coulomb's Law
- Experiments with electric charges have shown that if two objects each have electric charge, then they exert an electric force on each other. The magnitude of the force is linearly proportional to the net charge on each object and inversely proportional to the square of the distance between them. (Interestingly, the force does not depend on the mass of the objects.) The direction of the force vector is along the imaginary line joining the two objects and is dictated by the signs of the charges.
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- 5.6: Calculating Electric Fields of Charge Distributions
- The charge distributions we have seen so far have been discrete: made up of individual point particles. This is in contrast with a continuous charge distribution, which has at least one nonzero dimension. If a charge distribution is continuous rather than discrete, we can generalize the definition of the electric field. We simply divide the charge into infinitesimal pieces and treat each piece as a point charge.
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- 5.7: Electric Field Lines
- Our model is that the charge on an object (the source charge) alters space in the region around it in such a way that when another charged object (the test charge) is placed in that region of space, that test charge experiences an electric force. The concept of electric field lines, and of electric field line diagrams, enables us to visualize the way in which the space is altered, allowing us to visualize the field.
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- 5.8: Electric Dipoles
- Earlier we discussed, and calculated, the electric field of a dipole: two equal and opposite charges that are “close” to each other. (In this context, “close” means that the distance d between the two charges is much, much less than the distance of the field point P, the location where you are calculating the field.) Let’s now consider what happens to a dipole when it is placed in an external field.
Thumbnail: The eight source charges each apply a force on the single test charge Q. Each force can be calculated independently of the other seven forces. This is the essence of the superposition principle.


7.4: Developing Probable Cause
Basic Principles
Having given up on a mathematical solution to the problem, we must rely on certain basic principles. And the most basic principle is this: Neither probable cause nor reasonable suspicion can exist unless officers can cite “specific and articulable facts” that support their judgment. This demand for specificity is so important that the Supreme Court called it the “central teaching of this Court’s Fourth Amendment jurisprudence.” The question, then, is this: How can officers determine whether their “specific and articulable” facts are sufficient to establish probable cause or reasonable suspicion? That is the question we will address in the remainder of this article.
The Totality of the Circumstances
Almost as central as the need for facts is the requirement that, in determining whether officers have probable cause and reasonable suspicion, the courts will consider the totality of circumstances. This is significant because it is exactly the opposite of how some courts did things many years ago. That is, they would utilize a “divide-and-conquer” approach which meant subjecting each fact to a meticulous evaluation, then frequently ruling that the officers lacked probable cause or reasonable suspicion be- cause none of the individual facts were compelling. This practice officially ended in 1983 when, in the landmark decision in Illinois v. Gates , the Supreme Court announced that probable cause and reasonable suspicion must be based on an assessment of the convincing force of the officers’ information as a whole.  We weigh not individual layers but the laminated total. Thus, in People v. McFadin the court responded to the defendant’s “divide-and-conquer” strategy by utilizing the following analogy:
The defendant would apply the axiom that a chain is no stronger than its weakest link. Here, however, there are strands that have been spun into a rope. Although each alone may have insufficient strength, and some strands may be slightly frayed, the test is whether when spun together they will serve to carry the load of upholding [the probable cause determination].
Here is an example of how the “totality of the circumstances” test works and why it is so important. In Maryland v. Pringle , an officer made a traffic stop on a car occupied by three men and, in the course of the stop, saw some things that caused him to suspect that the men were drug dealers. One of those things was a wad of cash ($763) that the officer had seen in the glove box. He then conducted a search of the vehicle and found cocaine. But a Maryland appellate court ruled the search was unlawful because the presence of money is “innocuous.” The Supreme Court reversed, saying the Maryland court’s “consideration of the money in isolation, rather than as a factor in the totality of the circumstances, is mistaken.”
Common Sense
Not only did the Court in Gates rule that probable cause must be based on a consideration of the totality of circumstances, but it also ruled that the significance of the circumstances must be evaluated by applying common sense, not hypertechnical analysis. In other words, the circumstances must be “viewed from the standpoint of an objectively reasonable police officer.” As the Court explained:
Perhaps the central teaching of our decisions bearing on the probable cause standard is that it is a practical, nontechnical conception. In dealing with probable cause, as the very name implies, we deal with probabilities. These are not technical; they are the factual and practical considerations of everyday life on which reasonable and prudent men, not legal technicians, act.
Legal, but Suspicious, Activities
It follows from the principles discussed so far that it is significant that officers saw the suspect do something that, while not illegal, was suspicious considering other circumstances. As the Supreme Court explained, the distinction between criminal and non-criminal conduct “cannot rigidly control” because probable cause and reasonable suspicion “are fluid concepts that take their substantive content from the particular contexts in which they are being assessed.” For example, in Massachusetts v. Upton, the state court ruled that probable cause could not have existed because the evidence “related to innocent, non-suspicious conduct or related to an event that took place in public.” Acknowledging that no single piece of evidence was conclusive, the Supreme Court reversed, saying the “pieces fit neatly together.” Similarly, the Court of Appeal noted that seeing a man running down a street “is indistinguishable from the action of a citizen engaged in a program of physical fitness.” But it becomes “highly suspicious” when it is “viewed in the context of immediately preceding gunshots.”
Another example of how noncriminal activities can become highly suspicious is found in Illinois v. Gates . It started with an anonymous letter to a police department saying that a local resident, Lance Gates, was a drug trafficker; and it explained in some detail the procedure that Gates and his wife, Sue, would follow in obtaining drugs in Florida. DEA agents followed both of them (Gates flew, Sue drove) and both generally followed the procedure described by the letter writer. This information led to a search warrant and Gates’ arrest. On appeal, he argued that the warrant was not supported by probable cause because the agents did not see him or his wife do anything illegal. It didn’t matter, said the Supreme Court because the “seemingly innocent activity became suspiciously in light of the initial tip.”
Multiple Incriminating Circumstances
Here is a principle that, while critically important, is often overlooked or under-appreciated: The chances of having probable cause or reasonable suspicion increase exponentially with each additional piece of independent incriminating evidence that comes to light. This is because of the unlikelihood that each “coincidence of information” could exist in the absence of a fair or moderate possibility of guilt.
For example, in a Kings County murder case probable cause to arrest the defendant was based on the following: When the crime occurred, a car similar to the defendant’s “uniquely painted” vehicle had been seen in a rural area, two-tenths of a mile from where a 15-year old girl had been abducted. In addition, an officer saw “boot prints and tire prints” nearby, and “he compared them visually with boots seen in, and the treads of the tires of the defendant’s car, which he knew was parked in front of defendant’s hotel and registered to defendant. He saw the condition of the victim’s body; he knew that defendant had a prior record of conviction for forcible rape. He also knew of the victim’s occasional employment as a babysitter at the farm where the defendant worked.” In ruling that these pieces of independent incriminating evidence constituted probable cause, the California Supreme Court said:
The probability of the independent concurrence of these factors in the absence of the guilt of the defendant was slim enough to render suspicion of the defendant reasonable and probable.
