Chapter 12 NERVOUS TISSUE Chapter Synopsis An overview of the nervous system describes the structures of the nervous system and their basic functions, along with the organization of the nervous system. Then the histology of neurons and neuroglia is considered along with myelination. Gray and white matter are compared and contrasted. Electrical signals in neurons are discussed based on the ions channels, the resting membrane potential, graded potentials, the action potential, continuous and saltatory conduction, speed of nerve impulse conduction, encoding of stimulus intensity, and comparison of electrical signals produced by excitable cells. The signal transmission at synapses study includes discussion of electrical and chemical synapses, excitatory and inhibitory postsynaptic potentials, removal of neurotransmitters, and spatial and temporal summation of postsynaptic potential. The different classes of neurotransmitters are covered as are circuits in the nervous system. The regeneration and repair of nervous tissue is also covered. Clinical applications discussed include tetanus, local anesthetics, strychnine poisoning, and excitotoxicity. Multiple sclerosis and epilepsy are discussed as two areas of homeostatic imbalance. Chapter Outline and Objectives INTRODUCTION 1. Compare the nervous system and endocrine system in maintaining homeostasis. OVERVIEW OF THE NERVOUS SYSTEM Structures of the Nervous System 2. Identify the structures that make up the nervous system. Functions of the Nervous System 3. List and explain the three basic functions of the nervous system. Organization of the Nervous System 4. Classify the organs of the nervous system into central and peripheral divisions and their subdivisions, and indicate the paths of afferent and efferent information. HISTOLOGY OF NERVOUS TISSUE 5. Contrast the general functions of neuroglia and neurons. Neurons 6. Discuss the property of electrical excitability in regards to neurons. Parts of a Neuron 7. Describe the internal and external structures of the neuron and their functions. 8. Characterize the two means of axonal transport and their use. 9. Discuss the disease tetanus in regards to axonal transport systems. Diversity in Neurons 10. Identify neurons on the basis of their structural and functional classifications. Neuroglia 11. Describe the functions and relative number of neuroglia compared to neurons. 12. Describe the different forms, locations, and purposes of the four types of neuroglia. Myelination 13. Identify the cells that produce myelin, describe how the sheath is formed, and discuss its function. Gray and White Matter 14. Describe the difference between gray and white matter, and give examples of each. ELECTRICAL SIGNALS IN NEURONS 15. Distinguish between action potential and graded potentials. Ion Channels 16. Identify the basic types of ion channels and the stimuli that operate gated ion channels. Resting Membrane Potentials 17. Describe the ions, channels, and integral-protein pumps that contribute to generation of a resting membrane potential. Graded Potentials 18. Discuss the features of the graded potential including areas where generated, size, properties, and type. Generation of an Action Potential 19. List the sequence of events involved in generation of a nerve impulse. 20. Explain why an initial threshold voltage necessitates a complete subsequent sequence of events that produces the set voltage changes of an action potential. Depolarizing Phase 21. Describe the events involved in depolarization of the nerve cell membrane. Repolarizing Phase 22. Describe the repolarization of the nerve cell membrane. Refractory Period 23. Compare the absolute and relative refractory periods and the relation of axon diameter to action potential generation frequency. Propagation of Action Potentials 24. Discuss how the sodium ion flow in one area of an axon leads to initiation of an action potential in an adjacent region of the axon membrane. 25. Discuss the effects of neurotoxins on the nervous system. 26. Discuss the use of local anesthetics to block pain and other somatic sensations. Continuous and Saltatory Conduction 27. Compare and contrast continuous and saltatory conduction. Effect of Axon Diameter 28. Outline the physical and cellular factors and how they alter the rate of action potential propagation along an axon. Encoding of Stimulus Intensity 29. Note the two means through which strength of stimulus is conveyed to the brain even though all action potentials are the same size. Comparison of Electrical Signals Produced by Excitable Cells 30. Describe the differences in magnitude and timing between nerve and various muscle action potentials. SIGNAL TRANSMISSION AT SYNAPSES 31. Explain the events of synaptic transmission. Electrical Synapses 32. Describe the properties of an electrical synapse, the way impulses are transmitted, and the advantages of an electrical synapse. Chemical Synapse 33. Define the anatomic, chemical, enzymatic, and receptor components of a chemical synapse. 34. Go through the sequence of events that allow an action potential on an axon to be transmitted into a graded potential on a postsynaptic membrane. Excitatory and Inhibitory Postsynaptic Potentials 35. Indicate the voltage changes associated with EPSPs and IPSPs, and how these potentials are related to various ion channels. Removal of Neurotransmitter 36. Note the means by which neurotransmitter concentrations in the synaptic cleft are diminished, and the effect on impulse transmission. Spatial and Temporal Summation of Postsynaptic Potentials 37. Distinguish between spatial and temporal summation. 38. Describe the effect the sum of the excitatory and inhibitory effects have on the postsynaptic neuron. 39. Describe the effect of strychnine on normal inhibition. NEUROTRANSMITTERS 40. Describe and give examples and functions of the various neurotransmitter classes. Small-Molecule Neurotransmitters Acetylcholine Amino Acids Biogenic Amines ATP and Other Purines Nitric Oxide Neuropeptides 41. Discuss excitotoxicity. 42. Examine the ways in which substances in the body, drugs, and toxins can modify the effects of neurotransmitters. CIRCUITS IN THE NERVOUS SYSTEM 43. Describe the various types of neuronal circuits in the nervous system. REGENERATION AND REPAIR OF THE NERVOUS SYSTEM 44. Discuss the plasticity of the nervous system. Neurogenesis in the Central Nervous System 45. Describe mechanisms that encourage neurogenesis and neuronal growth. Damage and Repair of the Peripheral Nervous System 46. Discuss the effects of damage on the peripheral nervous system and the steps required for repair. DISORDERS: HOMEOSTATIC IMBALANCES 47. Discuss multiple sclerosis in terms of symptoms, anatomical changes, causes, and treatments. 48. Discuss epilepsy in terms of symptoms, anatomical changes, causes, and treatments. MEDICAL TERMINOLOGY 49. Define the medical terminology associated with the nervous tissue. What’s New and Different in This Chapter The structures and functions of the nervous system are now considered in separate sections. Figure 12.6 includes of photomicrograph of an unmyelinated neuron. Figure 12.8 has been redrawn to enhance voltage gated channels. Neurotoxins have been added to the clinical application, which discusses local anesthetics. Continuous and saltatory conduction has been extensively rewritten. The effects of substances present in the body, drugs, and toxins on neurotransmitters is now a clinical application. Suggested Lecture Outline I. INTRODUCTION A. The nervous system, along with the endocrine system, helps to keep controlled conditions within limits that maintain health and helps to maintain homeostasis. B. The nervous system is responsible for all our behaviors, memories, and movements. C. The branch of medical science that deals with the normal functioning and disorders of the nervous system is called neurology. II. OVERVIEW OF THE NERVOUS SYSTEM A. Structures of the Nervous System 1. The nervous system is made up of the brain, cranial nerves, spinal cord, spinal nerves, ganglia, enteric plexus, and sensory receptors (Figure 12.1). 2. The brain is housed within the skull. 3. Twelve pairs of cranial nerves emerge from the base of the brain through foramina of the skull. 4. A nerve is a bundle of hundreds or thousands of axons, each of which courses along a defined path and serves a specific region of the body. 5. The spinal cord connects to the brain through the foramen magnum of the skull and is encircled by the bones of the vertebral column. 6. Thirty-one pairs of spinal nerves emerge from the spinal cord, each serving a specific region of the body. 7. Ganglia, located outside the brain and spinal cord, are small masses of nervous tissue, containing primarily cell bodies of neurons. 8. Enteric plexuses help regulate the digestive system. 9. Sensory receptors are either parts of neurons or specialized cells that monitor changes in the internal or external environment. B. Functions of the Nervous Systems 1. The sensory function of the nervous system is to sense changes in the internal and external environment through sensory receptors. Sensory neurons serve this function. 2. The integrative function is to analyze the sensory information, store some aspects, and make decisions regarding appropriate behaviors. Association or interneurons serve this function. 3. The motor function is to respond to stimuli by initiating action. Motor neurons serve this function. C. Organization of the Nervous System 1. The central nervous system (CNS) consists of the brain and spinal cord (Figure 12.2). 2. The peripheral nervous system (PNS) consists of cranial and spinal nerves with sensory (efferent) and motor (afferent) components, ganglia, and sensory receptors. a. The sensory system consists of a variety of different receptors as well as sensory neurons. b. The motor system conducts nerve impulses from the CNS to muscles and glands. 3. The PNS is also subdivided into somatic (voluntary), autonomic (involuntary), and enteric nervous systems. a. The somatic nervous system (SNS) consists of neurons that conduct impulses from cutaneous and special sense receptors to the CNS, and motor neurons that conduct impulses from the CNS to skeletal muscle tissue. b. The autonomic nervous system (ANS) contains sensory neurons from visceral organs and motor neurons that convey impulses from the CNS to smooth muscle tissue, cardiac muscle tissue, and glands. 1) The motor part of the ANS consists of the sympathetic division and the parasympathetic division. 2) Usually, the two divisions have opposing actions. c. The enteric nervous system (ENS) consists of neurons in enteric plexuses that extend the length of the GI tract. 