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12: The Central Nervous System Objectives The Brain 1. Describe the process of brain development. 2. 3. 4. 5. 6. 7.

Name the major regions of the adult brain. Name and locate the ventricles of the brain. List the major lobes, fissures, and functional areas of the cerebral cortex. Explain lateralization of hemisphere function. Differentiate between commissures, association fibers, and projection fibers. Describe the general function of the basal nuclei (basal ganglia).

8. Describe the location of the diencephalon, and name its subdivisions and functions. 9. Identify the three major regions of the brain stem, and note the functions of each area. 10. Describe the structure and function of the cerebellum. 11. Locate the limbic system and the reticular formation, and explain the role of each functional system. Higher Mental Functions 12. Define EEG and distinguish between alpha, beta, theta, and delta brain waves. 13. Describe consciousness clinically. 14. Compare and contrast the events and importance of slow-wave and REM sleep, and indicate how their patterns change through life. 15. Compare and contrast the stages and categories of memory. 16. Describe the relative roles of the major brain structures believed to be involved in declarative and procedural memories. Protection of the Brain 17. Describe how meninges, cerebrospinal fluid, and the blood-brain barrier protect the CNS. 18. Describe the formation of cerebrospinal fluid, and follow its circulatory pathway. 19. Indicate the cause (if known) and major signs and symptoms of cerebrovascular accidents, Alzheimer’s disease, Parkinson’s disease, and Huntington’s disease. The Spinal Cord 20. Describe the embryonic development of the spinal cord. 21. Describe the gross and microscopic structure of the spinal cord. 22. List the major spinal cord tracts, and classify each as a motor or sensory tract. 23. Distinguish between flaccid and spastic paralysis, and between paralysis and paresthesia. Diagnostic Procedures for Assessing CNS Dysfunction 24. List and explain several techniques used to diagnose brain disorders.

Developmental Aspects of the Central Nervous System 25. Indicate several maternal factors that can impair development of the nervous system in an embryo. 26. Explain the effects of aging on the brain.

Chapter Outline I. The Brain (pp. 430–453; Figs. 12.1–12.4; Table 12.1) A. Embryonic Development (pp. 430–431; Figs. 12.1–12.4) 1. At three weeks’ gestation, the ectoderm forms the neural plate, which invaginates, forming the neural groove, flanked on either side by neural folds. 2. By the fourth week of pregnancy, the neural groove fuses, giving rise to the neural tube, which rapidly differentiates into the CNS. 3. The neural tube develops constrictions that divide the three primary brain vesicles: the prosencephalon (forebrain), mesencephalon (midbrain), and rhombencephalon (hindbrain). B. Regions and Organization (p. 431) 1. The basic pattern of the CNS consists of a central cavity surrounded by a gray matter core, external to which is white matter. 2. In the brain, the cerebrum and cerebellum have an outer gray matter layer, which is reduced to scattered gray matter nuclei in the spinal cord. C. Ventricles (pp. 431–433; Fig. 12.5) 1. The ventricles of the brain are continuous with one another, and with the central canal of the spinal cord. They are lined with ependymal cells, and are filled with cerebrospinal fluid. a. The paired lateral ventricles lie deep within each cerebral hemisphere, and are separated by the septum pellucidum. b. The third ventricle lies within the diencephalon, and communicates with the lateral ventricles via two interventricular foramina. c. The fourth ventricle lies in the hindbrain and communicates with the third ventricle via the cerebral aqueduct. D. Cerebral Hemispheres (pp. 433–441; Figs. 12.6–12.11; Table 12.1) 1. The cerebral hemispheres form the superior part of the brain, and are characterized by ridges and grooves called gyri and sulci. 2. The cerebral hemispheres are separated along the midline by the longitudinal fissure, and are separated from the cerebellum along the transverse cerebral fissure. 3. The five lobes of the brain separated by specific sulci are: frontal, parietal, temporal, occipital, and insular. 4. The cerebral cortex is the location of the conscious mind, allowing us to communicate, remember, and understand. 5. The cerebral cortex has several motor areas located in the frontal lobes, which control voluntary movement.