Similarly, in a case from Santa Clara County, a man named Anthony Spears, who worked at a Chili’s in Cupertino, arrived at the restaurant one morning and “discovered” that the manager had been shot and killed before the restaurant had opened for the day. During their investigation, sheriff’s deputies learned that Spears had left home shortly before the murder even though it was his day off, there were no signs of forced entry, and that Marlboro cigarette butts (the same brand that Spears smoked) had been found in an alcove near the manager’s office. Moreover, Spears had given conflicting statements about his whereabouts when the murder occurred; and, after “discovering” the manager’s body, he told other employees that the manager had been “shot” but the cause of death was not apparent from the condition of the body.
Based on this evidence, detectives obtained a warrant to search Spears’ apartment and the search netted, among other things, “large amounts of blood-stained cash.” On appeal, Spears argued that the detectives lacked probable cause for the warrant but the court disagreed, saying, “[W]e believe that all of the factors, considered in their totality, supplied a degree of suspicion sufficient to support the magistrate's finding of probable cause.”
While this principle also applies to reasonable suspicion to detain, a lesser amount of independent incriminating evidence will be required. The following are examples from various cases:
- The suspect’s physical description and his clothing were similar to that of the perpetrator.
- In addition to a description similarity, the suspect was in a car similar in appearance to that of the perpetrator.
- The suspect resembled the perpetrator and he was in the company of a person who was positively identified as one of two men who had just committed the crime.
- The suspect resembled the perpetrator plus he was detained shortly after the crime occurred at the location where the perpetrator was last seen or on a logical escape route.
- In addition to resembling the perpetrator, the suspect did something that tended to demonstrate consciousness of guilt; e.g., he lied to officers or made inconsistent statements, he made a furtive gesture, he reacted unusually to the officer’s presence, he is attempting to elude officers.
- The suspect resembled the perpetrator and possessed the fruits of the crime.
- The number of suspects in the vehicle corresponded with the number of people who had just committed the crime, plus they were similar in age, sex, and nationality.
The odds of having reasonable suspicion or probable cause also increase dramatically if the matching or similar characteristics were unusual or distinctive. As the Court of Appeal observed, “Uniqueness of the points of comparison must also be considered in testing whether the description would be inapplicable to a great many others.”
For example, the courts have taken note of the following unique circumstances:
- The suspect and perpetrator both had bandages on their left hands;
- The suspect and perpetrator were in vehicles of the same make and model with tinted windows and a dark-colored top with light-colored sides. Conversely, the Second Circuit noted that “when the points of similarity are less unique or distinctive, more similarities are required before the probability of identity between the two becomes convincing.”


10: Concepts and Content -- Introduction to Philosophy- Philosophy of Mind
Eran Asoulin
Introduction
The problem of intentionality is the problem of how some entities can be “about” something. That is, sentences, thoughts, or concepts, among others, display intentionality in that they are about something else; they are said to be a representation of something. The notion of intentionality can be traced back at least as far as Aristotle (384 BCE-322 BCE), though the German philosopher Franz Brentano (1838-1917) is generally credited with introducing the notion to contemporary philosophy in the late nineteenth century. Brentano’s oft-quoted remark is that “Every mental phenomenon is characterized by … the intentional (or mental) inexistence of an object” and “reference to a content, direction toward an object.” In other words, “Every mental phenomenon includes something as object within itself, although they do not all do so in the same way. In presentation something is presented, in judgement something is affirmed or denied, in love loved, in hate hated, in desire desired and so on” (Brentano [1874] 1995, 68). The usual way to frame the problem of intentionality is in terms of the notion of meaning or content. What is the status of the meaning of a sentence over and above its formal and syntactic aspects? What makes it the case that a particular proposition has the content that it does? Is content only dependent upon mind-internal properties? Or must we make use of mind-external factors such as the context of the utterance or the speaker’s social history in order to determine the content? Those who argue that the relevant and scientifically interesting properties that are involved in content are overwhelmingly, though not entirely, within the mind are referred to as internalists. On the other hand, externalists argue that there is something more to content than merely mind-internal events and their happenstance connection to the world: externalists insist that the meanings of our words (or sentences, or the contents of our thoughts, etc.) depend on some deep metaphysical (perhaps causal) connection between the mind and other worldly objects that are independent of the mind.
Externalists argue that a theory of content needs to provide an account of the relation between linguistic expressions and what may be called things in the world. In other words, the claim is that in order to explain content we must provide an account of the relation between linguistic expressions and the things that they can be used to talk about. Or as Colin McGinn puts it: “[E]xternalism supposes there to be a deep connection between states of mind and conditions in the nonmental world. Is the mind fundamentally autonomous with respect to the world, or does the world enter into the very nature of the mind?” (McGinn 1989, 1) He remarks further that according to externalism, “The environment is thus held to be constitutive of the very nature of mental states, determining what they are.” McGinn argues that internalism “insists upon … drawing a sharp line between mind and world; but the externalist holds that the mind is penetrated by the world, configured by it” (1989, 3). That said, however, we will see that the main force and substance of the internalist position is not exactly a mirror image or a negation of the externalist position, for internalism only denies that there is a deep metaphysical relation between the things in the world and linguistic expressions. That is, internalists dispute the externalist claim that the relations between linguistic expressions and the things in the world are desirable or even tractable in an explanatory theory of content.
This chapter is structured as follows. First I discuss the nature of concepts. I then discuss externalism and the way in which it explains the nature of concepts and their content. I discuss one of the major thought experiments that have motivated many philosophers to adopt the externalist position. I then discuss the internalist position, which not only provides objections to the main claims of externalism but also provides its own positive account of concepts and their content.
What is a Concept?
A concept is generally understood in the philosophy of mind to refer to a constituent of thought. Consider the proposition “John thinks that the book is on the table.” Following Bertrand Russell (1872-1970), philosophers speak of propositional attitudes, which include beliefs, desires, hopes, fears, expectations, and any other attitude that involves a proposition. A propositional attitude of the form “X thinks that P” has two parts. The first constitutes the verb of the psychological-state description and contains information about the agent and the agent’s psychological state. That is, the first part gives information about who takes which propositional attitude (for example, “John thinks”). The second part completes the description by revealing what the proposition is, or what the attitude refers to (for example, “that the book is on the table”). Concepts are said to be the constituents of the propositions expressed by propositional attitudes (in this case the concepts are, roughly, “book,” “table,” and “on”). Propositional attitudes and thus concepts are used in folk psychological (or intentional) explanations of behavior.
A simple example of the explanations and predictions that folk psychology allows is as follows. Suppose that we wish to explain why Leila chose to take her umbrella with her when she departed today. We can make use of some propositional attitudes and certain laws of folk psychology to formulate such an explanation. For instance, Leila believes that it will rain today (perhaps she heard the weather forecast on the radio), Leila believes that using an umbrella will help her seek shelter from rain, Leila desires not to get wet today. Therefore, since, all things being equal, humans act in accordance with their beliefs and desires, we can explain why Leila took her umbrella with her today. In other words, she took the umbrella because she believed X and desired Y, and believed that by doing Z she can bring it about that Y (notice that this is a counterfactual, so that if she did not believe that X and did not desire that Y then she would not do Z). Since beliefs and desires are integral parts of human thought, and since beliefs, say, are thought of as expressing propositions, the central role of concepts in philosophy and psychology is clear. That is, since the constituents of propositions are concepts, the need to explain the nature of concepts is inseparable from a theory of how the mind works.
