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The pelvic girdle attaches the legs to the axial skeleton. The hip joint is where the pelvic girdle and the leg come together. The hip is joined to the pelvic girdle by many muscles. In the gluteal region, the psoas major and iliacus form the iliopsoas. The large and strong gluteus maximus, gluteus medius, and gluteus ... | {
"Header 1": "**11.6 | Appendicular Muscles of the Pelvic Girdle and Lower Limbs**",
"Header 3": "**[11.6 Appendicular Muscles of the Pelvic Girdle and Lower Limbs](#page-459-0)**",
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After studying this chapter, you will be able to:
- Name the major divisions of the nervous system, both anatomical and functional
- Describe the functional and structural differences between gray matter and white matter structures
- Name the parts of the multipolar neuron in order of polarity
- List the types of g... | {
"Header 1": "**Chapter Objectives**",
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By the end of this section, you will be able to:
- Identify the anatomical and functional divisions of the nervous system
- Relate the functional and structural differences between gray matter and white matter structures of the nervous system to the structure of neurons
- List the basic functions of the nervous syste... | {
"Header 1": "**12.1 | Basic Structure and Function of the Nervous System**",
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"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
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The nervous system can be divided into two major regions: the central and peripheral nervous systems. The **central nervous system (CNS)** is the brain and spinal cord, and the **peripheral nervous system (PNS)** is everything else (**[Figure 12.2](#page-482-0)**). The brain is contained within the cranial cavity of th... | {
"Header 1": "**12.1 | Basic Structure and Function of the Nervous System**",
"Header 3": "**The Central and Peripheral Nervous Systems**",
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The nervous system can also be divided on the basis of its functions, but anatomical divisions and functional divisions are different. The CNS and the PNS both contribute to the same functions, but those functions can be attributed to different regions of the brain (such as the cerebral cortex or the hypothalamus) or t... | {
"Header 1": "**12.1 | Basic Structure and Function of the Nervous System**",
"Header 3": "**Functional Divisions of the Nervous System**",
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The nervous system is involved in receiving information about the environment around us (sensation) and generating responses to that information (motor responses). The nervous system can be divided into regions that are responsible for **sensation** (sensory functions) and for the **response** (motor functions). But th... | {
"Header 1": "**12.1 | Basic Structure and Function of the Nervous System**",
"Header 3": "**Basic Functions**",
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The nervous system can be divided into two parts mostly on the basis of a functional difference in responses. The **somatic nervous system (SNS)** is responsible for conscious perception and voluntary motor responses. Voluntary motor response means the contraction of skeletal muscle, but those contractions are not alwa... | {
"Header 1": "**12.1 | Basic Structure and Function of the Nervous System**",
"Header 3": "**Controlling the Body**",
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Have you ever heard the claim that humans only use 10 percent of their brains? Maybe you have seen an advertisement on a website saying that there is a secret to unlocking the full potential of your mind—as if there were 90 percent of your brain sitting idle, just waiting for you to use it. If you see an ad like that, ... | {
"Header 1": "**12.1 | Basic Structure and Function of the Nervous System**",
"Header 3": "**How Much of Your Brain Do You Use?**",
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As you learned in the first section, the main part of a neuron is the cell body, which is also known as the soma (soma = "body"). The cell body contains the nucleus and most of the major organelles. But what makes neurons special is that they have many extensions of their cell membranes, which are generally referred to... | {
"Header 1": "**12.2 | Nervous Tissue**",
"Header 3": "**Parts of a Neuron**",
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There are many neurons in the nervous system—a number in the trillions. And there are many different types of neurons. They can be classified by many different criteria. The first way to classify them is by the number of processes attached to the cell body. Using the standard model of neurons, one of these processes is... | {
"Header 1": "**12.2 | Nervous Tissue**",
"Header 3": "**Types of Neurons**",
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Glial cells, or neuroglia or simply glia, are the other type of cell found in nervous tissue. They are considered to be supporting cells, and many functions are directed at helping neurons complete their function for communication. The name glia comes from the Greek word that means "glue," and was coined by the German ... | {
"Header 1": "**12.2 | Nervous Tissue**",
"Header 3": "**Glial Cells**",
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One cell providing support to neurons of the CNS is the **astrocyte**, so named because it appears to be star-shaped under the microscope (astro- = "star"). Astrocytes have many processes extending from their main cell body (not axons or dendrites like neurons, just cell extensions). Those processes extend to interact ... | {
"Header 1": "**12.2 | Nervous Tissue**",
"Header 3": "**Glial Cells of the CNS**",
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One of the two types of glial cells found in the PNS is the **satellite cell**. Satellite cells are found in sensory and autonomic ganglia, where they surround the cell bodies of neurons. This accounts for the name, based on their appearance under the microscope. They provide support, performing similar functions in th... | {
"Header 1": "**12.2 | Nervous Tissue**",
"Header 3": "**Glial Cells of the PNS**",
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The insulation for axons in the nervous system is provided by glial cells, oligodendrocytes in the CNS, and Schwann cells in the PNS. Whereas the manner in which either cell is associated with the axon segment, or segments, that it insulates is different, the means of myelinating an axon segment is mostly the same in t... | {
"Header 1": "**12.2 | Nervous Tissue**",
"Header 3": "**Myelin**",
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Several diseases can result from the demyelination of axons. The causes of these diseases are not the same; some have genetic causes, some are caused by pathogens, and others are the result of autoimmune disorders. Though the causes are varied, the results are largely similar. The myelin insulation of axons is compromi... | {
"Header 1": "**12.2 | Nervous Tissue**",
"Header 3": "**Nervous Tissue**",
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By the end of this section, you will be able to:
- Distinguish the major functions of the nervous system: sensation, integration, and response
- List the sequence of events in a simple sensory receptor–motor response pathway
Having looked at the components of nervous tissue, and the basic anatomy of the nervous sys... | {
"Header 1": "**12.3 | The Function of Nervous Tissue**",
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Understanding how the nervous system works could be a driving force in your career. Studying neurophysiology is a very rewarding path to follow. It means that there is a lot of work to do, but the rewards are worth the effort.