a. The primary motor cortex allows conscious control of skilled voluntary movement of skeletal muscles. b. The premotor cortex is the region controlling learned motor skills. c. Broca’s area is a motor speech area that controls muscles involved in speech production. d. The frontal eye field controls eye movement. 6. There are several sensory areas of the cerebral cortex that occur in the parietal, temporal, and occipital lobes. a. The primary somatosensory cortex allows spatial discrimination and the ability to detect the location of stimulation. b. The somatosensory association cortex integrates sensory information and produces an understanding of the stimulus being felt. c. The primary visual cortex and visual association area allow reception and interpretation of visual stimuli. d. The primary auditory cortex and auditory association area allow detection of the properties and contextual recognition of sound. e. The olfactory cortex allows detection of odors. f. The gustatory cortex allows perception of taste stimuli. g. The vestibular cortex is responsible for conscious awareness of balance. 7. Several association areas are not connected to any sensory cortices. a. The prefrontal cortex is involved with intellect, cognition, recall, and personality, and is closely linked to the limbic system. b. The language areas involved in comprehension and articulation include Wernicke’s area, Broca’s area, the lateral prefrontal cortex, and the lateral and ventral parts of the temporal lobe. c. The posterior association area receives input from all sensory areas, integrating signals into a single thought. d. The visceral association area is involved in conscious visceral sensation. 8. There is lateralization of cortical functioning, in which each cerebral hemisphere has unique abilities not shared by the other half. a. One hemisphere (often the left) dominates language abilities, math, and logic, and the other hemisphere (often the right) dominates visualspatial skills, intuition, emotion, and artistic and musical skills. 9. Cerebral white matter is responsible for communication between cerebral areas and the cerebral cortex and lower CNS centers. 10. Basal nuclei consist of a group of subcortical nuclei, which play a role in motor control and regulating attention and cognition. E. The diencephalon is a set of gray matter areas, and consists of the thalamus, hypothalamus, and epithalamus (pp. 441–445; Figs. 12.11–12.15; Table 12.1). 1. The thalamus plays a key role in mediating sensation, motor activities, cortical arousal, learning, and memory. 2. The hypothalamus is the control center of the body, regulating ANS activity such as emotional response, body temperature, food intake, sleepwake cycles, and endocrine function. 3. The epithalamus includes the pineal gland, which secretes melatonin and regulates the sleep-wake cycle.

F.

The brain stem, consisting of the midbrain, pons, and medulla oblongata, produces rigidly programmed, automatic behaviors necessary for survival (pp. 445–450; Figs. 12.15–12.16; Table 12.1). 1. The midbrain is comprised of the cerebral peduncles, corpora quadrigemina, and substantia nigra. 2. The pons contains fiber tracts that complete conduction pathways between the brain and spinal cord. 3. The medulla oblongata is the location of several visceral motor nuclei controlling vital functions such as cardiac and respiratory rate.

G. Cerebellum (pp. 450–451; Fig. 12.17; Table 12.1) 1. The cerebellum processes inputs from several structures and coordinates skeletal muscle contraction to produce smooth movement. a. There are two cerebellar hemispheres consisting of three lobes each. Anterior and posterior lobes coordinate body movements and the flocculonodular lobes adjust posture to maintain balance. b. Three paired fiber tracts, the cerebellar peduncles, communicate between the cerebellum and the brain stem. 2. Cerebellar processing follows a functional scheme in which the frontal cortex communicates the intent to initiate voluntary movement to the cerebellum, the cerebellum collects input concerning balance and tension in muscles and ligaments, and the best way to coordinate muscle activity is relayed back to the cerebral cortex. H. Functional brain systems consist of neurons that are distributed throughout the brain but work together (pp. 451–453; Figs. 12.18–12.19). 1. The limbic system is involved with emotions, and is extensively connected throughout the brain, allowing it to integrate and respond to a wide variety of environmental stimuli. 2. The reticular formation extends through the brain stem, keeping the cortex alert via the reticular activating system, and dampening familiar, repetitive, or weak sensory inputs.

II. Higher Mental Functions (pp. 453–460; Figs. 12.20–12.23) A. Brain Wave Patterns and the EEG (pp. 453–455; Fig. 12.20) 1. Normal brain function results from continuous electrical activity of neurons, and can be recorded with an electroencephalogram, or EEG. 2. Patterns of electrical activity are called brain waves, and fall into four types: alpha, beta, theta, and delta waves. B. Consciousness encompasses conscious perception of sensations, voluntary initiation and control of movement, and capabilities associated with higher mental processing (p. 455). C. Sleep and Sleep-Awake Cycles (pp. 455–457; Fig. 12.21) 1. Sleep is a state of partial unconsciousness from which a person can be aroused, and has two major types that alternate through the sleep cycle. a. Non-rapid eye movement (NREM) sleep has four stages. b. Rapid eye movement (REM) sleep is when most dreaming occurs. 2. Sleep patterns change throughout life, and are regulated by the hypothalamus.