Concepts are clearly shared between different people, and the question of what it is that is shared can be understood as the question of what the nature of content is. That is, if both John and Leila think that P, then they both share the content inherent in the concepts of the proposition P. What this claim amounts to is cashed out in very different ways by externalists and internalists, especially in terms of what explanatory role content is supposed to play. Externalists are mostly interested in concepts insofar as they figure in explanations of behavior (linguistic or other), whereas internalists are interested in concepts insofar as they serve as the meanings of linguistic items. Thus, a focus of internalist semantics is the underlying mechanisms of conceptual structure in virtue of which language production and comprehension is made possible. Let us now see what each claim amounts to.
Externalist Explanations of Content
Since the 1970’s externalism has become a widely held position in the philosophy of mind. The classic arguments for externalism are found in Hilary Putnam’s (1926-2016) “The Meaning of ‘Meaning’”, Tyler Burge’s “Individualism and the Mental”, and Saul Kripke’s Naming and Necessity . Putnam argues that “a better philosophy and a better science of language” must encompass the “social dimension of cognition” and the “contribution of the environment, other people, and the world” to semantics (Putnam 1975, 49). Burge argues against any theory about the mind in which “the mental natures of all a person’s or animal’s mental states (and events) are such that there is no necessary or deep individuative relation between the individual’s being in states of those kinds and the nature of the individual’s physical or social environment” (Burge 1986, 3-4).
The Twin Earth thought experiment of Putnam is the most famous argument in favor of externalism; it claims to show that two subjects can have identical internal psychological mental states but that the content of these states can be different due to particular variations in the environment. Putnam asks us to imagine a world (Twin-Earth) in which water is not composed of H 2 O like it is on our world but is rather composed of XYZ. When a person (call him Oscar) says “water” on Earth the word refers to H 2 O, but when a different person (call him Twin-Oscar) says “water” in a different place (on Twin-Earth) the word refers to XYZ. This seems intuitively clear; the word “water” refers to what the word is about in that particular environment (so when Oscar utters “water” that word is about H 2 O in his environment). Putnam asks what would happen if Oscar is transported to Twin-Earth. Would the word “water” uttered by Oscar on Twin-Earth now refer to H 2 O or XYZ? Notice that the thought experiment legislates that the only change that takes place when Oscar is transported from Earth to Twin-Earth is the change in his environment (i.e., all of his psychological states remain unchanged). Now, Putnam reasons that if knowing the meaning of a term is just a matter of being in a certain psychological state, then “water” on Twin-Earth when uttered by Oscar should refer to H 2 O and not to XYZ as we might expect. This is because Oscar’s psychological state was fixed on Earth, and if the psychological state fixes the reference then “water” refers to H 2 O regardless of the environment the subject is in (Putnam 1975).
Another way to put the matter is as follows: when Twin-Oscar on Twin-Earth says “water” whilst pointing to a lake that is entirely composed of XYZ, as all watery things are composed of on Twin-Earth, “water” refers to XYZ and not to H 2 O. But, Putnam’s argument claims, if knowing the meaning of a term is just a matter of being in a certain psychological state then “water” uttered on Twin-Earth by Oscar transported from Earth cannot mean XYZ and must mean H 2 O. Something seems to be wrong here. If two people utter the same word in the same environment we expect that word to refer to the same thing. Thus, if we want to hold on to the claim that the meaning of a term determines its reference or extension then, the argument claims, we must concede that, as Putnam famously put it, “Cut the pie any way you like, ‘meanings’ just ain’t in the head!” (1975, 144) That is, the claim is that mind-internal properties on their own cannot fix the meanings of words or what their reference is.
Putnam’s argument is directed at the meanings of words, of course, but it was soon noticed by Colin McGinn, Tyler Burge, and others that the same argument also applies to the contents of our propositional attitudes, hence to the contents of our thoughts. The main claim of externalism, then, is that even though thoughts are said to be inside a person’s head, the content of these thoughts supervene [1] on external factors in the environment of the person who has them. Thus, as Ben-Menahem remarks in regard to one of Putnam’s examples, “to speak of coffee tables it does not suffice for us merely to have the concept of a coffee table, but we must be in contact with actual coffee tables” (Ben-Menahem 2005, 10; emphasis in original).
Internalist Semantics
Now, it could be objected that externalism has to be right: How could content not depend on the outside world? Surely the meaning of the word “elephant” cannot be due to only mind-internal properties. The word is about elephants, it could be argued, which are in the mind-external world, not inside the mind. As we will now see, internalists argue that there are good reasons to question the externalist claim that concepts are connected to the world in the way in which externalists claim they are. In other words, internalism does not deny the link to the outside world but rather has a different explanation of how our mind generates and interprets the content of our concepts. Internalism argues that, for the purposes of scientific inquiry into language and mind, the internal properties of the human mind are the most relevant and fruitful subject matter. Thus construed, internalism is not so much a solution to the issues that externalists grapple with. Rather, as we will see below, internalism is a different research program, and so there is a difference in the sorts of questions externalism and internalism attempt to answer.
A succinct definition of internalism is provided by Wolfram Hinzen: “Internalism is an explanatory strategy that makes the internal structure and constitution of the organism a basis for the investigation of its external function and the ways in which it is embedded in an environment” (Hinzen 2006, 139). Internalism studies the internal structure and mechanisms of an organism; the external environment comes into the picture when the internal processes are ascribed content by the theorist, thus explaining how the internal mechanisms constitute a cognitive process in a particular environment. Such content ascriptions, claim internalists, vary with the theorist’s interests and aims, but the content and its ascription are not an essential part of the theory itself. So, for example, the mechanism that detects vertical lines in the visual input will be in the scope of an internalist theory, but not the representational content ascribed to the output of this mechanism. The latter could be any number of things (the vertical line could represent the edge of a building or be part of a larger representation of a human face) but its underlying mechanism remains unchanged.
In other words, as discussed by Frances Egan in work spanning the last few decades, the internalist claim is that the computational characterization of an internal mechanism abstracts away from specific content ascriptions. So one can separate the content of, say, a visual state, from the computational machinery in virtue of which that content is made possible. For example, a particular mechanism may receive as input a certain set of parameters that require computation. The theorist then examines the output of these computations. One can imagine a mechanism that is embedded in the visual system being ascribed visual contents befitting the theory of vision. However, that same mechanism can be embedded in the auditory system and thus be ascribed different (auditory) contents that are defined not in terms of visual properties but rather in terms of acoustical properties. In other words, there is nothing inherent to the internalist computations performed that makes them visual or auditory. As Egan has discussed, there is an underlying set of computations that are required for both visual and auditory processing. The label we give to the output of such computations (the content we ascribe to them) depends on where the input to the mechanism came from. If the input is visual then the theorist will ascribe the output of the mechanism a visual content. But nothing in the internal mechanism itself tells us that. Internalism studies the internal mechanism itself, which remains unchanged regardless of whether it happens to be embedded or used by, say, the visual system or the auditory system.
