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CHAPTER
12
The Central Nervous System
Objectives
The Brain
1. Describe how space constraints affect brain development.
2. Name the major regions of the adult brain.
3. Name and locate the ventricles of the brain.
4. List the major lobes, fissures, and functional areas of the cerebral cortex.
Higher Mental Functions
12. Define EEG and distinguish between alpha, beta, theta, and delta brain waves.
13. Describe consciousness clinically.
Protection of the Brain
17. Describe how meninges, cerebrospinal fluid, and the blood brain barrier protect the CNS.
18. Explain how cerebrospinal fluid is formed and describe its circulatory pathway.
Homeostatic Imbalances of the Brain
The Spinal Cord
20. Describe the gross and microscopic structure of the spinal cord.
Diagnostic Procedures for Assessing CNS Dysfunction
23. List and explain several techniques used to diagnose brain disorders.
Developmental Aspects of the Central Nervous System
24. Describe the development of the brain and spinal cord.
Suggested Lecture Outline
I. The Brain (pp. 429–452; Figs. 12.1–12.17; Table 12.1)
A. Embryonic Development (pp. 429–430; Figs. 12.1–12.2)
1. The brain and spinal cord begin as the neural tube, which rapidly differentiates into the
CNS.
2. The neural tube develops constrictions that divide the three primary brain vesicles:
the prosencephalon (forebrain), mesencephalon (midbrain), and rhombencephalon
(hindbrain).
3. Since the brain grows more rapidly than the developing skull, the brain forms folds,
allowing it to fit inside the space of the skull.
B. Regions and Organization (p. 430)
1. The medical scheme of brain anatomy divides the adult brain into four parts: the cere-
bral hemispheres, the diencephalon, the brain stem (consisting of the midbrain, pons,
C. Ventricles (p. 430; Fig. 12.3)
1. The ventricles of the brain are continuous with one another and with the central canal
of the spinal cord.
a. The ventricles are lined with ependymal cells and are filled with cerebrospinal
fluid.
d. The fourth ventricle lies in the hindbrain and communicates with the third ventricle
via the cerebral aqueduct.
e. The lateral and median apertures within the fourth ventricle connect the ventricles
with the subarachnoid space surrounding the brain.
D. Cerebral Hemispheres (pp. 430–441; Figs. 12.4–12.10, 12.12; 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.
a. The central sulcus separates the frontal and parietal lobes.
b. The precentral gyrus lies anterior to the central sulcus, while the postcentral gyrus
lies posterior to the central sulcus.
4. The cerebral cortex is the location of the conscious mind, allowing us to communicate,
remember, and understand, and comprises about 40% of the total brain mass.
5. The cerebral cortex has three kinds of functional areas: motor areas, sensory areas, and
association areas.
7. The hemispheres exhibit lateralization of function, meaning that there is specialization
of one side of the brain for certain functions.
8. Areas in the posterior part of the frontal lobes control voluntary movement.
a. The primary motor cortex allows conscious control of skilled voluntary movement
9. 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.
10. Multimodal association areas are not connected to any specific sensory cortex, but are
highly interconnected areas throughout the cerebral cortex.
11. There is lateralization of cortical functioning, in which each cerebral hemisphere has
unique control over abilities not shared by the other half.
12. Cerebral white matter is responsible for communication between cerebral areas and
the cerebral cortex and lower CNS centers.
a. Association fibers are tracts of cerebral white matter that run horizontally, connect-
13. Basal nuclei consist of a group of subcortical nuclei that have overlapping motor
control with the cerebellum that regulate cognition and emotion.
E. The diencephalon is a set of gray matter areas and consists of the thalamus,
hypothalamus, and epithalamus (pp. 441–443; Figs. 12.11, 12.13; Table 12.1).
1. The thalamus plays a key role in mediating sensation, motor activities, cortical
arousal, learning, and memory.
F. The brain stem, consisting of the midbrain, pons, and medulla oblongata, produces
rigidly programmed, automatic behaviors necessary for survival (pp. 443–447;
Figs. 12.12–12.14; Table 12.1).
1. The midbrain is comprised of the cerebral peduncles, corpora quadrigemina, and
G. Cerebellum (pp. 447–449; Fig. 12.15; Table 12.1)
1. The cerebellum processes inputs from several structures and coordinates skeletal
muscle contraction to produce smooth movement.
2. There are two cerebellar hemispheres consisting of three lobes each:
3. Cerebellar processing follows a functional scheme in which the frontal cortex commu-
nicates 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.
II. Higher Mental Functions (pp. 452–458; Figs. 12.18–12.20)
A. Brain Wave Patterns and the EEG (pp. 452–453; Fig. 12.18)
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:
a. Alpha waves are regular, rhythmic, low-amplitude, synchronous waves that indicate
calm wakefulness.