The career path of a research scientist can be straightforward: college, graduate school, p... | {
"Header 1": "**12.3 | The Function of Nervous Tissue**",
"Header 3": "**Neurophysiologist**",
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Most cells in the body make use of charged particles, ions, to build up a charge across the cell membrane. Previously, this was shown to be a part of how muscle cells work. For skeletal muscles to contract, based on excitation–contraction coupling, requires input from a neuron. Both of the cells make use of the cell me... | {
"Header 1": "**12.4 | The Action Potential**",
"Header 3": "**Electrically Active Cell Membranes**",
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The electrical state of the cell membrane can have several variations. These are all variations in the **membrane potential**. A potential is a distribution of charge across the cell membrane, measured in millivolts (mV). The standard is to compare the inside of the cell relative to the outside, so the membrane potenti... | {
"Header 1": "**12.4 | The Action Potential**",
"Header 3": "**The Membrane Potential**",
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Resting membrane potential describes the steady state of the cell, which is a dynamic process that is balanced by ion leakage and ion pumping. Without any outside influence, it will not change. To get an electrical signal started, the membrane potential has to change.
This starts with a channel opening for Na<sup>+</... | {
"Header 1": "**12.4 | The Action Potential**",
"Header 3": "**The Action Potential**",
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While an action potential is in progress, another one cannot be initiated. That effect is referred to as the **refractory period**. There are two phases of the refractory period: the **absolute refractory period** and the **relative refractory period**. During the absolute phase, another action potential will not start... | {
"Header 1": "**12.4 | The Action Potential**",
"Header 3": "**The Action Potential**",
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The action potential is initiated at the beginning of the axon, at what is called the initial segment. There is a high density of voltage-gated Na<sup>+</sup> channels so that rapid depolarization can take place here. Going down the length of the axon, the action potential is propagated because more voltage-gated Na<su... | {
"Header 1": "**12.4 | The Action Potential**",
"Header 3": "**Propagation of the Action Potential**",
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Glial cells, especially astrocytes, are responsible for maintaining the chemical environment of the CNS tissue. The concentrations of ions in the extracellular fluid are the basis for how the membrane potential is established and changes in electrochemical signaling. If the balance of ions is upset, drastic outcomes ar... | {
"Header 1": "**12.4 | The Action Potential**",
"Header 3": "**Potassium Concentration**",
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Local changes in the membrane potential are called graded potentials and are usually associated with the dendrites of a neuron. The amount of change in the membrane potential is determined by the size of the stimulus that causes it. In the example of testing the temperature of the shower, slightly warm water would only... | {
"Header 1": "**12.5 | Communication Between Neurons**",
"Header 3": "**Graded Potentials**",
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For the unipolar cells of sensory neurons—both those with free nerve endings and those within encapsulations—graded potentials develop in the dendrites that influence the generation of an action potential in the axon of the same cell. This is called a **generator potential**. For other sensory receptor cells, such as t... | {
"Header 1": "**12.5 | Communication Between Neurons**",
"Header 3": "**Types of Graded Potentials**",
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All types of graded potentials will result in small changes of either depolarization or hyperpolarization in the voltage of a membrane. These changes can lead to the neuron reaching threshold if the changes add together, or **summate**. The combined effects of different types of graded potentials are illustrated in **[... | {
"Header 1": "**12.5 | Communication Between Neurons**",
"Header 3": "**Summation**",
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There are two types of connections between electrically active cells, chemical synapses and electrical synapses. In a **chemical synapse**, a chemical signal—namely, a neurotransmitter—is released from one cell and it affects the other cell. In an **electrical synapse**, there is a direct connection between the two cel... | {
"Header 1": "**12.5 | Communication Between Neurons**",
"Header 3": "**Synapses**",
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When an action potential reaches the axon terminals, voltage-gated Ca2+ channels in the membrane of the synaptic end bulb open. The concentration of Ca2+ increases inside the end bulb, and the Ca2+ ion associates with proteins in the outer surface of neurotransmitter vesicles. The Ca2+ facilitates the merging of the ve... | {
"Header 1": "**12.5 | Communication Between Neurons**",
"Header 3": "**Neurotransmitter Release**",
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There are several systems of neurotransmitters that are found at various synapses in the nervous system. These groups refer to the chemicals that are the neurotransmitters, and within the groups are specific systems.