1) Many neurons of the enteric plexuses function independently of the ANS and CNS. 2) Sensory neurons of the ENS monitor chemical changes within the GI tract and stretching of its walls, whereas enteric motor neurons govern contraction of GI tract organs, and activity of the GI tract endocrine cells. III. HISTOLOGY OF THE NERVOUS SYSTEM A. Neurons 1. Neurons have the property of electrical excitability. 2. Most neurons, or nerve cells, consist of a cell body (soma), many dendrites, and usually a single axon (Figure 12.3). a. The cell body contains a nucleus, lysosomes, mitochondria, a Golgi complex, cytoplasmic inclusions such as lipofuscin, chromatophilic substances, and neurofibrils. 1) Chromatophilic substances (Nissl bodies) are an orderly arrangement of rough ER. 2) Neurofibrils form the cytoskeleton. b. The dendrites are the receiving or input portions of a neuron. c. The axon conducts nerve impulses from the neuron to the dendrites or cell body of another neuron or to an effector organ of the body (muscle or gland). d. The site of functional contact between two neurons or between a neuron and an effector cell is called a synapse. 3. Axonal transport, a natural mechanism of intracellular transport in neurons, is exploited by certain microorganisms to reach other parts of the nervous system. 4. Fast axonal transport is the route by which some toxins (such as toxins produced by Clostridium tetani bacteria) and disease causing viruses make their way from axon terminals near skin cuts to cell bodies, where they cause damage. (Clinical Application) 5. Diversity in Neurons a. Both structural and functional features are used to classify the various neurons in the body. b. On the basis of the number of processes extending from the cell body (structure), neurons are classified as multipolar, biopolar, and unipolar (Figure 12.4). c. Most neurons in the body are interneurons and are often named for the histologist who first described them. Examples are Purkinje cells (Figure 12.5a) or Renshaw cells. Interneurons named for the shape or appearance include pyramidal cells (Figure 12.5b). B. Neuroglia 1. Neuroglia (or glia) are specialized tissue cells that support neurons, attach neurons to blood vessels, produce the myelin sheath around axons, and carry out phagocytosis. 2. The types of neuroglia include astrocytes, oligodendrocytes, microglia, ependymal cells, neurolemmocytes, (Schwann cells), and satellite cells. 3. Table 12.1 summarizes the types of neuroglia. C. Myelination 1. A multilayered lipid and protein covering called the myelin sheath and produced by Schwann cells and oligodendrocytes surrounds the axons of most neurons (Figure 12.6). 2. The sheath electrically insulates the axon and increases the speed of nerve impulse conduction. 3. Schwann cells produce the myelin sheath in the PNS. a. The outer nucleated cytoplasmic layer of the Schwann cell, which encloses the myelin sheath, is called the neurolemma (sheath of Schwann) and is found only around axons in the PNS. b. The neurolemma aids in regeneration in an injured axon by forming a regeneration tube that guides and stimulates regrowth of the axon (Figure 12.18). c. The myelin sheath has gaps called neurofibril nodes or nodes of Ranvier (Figure 12.4) along the axon. 4. Oligodendrocytes form myelin sheaths for CNS axons. a. No neurolemma is formed. b. No regrowth after injury occurs. D. Gray and White Matter 1. White matter is composed of aggregations of myelinated processes whereas gray matter contains nerve cell bodies, dendrites, and axon terminals or bundles of unmyelinated axons and neuroglia (Figure 12.7). 2. In the spinal cord, gray matter forms an H-shaped inner core, surrounded by white matter; in the brain a thin outer shell of gray matter covers the cerebral hemispheres. 3. A nucleus is a mass of nerve cell bodies and dendrites inside the CNS. IV. ELECTRICAL SIGNALS IN NEURONS A. Excitable cells communicate with each other by action potentials or graded potentials. 1. Action potentials allow communication over short and long distances whereas graded potentials allow communication over short distances only. 2. Production of both types of potentials depend upon the existence of a resting membrane potential and the presence of certain types of ion channels. a. The membrane potential is an electrical voltage across the membrane. b. Graded and action potentials occur because of ion channels in the membrane that allow ion movement across the membrane that can change the membrane potential. B. Ion Channels 1. The two basic types of ion channels are leakage (nongated) and gated. 2. Leakage (nongated) channels are always open. 3. Gated channels open and close in response to some sort of stimulus. a. Gated ion channels respond to voltage changes, ligands (chemicals), and mechanical pressure. b. Voltage-gated channels respond to a direct change in the membrane potential (Figure 12.8a). c. Ligand-gated channels respond to a specific chemical stimulus (Figure 12.8b). d. Mechanically gated ion channels respond to mechanical vibration or pressure. C. Resting Membrane Potential 1. The membrane of a nonconducting neuron is positive outside and negative inside owing to the distribution of different ions across the membrane and the relative permeability of the membrane toward Na+ and K+ (Figure 12.9a). 2. A typical value for the resting membrane potential is -70mV, and the membrane is said to be polarized. 3. The resting membrane potential is determined by the unequal distribution of ions across the plasma membrane and the selective permeability of the membrane to Na+ and K+ . 4. The sodium-potassium pumps compensate for slow leakage of Na+ into the cell by pumping it back out. D. Graded Potentials 1. A graded potential is a small deviation from the resting membrane potential that makes the membrane either more polarized (hyperpolarization) or less polarized (depolarization) (Figure 12.10). 2. Graded potentials occur most often in the dendrites and cell body of a neuron. 3. The signals are graded, meaning they vary in amplitude (size), depending on the strength of the stimulus and localized. E. Generation of an Action Potential 1. An action potential (AP) or impulse is a sequence of rapidly occurring events that decrease and eventually reverse the membrane potential (depolarization) and then restore it to the resting state (repolarization). 2. During an action potential, voltage-gated Na+ and K+ channels open in sequence (Figure 12.11). 3. Rapid opening of voltage-gated Na+ channels causes depolarization. If the depolarization is to threshold, the membrane potential reverses. Depolarization occurs due to the interaction of the two voltage-gated Na+ channel gates: an activation gate and an inactivation gate (Figure 12.12). 4. The slower opening of voltage-gated K+ channels and closing of previously open Na+ channels leads to repolarization, the recovery of the resting membrane potential. 5. According to the all-or-none principle, if a stimulus is strong enough to generate an action potential, the impulse travels at a constant and maximum strength for the existing conditions; a stronger stimulus will not cause a large impulse. 6. During the refractory period (Figure 12.11), another impulse cannot be generated at all (absolute refractory period) or can be triggered only by a suprathreshold stimulus (relative refractory period). 7. An action potential conducts or propagates (travels) from point to point along the membrane; the traveling action potential is a nerve impulse. 8. Local anesthetics and certain neurotoxins prevent opening of voltage-gated Na+ channels so nerve impulses cannot pass the obstructed region. 9. The step-by-step depolarization of each adjacent area of the plasma membrane is called continuous conduction (Figure 12.13a). Nerve impulse conduction in which the impulse jumps from neurofibral node to node is called saltatory conduction (Figure 12.13b). 10. The propagation speed of a nerve impulse is not related to stimulus strength. a. Larger-diameter fibers conduct impulses faster than those with smaller diameters. b. Myelinated fibers conduct impulses faster than unmyelinated fibers. c. Nerve fibers conduct impulses faster when warmed and slower when cooled. 11. The intensity of a stimulus is coded in the rate of impulse production, i.e., the frequency of action potentials. 12. Nerve and muscle action potentials differ in size of the resting membrane potential, duration of the impulses, and velocity of conduction of the impulse. 13. Graded and action potentials differ in amplitude, duration, types of channels used, location, polarity, propagation, and refractory period. The various differences between graded potentials and action potentials are summarized in Table 12.2. VI. SIGNAL TRANSMISSION AT SYNAPSES A. A synapse is the functional junction between one neuron and another or between a neuron and an effector such as a muscle or gland. B. Electrical Synapses 1. At an electrical synapse, ionic current spreads directly from one cell to another through gap junctions (Figure 4.1e). 2. Electrical synapses allow faster communication, can synchronize the activity of a group of neurons or muscle fibers. C. Chemical Synapses 1. At a chemical synapse, there is only one-way information transfer from a presynaptic neuron to a postsynaptic neuron (Figure12.14). 2. Neurotransmitters at chemical synapses cause either an excitatory or inhibitory graded potential. a. An excitatory neurotransmitter is one that can depolarize or make less negative the postsynaptic neuron’s membrane, bringing the membrane potential closer to threshold (Figure 12.10b). 1) A depolarizing postsynaptic potential (PSP) is called an excitatory postsynaptic potential (EPSP). 2) Although a single EPSP normally does not initiate a nerve impulse, the postsynaptic neuron does become more excitable; it is already partially depolarized and thus more likely to reach threshold when the next EPSP occurs. b. An inhibitory neurotransmitter hyperpolarizes the membrane of the postsynaptic neuron, making the inside more negative and generation of a nerve impulse more difficult. A hyperpolarizing PSP is inhibitory and is termed an inhibitory postsynaptic potential (IPSP) (Figure 12.10a). 3. Neurotransmitter is removed from the synaptic cleft in three ways: diffusion, enzymatic degradation, and uptake into cells (neurons and glia). 4. If several presynaptic end bulbs release their neurotransmitter at about the same time, the combined effect may generate a nerve impulse due to summation; summation may be spatial or temporal (Figure 12.15). 5. The postsynaptic neuron is an integrator, receiving and integrating signals, then responding. a. If the excitatory effect is greater than the inhibitory effect but less that the threshold level of stimulation, the result is a subthreshold EPSP, making it easier to generate a nerve impulse. b. If the excitatory effect is greater than the inhibitory effect and reaches or surpasses the threshold level of stimulation, the result is a threshold or suprathreshold EPSP and a nerve impulse. c. If the inhibitory effect is greater than the excitatory effect, the membrane hyperpolarizes (IPSP) with failure to produce a nerve impulse. 