Let us unpack these claims. First, note that the externalist claim that states of individual organisms cannot be understood in complete isolation from the environment in which they happen to be is not in dispute. The argument is about whether what happens in the environment should be part of what the theory is supposed to explain. So what is the problem that internalists see with the externalists’ relation between words and the things words are used to talk about? In a classic paper that formed one of the foundations of internalist semantics, Jerrold Katz (1932-2002) and Jerry Fodor (1935-2017) discussed this issue (though they did not frame it in terms of internalism versus externalism). Katz and Fodor ask the reader to compare the following three sentences:
(1) “Should we take junior back to the zoo?”
(2) “Should we take the lion back to the zoo?”
(3) “Should we take the bus back to the zoo?”
They then remark that information that figures in the choice of the correct interpretation for each of these sentences includes the fact that, say, lions, but not children and busses, are often kept in cages. That is, unlike (2), the meaning of (1) cannot be that we should take a living being back to the zoo and put them in a cage. (1) means that we should take a child and show them the animals around the zoo. (3), on the other hand, has neither of these interpretations. (3) cannot mean that we should take the bus to the zoo and put it in a cage, nor can it mean that we should take the bus and show it the animals around the zoo. In order to decipher these meanings one needs to know certain facts about the world; these facts are not semantic or grammatical facts (Katz and Fodor 1963).
After listing a handful of other examples of what information is needed for interpretation, Katz and Fodor note that the reader will find it easy to construct an ambiguous sentence whose resolution requires the prior representation of practically any relevant item of information about the world. This is because, in order to resolve a great deal of ambiguous sentences, one needs to have certain facts about the world without which certain interpretations of sentences are unavailable. For example, consider the sentence “I saw the man with the binoculars.” If one didn’t know what binoculars were, then the only interpretation available would be that a person saw a man holding an object that is called “binoculars.” However, once one’s world knowledge is expanded to include facts about binoculars (namely, that they are used to see objects far away) then further interpretations become available and then the sentence becomes ambiguous. That is, the sentence then has the additional interpretation that “I saw a man and I used binoculars to see that man.” Katz and Fodor’s claim is that in order to disambiguate such sentences one needs to know things that are not purely semantic (what binoculars are used for is a fact about the world and not a grammatical fact). The problem is that a theory of meaning that aims to include all relevant information that is needed in order to disambiguate sentences and determine the correct interpretation will run into great difficulties, for such a theory cannot predict in advance what sort of information will be needed for sentence interpretation.
The upshot is that a theory that insists (as externalism does) on including the mind’s relations to the external world in a theory of language cannot hope to find reliable relations of the sort described above (let alone systematizing them into a fruitful explanatory theory). However, in regard to the underlying mechanisms of the mind in virtue of which the generation and interpretation of content is made possible, internalists claim that a fruitful theory is possible. The most famous proponent of internalist semantics is Noam Chomsky, and his work stands in stark contrast to the externalist semantics of Hilary Putnam or Donald Davidson (1917-2003). The recent work of Paul Pietroski (2008, 2010) is an excellent example of internalist semantics. Pietroski construes meaning in terms of blueprints that are used by the language faculty in the mind in order to construct concepts. This is an attempt to explain the underlying mental mechanisms in virtue of which we can generate and interpret thought contents. The meaning of a word in internalist semantics is cashed out not in terms of the word’s relation to the outside world but rather in terms of the word’s internal role in the mind’s construction of the concept that has the required content. Note the difference here. Internalist semantics studies the mechanisms in the mind that build concepts. Once these concepts are generated they are transferred from the language faculty to the mind-internal systems of thought and to the articulatory-perceptual system. [2] These systems then make use of concepts for various ends such as thinking and talking about the world.
In other words, the internalist claim is that the mind has certain mechanisms that include instructions to build concepts, which then provide the inputs to other (mind-internal) systems that enter into various human actions, one of which is communication. Internalist semantics, then, concerns the nature of the computational mechanisms of the language faculty and their relation to the systems of thought; it concerns not the concepts themselves but the mechanisms that fetch, build, and combine concepts within the mind. That is, internalism is concerned with the mind-internal mechanisms of concept creation. This is of course one step removed from what externalist semantics studies, which are the concepts themselves, their role in language use, and their relation to the speaker’s environment.
Conclusion
The difference between the externalist and internalist position in regard to mental content is a difference in the sort of questions that each attempts to answer. It is a difference in the way in which each construes the role that content plays in the explanation of language and mind. The argument in favor of either approach to the science and philosophy of language and mind is of course not a knockdown argument, nor is it a guarantee that one side will turn out to be the correct path. As Gabriel Segal correctly remarks, “The point is that we should not expect to discover too much from the armchair. Discovering the true nature of content should be a scientific enterprise (whether we also call it ‘philosophical’ or not)” (Segal 2000, 20).
References
Ben-Menahem, Yemima, ed. 2005. Hilary Putnam . Cambridge: Cambridge University Press.
Brentano, Franz. (1874) 1995. Psychology from an Empirical Standpoint . London: Routledge.
Burge, Tyler. 1986. “Individualism and Psychology.” The Philosophical Review 95(1).
Hinzen, Wolfram. 2006. “Internalism about Truth.” Mind & Society 5.
Katz, Jerrold and Jerry A. Fodor. 1963. “The Structure of a Semantic Theory.” Language 39(2): 170-210.
McGinn, Colin. 1989. Mental Content . Oxford: Blackwell.
Pietroski, Paul M. 2008. “Minimalist Meaning, Internalist Interpretation.” Biolinguistics 2(4) (2008): 317-341.
Pietroski, Paul M. 2010. “Concepts, Meanings and Truth: First Nature, Second Nature and Hard Work.” Mind & Language 25(3): 274-278.
Putnam, Hilary. 1975. “The Meaning of ‘Meaning.’” Minnesota Studies in the Philosophy of Science 7.
Segal, Gabriel M. 2000. A Slim Book about Narrow Content . Cambridge, MA: MIT Press.
Further Reading
On Concepts
Baker, Mark. 2001. The Atoms of Language: The Mind’s Hidden Rules of Grammar. New York: Basic Books.
Block, Ned. 1986. “Advertisement for a Semantics for Psychology.” In Peter A. French, Theodore E. Uehling and Howard K. Wettstein, eds. Studies in the Philosophy of Mind. Minneapolis: University of Minnesota Press.
Carey, Susan. 2009. The Origin of Concepts. Oxford: Oxford University Press.
Fodor, Jerry. 1998. Concepts: Where Cognitive Science Went Wrong. New York: Oxford University Press.
Fodor, Jerry. 1975. The Language of Thought. Cambridge, MA: Harvard University Press.
Fodor, Jerry. 2008. LOT 2: The Language of Thought Revisited. New York: Oxford University Press.
Jackendoff, Ray. 1989. What is a Concept, that a Person may Grasp It? Mind & Language 4: 68-102.
McGilvray, James. 2002. “MOPs: The Science of Concepts.” In Wolfram Hinzen and Hans Rott, eds. Belief and Meaning: Essays at the Interface. Frankfurt: Ontos.
Pinker, Steven. 2007. The Stuff of Thought: Language as a Window into Human Nature . London: Penguin.
On Internalism
Chomsky, Noam. 1995. “Language and Nature.” Mind 104(416): 1-59.
Chomsky, Noam. 2000. New Horizons in the Study of Language and Mind. Cambridge: Cambridge University Press.
Chomsky, Noam. 2013. “What Kind of Creatures are We?” The Journal of Philosophy 90(12): 645-700.