3. NREM sleep is considered restorative, and REM sleep allows the brain to analyze events or eliminate meaningless information. D. Memory is the storage and retrieval of information (pp. 457–460; Figs. 12.22– 12.23). 1. Short-term memory, or working memory, allows the memorization of a few units of information for a short period of time. 2. Long-term memory allows the memorization of potentially limitless amounts of information for very long periods. 3. Transfer of information from short-term to long-term memory can be affected by a high emotional state, repetition, association of new information with old, or the automatic formation of memory while concentrating on something else. 4. Declarative memory entails learning explicit information, is often stored with the learning context, and is related to the ability to manipulate symbols and language. 5. Nondeclarative memory usually involves motor skills, is often stored without details of the learning context, and is reinforced through performance. 6. Learning causes changes in neuronal RNA, dendritic branching, deposition of unique proteins at LTM synapses, increase of presynaptic terminals, increase of neurotransmitter, and development of new neurons in the hippocampus.

III. Protection of the Brain (pp. 460–466; Figs. 12.24–12.27) A. Meninges are three connective tissue membranes that cover and protect the CNS, protect blood vessels and enclose venous sinuses, contain cerebrospinal fluid, and partition the brain (pp. 461–463; Figs. 12.24–12.25). 1. The dura mater is the most durable, outermost covering that extends inward in certain areas to limit movement of the brain within the cranium. 2. The arachnoid mater is the middle meninx that forms a loose brain covering. 3. The pia mater is the innermost layer that clings tightly to the brain. B. Cerebrospinal Fluid (p. 463; Figs. 12.26–12.27) 1. Cerebrospinal fluid (CSF) is the fluid found within the ventricles of the brain and surrounding the brain and spinal cord. 2. CSF gives buoyancy to the brain, protects the brain and spinal cord from impact damage, and is a delivery medium for nutrients and chemical signals. C. The blood-brain barrier is a mechanism that helps maintain a protective environment for the brain (pp. 463–464). D. Homeostatic Imbalances of the Brain (pp. 464–466) 1. Traumatic head injuries can lead to brain injuries of varying severity: concussion, contusion, and subdural or subarachnoid hemorrhage. 2. Cerebrovascular accidents (CVAs), or strokes, occur when blood supply to the brain is blocked, resulting in tissue death. 3. Alzheimer’s disease is a progressive degenerative disease that ultimately leads to dementia.

4. Parkinson’s disease results from deterioration of dopamine-secreting neurons of the substantia nigra, and leads to a loss in coordination of movement and a persistent tremor. 5. Huntington’s disease is a fatal hereditary disorder that results from deterioration of the basal nuclei and cerebral cortex.

IV. The Spinal Cord (pp. 466–477; Figs. 12.28–12.35; Tables 12.2– 12.3) A. Embryonic Development (p. 466; Fig. 12.28) 1. The spinal cord develops from the caudal portion of the neural tube. 2. Axons from the alar plate form white matter, and expansion of both the alar and ventral plates gives rise to the central gray matter of the cord. 3. Neural crest cells form the dorsal root ganglia, and send axons to the dorsal aspect of the cord. B. Gross Anatomy and Protection (pp. 466–468; Figs. 12.29–12.30) 1. The spinal cord extends from the foramen magnum of the skull to the level of the first or second lumbar vertebra. It provides a two-way conduction pathway to and from the brain and serves as a major reflex center. 2. Fibrous extensions of the pia mater anchor the spinal cord to the vertebral column and coccyx, preventing excessive movement of the cord. 3. The spinal cord has 31 pairs of spinal nerves along its length that define the segments of the cord. 4. There are cervical and lumbar enlargements for the nerves that serve the limbs, and a collection of nerve roots (cauda equina) that travel through the vertebral column to their intervertebral foramina. C. Cross-Sectional Anatomy (pp. 468–476; Figs. 12.31–12.35; Tables 12.2–12.3) 1. Two grooves partially divide the spinal cord into two halves: the anterior and posterior median fissures. 2. Two arms that extend posteriorly are dorsal horns, and the two arms that extend anteriorly are ventral horns. 3. In the thoracic and superior lumbar regions, there are also paired lateral horns that extend laterally between the dorsal and ventral horns. 4. Afferent fibers from peripheral receptors form the dorsal roots of the spinal cord. 5. The white matter of the spinal cord allows communication between the cord and brain. 6. All major spinal tracts are part of paired multineuron pathways that mostly cross from one side to the other, consist of a chain of two or three neurons, and exhibit somatotropy. 7. Ascending pathways conduct sensory impulses upward through a chain of three neurons. a. Nonspecific ascending pathways receive input from many different types of sensory receptors, and make multiple synapses in the brain. b. Specific ascending pathways mediate precise input from a single type of sensory receptor. c. Spinocerebellar tracts convey information about muscle and tendon stretch to the cerebellum.