The first group, which is a neurotransmitter system of its own, is the **cholinergic system**. It is ... | {
"Header 1": "**12.5 | Communication Between Neurons**",
"Header 3": "**Neurotransmitter Systems**",
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The underlying cause of some neurodegenerative diseases, such as Alzheimer's and Parkinson's, appears to be related to proteins—specifically, to proteins behaving badly. One of the strongest theories of what causes Alzheimer's disease is based on the accumulation of beta-amyloid plaques, dense conglomerations of a prot... | {
"Header 1": "**12.5 | Communication Between Neurons**",
"Header 3": "**Nervous System**",
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- **absolute refractory period** time during an action period when another action potential cannot be generated because the voltage-gated Na<sup>+</sup> channel is inactivated
- **action potential** change in voltage of a cell membrane in response to a stimulus that results in transmission of an electrical signal; uniq... | {
"Header 1": "**12.5 | Communication Between Neurons**",
"Header 3": "**KEY TERMS**",
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The nervous system can be separated into divisions on the basis of anatomy and physiology. The anatomical divisions are the central and peripheral nervous systems. The CNS is the brain and spinal cord. The PNS is everything else. Functionally, the nervous system can be divided into those regions that are responsible fo... | {
"Header 1": "**12.5 | Communication Between Neurons**",
"Header 2": "**CHAPTER REVIEW**",
"Header 3": "**[12.1 Basic Struct](#page-480-1)[ure and Function of the Nervous System](#page-481-0)**",
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Nervous tissue contains two major cell types, neurons and glial cells. Neurons are the cells responsible for communication through electrical signals. Glial cells are supporting cells, maintaining the environment around the neurons.
Neurons are polarized cells, based on the flow of electrical signals along their memb... | {
"Header 1": "**12.5 | Communication Between Neurons**",
"Header 2": "**CHAPTER REVIEW**",
"Header 3": "**[12.2 Nervous Tissue](#page-488-0)**",
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Sensation starts with the activation of a sensory ending, such as the thermoreceptor in the skin sensing the temperature of the water. The sensory endings in the skin initiate an electrical signal that travels along the sensory axon within a nerve into the spinal cord, where it synapses with a neuron in the gray matter... | {
"Header 1": "**12.5 | Communication Between Neurons**",
"Header 2": "**CHAPTER REVIEW**",
"Header 3": "**[12.3 The Function of Nervous Tissue](#page-495-0)**",
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The nervous system is characterized by electrical signals that are sent from one area to another. Whether those areas are close or very far apart, the signal must travel along an axon. The basis of the electrical signal is the controlled distribution of ions across the membrane. Transmembrane ion channels regulate when... | {
"Header 1": "**12.5 | Communication Between Neurons**",
"Header 2": "**CHAPTER REVIEW**",
"Header 3": "**[12.4 The Action Potential](#page-498-0)**",
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The basis of the electrical signal within a neuron is the action potential that propagates down the axon. For a neuron to generate an action potential, it needs to receive input from another source, either another neuron or a sensory stimulus. That input will result in opening ion channels in the neuron, resulting in a... | {
"Header 1": "**12.5 | Communication Between Neurons**",
"Header 2": "**CHAPTER REVIEW**",
"Header 3": "**[12.5 Communication Between Neurons](#page-506-0)**",
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**34.** What responses are generated by the nervous system when you run on a treadmill? Include an example of each type of tissue that is under nervous system control.
**35.** When eating food, what anatomical and functional divisions of the nervous system are involved in the perceptual experience?