Egan, Frances. 2014. “How to Think about Mental Content.” Philosophical Studies 170: 115-135.
Farkas, Katalin. 2003. “Does Twin Earth Rest on a Mistake?” Croatian Journal of Philosophy 3(8): 155-69.
Lohndal, Terje and Hiroki Narita. 2009. “Internalism as Methodology.” Biolinguistics 3(4): 321-331.
McGilvray, James. 1998. “Meanings are Syntactically Individuated and Found in the Head.” Mind & Language 13(2): 225-280.
Mendola, Joseph. 2009. Anti- Externalism. Oxford: Oxford University Press.
Pietroski, Paul M. 2010. “Concepts, Meanings and Truth: First Nature, Second Nature and Hard Work.” Mind & Language 25(3): 247-278.
Segal, Gabriel M. 2000. A Slim Book about Narrow Content. Cambridge, MA: MIT Press.
On Externalism
Ben-Menahem, Yemima, ed. 2005. Hilary Putnam. Cambridge: Cambridge University Press.
Burge, Tyler. 1979. “Individualism and the Mental.” Midwest Studies in Philosophy 4: 73-121.
Davidson, Donald. 1987. “Knowing One’s Own Mind.” Proceedings and Addresses of the American Philosophical Association 60(3): 441-458.
Davies, Martin. 1993. “Aims and Claims of Externalist Arguments.” Philosophical Issues 4: 227-249.
Farkas, Katalin. 2003. “What is Externalism?” Philosophical Studies 112(3): 187-208.
Fodor, Jerry. 1994. The Elm and the Expert: Mentalese and its Semantics. Cambridge, MA: MIT Press.
Horwich, Paul. 2005. Reflections on Meaning. Oxford: Oxford University Press.
Kripke, Saul. 1980. Naming and Necessity . Oxford: Blackwell.
McGinn, Colin. 1989. Mental Content . Oxford: Blackwell.
Millikan, Ruth. 1984. Language, Thought and Other Biological Categories . Cambridge, MA: MIT Press.
Nuccetelli, Susana, ed. 2003. New Essays on Semantic Externalism and Self-Knowledge. Cambridge, MA: MIT Press.
Pessin, Andrew and Sanford Goldberg, eds. 1996. The Twin Earth Chronicles: Twenty Years of Reflection on Hilary Putnam’s “The Meaning of ‘Meaning.’” New York: M. E. Sharpe.
Putnam, Hilary. 1975. “The Meaning of ‘Meaning.’” Minnesota Studies in the Philosophy of Science 7: 131-193.
Wikforss, Åsa. 2008. “Semantic Externalism and Psychological Externalism.” Philosophy Compass 3(1): 158-181.
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Supervenience here refers to a certain set of properties in virtue of which some other set is made possible. If A supervenes on B then changing anything in B would also change A. So, for example, the colour blue supervenes on a certain set of physical properties such the wavelength of light. What follows is that if we change the wavelength of the light then we also change the colour. In regard to content, the externalist claim is that content supervenes on both what’s in the head and on the environment. It follows, then, that if we change the relevant features in the environment then the content would also change. Internalists, of course, reject this claim.
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This is the system responsible for externalising language via sound or sign. The way a particular word is pronounced, for example, will be determined by the articulatory-perceptual system, whereas the word’s meaning will be determined by the systems of thought (sometimes known as the conceptual-intentional system).
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1: Overview and the Microscope
WHAT YOU’LL LEARN TO DO: Describe and identify anatomical position and locate major organs.
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- 1.1: Learning Objectives and Activities
- This page details lab activities centered on human anatomy, covering anatomical positions, body cavities, organ systems, and microscope use. It includes tasks on virtual and real images and line drawings of specimens. The content is licensed under Creative Commons and attributed to Mississippi University for Women.
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- 1.2: Anatomical Position and Planes
- This page discusses the importance of anatomical terminology for health professionals, explaining the anatomical position and directional terms such as medial/lateral, anterior/posterior, and superior/inferior. It highlights various anatomical planes and their relevance in identifying body structures.
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- 1.3: Human Body Cavities and Organ Systems
- This page outlines the major body cavities in the human body, including the dorsal and ventral divisions, and details the cranial, spinal, thoracic, abdominal, and pelvic cavities. It highlights the concept of organ systems, consisting of eleven interdependent systems that work together, and describes various organs within these systems. Additionally, the document includes lab exercises for identifying cavities and organ systems.
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- 1.4: Microscopes
- This page covers the importance and function of the compound light microscope for viewing small specimens, emphasizing proper handling and storage, and explaining key components such as the eyepiece, lenses, and stage. It provides instructions for a microscope lab exercise, including questions about component locations and magnification calculations. Concepts of magnification and resolution are explained, guiding students to apply their knowledge through practical observation and documentation.
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- 1.5: Setting Up a Microscope and Slide Properly
- This page outlines the use of parfocal microscopes, detailing steps for maintaining focus while switching objectives, including setup, cleaning, and understanding image types. It emphasizes techniques for accurately drawing microscopic specimens, urging simplicity over detail, and focusing on key features. A lab exercise on drawing human blood smears reinforces this, highlighting the identification of red and white blood cells, and the importance of proper microscope storage.
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8.4: Vectors
A woman leaves home, walks 3 miles north, then 2 miles southeast. How far is she from home, and in which direction would she need to walk to return home? How far has she walked by the time she gets home?
This question may seem familiar – indeed we did a similar problem with a boat in the first section of this chapter. In that section, we solved the problem using triangles. In this section, we will investigate another way to approach the problem using vectors, a geometric entity that indicates both a distance and a direction. We will begin our investigation using a purely geometric view of vectors.
A Geometric View of Vectors
Definition: VECTOR
A vector is an object that has both a length and a direction.
Geometrically, a vector can be represented by an arrow that has a fixed length and
indicates a direction. If, starting at the point \(A\), a vector, which means “carrier” in Latin, moves toward point \(B\), we write \(\overrightarrow{AB}\) to represent the vector.
A vector may also be indicated using a single letter in boldface type, like u , or by capping the letter representing the vector with an arrow, like \(\vec{u}\).
Example \(\PageIndex{1}\)
Draw a vector that represents the movement from the point \(P\) (-1, 2) to the point \(Q\) (3, 3)
Solution
By drawing an arrow from the first point to the second, we can construct a vector \(\overrightarrow {PQ}\).
Exercise \(\PageIndex{1}\)
Draw a vector, \(\vec{v}\), that travels from the origin to the point (3, 5).
- Answer
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Using this geometric representation of vectors, we can visualize the addition and scaling of vectors.
To add vectors, we envision a sum of two movements. To find \(\vec{u} + \vec{v}\), we first draw the vector \(\vec{u}\), then from the end of \(\vec{u}\) we drawn the vector \(\vec{v}\). This corresponds to the notion that first we move along the first vector, and then from that end position we move along the second vector. The sum \(\vec{u} + \vec{v}\) is the new vector that travels directly from the beginning of \(\vec{u}\) to the end of \(\vec{v}\) in a straight path.
ADDING VECTORS GEOMETRICALLY
To add vectors geometrically, draw \(\vec{v}\) starting from the end of \(\vec{u}\). The sum \(\vec{u} + \vec{v}\) is the vector from the beginn ing of \(\vec{u}\) to the end of \(\vec{v}\).