6. Table 12.3 summarizes the structural and functional elements of a neuron. 7. Strychnine poisoning demonstrates the importance of inhibitory neurons. (Clinical Application) C. Neurotransmitters 1. Both excitatory and inhibitory neurotransmitters are present in the CNS and PNS; the same neurotransmitter may be excitatory in some locations and inhibitory in others. 2. Important neurotransmitters include acetylcholine, glutamate, aspartate, gamma aminobutyric acid, glycine, norepinephrine, epinephrine, and dopamine. 3. Neurotransmitters can be modified by stimulating or inhibiting neurotransmitter synthesis, blocking or enhancing neurotransmitter release, stimulating or inhibiting neurotransmitter removal, and/or blocking or activating the receptor site. 4. Neurotransmitters can be divided into two classes: small-molecule neurotransmitters and neuropeptides. a. Small-molecule neurotransmitters include acetylcholine, amino acids, biogenic amines, ATP and other purines, and gases. b. Neurotransmitters consisting of 3-40 amino acids linked by peptide bonds are called neuropeptides. 5. Table 12.4 describes neuropeptides and some other neurotransmitters. 6. Substances naturally present in the body, drugs, and toxins can modify the effects of neurotransmitters by: stimulating or inhibiting neurotransmitter synthesis, enhancing or blocking neutotransmitter release. activating or blocking neurotransmitter receptors, or stimulating or inhibiting neurotransmitter removal. VI. NEURONAL CIRCUITS A. Neurons in the CNS are organized into definite patterns called neuronal pools; each pool differs from all others and has its own role in regulating homeostasis. A neuronal pool may contain thousands or even millions of neurons. B. Neuronal pools are organized into circuits. These include simple series, diverging, converging, reverberating, and parallel after-discharge circuits (Figure 12.16). VII. REGENERATION AND REPAIR OF NERVOUS TISSUE A. Throughout life, the nervous system exhibits plasticity, the capability for change with learning. 1. Despite plasticity, neurons have a limited capacity to repair or replicate themselves. 2. In the PNS, damage to dendrites and myelinated axons may be repaired if the cell body remains intact and if Schwann cells are active (Figure 12.19b). 3. In the CNS, there is little or no repair of damage to neurons. B. Current research is going on to find ways to promote neurogenesis and to find ways to encourage and promote regrowth in the CNS. C. Damage and Repair in the Peripheral Nervous System 1. When there is damage to an axon, usually there are changes, called chromatolysis, which occur in the cell body of the affected cell; this causes swelling of the cell body and peaks between 10 and 20 days after injury. 2. By the third to fifth day, degeneration of the distal portion of the neuronal process and myelin sheath (Wallerian degeneration) occurs; afterward, macrophages phagocytize the remains. Retrograde degeneration of the proximal portion of the fiber extends only to the first neurofibral node. 3. Regeneration follows chromatolysis; synthesis of RNA and protein accelerates, favoring rebuilding of the axon and often taking several months. VIII. DISORDERS: HOMEOSTATIC IMBALANCES A. Multiple Sclerosis (MS) 1. Multiple sclerosis is an autoimmune disease that results in the progressive destruction of myelin sheaths in neurons in the CNS. 2. Myelin sheaths deteriorate to scleroses, which are hardened scars or plaques, in multiple regions. 3. This is a progressive debilitating disease. B. Epilepsy 1. The second most common neurological disorder after stroke is epilepsy, which affects 1% of the population. It is characterized by short, recurrent, periodic attacks of motor, sensory, or psychological malfunction called epileptic seizures. 2. These seizures are initiated by abnormal synchronous electrical discharges from millions of neurons in the brain, perhaps resulting from abnormal reverberating circuits. 3. Epilepsy has many causes, including brain damage at birth, the most common cause; metabolic disturbances, infections, toxins, vascular disturbances, head injuries, and tumors and abscesses of the brain. Most epileptic seizures, however, are idiopathic (i.e., they have no demonstrable cause). 4. Epileptic seizures can be eliminated or alleviated by drugs that depress neuronal excitability. Teaching Tips Since myelination is incomplete at birth and continues through childhood, certain functions of the nervous system are modified during that time period. One example is coordination of movements. Another is voluntary control of the external urethral sphincter muscle at the outlet of the urinary bladder. Children gradually gain greater ability to voluntarily constrict the external urethral sphincter when there is an urge to urinate, to control the timing of voiding urine. Myelination of the nerves that control this set of muscles is usually complete by sometime in the third year; prior to this time, efforts to teach toileting are often frustrating for both parent and child. Remind students that muscle fibers (cells) are also capable of producing action potentials. Also, if you have not already done so, point out that muscle fibers (cells) are not analogous to nerve fibers (a term that usually refers to axons, and sometimes dendrites, and their enclosing sheaths). A nerve fiber is only a portion of the entire neuron, unlike a muscle fiber, which includes the whole cell. These terms are often confusing unless care is taken to distinguish their meanings in class. Since students generally have some difficulty in understanding the concepts presented in this chapter due to the complexity of the information, it would be helpful to their understanding to direct them to view the A.D.A.M. Interactive Physiology CD-ROMs: Nervous System I and Nervous System II. These CDs present the information in an interactive format and have proved to be very helpful in student understanding. Critical Thinking Questions 1. Given a diagram of a multi-polar neuron, carefully detail the events that occur in each part of the neuron and the functions of each part of the neuron. 2. You have a patient who has been diagnosed with MS. The patient wants to know exactly what is happening to his body. Explain the normal formation and function of the myelin sheaths and what is occurring to the myelin sheaths in your patient’s body. Educational Resources (refer to Education Resources Appropriate for All Chapters following the list of Suppliers and Distributors) Videocassettes The Anatomy and Physiology Video Series: The Nervous System (27 min; NIMCO) - contains a complete discussion of the parts of the nervous system and their functions Animated Neuroscience and the Action of Nicotine, Cocaine, and Marijuana in the Brain (24 min; FHS) - shows nerve cell communication and nerve impulse conduction The Brain (23 min; FHS) - topics include how nerve impulses are transmitted, how chemical neurotransmitters work Brain and Nervous System (25 min; FHS) - topics include electrical impulses The Human Body: Nervous System (14 min; 1993; COR) - discusses all aspects of the nervous system The Human Body Series: The Biological Basis of Thinking (28 min; 1993; NIMCO) discusses the chemical and neural process of brain activity The Human Body Series: Nerves and Nerve Cells (28 min; 1993; NIMCO) - shows the structure and functioning of nerve cells The Human Nervous System (12 min; SVE) - describes the functions of neurons among other topics The Living Body: Decision (28 min; 1990; FHS) - shows how circuits and individual nerve cells work; describes how the brain coordinates function The Living Body: Nerves at Work ( 27 min; 1990; FHS) - looks at nerve signals and how they are transmitted and reflex signals The Nature of the Nerve Impulse (15 min; 1988; FHS) - describes the nerve impulse Computer Resources (CD-ROMs for Windows and Macintosh platforms unless otherwise noted) A.D.A.M. Interactive Physiology CD-ROM: The Nervous System I (ADAM) - discusses neurons and the action potential A.D.A.M. Interactive Physiology CD-ROM: The Nervous System II (1999, ADAM) - discusses the neuron, synaptic potentials and neurotransmitters A Primer of Brain Anatomy and Function (1997; DGI) - discusses nervous system cell structure and function and electrochemical signaling including conduction and neurotransmission Slides: 35 MM Histology of the Nervous System (20 slides; CVB) - shows cell components of the nervous system The Nervous System and Its Function (20 slides; CVB) - includes neural transmission, major brain area, spinal cord Selected Readings Barinaga, M. “Dendrites Shed Their Dull Image,” Science 268:200-201 (1995) Blood, R. E. “Neuropeptides,” Scientific American (October 1981) Dunant, Y., and M. Israel, “The Release of Acetylcholine,” Scientific American (March 1985) Kimelberg, H. and M. Norenberg. “Astrocytes,” Scientific American (April 1989) Lipkin, R. “Neural Code Breakers,” Science News 149:392-393 (1996) Morell, P., and W. T. Norton. “Myelin,” Scientific American (May 1980) Stevens, C. F. “The Neuron,” Scientific American (September 1979) Streit, W. and C. Kincaid-Coltron. “The Brain’s Immune System,” Scientific American (November 1995) Travis, J. “Glia: The Brain’s Other Cells,” Science 266:970-972 (1994) Chapter 13 THE SPINAL CORD AND SPINAL NERVES Chapter Synopsis This chapter first considers the principal anatomical and functional features of the spinal cord and its coverings, the meninges, and the vertebral column. Next, the spinal cord is discussed in terms of its functions as a conduction pathway and a reflex center. Reflexes are explained, important reflexes are categorized according to type, and several clinically important reflexes are discussed. The disorders of the nervous system considered are neuritis, shingles, and poliomyelitis. Clinical applications include spinal tap (lumbar puncture), use of reflexes to assess neurological impairment, spinal cord transection and muscle function, injuries to the phrenic nerves, injuries to the nerves emerging from the brachial plexus, lumbar injuries, and sciatic nerve injury. Chapter Outline and Objectives INTRODUCTION 1. Give a general overview of the function of the spinal cord and its interactions with the brain and peripheral nerves. SPINAL CORD ANATOMY Protective Structures 2. List the protective coverings for the spinal cord. Vertebral Column 3. Review the structure of the vertebrae and associated connective tissue, and how they protect the spinal cord and spinal nerves. Meninges 4. Describe the characteristics and purpose of the three layers, spaces, and attachments of the meningeal structures. External Anatomy of the Spinal Cord 5. Describe the external features of the spinal cord and nerves, and discuss its relative length within the vertebral column during development. 