**36.** Multiple... | {
"Header 1": "**12.5 | Communication Between Neurons**",
"Header 2": "**CRITICAL THINKING QUESTIONS**",
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After studying this chapter, you will be able to:
- Relate the developmental processes of the embryonic nervous system to the adult structures
- Name the major regions of the adult nervous system
- Locate regions of the cerebral cortex on the basis of anatomical landmarks common to all human brains
- Describe the reg... | {
"Header 1": "**Chapter Objectives**",
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By the end of this section, you will be able to:
- Describe the growth and differentiation of the neural tube
- Relate the different stages of development to the adult structures of the central nervous system
- Explain the expansion of the ventricular system of the adult brain from the central canal of the neural tub... | {
"Header 1": "**13.1 | The Embryologic Perspective**",
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To begin, a sperm cell and an egg cell fuse to become a fertilized egg. The fertilized egg cell, or zygote, starts dividing to generate the cells that make up an entire organism. Sixteen days after fertilization, the developing embryo's cells belong to one of three germ layers that give rise to the different tissues in... | {
"Header 1": "**13.1 | The Embryologic Perspective**",
"Header 3": "**The Neural Tube**",
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As the anterior end of the neural tube starts to develop into the brain, it undergoes a couple of enlargements; the result is the production of sac-like vesicles. Similar to a child's balloon animal, the long, straight neural tube begins to take on a new shape. Three vesicles form at the first stage, which are called *... | {
"Header 1": "**13.1 | The Embryologic Perspective**",
"Header 3": "**Primary Vesicles**",
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The brain continues to develop, and the vesicles differentiate further (see **[Figure 13.3b](#page-527-0)**). The three primary vesicles become five **secondary vesicles**. The prosencephalon enlarges into two new vesicles called the **telencephalon** and the **diencephalon**. The telecephalon will become the cerebrum.... | {
"Header 1": "**13.1 | The Embryologic Perspective**",
"Header 3": "**Secondary Vesicles**",
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Embryonic development can help in understanding the structure of the adult brain because it establishes a framework on which more complex structures can be built. First, the neural tube establishes the anterior–posterior dimension of the nervous system, which is called the **neuraxis**. The embryonic nervous system in ... | {
"Header 1": "**13.1 | The Embryologic Perspective**",
"Header 3": "**Relating Embryonic Development to the Adult Brain**",
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Early formation of the nervous system depends on the formation of the neural tube. A groove forms along the dorsal surface of the embryo, which becomes deeper until its edges meet and close off to form the tube. If this fails to happen, especially in the posterior region where the spinal cord forms, a developmental def... | {
"Header 1": "**13.1 | The Embryologic Perspective**",
"Header 2": "**Stages of Embryonic Development**",
"Header 3": "**Nervous System**",
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The iconic gray mantle of the human brain, which appears to make up most of the mass of the brain, is the **cerebrum** (**[Figure 13.6](#page-532-0)**). The wrinkled portion is the **cerebral cortex**, and the rest of the structure is beneath that outer covering. There is a large separation between the two sides of the... | {
"Header 1": "**13.2 | The Central Nervous System**",
"Header 3": "**The Cerebrum**",
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The cerebrum is covered by a continuous layer of gray matter that wraps around either side of the forebrain—the cerebral cortex. This thin, extensive region of wrinkled gray matter is responsible for the higher functions of the nervous system. A **gyrus** (plural = gyri) is the ridge of one of those wrinkles, and a **s... | {
"Header 1": "**13.2 | The Central Nervous System**",
"Header 3": "**Cerebral Cortex**",
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Beneath the cerebral cortex are sets of nuclei known as **subcortical nuclei** that augment cortical processes. The nuclei of the basal forebrain serve as the primary location for acetylcholine production, which modulates the overall activity of the cortex, possibly leading to greater attention to sensory stimuli. Alzh... | {
"Header 1": "**13.2 | The Central Nervous System**",
"Header 3": "**Subcortical structures**",
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There is a persistent myth that people are "right-brained" or "left-brained," which is an oversimplification of an important concept about the cerebral hemispheres. There is some lateralization of function, in which the left side of the brain is devoted to language function and the right side is devoted to spatial and ... | {
"Header 1": "**13.2 | The Central Nervous System**",
"Header 3": "**The Myth of Left Brain/Right Brain**",
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The diencephalon is the one region of the adult brain that retains its name from embryologic development. The etymology of the word diencephalon translates to "through brain." It is the connection between the cerebrum and the rest of the nervous system, with one exception. The rest of the brain, the spinal cord, and th... | {
"Header 1": "**13.2 | The Central Nervous System**",
"Header 3": "**The Diencephalon**",
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The **thalamus** is a collection of nuclei that relay information between the cerebral cortex and the periphery, spinal cord, or brain stem. All sensory information, except for the sense of smell, passes through the thalamus before processing by the cortex. Axons from the peripheral sensory organs, or intermediate nucl... | {
"Header 1": "**13.2 | The Central Nervous System**",