Example \(\PageIndex{2}\)
Given the two vectors shown below, draw \(\vec{u} + \vec{v}\)
Solution
We draw \(\vec{v}\) starting from the end of \(\vec{u}\), then draw in the sum \(\vec{u} + \vec{v}\) from the beginning of \(\vec{u}\) to the end of \(\vec{v}\).
Notice that path of the walking woman from the beginning of the section could be visualized as the sum of two vectors. The resulting sum vector would indicate her end position relative to home.
Although vectors can exist anywhere in the plane, if we put the starting point at the origin it is easy to understand its size and direction relative to other vectors.
To scale vectors by a constant, such as \(3\vec{u}\), we can imagine adding \(\vec{u} + \vec{u} + \vec{u}\). The result will be a vector three times as long in the same direction as the original vector. If we were to scale a vector by a negative number, such as \(-\vec{u}\), we can envision this as the opposite of \(\vec{u}\); the vector so that \(\vec{u} + (-\vec{u}\) returns us to the starting point. This vector \(-\vec{u}\) would point in the opposite direction as \(\vec{u}\) but have the same length.
Another way to think about scaling a vector is to maintain its direction and multiply its length by a constant, so that \(3\vec{u}\) would point in the same direction but will be 3 times as long.
SCALING A VECTOR GEOMETRICALLY
To geometrically scale a vector by a constant, scale the length of the vector by the constant.
Scaling a vector by a negative constant will reverse the direction of the vector.
Example \(\PageIndex{3}\)
Given the vector shown, draw \(3\vec{u}\), \(-\vec{u}\), and \(-2\vec{u}\).
Solution
The vector \(3\vec{u}\) will be three times as long. The vector \(-\vec{u}\) will have the same length but point in the opposite direction. The vector \(-2\vec{u}\) will point in the opposite direction and be twice as long.
By combining scaling and addition, we can find the difference between vectors geometrically as well, since \(\vec{u} - \vec{v} = \vec{u} + (-\vec{v})\).
Example \(\PageIndex{4}\)
Given the vectors shown, draw \(\vec{u} - \vec{v}\)
Solution
From the end of \(\vec{u}\) we draw \(-\vec{v}\), then draw in the result.
Notice that the sum and difference of two vectors are the two diagonals of a parallelogram with the vectors \(\vec{u}\) and \(\vec{v}\) as e dges.
Exercise \(\PageIndex{2}\)
Using vector \(\vec{v}\) from previous Exercise, draw \(-2 \vec{v}\).
- Answer
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Component Form of Vectors
While the geometric interpretation of vectors gives us an intuitive understanding of vectors, it does not provide us a convenient way to do ca lculations. For that, we need a handy way to represent vectors. Since a vector involves a length and direction, it would be logical to want to represent a vector using a length and an angle \(\theta\), usually measured from standard position.
Definition: MAGNITUDE AND DIRECTION OF A VECTOR
A vector \(\vec{u}\) can be described by its magnitude, or length, \(|\vec{u}|\), and an angle \(\theta\).
A vector with length 1 is called unit vector.
While this is very reasonable, and a common way to describe vectors, it is often more convenient for calculations to represent a vector by horizontal and vertical components.
COMPONENT FORM OF A VECTOR
The component form of a vector represents the vector using two components. \(\vec{u} = \langle x, y \rangle\) indicates the vector represents a displacement of \(x\) units horizontally and \(y\) units vertically.
Notice how we can see the magnitude of the vector as the length of the hypotenuse of a right triangle, or in polar form as the radius, \(r\).
ALTERNATE NOTATION FOR VECTOR COMPONENTS
Sometimes you may see vectors written as the combination of unit vectors \(\vec{i}\) and \(\vec{j}\), where \(\vec{i}\) points the right and \(\vec{j}\) points up. In other words, \(\vec{i} = \langle 1, 0 \rangle\) and \(\vec{j} = \langle \theta, 1 \rangle\).
In this notation, the vector \(\vec{u} = \langle 3, -4 \rangle\) would be written as \(\vec{u} = 3\vec{i} - 4\vec{j}\) since both indicate a displacement of 3 units to the right, and 4 units down.
While it can be convenient to think of the vector \(\vec{u} = \langle x, y \rangle\) as an arrow from the origin to the point (\(x\), \(y\)), be sure to remember that most vectors can be situated anywhere in the plane, and simply indicate a displacement (change in position) rather than a position.
It is common to need to convert from a magnitude and angle to the component form of the vector and vice versa. Happily, this process is identical to converting from polar coordinates to Cartesian coordinates, or from the polar form of complex numbers to the \(a+bi\) form.
Example \(\PageIndex{5}\)
Find the component form of a vecor with length 7 at an angle of 135 degrees.
Solution
Using the conversion formulas \(x = r\cos(\theta)\) and \(y = r\sin(\theta)\), we can find the components
\[x = 7 \cos (135^{\circ}) = -\dfrac{7\sqrt{2}}{2}\nonumber\]
\[y = 7 \sin (135^{\circ}) = \dfrac{7\sqrt{2}}{2}\nonumber\]
The vector can be written in component form as \(\langle -\dfrac{7\sqrt{2}}{2}, \dfrac{7\sqrt{2}}{2} \rangle\)
Example \(\PageIndex{6}\)
Find the magnitude and angle \(\theta\) representing the vector \(\vec{u} = \langle 3, -2 \rangle\).
Solution
First we can find the magnitude by remembering the relationship between \(x\), \(y\) and \(r\):
\[r^2 = 3^2 + (-2)^2 = 13\nonumber\]
\[r = \sqrt{13}\nonumber\]
Second we can find the angle. Using the tangent,
\[\tan(\theta) = \dfrac{-2}{3}\nonumber\]
\[\theta = \tan^{-1}(-\dfrac{2}{3}) \approx -33.69^{\circ}\nonumber\]or written as a coterminal positive angle, \(326.31^{\circ}\). This angle is in the \(4^{\text{th}}\) quadrant as desired.
Exercise \(\PageIndex{3}\)
Using vector \(\vec{v}\) from the first Exercise, the vector that travels from the origin to the point (3, 5), find the components, magnitude and angle \(\theta\) that represent this vector.
- Answer
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\[\vec{v} = \langle 3, 5 \rangle \nonumber\]
\[\text{magnitude} = \sqrt{34}\nonumber\]
\[\theta = \tan^{-1} (\dfrac{5}{3}) = 59.04^{\circ}\nonumber\]
In addition to representing distance movements, vectors are commonly used in physics and engineering to represent any quantity that has both direction and magnitude, including velocities and forces.
Example \(\PageIndex{7}\)
An object is launched with initial velocity 200 meters per second at an angle of 30 degrees. Find the initial horizontal and vertical velocities.
Solution
By viewing the initial velocity as a vector, we can resolve the vector into horizontal and vertical components.
\[x = 200 \cos(30^{\circ} = 200 \cdot \dfrac{\sqrt{3}}{2} \approx 173.205\text{ m/sec}\nonumber\]
\[y = 200 \sin(30^{\circ} = 200 \cdot \dfrac{1}{2} = 100\text{ m/sec}\nonumber\]
This tells us that, absent wind resistance, the object will travel horizontally at about 173 meters each second. Gravity will cause the vertical velocity to change over time – we’ll leave a discussion of that to physics or calculus classes.