6. Describe the features of the spinal nerves as they emerge from the vertebral column. 7. Discuss how the position of the end of the spinal cord within the vertebral column facilitates cerebrospinal fluid sampling for analysis. Internal Anatomy of the Spinal Cord 8. Describe the anatomic position of gray and white matter within a cross section of the spinal cord, and their relationships with the spinal nerves and tracts leading to and from the brain. SPINAL CORD PHYSIOLOGY 9. List the functions of the spinal cord. Sensory and Motor Tracts 10. Describe the functions of the principal sensory and motor tracts of the spinal cord with respect to sensory receptors, brain integration, and motor operation. 11. Identify the designations for the tracts that transmit specific types of information along ascending and descending neural pathways of the spinal cord. 12. Discuss the significance of axons developing myelin sheaths at different times. Reflexes and Reflex Arc 13. Define a reflex and distinguish between somatic and autonomic reflexes. 14. Describe the components of a reflex arc and its relationship to homeostasis. Stretch Reflex 15. Explain the purpose of the stretch reflex, and then diagram the specific components of the neural circuit pathways through the spinal cord to effectors to show how the reflex operates. Tendon Reflex 16. Explain the purpose of the tendon reflex, and then diagram the specific components of the neural circuit pathways through the spinal cord to effectors to show how the reflex operates. The Flexor and Crossed Extensor Reflexes 17. Explain the purpose of the flexor and crossed extensor reflexes, and then diagram the specific components of the neural circuit pathways through the spinal cord to effectors to show how the reflex operates. 18. Explain how knowledge of reflex circuits helps interpret neurological impairment in the plantar flexion and Babinski reflex tests. SPINAL NERVES 19. Discuss the naming and numbering of spinal nerves, the arrangement of spinal nerves relative to the vertebrae, and the attachment of the spinal nerves to the spinal cord. Connective Tissue Coverings of Spinal Nerves 20. Describe the connective tissue coverings of the spinal cord. Distribution of Spinal Nerves Branches 21. Discuss the branching of the spinal nerves once they emerge from the vertebral column. Plexuses 22. Define a plexus, then describe the spinal root origins, interconnections, and names of major nerves of the cervical, brachial, lumbar, and sacral plexuses according to their anatomic destinations. Intercostal Nerves 23. Describe the spinal root origins and destinations of the intercostal nerves. Dermatomes 24. Illustrate the topographic relationship between spinal nerves and the location of sensory receptors for which they transmit impulses. 25. Describe spinal cord injury and list the immediate and long-range effects. DISORDERS: HOMEOSTATIC IMBALANCES 26. Explain the causes and symptoms of shingles, and poliomyelitis. MEDICAL TERMINOLOGY 27. Define the medical terms related to the spinal cord. What’s New and Different in This Chapter The vertebral column is discussed before the meninges as protective structures of the spinal cord. Neuritis is no longer discussed in homeostatin imbalances. Suggested Lecture Outline I. INTRODUCTION A. The spinal cord and spinal nerves mediate reactions to environmental changes. B. The spinal cord has several functions. 1. It processes reflexes. 2. It is the site for integration of EPSPs and IPSPs that arise locally or are triggered by nerve impulses from the periphery and brain. 3. It is a conduction pathway for sensory and motor nerve impulses. II. SPINAL CORD ANATOMY A. The spinal cord is protected by two connective tissue coverings, the meninges and vertebra, and a cushion of cerebrospinal fluid. 1. The vertebral column provides a bony covering of the spinal cord (Figure 13.1b). 2. Meninges a. The meninges are three coverings that run continuously around the spinal cord and brain (Figures 13.1a, 14.4a). 1) The outermost layer is the dura mater. 2) The middle layer is the arachnoid. 3) The innermost meninx is the pia mater, a thin, transparent connective tissue layer that adheres to the surface of the spinal cord and brain. 4) Inflammation of the meninges is known as meningitis. 5) Denticulate ligaments are thickenings of the pia mater that suspend the spinal cord in the middle of its dural sheath. B. External Anatomy of the Spinal Cord 1. The spinal cord begins as a continuation of the medulla oblongata and terminates at about the second lumbar vertebra in an adult (Figure 13.2). 2. It contains cervical and lumbar enlargements that serve as points of origin for nerves to the extremities. 3. The tapered portion of the spinal cord is the conus medullaris, from which arise the filum terminale and cauda equina. 4. Spinal nerves a. The 31 pairs of spinal nerves are named and numbered according to the region and level of the spinal cord from which they emerge (Figure 13.2). b. There are 8 pairs of cervical nerves, 12 pairs of thoracic nerves, 5 pairs of lumbar nerves, 5 pairs of sacral nerves, and 1 pair of coccygeal nerves. c. Spinal nerves are the paths of communication between the spinal cord and most of the body. d. Roots are the two points of attachment that connect each spinal nerve to a segment of the spinal cord (Figure 13.3a). 1) The posterior or dorsal (sensory) root contains sensory nerve fibers and conducts nerve impulses from the periphery into the spinal cord; the posterior root ganglion contains the cell bodies of the sensory neurons from the periphery. 2) The anterior or ventral (motor) root contains motor neuron axons and conducts impulses from the spinal cord to the periphery; the cell bodies of motor neurons are located in the gray matter of the cord. 5. Removal of cerebrospinal fluid from the subarachnoid space is called a spinal tap (lumbar puncture). This procedure is used to diagnose pathologies and to introduce antibiotics, contrast media, anesthetics, and chemotherapeutic drugs. (Clinical Application) C. Internal Anatomy of the Spinal Cord 1. The anterior median fissure and the posterior median sulcus penetrate the white matter of the spinal cord and divide it into right and left sides (Figure 13.3). 2. The gray matter of the spinal cord is shaped like the letter H or a butterfly and is surround by white matter. a. The gray matter consists primarily of cell bodies of neurons and neuroglia and unmyelinated axons and dendrites of association and motor neurons. b. The white matter consists of bundles of myelinated axons of motor and sensory neurons. 3. The gray commissure forms the cross bar of the H-shaped gray matter. 4. In the center of the gray commissure is the central canal, which runs the length of the spinal cord and contains cerebrospinal fluid. 5. Anterior to the gray commissure is the anterior white commissure, which connects the white matter of the right and left sides of the spinal cord. 6. The gray matter is divided into horns, which contain cell bodies of neurons. 7. The white matter is divided into columns. a. Each column contains distinct bundles of nerve axons that have a common origin or destination and carry similar information. b. These bundles are called tracts. 1) Sensory (ascending) tracts conduct nerve impulses toward the brain. 2) Motor (descending) tracts conduct impulses down the cord. III. SPINAL CORD PHYSIOLOGY A. The spinal cord has two principal functions. 1. The white matter tracts are highways for nerve impulse conduction to and from the brain. 2. The gray matter receives and integrates incoming and outgoing information. B. Sensory and Motor Tracts 1. Figure 13.4 shows the principal sensory and motor tracts in the spinal cord. These tracts are summarized in tables 15.3 and 15.4. 2. Sensory information from receptors travels up the spinal cord to the brain along two main routes on each side of the cord: the spinothalamic tracts and the posterior column tract. 3. Motor information travels from the brain down the spinal cord to effectors (muscles and glands) along two types of descending tracts: direct pathways and indirect pathways. 4. The axons of various nerves and CNS tracts develop myelin sheaths at different times which explains the poor sensory and motor development of newborns. (Clinical Application) C. Reflexes and Reflex Arcs 1. The spinal cord serves as an integrating center for spinal reflexes. This occurs in the gray matter. 2. A reflex is a fast, predictable, automatic response to changes in the environment that helps to maintain homeostasis. 3. Reflexes may be spinal, cranial, somatic, or autonomic. D. Reflex Arc 1. A reflex arc is the simplest type of pathway; pathways are specific neuronal circuits and thus include at least one synapse. 2. The five functional components of a reflex arc are the receptor, sensory neuron, motor neuron, integrating center neuron, and effector (Figure 13.5). 3. Reflexes help to maintain homeostasis by permitting the body to make exceedingly rapid adjustments to homeostatic imbalances. 4. Somatic spinal reflexes include the stretch reflex, tendon reflex, flexor (withdrawal) reflex, and crossed extensor reflex; all exhibit reciprocal innervation. a. Stretch Reflex 1) The stretch reflex is ipsilateral and is important in maintaining muscle tone and muscle coordination during exercise (Figure 13.6). 2) A two-neuron or monosynaptic reflex arc contains one sensory neuron and one motor neuron. A stretch reflex, such as the patellar reflex, is an example. 3) It operates as a feedback mechanism to control muscle length by causing muscle contraction. b. Tendon Reflex 1) The tendon reflex is ipsilateral and prevents damage to muscles and tendons as a result of stretching (Figure 13.7). 2) It operates as a feedback mechanism to control muscle tension by causing muscle relaxation when muscle force becomes too extreme. c. Flexor and Crossed Extensor Reflexes 1) Flexor or Withdrawal Reflex a) The flexor (withdrawal) reflex is ipsilateral and is a protective withdrawal reflex that moves a limb to avoid pain (Figure 13.8). b) This reflex results in contraction of flexor muscles to move a limb to avoid injury or pain. c) It works with the crossed extensor reflex to maintain balance. 2) Crossed Extensor Reflex a) This is a balance-maintaining reflex that causes a synchronized extension of the joints of one limb and flexion of the joints in the opposite limb (Figure 13.9). b) The crossed extensor reflex, which is contralateral, helps to maintain balance during the flexor reflex. 