3. Brain waves change with age, sensory stimuli, brain disease, and chemical state of the
body.
4. An absence of brain waves defines brain death.
1. Consciousness involves simultaneous activity of large areas of the cerebral cortex, is
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: non–rapid eye movement
(NREM) and rapid eye movement (REM).
2. Sleep patterns change throughout life and are regulated by the hypothalamus.
3. The hypothalamus inhibits the reticular activating system, which mediates some sleep
stages, especially dreaming.
5. NREM sleep is considered restorative, and REM sleep allows the brain to analyze
events or eliminate meaningless information.
6. A person’s sleep requirement declines throughout life; REM sleep declines and then
stabilizes at around age ten, with stage 4 sleep declining steadily from birth.
D. The ability to both speak and understand language is produced through coordination of
several brain areas, notably Broca’s area and Wernicke’s area (pp. 455–456).
E. Memory is the storage and retrieval of information (pp. 456–458; Figs. 12.20–12.21).
2. Long-term memory (LTM) 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
5. Nondeclarative memory is less conscious and is categorized into procedural memory,
motor memory, and emotional memory.
III. Protection of the Brain (pp. 458–462; Figs. 12.22–12.25)
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. 459–460; Figs. 12.22–12.23).
2. The arachnoid mater is the middle meninx that forms a loose brain covering.
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
2. Lipid-soluble molecules easily cross the blood brain barrier.
D. Homeostatic Imbalances of the Brain (pp. 462–464)
1. Traumatic head injuries can lead to brain injuries of varying severity: concussion,
contusion, and subdural or subarachnoid hemorrhage.
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. 464–474; Figs. 12.26–12.32; Tables 12.2–12.3)
A. Gross Anatomy and Protection (pp. 464–466; Figs. 12.26–12.27)
1. The spinal cord extends from the foramen magnum of the skull to the level of the first
or second lumbar vertebra and provides a two-way conduction pathway to and from
the brain and serves as a major reflex center.
B. Spinal Cord Cross-Sectional Anatomy (pp. 466–468; Figs. 12.28–12.30)
1. Two grooves partially divide the spinal cord into two halves: the anterior and posterior
median fissures.
C. Neuronal Pathways (pp. 468–473; Figs. 12.31–12.32; Tables 12.2–12.3)
1. 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
somatotopy.
2. Ascending pathways conduct sensory impulses upward through a chain of three
neurons.
a. Nonspecific ascending pathways receive input from many different types of sensory
3. 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.
D. Spinal Cord Trauma and Disorders (p. 474)
1. Any localized damage to the spinal cord or its roots leads to paralysis (loss of motor
function) or paresthesias (loss of sensory function).
a. Severe damage to the ventral root or ventral horn results in flaccid paralysis, since
nerve impulses are not transmitted to the skeletal muscles.
limbs are affected, resulting in quadriplegia.
2. Poliomyelitis results from destruction of ventral horn motor neurons by the poliovirus.
3. Amyotrophic lateral sclerosis (ALS), or Lou Gehrig’s disease, is a neuromuscular
condition that involves progressive destruction of ventral horn motor neurons and
fibers of the pyramidal tracts.
V. Diagnostic Procedures for Assessing CNS Dysfunction (pp. 474–475)
A. CT scans and MRI scanning techniques allow visualization of most tumors, intracranial
lesions, multiple sclerosis plaques, and areas of dead brain tissue (p. 474).
VI. Developmental Aspects of the Central Nervous System (pp. 475–477;
Figs. 12.33–12.35)
A. In a three-week-old embryo, the ectoderm thickens, forming a neural plate that in turn
folds inward to form a neural groove between neural folds (p. 475; Fig. 12.33).
B. Neural fold cells migrate laterally which, after the superior edges fuse, form the neural
crest (p. 475; Fig. 12.33).
E. Neural crest cells alongside the cord form the dorsal root ganglia and send axons into the
dorsal side of the cord (p. 475; Fig. 12.34).
F. Gender-specific areas of the brain and spinal cord develop depending on the presence or
absence of testosterone (p. 475).
severe.
H. Growth and maturation of the nervous system continue throughout childhood and largely
reflect development of myelination, which progresses in a superior-to-inferior direction
(p. 477).
Cross References
Additional information on topics covered in Chapter 12 can be found in the chapters listed below.