Adding and Scaling Vectors in Component Form
To add vectors in component form, we can simply add the corresponding components. To scale a vector by a constant, we scale each component by that constant.
 For a simple example, we revisit the problem from the opening of the section. The general procedure we will follow is:
1) Convert vectors to component form
2) Add the components of the vectors
3) Convert back to length and direction if needed to suit the context of the question
Example \(\PageIndex{9}\)
A woman leaves home, walks 3 miles north, then 2 miles southeast. How far is she from home, and what direction would she need to walk to return home? How far has she walked by the time she gets home?
Solution
Let’s begin by understanding the question in a little more depth. When we use vectors to describe a traveling direction, we often position thin gs so north points in the upward direction, east points to the right, and so on, as pictured here.
Consequently, travelling NW, SW, NE or SE, means we are travelling through the quadrant bordered by the given directions at a 45 degree angle.
With this in mind, we begin by converting each vector to components.
A walk 3 miles north would, in components, be \(\langle 0, 3 \rangle\).
A walk of 2 miles southeast would be at an angle of \(45^{\circ}\) South of East. Measuring from standard position the angle would be \(315^{\circ}\).
Converting to components, we choose to use the standard position angle so that we do not have to worry about whether the signs are negative or positive; they will work out automatically.
\[\langle 2\cos (315^{\circ}),\: 2\sin (315^{\circ })\rangle = \langle 2\cdot\frac{\sqrt{2}}{2},\:2\cdot\frac{-\sqrt{2}}{2}\rangle\approx\langle 1.414, -1.414\rangle\nonumber\]
Adding these vectors gives the sum of the movements in component form
\[\langle 0, 3 \rangle + \langle 1.414, -1.414 \rangle = \langle 1.414 1.586 \rangle\nonumber\]
To find how far she is from home and the direction she would need to walk to return home, we could find the magnitude and angle of this vector.
\[\text{Length} = \sqrt{1.414^2 + 1.586^2} = 2.125\nonumber\]
To find the angle, we can use the tangent
\[\tan(\theta) = \dfrac{1.586}{1.414}\nonumber\]
\[\theta = tan^{-1} (\dfrac{1.586}{1.414}) = 48.273^{\circ}\text{ north of east}\nonumber\]
Of course, this is the angle from her starting point to her ending point. To return home, she would need to head the opposite direction, which we could either describe as \(180^{\circ} + 48.273^{\circ} = 228.273^{\circ}\) measured in standard position, or as \(48.273^{\circ}\) south of west (or \(41.727^{\circ}\) west of south).
She has walked a total distance of 3 + 2 + 2.125 = 7.125 miles.
Keep in mind that total distance traveled is not the same as the length of the resulting displacement vector or the “return” vector.
Exercise \(\PageIndex{4}\)
In a scavenger hunt, directions are given to find a buried treasure. From a starting point at a flag pole you must walk 30 feet east, turn 30 degrees to the north and travel 50 feet, and then turn due south and travel 75 feet. Sketch a picture of these vectors, find their components, and calculate how far and in what direction you must travel to go directly to the treasure from the flag pole without following the map.
- Answer
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\[\vec{v}_1 = \langle 30, 0 \rangle\quad \vec{v}_2 = \langle 50\cos(30^{\circ}), 50\sin(30^{circ}) \rangle\quad \vec{v}_3 = \langle 0, -75 \rangle\nonumber\]
\[\vec{v}_f = \langle 30 + 50 \cos(30^{\circ}), 50 \sin(30^{\circ}) - 75 \rangle = \langle 73.301, -50 \rangle\nonumber\]
Magnitude = 88.73 feet at an angle of \(34.3^{\circ}\) south of east.
While using vectors is not much faster than using law of cosines with only two movements, when combining three or more movements, forces, or other vector quantities, using vectors quickly becomes much more efficient than trying to use triangles.
Example \(\PageIndex{10}\)
Three forces are acting on an object as shown below, each measured in Newtons (N). What force must be exerted to keep the object in equilibrium (where the sum of the forces is zero)?
Solution
We start by resolving each vector into components.
The first vector with magnitude 6 Newtons at an angle of 30 degrees will have components
\[\langle 6\cos(30^{\circ}). 6\sin(30^{\circ}) \rangle = \langle 6 \cdot \dfrac{\sqrt{3}}{2}, 6 \cdot \dfrac{1}{2} \rangle = \langle 3\sqrt{3} 3 \rangle\nonumber\]
The second vector is only in the horizontal direction, so can be written as \(\langle -7, 0 \rangle\).
The third vector with magnitude 4 Newtons at an angle of 300 degrees will have components
\[\langle 4 \cos(300^{\circ}), 4\sin(300^{\circ}) \rangle = \langle 4 \cdot \dfrac{1}{2}, 4 \cdot \dfrac{-\sqrt{3}}{2} \rangle = \langle 2, -2\sqrt{3} \rangle\nonumber\]
To keep the object in equilibrium, we need to find a force vector \(x\), \(y\) so the sum of the four vectors is the zero vector, \(\langle 0, 0 \rangle\).
\[\langle 3\sqrt{3}, 3 \rangle + \langle -7, 0 \rangle + \langle 2, -2\sqrt{3} \rangle + \langle x, y \rangle = \langle 0, 0 \rangle\nonumber\]Add component-wise
\[\langle 3\sqrt{3} - 7 + 2, 3 + 0 - 2\sqrt{3} \rangle + \langle x, y \rangle = \langle 0, 0 \rangle\nonumber\]Simplify
\[\langle 3\sqrt{3} - 5, 3 - 2\sqrt{3} \rangle + \langle x, y \rangle = \langle 0, 0 \rangle\nonumber\]Solve
\[\langle x, y \rangle = \langle 0, 0 \rangle - \langle 3\sqrt{3} - 5, 3 - 2\sqrt{3} \rangle\nonumber\]
\[\langle x, y \rangle = \langle -3\sqrt{3} + 5, -3 + 2\sqrt{3} \rangle \approx \langle -0.196, 0.464 \rangle\nonumber\]
This vector gives in components the force that would need to be applied to keep the object in equilibrium. If desired, we could find the magnitude of this force and direction it would need to be applied in.
\[\text{Magnitude} = \sqrt{(-0.196)^2 + 0.464^2} = 0.504\text{ N}\nonumber\]
Angle:
\[\tan(\theta) = \dfrac{0.464}{-0.196}\nonumber\]
\[\theta = \tan^{-1} (\dfrac{0.464}{-0.196} = -67.089^{\circ}\nonumber\]
This is in the wrong quadrant, so we adjust by finding the next angle with the same tangent value by adding a full period of tangent:
\[\theta = -67.089^{\circ} + 180^{\circ} = 112. 911^{circ}\nonumber\]
To keep the object in equilibrium, a force of 0.504 Newtons would need to be applied at an angle of \(112.911^{\circ}\)
Important Topics of This Section
- Vectors, magnitude (length) & direction Addition of vectors
- Scaling of vectors
- Components of vectors
- Vectors as velocity
- Vectors as forces
- Adding & Scaling vectors in component form Total distance travelled vs. total displacement


9.5: Physiology of the Cardiovascular System
Pulmonary and Systemic Circulation
There are two distinct but linked circuits in the human circulation called pulmonary and systemic circuits.