5. Reflexes are often used for diagnosing disorders of the nervous system and locating injured tissue. (Clinical Application) a. If a reflex is absent, or abnormal, the damage may be somewhere along a particular conduction pathway. b. Among the clinically important reflexes are the plantar flexion and Babinski reflexes. IV. SPINAL NERVES A. Spinal nerves connect the CNS to sensory receptors, muscles, and glands and are part of the peripheral nervous system. 1. The 31 pairs of spinal nerves are named and numbered according to the region and level of the spinal cord from which they emerge (Figure 13.2a). 2. Roots of the lower lumbar, sacral, and coccygeal nerves are not in line with their corresponding vertebrae and thus form the cauda equina (Figure 13.2). 3. Spinal nerves connect to the cord via an anterior and a posterior root (Figure 13.3a). Since the posterior root contains sensory axons and the anterior root contains motor axons, a spinal nerve is a mixed nerve, at least at its origin. B. Connective Tissue Covering of Spinal Nerves 1. Spinal nerve axons are grouped within connective tissue sheathes (Figure 13.10). a. A fiber is a single axon within an endoneurium. b. A fascicle is a bundle of fibers within a perineurium. c. A nerve is a bundle of fascicles within an epineurium. 2. Numerous blood vessels are within the coverings. C. Distribution of Spinal Nerves 1. Shortly after passing through its intervertebral foramen, a spinal nerve divides into several branches; these branches are known as rami (Figure 13.11). 2. Branches of a spinal nerve include the dorsal ramus, ventral ramus, meningeal branch, and rami communicantes. 3. The anterior rami of spinal nerves T2-T12 do not enter into the formation of plexuses and are known as intercostal or thoracic nerves. a. These nerves directly innervate structures they supply in the intercostal spaces (Figure 13.2). b. Their posterior rami supply the deep back muscles and skin of the posterior aspect of the thorax. 4. The ventral rami of spinal nerves, except for T2-T12, form networks of nerves called plexuses (Figure 13.2 and Exhibits 13.1-13.4). a. Emerging from the plexuses are nerves bearing names that are often descriptive of the general regions they supply or the course they take. b. The cervical plexus supplies the skin and muscles of the head, neck, and upper part of the shoulders; connects with some cranial nerves; and supplies the diaphragm (Figure 13.12, Exhibit 13.1). 1) Damage to the spinal cord above the origin of the phrenic nerves (C3-C5) causes respiratory arrest. 2) Breathing stops because the phrenic nerves no longer send impulses to the diaphragm. c. The brachial plexus constitutes the nerve supply for the upper extremities and a number of neck and shoulder muscles (Figures 13.13 and 13.14, Exhibit 13.2). 1) A number of nerve disorders may result from injury to the brachial plexus. 2) Among these injuries are Erb-Duchene palsy or waiter’s tip palsy, Klumphe’s palsy, wrist drop, carpal tunnel syndrome, claw hand, and winged scapula. d. The lumbar plexus supplies the anterolateral abdominal wall, external genitals, and part of the lower extremities (Figure 13.15, Exhibit 13.3). 1) The largest nerve arising from the lumbar plexus is the femoral nerve. 2) Injury to the femoral nerve is indicated by an inability to extend the leg and by loss of sensation in the skin over the anteromedial aspect of the thigh. 3) Obturator nerve injury is a common complication of childbirth and results in paralysis of the adductor muscles of the leg and loss of sensation over the medial aspect of the thigh. e. The sacral plexus supplies the buttocks, perineum, and part of the lower extremities (Figure 13.16, Exhibit 13.4). 1) The largest nerve arising from the sacral plexus (and the largest nerve in the body) is the sciatic nerve. 2) Injury to the sciatic nerve (common peroneal portion) and its branches results in sciatica, pain that extends from the buttock down the back of the leg. 3) Sciatic nerve injury can occur due to a herniated (slipped) disc, dislocated hip, osteoarthritis of the lumbosacral spine, pressure from the uterus during pregnancy, or an improperly administered gluteal injection. D. Dermatomes 1. The skin over the entire body is supplies by spinal nerves that carry somatic sensory nerves impulses into the spinal cord. 2. All spinal nerves except C1 innervate specific, constant segments of the skin; the skin segments are called dermatomes (Figure 13.17). 3. Knowledge of dermatomes helps a physician to determine which segment of the spinal cord or which spinal nerve is malfunctioning. E. An injury that entirely severs the spinal cord is said to cause a complete transection. (Clinical Application) 1. After the injury, there will be a permanent loss of sensations in dermatomes below the injury. 2. Voluntary muscle contractions will also be lost below the transection. V. DISORDERS; HOMEOSTATIC IMBALANCES A. Shingles is an acute infection of the peripheral nerves by the herpes zoster virus; the virus migrates down peripheral nerves, causing pain, skin discoloration, and a characteristic line of skin blisters. B. Poliomyelitis (infantile paralysis or polio) is a viral infection characterized by fever, headache, stiff neck and back, deep pain and weakness, and loss of certain somatic reflexes. Paralysis is produced when the virus destroys motor neuron cell bodies. Teaching Tips When discussing the anatomy of the spinal nerve branches, use a model for clarity. Various scientific supply companies are sources for these models. Electrical wiring samples can be used to demonstrate the connective tissue coverings of the spinal nerve. Try to find a sample that has several wires wrapped with insulation. This is an excellent model to be passed around to the students. Ask a neurologist and/or neurosurgeon to talk to your class about spinal cord injuries: causes, symptoms and prognosis. Ask an individual who has suffered a spinal cord injury to talk to your class about the challenges of living after the injury. Critical Thinking Questions 1. After touching a very hot barbecue grill, you immediately withdraw your hand. What kind of reflex arc is involved? Where are the receptors located? What is the function of the receptors? Where is the center in this reflex arc? What is the role of the effector? 2. A patient with a suspected neurological disorder is examined and found to have an exaggerated patellar reflex and no abdominal reflex. Describe a normal patellar reflex and a normal abdominal reflex. In view of the findings, where is the probable site of injury or disease in the central nervous system? If your diagnosis is correct, what body activities are most likely to be affected? 3. Explain why spinal segment #25 does not lie under vertebra #25 (lumbar vertebra #5, or L5). Why is this knowledge useful in performing a spinal tap (lumbar puncture)? Educational Resources (refer to Education Resources Appropriate for All Chapters following the list of Suppliers and Distributors) Videocassettes The Anatomy and Physiology Series: The Nervous System (27 min; NIMCO) - gives a full discussion of the nervous system parts and functions Brain and Nervous System: Your Information Superhighway (25 min; FHS) - topics include how the brain and spinal cord are protected and parts of the brain and spinal cord The Human Body Series: Reflexes and Conscious Movement(28 min; 1993; NIMCO) - looks at the range of reflexive and controlled, conscious and unconscious movements of the body, showing how the nerve impulses originate and work The Human Nervous System (12 min; SVE) - describes the functions of neurons among other topics The Living Body: Nerves at Work ( 27 min; 1990; FHS) - looks at nerve signals and how they are transmitted and reflex signals Multiple Sclerosis (26 min; FHS) - discusses all aspects of multiple sclerosis Spinal Cord and Its Relations (13 min; TF) - describes the structure of the spinal cord and the spinal nerves Spinal Cord and Spinal Nerves (BC) - live action video study of the spinal cord and spinal nerves Computer Resources (CD-ROMs for Windows and Macintosh platforms unless otherwise noted) The Anatomy Project: Neuroanatomy 3: the Spinal Cord, Meninges and Blood Supply (NIMCO) - interactive study of the spinal cord and spinal nerves, meninges and blood supply A Primer of Brain Anatomy and Function (1997; DGI) - discusses nervous system cell structure and function and electrochemical signaling including conduction and neurotransmission McMinn’s Interactive Clinical Anatomy CD-ROM (1966; DGI) - topics include a complete 3-D human body showing dermatomes Slides: 35 MM Histology of the Nervous System (20 slides; CVB) - shows cell components of the nervous system The Nervous System and Its Function (20 slides; CVB) - includes neural transmission, major brain area, spinal cord Selected Readings Miller, J. “Sex in the Spinal Cord,” Science News 118:329 (1980) Romeo, J. “The Critical Minutes After Spinal Cord Injury,” RN (April 1988) Thompson, C. “Paralysis Lost,” New Scientist 150:26-27 (1996) Weiss, R. “Neurons Regenerate into Spinal Cord,” Science News 132:324 (1987) Chapter 14 THE BRAIN AND CRANIAL NERVES Chapter Synopsis This chapter considers the principal anatomical and functional features of the brain, cranial meninges, and blood supply and the formation and circulation of cerebrospinal fluid (CSF). Also discussed are the electroencephalogram (EEG),hemispheric lateralization, the locations and functions of the cranial nerves, developmental anatomy of the nervous system, and the effects of aging on the nervous system. The disorders of the nervous system that are covered include cerebrovascular accident (CVA), transient ischemic attack (TIA), and Alzheimer’s disease (AD). Clinical applications covered include breaching the blood-brain barrier, hydrocephalus, injury of the medulla, brain injuries, dental anesthesia, and aphasia. There is also a glossary of medical terminology related to the central nervous system. Chapter Outline and Objectives INTRODUCTION 1. Give an overview of the capacity of the brain as it determines the activities of one’s life. OVERVIEW OF BRAIN ORGANIZAGION AND BLOOD SUPPLY Major Parts of the Brain 2. Introduce the principle parts of the brain in terms of their relative positions and connections. Blood Flow and the Blood-Brain Barrier 3. Describe the blood supply to the brain and the concept of the blood-brain barrier and the effect of their compromise. 4. Discuss how the blood-brain barrier can be breached. Protective Coverings of the Brain 5. Identify the three layers of the meninges and their extensions that surround the brain and spinal cord. CEREBROSPINAL FLUID Formation of Cerebrospinal Fluid in the Ventricles 6. Explain the formation of cerebrospinal fluid (CSF) in the ventricles 7. List the functions the CSF performs to protect the central nervous system. Circulation of Cerebrospinal Fluid 8. Discuss the circulation of CSF through the ventricles, spaces, and associated structures along the fluid’s path back to the blood. 