8. Descending pathways involve two neurons: upper motor neurons and lower motor neurons. a. The direct, or pyramidal, system regulates fast, finely controlled, or skilled movements. b. The indirect, or extrapyramidal, system regulates muscles that maintain posture and balance, control coarse limb movements, and head, neck, and eye movements involved in tracking visual objects. D. Spinal Cord Trauma and Disorders (pp. 476–477) 1. Any localized damage to the spinal cord or its roots leads to paralysis (loss of motor function) or paresthesias (loss of sensory function). 2. Poliomyelitis results from destruction of anterior horn neurons by the polio virus. 3. Amyotrophic lateral sclerosis (ALS), or Lou Gehrig’s disease, is a neuromuscular condition that involves progressive destruction of anterior horn motor neurons and fibers of the pyramidal tract.

V. Diagnostic Procedures for Assessing CNS Dysfunction (p. 477) A. Pneumoencephalography is used to diagnose hydrocephalus, and allows X-ray visualization of the ventricles of the brain. B. A cerebral angiogram is used to assess the condition of cerebral arteries to the brain in individuals that have suffered a stroke or TIA. C. CT scans and MRI scanning techniques allow visualization of most tumors, intracranial lesions, multiple sclerosis plaques, and areas of dead brain tissue. D. PET scans can localize brain lesions that generate seizures and diagnose Alzheimer’s disease.

VI. Developmental Aspects of the Central Nervous System (pp. 477– 478; Fig. 12.36) A. The brain and spinal cord grow and mature throughout the prenatal period due to influence from several organizer centers (p. 477). B. Gender-specific areas of the brain and spinal cord develop depending on the presence or absence of testosterone (p. 477). C. Lack of oxygen to the developing fetus may result in cerebral palsy, a neuromuscular disability in which voluntary muscles are poorly controlled or paralyzed as a result of brain damage (p. 477). D. Age brings some cognitive decline but losses are not significant until the seventh decade (p. 478).

Laboratory Correlations 1. Marieb, E. N., and S. J. Mitchell. Human Anatomy & Physiology Laboratory Manual: Main Version. Eighth Edition Update. Benjamin Cummings, 2009. Exercise 19: Gross Anatomy of the Brain and Cranial Nerves Exercise 20: Electroencephalography Exercise 21: Spinal Cord, Spinal Nerves, and the Autonomic Nervous System

Online Resources for Students

myA&P™ www.myaandp.com The following shows the organization of the Chapter Guide page in myA&P™. The Chapter Guide organizes all the chapter-specific online media resources for Chapter 12 in one convenient location, with e-book links to each section of the textbook. Students can also access A&P Flix animations, MP3 Tutor Sessions, Interactive Physiology® 10-System Suite, Practice Anatomy Lab™ 2.0, PhysioEx™ 8.0, and much more. Objectives Section 12.1 The Brain (pp. 430–453) Art Labeling: Art Labeling: 436) Art Labeling: Art Labeling: Art Labeling:

Lobes and Fissures of the Cerebral Hemispheres (Fig. 12.6a, p. 434) Functional and Structural Areas of the Cerebral Cortex (Fig. 12.8a, p. Basal Nuclei (Fig. 12.11, p. 442) Midsagittal Section of the Brain, Part 1 (Fig. 12.12, p. 443) Midsagittal Section of the Brain, Part 2 (Fig. 12.12, p. 443)

Art Labeling: Selected Structures of the Diencephalon (Fig. 12.13, p. 444) Art Labeling: Ventral and Left Lateral Views of the Brain Stem and the Diencephalon (Fig. 12.15a–b, p. 446) Art Labeling: Dorsal View of the Brain Stem and the Diencephalon (Fig. 12.15c, p. 447) Art Labeling: Cross Section Through Different Regions of the Brain Stem, Midbrain (Fig. 12.16a, p. 448) Art Labeling: Cross Section Through Different Regions of the Brain Stem, Pons (Fig. 12.16b, p. 448) Art Labeling: Cross Section Through Different Regions of the Brain Stem, Medulla Oblongata (Fig. 12.16c, p. 448) Memory Game: Brain Structures Section 12.2 Higher Mental Functions (pp. 453–460) Section 12.3 Protection of the Brain (pp. 460–466) Art Labeling: Meninges: Dura Mater, Arachnoid Mater, and Pia Mater (Fig. 12.24, p. 460) Art Labeling: Location and Circulation of CSF (Fig. 12.26a, p. 462) Case Study: Cerebrovascular Accident Case Study: Parkinson’s Disease Section 12.4 The Spinal Cord (pp. 466–477) MP3 Tutor Session: Sensory and Motor Pathways Art Labeling: Anatomy of the Spinal Cord (Fig. 12.31a–b, p. 469) Memory Game: Major Nerves of the Central Nervous System Case Study: Nervous System Section 12.5 Diagnostic Procedures for Assessing CNS Dysfunction (p. 477) Section 12.6 Developmental Aspects of the Central Nervous Syst...