The pulmonary circuit transports oxygenated blood from the right ventricle to the lungs, where carbon dioxide is delivered for exhalation, oxygen is picked up, and this newly oxygenated blood returns to the left atrium of the heart. [1]
The systemic circuit transports oxygenated blood from the left ventricle of the heart, through the aorta, and into the systemic arteries throughout the body where it diffuses into the tissues at the capillaries. Deoxygenated blood travels back to the heart by entering small veins that merge and eventually drain into the superior and inferior vena cava and into the right atrium of the heart. See Figure 9.7 [2] for an illustration of blood flow through the pulmonary and systemic circuits. [3]
Transportation
The systemic and pulmonary circuits transport blood and its components for physiological processes that occur throughout the body [4] :
- The right ventricle pumps deoxygenated blood through the pulmonary arteries away from the heart to the lungs. (Note this is the only place in the body where arteries carry deoxygenated blood.) Oxygen from air inhaled into the lungs diffuses into the pulmonary capillaries through the thin walls of the alveoli. At the same time, carbon dioxide diffuses out of the pulmonary capillaries into the alveoli and then exhaled out of the body. The pulmonary veins return oxygenated blood to the left atria of the heart, which moves into the left ventricle where it is pumped out to the rest of the body via the aorta to the systemic arteries.
- Nutrients from the foods eaten are absorbed in the small intestine, where they diffuse into the systemic circulation and are transported to the liver through the hepatic portal vein and then throughout the rest of the body.
- Systemic arteries carry oxygenated blood to the liver where it mixes with the nutrient-rich blood coming in from the hepatic portal vein. Wastes and toxins are filtered out of the blood, bile is produced to help remove wastes and break down fats, medications are metabolized, and nutrients are broken down.
- Systemic arteries carry blood to the kidneys, where wastes are filtered out and urine is created.
- Endocrine glands scattered throughout the body release hormones into the bloodstream where they are transported to distant target cells.
Heart Rate
Heart rate (HART RĀT) (HR) is the number of heart beats per minute (bpm). HR can vary considerably among people based on their age, as well as their fitness level. For an adult, normal resting HR is 60–100 bpm. Although similar to the pulse, the heart rate is auscultated directly using a stethoscope and is a more accurate measurement than the pulse. [5]
Abnormal heart rates are referred to as bradycardia and tachycardia. Bradycardia (brād-i-KARD-ē-ă) refers to a slow heart rate, less than 60 bpm in an adult. Tachycardia (tak-ē-KARD-ē-ă) refers to a fast heart rate, greater than 100 bpm in an adult. Read more about bradycardia and tachycardia in the “Diseases and Disorders of the Cardiovascular System” section.
Pulse
Each time the heart pumps, ejecting blood forcefully into the circulation, the arteries expand and recoil to accommodate the surge of blood moving through them. This expansion and recoiling of the arterial wall are called the pulse (PULS) and allow for the measurement of heart rate. The pulse can be palpated manually by placing the tips of the fingers across an artery that runs close to the body surface, such as the radial artery (on the thumb side of the wrist) or the common carotid artery (in the neck). [6] These sites and other pulse sites are shown in Figure 9.8 [7] below.
Both the rate and the strength of the pulse are important clinically. A high pulse rate can be temporarily caused by physical activity, but an extended fast or irregular pulse may indicate a heart condition. The pulse strength indicates the strength of ventricular contraction, cardiac output, and perfusion. Cardiac output (KAR-dē-ăk OUT-put) is the amount of blood pumped by the heart per minute. Perfusion (pĕr-FŪ-zhŏn) is the passage of blood through the blood vessels. [8]
If the pulse is strong, then cardiac output is high and perfusion to that site is good. If the pulse is weak, cardiac output is low or perfusion is impaired, and medical intervention may be warranted.
Cardiac Cycle
The period of time that begins with contraction of the atria, continues through ventricular contraction, and ends with ventricular relaxation is known as the cardiac cycle. The phase of the cardiac cycle when ventricles contract and eject blood is called systole (SIS-tŏ-lē). The phase of the cardiac cycle where the heart muscles relax, allowing the chambers to fill with blood, is called diastole (dī-AS-tŏ-lē). [9]
Blood Pressure
Blood pressure (BLŬD PRESH-ŭr) (BP) is the force of the blood against the vessel walls.  The cuff is placed over the brachial artery of the patient’s upper arm and inflated with air to temporarily occlude (ŏ-KLOOD) (block) blood flow and measure blood pressure. Blood pressure is recorded as a ratio of two numbers expressed as systolic pressure over diastolic pressure, measured in millimeters of mercury (mm Hg). For example, 120/80 mm Hg is a normal adult blood pressure. The systolic pressure is the higher value and reflects the arterial pressure resulting from the ejection of blood during ventricular contraction called systole. The diastolic pressure is the lower value and represents the arterial pressure of blood during ventricular relaxation called diastole. [10]
Low blood pressure, called hypotension (hī-pō-TEN-shŏn), has several causes, such as dehydration, vomiting, diarrhea, or medications used to treat hypertension. Treatment for hypotension typically includes fluid replacement. High blood pressure is called hypertension (hī-pĕr-TEN-shŏn) (HTN) . Hypertension has a variety of causes, with risk factors such as obesity, lack of exercise, smoking, high salt diet, diabetes, and kidney disease.
- This work is a derivative of Anatomy and Physiology by OpenStax licensed under CC BY 4.0. Access for free at https://openstax.org/books/anatomy-and-physiology/pages/1-introduction ↵
- “2003_Dual_System_of_Human_Circulation.jpg” by OpenStax College is licensed under CC BY 3.0 ↵
- This work is a derivative of Anatomy and Physiology by OpenStax licensed under CC BY 4.0. Access for free at https://openstax.org/books/anatomy-and-physiology/pages/1-introduction ↵
- This work is a derivative of Anatomy and Physiology by OpenStax licensed under CC BY 4.0. Access for free at https://openstax.org/books/anatomy-and-physiology/pages/1-introduction ↵
- This work is a derivative of Anatomy and Physiology by OpenStax licensed under CC BY 4.0. Access for free at https://openstax.org/books/anatomy-and-physiology/pages/1-introduction ↵
- This work is a derivative of Anatomy and Physiology by OpenStax licensed under CC BY 4.0. Access for free at https://openstax.org/books/anatomy-and-physiology/pages/1-introduction ↵
- “ 2110_Pulse_Sites.jpg ” by OpenStax College is licensed under CC BY 3.0 ↵
- This work is a derivative of Anatomy and Physiology by OpenStax licensed under CC BY 4.0. Access for free at https://openstax.org/books/anatomy-and-physiology/pages/1-introduction ↵
- This work is a derivative of Anatomy and Physiology by OpenStax licensed under CC BY 4.0. Access for free at https://openstax.org/books/anatomy-and-physiology/pages/1-introduction ↵
- This work is a derivative of Anatomy and Physiology by OpenStax licensed under CC BY 4.0. Access for free at https://openstax.org/books/anatomy-and-physiology/pages/1-introduction ↵