9. Describe the physical and physiological manifestations that occur when a channel of the ventricles becomes obstructed. THE BRAIN STEM Medulla Oblongata 10. Describe the position and identify of tracts, peduncles, cranial nerves, and nuclei of the medulla oblongata, and then discuss their connections and functions within the medulla and with other systems of the body. 11. Identify the vital reflex centers of the medulla oblongata and their functions. 12. Describe the consequences of injury to the medulla. Pons 13. Describe the position and identify of tracts, peduncles, cranial nerves, and nuclei of the pons, and then discuss their connections and functions within the pons and with other systems of the body. 14. Identify centers in the pons that coordinate with specific centers in the medulla to control respiration. Midbrain 15. Describe the position and identify of tracts, peduncles, cranial nerves, and nuclei of the midbrain, and then discuss their connections and functions within the medulla and with other systems of the body. 16. Indicate the distribution and connections of nuclei that constitute the reticular formation and the purpose of their interactions with other areas of the spinal cord and brain. CEREBELLUM 17. Specify the anatomic arrangement of the cerebellum relative to the rest of the brain, then describe its internal and surface features and how these features are involved with the overall duty of the cerebellum with respect to its interconnections to other movement control centers. DIENCEPHALON 18. Discuss the general regions, structures, connections, and operation of the diencephalon. Thalamus 19. Establish the position, connections, and general nuclear areas of the thalamus, and note their job in processing and transmitting neural impulses. Hypothalamus 20. Examine the numerous surface structures and regions of the hypothalamus along with their functions. 21. Explain how the hypothalamus interacts with other components of the nervous system to regulate the homeostasis of the autonomic nervous system, pituitary/endocrine system, behavior, nourishment, body temperature, and diurnal rhythms. Epithalamus 22. Discuss the pineal gland and habenular nuclei of the epithalamus in terms of location and function. Subthalamus 23. Discuss the location of the subthalamus, the subthalamic tracts and nuclei, and their function. Circumventricular Organs 24. Discuss the location and function of the circumventricular organs. THE CEREBRUM 25. Describe the folding of the cerebral cortex and the reasons for the folds. Lobes of the Cerebrum 26. Discuss the locations of the cerebral lobes with respect to the topical landmarks. Cerebral White Matter 27. Describe the pathway destinations for the three types of white matter tracts within the cerebrum. Basal Ganglia 28. Identify and locate the nuclei of the basal ganglia within the cortical structures, and discuss their relation to subthalamic nuclei in facilitating certain types of movements. The Limbic System 29. List the component structures of the limbic system, and discuss their contribution to behavioral responses and mental functions. 30. Discuss the effects of brain injury and the degrees of injury. CEREBRAL CORTEX AREAS AND FUNCTIONS 31. Note that specific areas of the brain have identifiable functions that correspond to sensory, motor, and associative capacities. Sensory Areas 32. Define the location, interconnections, and purpose of the somatosensory region, in addition to the primary sensory areas for the visual, auditory, gustatory, and olfactory systems. Motor Areas 33. Locate the primary motor area on the cortex and indicate the types of movements it directs. 34. Locate the language areas of the cortex and the other areas with which they communicate in the integration of information and the written or articulated expression of language. Association Areas 35. Explain the principle function of cortical association areas and how they are anatomically related to primary sensory and motor areas. 36. Describe how the thought processes occurring in the gnostic area of the parietal lobe differ from other association areas. 37. Discuss the causes, signs, and problems associated with aphasia. Hemispheric Lateralization 38. Discuss the functional asymmetry of the brain. Brain Waves 39. Attribute the origins, electrical characteristics, and mental states associated with the EEG waves. CRANIAL NERVES 40. Define a cranial nerve and identify the 12 pairs of cranial nerves by name, number, type, location, and function. 41. Describe the cranial nerves anesthesized during dental procedures. DEVELOPMENTAL ANATOMY OF THE NERVOUS SYSTEM 42. Describe the etiology of neural cells from the embryonic disk to the mature state during development of the nervous system. AGING AND THE NERVOUS SYSTEM 43. Describe the effects of aging on the nervous system. DISORDERS: HOMEOSTATIC IMBALANCES 44. List the clinical symptoms of these disorders of the nervous system: cerebrovascular accident (CVA), transient ischemic attack (TIA), and Alzheimer’s disease. MEDICAL TERMINOLOGY 45. Define medical terminology associated with the central nervous system. What’s New and Different in This Chapter This chapter now begins with a discussion of blood flow and the blood brain barrier. The material on the secretion of CSF has been divided into the subtopics of formation and secretion of the CSF. Figure 14.9, The Thalamus, now includes a medial view of the left hemisphere, a superolateral view of the thalamus, and a transverse cut of the right side of the thalamus. The discussion of the thalamus has been rewritten and expanded. The section on hemispheric lateralization has been rewritten. A table (14.2) listing the functional differences between the two cerebral hemispheres has been added. Figure 14.16 now shows a composite picture which illustrates the cortical areas activated by olfactory stimuli. In addition to Table 14.3 which summarizes the cranial nerves, each cranial nerve is now discussed in the text of the chapter. Several new drawings illustrating the areas innervated by the cranial nerves have been added. The discussion of Alzheimer’s Disease has been updated and now mentions anticholinesterase drugs used to treat the disease. A Clinical Application on dental anesthesia is new. Suggested Lecture Outline I. INTRODUCTION A. The brain is the center for registering sensations, correlating them with one another and with stored information, making decisions, and taking action. 1. It is also the center for intellect, emotions, behavior, and memory. 2. It also directs our behavior towards others. B. In this chapter we will consider the principal parts of the brain, how the brain is protected and nourished, and how it is related to the spinal cord and to the 12 pairs of cranial nerves. II. OVERVIEW OF BRAIN ORGANIZATION AND BLOOD SUPPLY A. The major parts of the brain are the brain stem, diencephalon, cerebrum, and cerebellum (Figure 14.1). B. Blood Flow and the Blood-Brain Barrier 1. Blood flows to the brain mainly via blood vessels that branch from the cerebral arterial circle (circle of Willis) at the base of the brain (Figure 21.20); the veins that return blood from the head to the heart are seen in Figure 21.25. 2. Although the brain comprises only about 2% of the total body weight, it utilizes about 20% of the oxygen used by the entire body. The brain is one of the most metabolically active organs of the body, and the amount of oxygen it uses varies with the degree of mental activity. 3. Any interruption of the oxygen supply to the brain can result in weakening, permanent damage, or death of brain cells. Interruption of the mother’s blood supply to a child during childbirth before it can breathe may result in paralysis, mental retardation, epilepsy, or death. 4. Because carbohydrate storage in the brain is limited, the supply of glucose to the brain must be continuous. Glucose deficiency may produce mental confusion, dizziness, convulsions, and unconsciousness. 5. A blood-brain barrier (BBB) protects brain cells from harmful substances and pathogens by serving as a selective barrier to prevent passage of many substances from the blood to the brain. 6. An injury to the brain due to trauma, inflammation, or toxins causes a breakdown of the BBB, permitting the passage of normally restricted substances into brain tissue. The BBB may also prevent entry of drugs that could be used as therapy for brain cancer or other CNS disorders, so research is exploring ways to transport drugs past the BBB. C. Protective Covering of the Brain 1. The brain is protected by the cranial bones (Figure 7.4) and the cranial meninges (Figure 14.2). 2. The cranial meninges are continuous with the spinal meninges and are named dura mater, arachnoid, and pia mater. 3. Three extensions of the dura mater separate parts of the brain: the falx cerebri, falx cerebelli, and the tentorium cerebelli. III. CEREBROSPINAL FLUID A. Cerebrospinal fluid (CSF) is a clear, colorless liquid that protects the brain and spinal cord against chemical and physical injuries and carries oxygen, glucose, and other needed chemicals from the blood to neurons and neuroglia. B. There are four CSF filled cavities within the brain called ventricles (Figure 14.3). C. CSF contributes to hemostasis by providing mechanical protection, chemical protection, and circulation. D. CSF is formed by filtration from networks of capillaries called choroid plexuses (found in the ventricles) and circulates through the subarachnoid space, ventricles, and central canal. E. Materials entering CSF from the choroid capillaries cannot leak between the surrounding ependymal cells; these constitute the blood-cerebrospinal fluid barrier, which permits certain substances to enter the fluid but excludes others and protects the brain and spinal cord from harmful elements (Figures 14.4, 4.1). F. Most of the fluid is absorbed by the arachnoid villi of the superior sagittal blood sinus (Figure 14.2); this absorption normally occurs at the same rate at which CSF is produced in the choroid plexuses, thereby maintaining a relatively constant CSF volume and pressure (Figure 14.2). G. If CSF cannot circulate or drain properly due to some obstruction in the ventricles or subarachnoid space, a condition called hydrocephalus develops. The fluid buildup that occurs causes increased pressure on the brain, either internally or externally, depending on where the blockage is present. Surgically draining the ventricles and diverting the flow of CSF by an implanted shunt can positively and dramatically affect the individual’s prognosis. (Clinical Application) IV. THE BRAIN STEM A. Medulla Oblongata 1. The medulla oblongata, or just medulla, is continuous with the upper part of the spinal cord and contains portions of both motor and sensory tracts (Figures 14.5, 14.1). 