1. Chapter 13: Spinal nerves and peripheral nervous system function; the relationship
between the peripheral nervous system and gray and white matter of the spinal cord;
different brain areas and neural integration
cerebellum in integration of sensory information
4. Chapter 16: Hypothalamus and hormone production
5. Chapter 18: Role of the medulla in cardiac rate regulation
6. Chapter 19: Capillaries of the brain (blood brain barrier); medulla and regulation of blood
vessel diameter (vasomotor center); hypothalamus and blood pressure regulation
Lecture Hints
1. Study of the central nervous system is difficult for most students. The complexity of
2. When discussing the ventricles, construct a rough diagram that shows a schematic repre-
3. Students often have difficulty understanding how the cerebellum is involved in the
control of motor activity. Try using a physical activity such as golf to illustrate cerebellar
4. Emphasize that the meningeal protection of the brain and spinal cord is continuous, but
that the spinal cord has an epidural space, whereas the brain does not.
Activities/Demonstrations
2. Present microslides to demonstrate cross-sectional anatomy of the spinal cord at several
different levels to show how gray and white matter changes with each level in the cord.
3. Obtain a 3-D model of a human brain and compare it with a dissected sheep brain. Point
4. Acquire a 3-D model of a spinal cord, both longitudinal section and cross section, to
illustrate its features.
Critical Thinking/Discussion Topics
1. Discuss the difference between encephalitis and meningitis.
2. Prefrontal lobotomies have been used in psychotherapy along with electrical shock. How
and why have these techniques been used?
3. Regarding cerebral dominance: What types of things could be done to increase the use of
the less dominant hemisphere?
Library Research Topics
1. What techniques are currently used to localize and treat tumors of the brain?
2. How has the human brain changed in size and shape over millions of years of evolution?
Explore the development of the human nervous system.
6. Describe the latest techniques used to examine structure/function of the CNS.
7. How can human stem cells be used to repair adult CNS dysfunctions?
List of Figures and Tables
All of the figures in the main text are available in JPEG format, PPT, and labeled & unlabeled
format on the Instructor Resource DVD. All of the figures and tables will also be available in
Transparency Acetate format. For more information, go to www.pearsonhighered.com/educator.
Figure 12.1 Embryonic development of the human brain.
Figure 12.2 Brain development.
of the cerebrum.
Figure 12.8 White fiber tracts of the cerebral hemispheres.
Figure 12.9 Basal nuclei.
Figure 12.10 Midsagittal section of the brain.
Figure 12.11 Selected structures of the diencephalon.
Figure 12.12 Inferior view of the brain, showing the three parts of the brain stem:
midbrain, pons, and medulla oblongata.
Figure 12.18 Electroencephalography (EEG) and brain waves.
Figure 12.19 Types and stages of sleep.
Figure 12.20 Memory processing.
Figure 12.21 Proposed memory circuits.
Figure 12.22 Meninges: dura mater, arachnoid mater, and pia mater.
Figure 12.23 Dural septa and dural venous sinuses.
Figure 12.31 Pathways of selected ascending spinal cord tracts.
Figure 12.32 Three descending pathways by which the brain influences movement.
Answers to End-of-Chapter Questions
Multiple-Choice and Matching Question answers appear in Appendix H of the main text.
Short Answer Essay Questions
14. a. Convolutions are an advantage because they produce an increase in the cortical surface
area, which allows more neurons to occupy the limited space. (p. 430)
15. a. See Figure 12.6 for a drawing of the functional areas of the brain. (p. 434)
b. The right side of the brain is the side involved in drawing for most people. The right
side of the brain is involved with visual-spatial and creative activities. (p. 437)
c. See pp. 433–436.
Primary motor cortex—All voluntary somatic motor responses arise from this region.
16. a. Lateralization of cortical functions means that certain functions in the brain are
localized in areas on certain sides of the brain. Cerebral dominance is a misnomer
17. See pp. 439–441.
a. The basal nuclei initiate slow and sustained movement, and help to coordinate and
18. Three paired fiber tracts (cerebellar peduncles) connect the cerebellum to the brain stem.
(p. 444)
19. The cerebellum acts like an automatic pilot by initiating and coordinating the activity of
skeletal muscle groups. (A step-by-step discussion is given on pp. 447–448.)
20. See p. 449.
a. The limbic system is located on the medial aspect of each cerebral hemisphere.