"Header 3": "**Thalamus**",
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Inferior and slightly anterior to the thalamus is the **hypothalamus**, the other major region of the diencephalon. The hypothalamus is a collection of nuclei that are largely involved in regulating homeostasis. The hypothalamus is the executive region in charge of the autonomic nervous system and the endocrine system ... | {
"Header 1": "**13.2 | The Central Nervous System**",
"Header 3": "**Hypothalamus**",
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The midbrain and hindbrain (composed of the pons and the medulla) are collectively referred to as the brain stem (**[Figure](#page-539-0) [13.12](#page-539-0)**). The structure emerges from the ventral surface of the forebrain as a tapering cone that connects the brain to the spinal cord. Attached to the brain stem, bu... | {
"Header 1": "**13.2 | The Central Nervous System**",
"Header 3": "**Brain Stem**",
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One of the original regions of the embryonic brain, the midbrain is a small region between the thalamus and pons. It is separated into the **tectum** and **tegmentum**, from the Latin words for roof and floor, respectively. The cerebral aqueduct passes through the center of the midbrain, such that these regions are the... | {
"Header 1": "**13.2 | The Central Nervous System**",
"Header 3": "**Midbrain**",
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"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
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The **cerebellum**, as the name suggests, is the "little brain." It is covered in gyri and sulci like the cerebrum, and looks like a miniature version of that part of the brain (**[Figure 13.13](#page-540-0)**). The cerebellum is largely responsible for comparing information from the cerebrum with sensory feedback from... | {
"Header 1": "**13.2 | The Central Nervous System**",
"Header 3": "**The Cerebellum**",
"token_count": 458,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
The description of the CNS is concentrated on the structures of the brain, but the spinal cord is another major organ of the system. Whereas the brain develops out of expansions of the neural tube into primary and then secondary vesicles, the spinal cord maintains the tube structure and is only specialized into certain... | {
"Header 1": "**13.2 | The Central Nervous System**",
"Header 3": "**The Spinal Cord**",
"token_count": 542,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
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In cross-section, the gray matter of the spinal cord has the appearance of an ink-blot test, with the spread of the gray matter on one side replicated on the other—a shape reminiscent of a bulbous capital "H." As shown in **[Figure 13.14](#page-542-0)**, the gray matter is subdivided into regions that are referred to a... | {
"Header 1": "**13.2 | The Central Nervous System**",
"Header 3": "**Gray Horns**",
"token_count": 362,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
Just as the gray matter is separated into horns, the white matter of the spinal cord is separated into columns. **Ascending tracts** of nervous system fibers in these columns carry sensory information up to the brain, whereas **descending tracts** carry motor commands from the brain. Looking at the spinal cord longitud... | {
"Header 1": "**13.2 | The Central Nervous System**",
"Header 3": "**White Columns**",
"token_count": 349,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
Parkinson's disease is a disorder of the basal nuclei, specifically of the substantia nigra, that demonstrates the effects of the direct and indirect pathways. Parkinson's disease is the result of neurons in the substantia nigra pars compacta dying. These neurons release dopamine into the striatum. Without that modulat... | {
"Header 1": "**13.2 | The Central Nervous System**",
"Header 3": "**Basal Nuclei**",
"token_count": 514,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
By the end of this section, you will be able to:
- Describe the vessels that supply the CNS with blood
- Name the components of the ventricular system and the regions of the brain in which each is located
- Explain the production of cerebrospinal fluid and its flow through the ventricles
- Explain how a disruption in... | {
"Header 1": "**13.3 | Circulation and the Central Nervous System**",
"token_count": 264,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
The major artery carrying recently oxygenated blood away from the heart is the aorta. The very first branches off the aorta supply the heart with nutrients and oxygen. The next branches give rise to the **common carotid arteries**, which further branch into the **internal carotid arteries**. The external carotid arteri... | {
"Header 1": "**13.3 | Circulation and the Central Nervous System**",
"Header 3": "**Arterial Supply**",
"token_count": 605,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
After passing through the CNS, blood returns to the circulation through a series of **dural sinuses** and veins (**[Figure 13.16](#page-546-0)**). The **superior sagittal sinus** runs in the groove of the longitudinal fissure, where it absorbs CSF from the meninges. The superior sagittal sinus drains to the confluence ... | {
"Header 1": "**13.3 | Circulation and the Central Nervous System**",
"Header 3": "**Venous Return**",
"token_count": 208,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
The outer surface of the CNS is covered by a series of membranes composed of connective tissue called the **meninges**, which protect the brain. The **dura mater** is a thick fibrous layer and a strong protective sheath over the entire brain and spinal cord. It is anchored to the inner surface of the cranium and verteb... | {
"Header 1": "**13.3 | Circulation and the Central Nervous System**",
"Header 3": "**Protective Coverings of the Brain and Spinal Cord**",
"token_count": 327,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