2. It also contains the nuclei of origin for cranial nerves VIII (cochlear and vestibular branches) through XII (Table 14.2). 3. Structural regions of the medulla include the pyramids (Figures 14.5, 14.6) and the inferior olivary nucleus (Figures 14.5, 14.6). a. Decussation of pyramids results in neurons in the left cerebral cortex controlling skeletal muscles on the right side of the body and neurons in the right cerebral cortex controlling skeletal muscles on the left side. b. Inferior olivary neurons relay impulses from proprioceptors to the cerebellum. 4. Functional regions include nuclei that are reflex centers for regulation of heart rate, respiratory rate, vasoconstriction, swallowing, coughing, vomiting, sneezing, and hiccuping; the first three are considered vital reflexes. 5. Injury to the medulla can be fatal or lead to serious problems. (Clinical Application) B. Pons 1. The pons is located superior to the medulla. It connects the spinal cord with the brain and links parts of the brain with one another by way of tracts (Figures 14.1, 14.5). 2. It relays nerve impulses related to voluntary skeletal movements from the cerebral cortex to the cerebellum. 3. The pons also contains the pneumotaxic and apneustic areas, which help control respiration along with the respiratory center in the medulla (Figure 23.24). 4. It contains nuclei for cranial nerves V through VII and the vestibular branch of VIII (Figure 14.5). C. Midbrain 1. The midbrain connects the pons and diencephalon. It conveys motor impulses from the cerebrum to the cerebellum and spinal cord, sends sensory impulses from the spinal cord to the thalamus, and regulates auditory and visual reflexes (Figures 14.1, 14.5, 14.7). 2. Structures within the midbrain include the cerebral peduncles, the corpora quadrigemina, the left and right substantia nigra, the left and right red nucleus, and the medial lemniscus. 3. It also contains nuclei of origin for cranial nerves III and IV. 4. A large portion of the brain stem is called the reticular formation (Figure 14.7b). a. It consists of small areas of gray matter interspersed among fibers of white matter and has both sensory and motor functions. b. It helps regulate muscle tone, alerts the cortex to incoming sensory signals (reticular activating system, or RAS) and is responsible for maintaining consciousness and awakening from sleep.(Figure 15.10) D. The functions of the brain stem are summarized in Table 14.1. V. THE CEREBELLUM A. The cerebellum occupies the inferior and posterior aspects of the cranial cavity and consists of two hemispheres and a central, constricted vermis (Figures 14.1, 14.4, 14.8). B. It is attached to the brain stem by three pairs of cerebellar peduncles (Figure 14.7). C. The cerebellum functions in the coordination of skeletal muscle contractions and in the maintenance of normal muscle tone, posture, and balance. VI. THE DIENCEPHALON A. Thalamus 1. The thalamus is located superior to the midbrain and contains nuclei that serve as relay stations for all sensory impulses, except smell, to the cerebral cortex (Figure 14.9). 2. There are seven major groups of thalamic nuclei on each side (Figure 14.9 c and d) 3. It also registers conscious recognition of pain and temperature and some awareness of light touch and pressure. 4. It plays an essential role in awareness and the acquisition of knowledge, which is termed cognition. B. Hypothalamus 1. The hypothalamus is found inferior to the thalamus, has four major regions (mammillary, tuberal, supraoptic, and preoptic), controls many body activities, and is one of the major regulators of homeostasis (Figure 14.10, Table 14.1). 2. The hypothalamus has a great number of functions. a. It functions in regulation of emotional and behavioral patterns. b. It regulates eating and drinking through the feeding center, satiety center, and thirst center. c. It aids in controlling body temperature. d. It regulates circadian rhythms and states of consciousness. C. Epithalamus 1. The epithalamus lies superior and posterior to the thalamus and contains the pineal gland and the habenular nuclei (Table 14.1, Figure 14.7). 2. The pineal gland secretes melatonin to influence diurnal cycles in conjunction with the hypothalamus. 3. The habenular nuclei are involved in olfaction, especially emotional responses to odors. D. Subthalamus 1. The subthalamus lies immediately inferior to the thalamus (Table 14.1) and includes tracts and the paired subthalamic nuclei, which connect to motor areas of the cerebrum. 2. The subthalamic nuclei and red nucleus and substantia nigra of the midbrain work together with the basal ganglia, cerebellum, and cerebrum in control of body movements. E. Table 14.1 summarizes the functions of the parts of the diencephalon. F. Circumventricular Organs 1. Parts of the diencephalon, called circumventricular organs (CVOs), can monitor chemical changes in the blood because they lack a blood-brain barrier. 2. CVOs include part of the hypothalamus, the pineal gland, the pituitary gland, and a few other nearby structures. 3. They function to coordinate homeostatic activities of the endocrine and nervous systems. 4. They are also thought to be the site of entry into the brain of HIV. VII. THE CEREBRUM A. The cerebrum is the largest part of the brain (Figure 14.11). 1. The surface layer, the cerebral cortex, is 2-4 mm thick and is composed of gray matter. The cortex contains billions of neurons. 2. The cortex contains gyri (convolutions), deep grooves called fissures, and shallower sulci. 3. Beneath the cortex lies the cerebral white matter, tracts that connect parts of the brain with itself and other parts of the nervous system. B. The cerebrum is nearly separated into right and left halves, called hemispheres, by the longitudinal fissure. Internally it remains connected by the corpus callosum, a bundle of transverse white fibers. C. Lobes 1. Each cerebral hemisphere is further subdivided into four lobes by sulci or fissures. 2. The cerebral lobes are named the frontal, parietal, temporal, and occipital. 3. A fifth part of the cerebrum, the insula, lies deep to the parietal, frontal, and temporal lobes and cannot be seen in an external view of the brain. D. White Matter 1. The white matter is under the cortex and consists of myelinated axons running in three principal directions (Figure 14.12). 2. Association fibers connect and transmit nerve impulses between gyri in the same hemisphere. 3. Commissural fibers connect gyri in one cerebral hemisphere to the corresponding gyri in the opposite hemisphere. 4. Projection fibers form ascending and descending tracts that transmit impulses from the cerebrum to other parts of the brain and spinal cord. E. Basal Ganglia 1. The basal ganglia are paired masses of gray matter in each cerebral hemisphere (Figure 14.13). 2. They are responsible for helping to control muscular movements. F. Limbic System 1. The limbic system is found in the cerebral hemispheres and diencephalon (Figure 14.14). 2. It functions in emotional aspects of behavior and memory, and is associated with pleasure and pain. G. Brain Injuries 1. Lapse in memory is one of many effects resulting from brain injuries; brain injuries are commonly associated with head injuries and result, in part, from displacement and distortion of neuronal tissue at the moment of impact and in part from the release of disruptive chemicals from injured brain cells. 2. Various degrees of brain injury are described by the terms concussion, contusion, and laceration. CEREBRAL CORTEX AREAS AND FUNCTIONS A. Specific types of sensory, motor, and integrative signals are processed in certain cerebral regions (Figure 14.15). 1. Sensory Areas a. The sensory areas of the cerebral cortex are concerned with the reception and interpretation of sensory impulses. b. Some important sensory areas include the primary somatosensory area, primary visual area, primary auditory area, and primary gustatory area. 2. Motor Areas a. The motor areas are the regions that govern muscular movement. b. Two important motor areas are the primary motor area and Broca’s speech area. 3. Association Areas a. The association areas are concerned with complex integrative functions such as memory, emotions, reasoning, will, judgment, personality traits, and intelligence. b. Association areas include the somatosensory association area, visceral association area, auditory association area, Wernicke’s (posterior language) area, common integrative area, premotor area, frontal eye field area, and language areas. 4. Table 14.1 summarizes the various functions of the cerebrum. 5. Injury to the association or motor speech areas results in aphasia, an inability to use or comprehend words. (Clinical Application) B. Hemispheric Lateralization 1. The two hemispheres of the cerebrum are not bilaterally symmetrical, either anatomically or functionally, with the functional asymmetry called hemispheric lateralization (Figure 14.16). 2. The left hemisphere is more important for right-handed control, spoken and written language, and numerical and scientific skills. 3. The right hemisphere is more important for left-handed control, musical and artistic awareness, space and pattern perception, insight, imagination, and generating mental images of sight, sound, touch, taste, and smell. 4. Table 14.2 summarizes some of the distinctive functions that are more likely to reside in the left or right hemisphere. C. Brain Waves 1. Electrical potentials generated by brain cells are called brain waves. 2. Brain waves generated by the cerebral cortex are recorded as an electroencephalogram (EEG) (Figure 14.17). 3. An EEG may be used to diagnose epilepsy and other seizure disorders, infectious diseases, tumors, trauma, hematomas, metabolic abnormalities, degenerative diseases, and periods of unconsciousness and confusion; it may also provide useful information regarding sleep and wakefulness. 4. An EEG may also be one criterion in confirming brain death (complete absence of brain waves in two EEGs taken 24 hours apart). 