21. See p. 450.
a. The reticular formation extends through the central core of the medulla, pons, and
22. An aura is a sensory hallucination that occurs just before a seizure, such as a taste, smell,
or flashes of light. (p. 453)
23. REM sleep occupies about 50% of the total sleeping time in infants, but then declines
24. STM is fleeting memory that serves as a sort of temporary holding bin for data and is
limited to seven or eight chunks of data. LTM seems to have unlimited capacity for
storage and is very long-lasting unless altered. (p. 456)
25. Memory consolidation is the process of transferring memories from STM to LTM by
26. Declarative memory is the ability to learn explicit information and is related to our
conscious thoughts and our ability to manipulate symbols and language. Procedural
memory is concerned with motor activities acquired through practice. (p. 457)
28. a. CSF is formed by the choroid plexus via a secretory process involving both active
transport and diffusion and is drained by the arachnoid villi. See Figure 12.24 for the
29. The blood brain barrier is formed mainly by capillaries with endothelial cells joined by
30. An incision into the brain would pass through the skin of the scalp, cranial bone,
periosteal and meningeal layers of the dura mater, subdural space, arachnoid mater,
subarachnoid space, and pia mater, finally reaching the brain tissue. (pp. 459–460)
31. a. A concussion occurs when brain injury is slight and the symptoms are mild and
32. The spinal cord is enclosed in the vertebral column and extends from the foramen mag-
num of the skull to the first or second lumbar vertebra, inferior to the ribs. It is composed
of both gray and white matter. The gray matter consists of a mixture of neuron cell
33. The direct pathway regulates fast and fine (skilled) movements, while the indirect path-
ways regulate the muscles responsible for maintaining balance, the muscles involved in
gross limb movements, and head, neck, and eye muscles involved in following objects in
the visual field. (pp. 471–472)
34. a. The lateral spinothalamic tract transmits pain, temperature, and course touch impulses,
and they are interpreted eventually in the somatosensory cortex. If cut, our sensory
perception of the occurrence of a stimulus, as well as our ability to detect the magnitude
35. Spastic paralysis is due to damage to upper motor neurons of the primary motor cortex.
Muscles can respond to reflex arcs initiated at spinal cord level. Flaccid paralysis is due
to damage to ventral root or ventral horn cells. Muscles do not respond because they
receive no stimuli. (p. 474)
36. Paraplegia results from damage to the spinal cord (lower motor neurons) between T1 and
37. a. CVA, also known as stroke, occurs when blood circulation to a brain area is blocked
and vital brain tissue dies. A new hypothesis suggests that the release of glutamate by
38. a. Continued myelination of neural tissue accounts for growth and maturation of the
nervous system.
b. There is a decline in brain weight and volume with age. (p. 477)
Critical Thinking and Clinical Application Questions
1. a. The only likely diagnosis is hydrocephalus. (pp. 460–462)
b. Hydrocephalus can be diagnosed with a CT or sonogram.
2. Mrs. Jones’ decline is likely due to Alzheimer’s disease. The basal forebrain is particu-
3. The damage to Robert’s brain probably involves the frontal lobes, specifically the
prefrontal cortex, which mediates personality and moral behavior. (pp. 436–437)
4. In myelomeningocele, a cyst containing parts of the spinal cord, nerve roots, and men-
inges protrudes from the spine. Pressure during vaginal delivery could cause the cyst to
rupture, leading to infection and further damage. A C-section is preferable. (p. 476)
5. a. Based on his symptoms, Parkinson’s disease.
b. Parkinson’s disease affects neurons of the substantia nigra, and results in deficiency of
6. Cynthia’s waist-down paralysis is a result of damage to nonspecific and specific ascend-
ing pathways, which causes a loss of sensory input to the brain from the extremities, and
damage to the upper, but not lower, motor neurons of the descending pathways. All of
7. The needle will be inserted in the lumbar area of the vertebral column below L2. The
needle will be inserted into the subarachnoid space to withdraw cerebrospinal fluid to be
tested for the presence of pathogens. (p. 466)
Suggested Readings
Birmingham, Karen. “Future of Neuroprotective Drugs in Doubt.” Nature Medicine 8 (1)
(Jan. 2002): 5.
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Dunnett, S. B., et al. “Cell Therapy in Parkinson’s Disease—Stop or Go?” Nature Reviews:
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Fricker-Gater, Rosemary A., and Stephen B. Dunnett. “Rewiring the Parkinsonian Brain.”
Nature Medicine 8 (2) (Feb. 2002): 105–106.
Hansel, D. E., et al. “Neuropeptide Y Functions as a Neuroproliferative Factor.” Nature 410
(6831) (April 2001): 940–944.
Macklis, Jeffrey D. “New Memories from New Neurons.” Nature 410 (6826) (March 2001):
314–315.
Manabe, Toshiya. “Does BDNF Have Pre- or Postsynaptic Targets?” Science 295 (5560)
(March 2002): 1651–1652.
Maquet, Pierre. “The Role of Sleep in Learning and Memory.” Science 294 (5544)
(Nov. 2001): 1048–1051.
Saurat, M., et al. “Walking Dreams in Congenital and Acquired Paraplegia.” Consciousness
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(Nov. 2001): 1851–1852.
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