The outer surface of the CNS is covered in the thin fibrous membrane of the pia mater. It is thought to have a continuous layer of cells providing a fluid-impermeable membrane. The name pia mater comes from the Latin for "tender mother," suggesting the thin membrane is a gentle covering for the brain. The pia extends i... | {
"Header 1": "**13.3 | Circulation and the Central Nervous System**",
"Header 3": "**Pia Mater**",
"token_count": 235,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
Meningitis is an inflammation of the meninges, the three layers of fibrous membrane that surround the CNS. Meningitis can be caused by infection by bacteria or viruses. The particular pathogens are not special to meningitis; it is just an inflammation of that specific set of tissues from what might be a broader infecti... | {
"Header 1": "**13.3 | Circulation and the Central Nervous System**",
"Header 3": "**Meninges**",
"token_count": 485,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
There are four ventricles within the brain, all of which developed from the original hollow space within the neural tube, the **central canal**. The first two are named the **lateral ventricles** and are deep within the cerebrum. These ventricles are connected to the **third ventricle** by two openings called the **int... | {
"Header 1": "**13.3 | Circulation and the Central Nervous System**",
"Header 3": "**The Ventricles**",
"token_count": 794,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
The choroid plexuses are found in all four ventricles. Observed in dissection, they appear as soft, fuzzy structures that may still be pink, depending on how well the circulatory system is cleared in preparation of the tissue. The CSF is produced from components extracted from the blood, so its flow out of the ventricl... | {
"Header 1": "**13.3 | Circulation and the Central Nervous System**",
"Header 3": "**Cerebrospinal Fluid Circulation**",
"token_count": 782,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
The supply of blood to the brain is crucial to its ability to perform many functions. Without a steady supply of oxygen, and to a lesser extent glucose, the nervous tissue in the brain cannot keep up its extensive electrical activity. These nutrients get into the brain through the blood, and if blood flow is interrupte... | {
"Header 1": "**13.3 | Circulation and the Central Nervous System**",
"Header 3": "**Central Nervous System**",
"token_count": 613,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
A ganglion is a group of neuron cell bodies in the periphery. Ganglia can be categorized, for the most part, as either sensory ganglia or autonomic ganglia, referring to their primary functions. The most common type of sensory ganglion is a **dorsal (posterior) root ganglion**. These ganglia are the cell bodies of neur... | {
"Header 1": "**13.4 | The Peripheral Nervous System**",
"Header 3": "**Ganglia**",
"token_count": 1315,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
Bundles of axons in the PNS are referred to as nerves. These structures in the periphery are different than the central counterpart, called a tract. Nerves are composed of more than just nervous tissue. They have connective tissues invested in their structure, as well as blood vessels supplying the tissues with nourish... | {
"Header 1": "**13.4 | The Peripheral Nervous System**",
"Header 3": "**Nerves**",
"token_count": 556,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
The nerves attached to the brain are the cranial nerves, which are primarily responsible for the sensory and motor functions of the head and neck (one of these nerves targets organs in the thoracic and abdominal cavities as part of the parasympathetic nervous system). There are twelve cranial nerves, which are designat... | {
"Header 1": "**13.4 | The Peripheral Nervous System**",
"Header 3": "**Cranial Nerves**",
"token_count": 1353,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
The nerves connected to the spinal cord are the spinal nerves. The arrangement of these nerves is much more regular than that of the cranial nerves. All of the spinal nerves are combined sensory and motor axons that separate into two nerve roots. The sensory axons enter the spinal cord as the dorsal nerve root. The mot... | {
"Header 1": "**13.4 | The Peripheral Nervous System**",
"Header 3": "**Spinal Nerves**",
"token_count": 1209,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
Anosmia is the loss of the sense of smell. It is often the result of the olfactory nerve being severed, usually because of blunt force trauma to the head. The sensory neurons of the olfactory epithelium have a limited lifespan of approximately one to four months, and new ones are made on a regular basis. The new neuron... | {
"Header 1": "**13.4 | The Peripheral Nervous System**",
"Header 3": "**Nervous System**",
"token_count": 336,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
**abducens nerve** sixth cranial nerve; responsible for contraction of one of the extraocular muscles - **alar plate** developmental region of the spinal cord that gives rise to the posterior horn of the gray matter - **amygdala** nucleus deep in the temporal lobe of the cerebrum that is related to memory and emotional... | {
"Header 1": "**13.4 | The Peripheral Nervous System**",
"Header 3": "**KEY TERMS**",
"token_count": 1752,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
The development of the nervous system starts early in embryonic development. The outer layer of the embryo, the ectoderm, gives rise to the skin and the nervous system. A specialized region of this layer, the neuroectoderm, becomes a groove that folds in and becomes the neural tube beneath the dorsal surface of the emb... | {
"Header 1": "**13.4 | The Peripheral Nervous System**",
"Header 3": "**[13.1 The Embryo](#page-524-1)[logic Perspective](#page-525-0)**",
"token_count": 366,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
The adult brain is separated into four major regions: the cerebrum, the diencephalon, the brain stem, and the cerebellum. The cerebrum is the largest portion and contains the cerebral cortex and subcortical nuclei. It is divided into two halves by the longitudinal fissure.