5. Figure 14.17 shows four kinds of brain waves that can be recorded from normal individuals. IX. CRANIAL NERVES A. Twelve pairs of cranial nerves originate from the brain (Figure 14.5) B. The pairs are named primarily on the basis of distribution and numbered by order of attachment to the brain. C. Some cranial nerves (I, II, and VIII) contain only sensory fibers and are called sensory nerves. The rest are mixed nerves because they contain both sensory and motor fibers. D. Figures 14.18 – 14.24 illustrate the distribution of many of the cranial nerves. E. Table 14.3 presents a summary of cranial nerves, including clinical applications related to their dysfunction. X. DEVELOPMENTAL ANATOMY OF THE NERVOUS SYSTEM A. The development of the nervous system begins with a thickening of the ectoderm called the neural plate (Figure 14.18). B. The parts of the brain develop from primary and secondary vesicles (Figure 14.19). XI. AGING AND THE NERVOUS SYSTEM A. Age-related effects involve loss of neurons and decreased capacity for sending nerve impulses to and from the brain; processing of information also diminishes. B. Other effects include decreased conduction velocity, slowing of voluntary motor movements, and increased reflex time. C. Degenerative changes and disease states involving the sense organs can alter vision, hearing, taste, smell, and touch. XII. DISORDERS: HOMEOSTATIC IMBALANCES A. The most common brain disorder is a cerebrovascular accident (CVA or stroke). 1. CVAs are classified into two principal types: ischemic (the most common type), due to a decreased blood supply, or hemorrhagic, due to a blood vessel in the brain that bursts. 2. Common causes of CVAs are intracerebral hemorrhage, emboli, and atherosclerosis. 3. CVAs are characterized by abrupt onset of persisting neurological symptoms that arise from destruction of brain tissue (infarction). B. A transient ischemic attack (TIA) is an episode of temporary cerebral dysfunction caused by impaired blood flow to the brain. 1. Symptoms include dizziness, weakness, numbness, or paralysis in a limb or in half of the body; drooping of one side of the face; headache; slurred speech or difficulty understanding speech; or a partial loss of vision or double vision. 2. Onset is sudden and a TIA usually persists for only a few minutes, rarely lasting as long as 24 hours. 3. Causes of the impaired blood flow include blood clots, atherosclerosis, and certain blood disorders; TIAs commonly are forerunners of future CVAs. C. Alzheimer’s disease (AD) is a disabling neurological disorder that afflicts about 11% of the population over age 65. 1. Its causes are unknown, its effects are irreversible and devastating, and it has no cure at the present time. 2. It involves widespread intellectual impairment, personality changes, sometimes delirium, and culminates in dementia, the loss of reason and ability to care for oneself. 3. A person with AD usually dies of some complication that affects bedridden patients, such as pneumonia. 4. Brains of AD victims show three distinct structural abnormalities: a. Great loss of neurons in specific regions (e.g., hippocampus and cerebral cortex). b. Plaques of abnormal proteins deposited outside neurons (amyloid plaques). c. Tangled protein filaments within neurons (neurofibrillary tangles). XIII. MEDICAL TERMINOLOGY - Alert students to the medical terminology associated with the central nervous system. Teaching Tips Ask a local neurologist and/or neurosurgeon to speak to your class about brain injuries. Ask an occupational therapist, physical therapist, and/or speech therapist to speak to your class about rehabilitation after brain injury. Critical Thinking Questions 1. A 35-year-old male exhibits the following symptoms: tremors of the arms and hands, rigidity of the facial muscles, wide-eyed unblinking stare, and saliva drooling from the corners of the mouth. What is the probable disorder? How may the condition be treated? 2. An 18-year-old male was involved in a car wreck where he suffered a whiplash injury. Based on your knowledge of the brain stem, what problems might he be facing depending on the extent of his injuries? Educational Resources (refer to Education Resources Appropriate for All Chapters following the list of Suppliers and Distributors) Videocassettes The Addicted Brain (26 min; 1990; FHS) - explores developments in the biochemistry of addiction and addictive behavior Alzheimers: The Tangled Mind (23 min; 1997; FHS) - discusses the symptoms, treatment, and prognosis of Alzheimer’s disease The Anatomical Basis of Brain Function Series (1988; TF) - shows a complete study of brain structure Anatomy of the Human Brain (34 min; 1998; FHS) - dissects a normal human brain The Anatomy and Physiology Video Series: The Nervous System (27 min; NIMCO) - discusses nerve interaction, the brain and its parts, cranial nerves, the ANS Animated Neuroscience and the Action of Nicotine, Cocaine, and Marijuana in the Brain (24 min; 1988; FHS) - studies the effects of these substances on the brain Autism: Breaking Through (26 min; 1988; FHS) - thoroughly discusses autism The Body Atlas Series: The Brain (30 Min; 1994; NCHCA/NIMCO) - studies the brain Brain Cancer: From Diagnosis to Treatment (30 min; 1998; FHS) - reviews brain cancer diagnosis, types, treatments, prognosis Brain and Nervous System: Your Information Superhighway (25 min, FHS) - topics include parts of the brain and their functions and protection of the brain Brain Transplant (60 min; CBSC) - discusses brain disease treatment with fetal tissue The Brain (A Video Workbook) (50 Min; EBEC) - an intensive study of brain physiology; ideal for lecture or lab The Brain: Our Universe Within Set (3 videos, 60 min each; CBSC) - shows functional MRI and Petscans of actual living brains; includes computer animations The Brain: The Ultimate Puzzle (2 video series, 18 min each; SVE) - details brain development and brain disorders The Brain, 2nd ed (3 videos in 4 hr 31 min; 1997; ACPB) - 32 teaching modules on 3 video cassettes studying all aspects of the brain Chronobiology: The Time of Our Lives (28 min; 1990; FHS/NIMCO) - examines time conflicts among the body, the brain, and society The Development of the Human Brain (40 min; CBSC) - follows the physiological development of the human brain from conception to birth to age 8 Epilepsy: The Storm Within (27 min; 1998; FHS) - examines the causes, diagnosis, treatment, and prognosis of epilepsy Fear and Anxiety (56 min; 1998; FHS) - describes anxiety disorders and fear Fetal Alcohol Syndrome: Life Sentence (24 min; FHS) - discusses the effect of alcohol on the fetal brain and the lifetime effects Fires In the Mind (60 min; CVB) - explores the human brain The Human Body Series: The Biological Preconditions of Learning (28 min; 1993; NIMCO) discusses learning and memory The Human Body Series: The Brain (28 min; 1993; NIMCO) - discusses the devellpment of the brain, its parts and their functions The Human Body Series: Reflexes and Conscious Movement (28 min; 1993; NIMCO) - looks at the range of reflexive and controlled, conscious and unconscious movements of the body The Human Body Series: Sleep (28 min; 1993; NIMCO) - describes what happens in the brain during sleep The Human Brain in Situ (19 min; 1998; FHS) - a basic anatomical exam of the brain and its connections in the skull using museum pieces In Control: Our Brain and Nervous System (24 min; SVE) - discusses functions of parts of the brain Inside Information: The Brain and How It Works (58 min; 1992; FHS) - studies brain structure and function Is Your Brain Really Necessary? (50 min; 1992; FHS/NIMCO) - studies three patients with different brain problems The Living Body: Decisions (28 min; 1990; FHS) - shows how the brain coordinates functions to make life-saving decisions The Living Body: Moving Parts (27 min; 1990; FHS) - topics include how the cerebellum coordinates muscle activity The Living Body: Our Talented Brain (28 min; 1990; FHS) - discusses the structure of the brain Memory (56 min; FHS) - details brain processes of data storage and retrieval Memory: Fabric of the Mind (28 min; 1988; FHS ) - discusses memory Men, Women, and the Brain (56 min; 1998; FHS) - describes differences between the male and female brain The Mind’s I (58 min; FHS) - shows how the brain parts work together to make an individual Mysteries of the Mind (58 min; NIMCO) - explores manic-depression, obsessive-compulsive disorder, alcoholism, and other mood disorders; includes neurochemical and genetic components The Nature of Memory (26 min; 1990; FHS) - discusses the physical and chemical aspects of memory The Neuroanatomy Series (1988; TF) - a comprehensive view of the structures of the nervous system The New Living Body: The Brain (20 min; 1995; FHS) - includes brain structure and function, motor and sensory neurons, simple reflex arcs Parkinson’s Disease (19 min; 1990; FHS) - a detailed look at the causes, symptoms, treatments, and prognosis of Parkinson’s disease Pathology Examples in the Human Brain (23 min; 1998; FHS) - describes various brain disorder pathologies The Seven Ages of the Brain (58 min; FHS) - shows basic development and aging of the brain The Sexual Brain (28 min; FHS/NIMCO) - shows differences in brain structure and function based on gender Teaching Modules: The Brain (32 teaching modules on 3 cassettes) (4 hr 31 min total; 1997; NIMCO) - discusses brain structure, physiology, disorders Computer Resources (CD-ROMs for Windows and Macintosh platforms unless otherwise noted) The Anatomy Project: Neuroanatomy I - the Forebrain (1998; NIMCO) - interactive study of brain structure The Anatomy Project: Neuroanatomy II - The Midbrain and Hindbrain (1998; NIMCO) interactive study of brain structure The Brain (NIMCO) - shows the brain’s anatomy and how it functions Brain Anatomy: Neural Function (CDI)- studies brain anatomy and physiology, conduction and synaptic transmission; interactive A Primer of Brain Anatomy and Function (1997; DGI) - discusses nervous system cell structure and function and electrochemical signaling including conduction and neurotransmission Slides: 35 MM Histology of the Nervous System (20 slides; CVB) - shows cell components of the nervous system The Nervous System and Its Function (20 slides; CVB) - includes neural transmission, major brain areas, spinal cord Selected Readings Angier, N. “Storming the Wall” (blood-brain barrier), Discover (May 1990) Barinaga, M. “Remapping the Motor Cortex,” Science 268:1696-1698 (1995) Barinaga, M. “Researchers Broaden the Attack on Parkinson’s Disease.” Science 67:455-456 (1995) “The Brain,” Scientific American (September 1979) (Entire issue devoted to the brain and the human nervous system) Dajer, T. “The Lost 24 Hours” (TIA), Discover (November 1991) Gazzaniga, M. S. “The Split Brain Revisited,” Scientific American (November 1995) Gibbons, A. “New Maps of the Human Brain,” Science 249:122-123 (1990) Mischkin, M. and T. Appenzeller. “The Anatomy of Memory,” Scientific American (February 1993) Streit, W. J. and C. A. Kincaid-Cotton. “The Brain’s Immune System,” Scientific American (November 1995) Thomanen, E. “Breaching the Blood-Brain Barrier,” Scientific American (February 1993) Zivin, J. and D. Choi. “Stroke Therapy,” Scientific American (July 1991) Book Guyton, A. C. Basic Neuroscience: Anatomy and Physiology. Philadelphia: Saunders, 1987.