The cortex is separated into the frontal, pa... | {
"Header 1": "**13.4 | The Peripheral Nervous System**",
"Header 3": "**[13.2 The Central Nervous System](#page-531-0)**",
"token_count": 506,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
The CNS has a privileged blood supply established by the blood-brain barrier. Establishing this barrier are anatomical structures that help to protect and isolate the CNS. The arterial blood to the brain comes from the internal carotid and vertebral arteries, which both contribute to the unique circle of Willis that pr... | {
"Header 1": "**13.4 | The Peripheral Nervous System**",
"Header 3": "**[13.3 Circulation and the Central Nervous System](#page-544-0)**",
"token_count": 362,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
The PNS is composed of the groups of neurons (ganglia) and bundles of axons (nerves) that are outside of the brain and spinal cord. Ganglia are of two types, sensory or autonomic. Sensory ganglia contain unipolar sensory neurons and are found on the dorsal root of all spinal nerves as well as associated with many of th... | {
"Header 1": "**13.4 | The Peripheral Nervous System**",
"Header 3": "**[13.4 The Peripheral Nervous System](#page-551-0)**",
"token_count": 281,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
After studying this chapter, you will be able to:
- Describe the components of the somatic nervous system
- Name the modalities and submodalities of the sensory systems
- Distinguish between general and special senses
- Describe regions of the central nervous system that contribute to somatic functions
- Explain the ... | {
"Header 1": "**Chapter Objectives**",
"token_count": 715,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
By the end of this section, you will be able to:
- Describe different types of sensory receptors
- Describe the structures responsible for the special senses of taste, smell, hearing, balance, and vision
- Distinguish how different tastes are transduced
- Describe the means of mechanoreception for hearing and balance... | {
"Header 1": "**14.1 | Sensory Perception**",
"token_count": 411,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
The cells that interpret information about the environment can be either (1) a neuron that has a **free nerve ending**, with dendrites embedded in tissue that would receive a sensation; (2) a neuron that has an **encapsulated ending** in which the sensory nerve endings are encapsulated in connective tissue that enhance... | {
"Header 1": "**14.1 | Sensory Perception**",
"Header 3": "**Structural Receptor Types**",
"token_count": 421,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
A third classification of receptors is by how the receptor transduces stimuli into membrane potential changes. Stimuli are of three general types. Some stimuli are ions and macromolecules that affect transmembrane receptor proteins when these chemicals diffuse across the cell membrane. Some stimuli are physical variati... | {
"Header 1": "**14.1 | Sensory Perception**",
"Header 3": "**Functional Receptor Types**",
"token_count": 296,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
Ask anyone what the senses are, and they are likely to list the five major senses—taste, smell, touch, hearing, and sight. However, these are not all of the senses. The most obvious omission from this list is balance. Also, what is referred to simply as touch can be further subdivided into pressure, vibration, stretch,... | {
"Header 1": "**14.1 | Sensory Perception**",
"Header 3": "**Sensory Modalities**",
"token_count": 488,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
Only a few recognized submodalities exist within the sense of taste, or **gustation**. Until recently, only four tastes were recognized: sweet, salty, sour, and bitter. Research at the turn of the 20th century led to recognition of the fifth taste, umami, during the mid-1980s. **Umami** is a Japanese word that means "d... | {
"Header 1": "**14.1 | Sensory Perception**",
"Header 3": "**Gustation (Taste)**",
"token_count": 1632,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
Like taste, the sense of smell, or **olfaction**, is also responsive to chemical stimuli. The olfactory receptor neurons are located in a small region within the superior nasal cavity (**[Figure 14.4](#page-578-0)**). This region is referred to as the **olfactory epithelium** and contains bipolar sensory neurons. Each ... | {
"Header 1": "**14.1 | Sensory Perception**",
"Header 3": "**Olfaction (Smell)**",
"token_count": 643,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
Blunt force trauma to the face, such as that common in many car accidents, can lead to the loss of the olfactory nerve, and subsequently, loss of the sense of smell. This condition is known as **anosmia**. When the frontal lobe of the brain moves relative to the ethmoid bone, the olfactory tract axons may be sheared ap... | {
"Header 1": "**14.1 | Sensory Perception**",
"Header 3": "**Olfactory System: Anosmia**",
"token_count": 304,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
Hearing, or **audition**, is the transduction of sound waves into a neural signal that is made possible by the structures of the ear (**[Figure 14.5](#page-579-0)**). The large, fleshy structure on the lateral aspect of the head is known as the **auricle**. Some sources will also refer to this structure as the pinna, t... | {
"Header 1": "**14.1 | Sensory Perception**",
"Header 3": "**Audition (Hearing)**",
"token_count": 2045,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
Frequencies in the higher ranges of 20 KHz are encoded by hair cells at the base of the cochlea, close to the round and oval windows (**[Figure 14.10](#page-583-0)**). Most auditory stimuli contain a mixture of sounds at a variety of frequencies and intensities (represented by the amplitude of the sound wave). The hair... | {
"Header 1": "**14.1 | Sensory Perception**",
"Header 3": "**Audition (Hearing)**",
"token_count": 493,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
Along with audition, the inner ear is responsible for encoding information about **equilibrium**, the sense of balance. A similar mechanoreceptor—a hair cell with stereocilia—senses head position, head movement, and whether our bodies are in motion. These cells are located within the vestibule of the inner ear. Head po... | {
"Header 1": "**14.1 | Sensory Perception**",
"Header 3": "**Equilibrium (Balance)**",
"token_count": 820,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
Somatosensation is considered a general sense, as opposed to the special senses discussed in this section. Somatosensation is the group of sensory modalities that are associated with touch, proprioception, and interoception. These modalities include pressure, vibration, light touch, tickle, itch, temperature, pain, pro... | {
"Header 1": "**14.1 | Sensory Perception**",
"Header 3": "**Somatosensation (Touch)**",
"token_count": 1086,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
**Vision** is the special sense of sight that is based on the transduction of light stimuli received through the eyes. The eyes are located within either orbit in the skull. The bony orbits surround the eyeballs, protecting them and anchoring the soft tissues of the eye (**Figure 14.13**). The eyelids, with lashes at t... | {
"Header 1": "**14.1 | Sensory Perception**",
"Header 3": "Vision",
"token_count": 2039,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
Light falling on the retina causes chemical changes to pigment molecules in the photoreceptors, ultimately leading to a change in the activity of the RGCs. Photoreceptor cells have two parts, the **inner segment** and the **outer segment** (**[Figure](#page-590-0) [14.16](#page-590-0)**). The inner segment contains t... | {
"Header 1": "**14.1 | Sensory Perception**",
"Header 3": "Vision",
"token_count": 1706,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
Generally, spinal nerves contain afferent axons from sensory receptors in the periphery, such as from the skin, mixed with efferent axons travelling to the muscles or other effector organs. As the spinal nerve nears the spinal cord, it splits into dorsal and ventral roots. The dorsal root contains only the axons of sen... | {
"Header 1": "**14.1 | Sensory Perception**",
"Header 3": "**Spinal Nerves**",
"token_count": 271,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
A sensory pathway that carries peripheral sensations to the brain is referred to as an **ascending pathway**, or ascending tract. The various sensory modalities each follow specific pathways through the CNS. Tactile and other somatosensory stimuli activate receptors in the skin, muscles, tendons, and joints throughout ... | {
"Header 1": "**14.2 | Central Processing**",
"Header 3": "**Spinal Cord and Brain Stem**",
"token_count": 2043,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
Finally, the vestibular nuclei project to the thalamus to join the proprioceptive pathway of the dorsal column system, allowing conscious perception of equilibrium.
**Figure 14.21 Vestibulo-ocular Reflex** Connections between the vestibular system and the cranial nerves controlling eye ... | {
"Header 1": "**14.2 | Central Processing**",
"Header 3": "**Spinal Cord and Brain Stem**",
"token_count": 870,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
The diencephalon is beneath the cerebrum and includes the thalamus and hypothalamus. In the somatic nervous system, the thalamus is an important relay for communication between the cerebrum and the rest of the nervous system. The hypothalamus has both somatic and autonomic functions. In addition, the hypothalamus commu... | {
"Header 1": "**14.2 | Central Processing**",
"Header 3": "**Diencephalon**",
"token_count": 340,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
As described earlier, many of the sensory axons are positioned in the same way as their corresponding receptor cells in the body. This allows identification of the position of a stimulus on the basis of which receptor cells are sending information. The cerebral cortex also maintains this sensory topography in the parti... | {
"Header 1": "**14.2 | Central Processing**",
"Header 3": "**Cortical Processing**",
"token_count": 1502,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
The visual field is projected onto the retinal surface, where photoreceptors transduce light energy into neural signals for the brain to interpret. The retina is a two-dimensional surface, so it does not encode three-dimensional information. However, we can perceive depth. How is that accomplished?
Two ways in which ... | {
"Header 1": "**14.2 | Central Processing**",
"Header 2": "**Depth Perception, 3-D Movies, and Optical Illusions**",
"token_count": 955,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
The failures of sensory perception can be unusual and debilitating. A particular sensory deficit that inhibits an important social function of humans is prosopagnosia, or face blindness. The word comes from the Greek words prosopa, that means "faces," and agnosia, that means "not knowing." Some people may feel that the... | {
"Header 1": "**14.2 | Central Processing**",
"Header 2": "**Depth Perception, 3-D Movies, and Optical Illusions**",
"Header 3": "**Brain: Prosopagnosia**",
"token_count": 491,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
Let's start with sensory stimuli that have been registered through receptor cells and the information relayed to the CNS along ascending pathways. In the cerebral cortex, the initial processing of sensory perception progresses to associative processing and then integration in multimodal areas of cortex. These levels of... | {
"Header 1": "**14.3 | Motor Responses**",
"Header 3": "**Cortical Responses**",
"token_count": 614,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
In generating motor responses, the executive functions of the prefrontal cortex will need to initiate actual movements. One way to define the prefrontal area is any region of the frontal lobe that does not elicit movement when electrically stimulated. These are primarily in the anterior part of the frontal lobe. The re... | {
"Header 1": "**14.3 | Motor Responses**",
"Header 3": "**Secondary Motor Cortices**",
"token_count": 378,
"source_pdf": "datasets/websources/Med_v1/med_textbook/AnatomyAndPhysiology-LR.pdf"
} |
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