I. Overview of the Central Nervous System (p. 491)

A. Major Landmarks (p. 491)

1. Two directional terms used to describe the human brain are rostral (closer to the forehead) and caudal (closer to the spinal cord).

2. The brain can be divided into three major portions: the cerebrum, cerebellum, and brainstem. (figs. 14.1, 14.2; TR 472–483)

3. The cerebrum consists of two cerebral hemispheres, each marked by folds called gyri and grooves called sulci, with a few deeper grooves called fissures.

a. The longitudinal fissure separates the left and right hemispheres, although they remain connected through the corpus callosum.

b. The cerebrum constitutes 83% of brain volume.

4. The cerebellum also has gyri, sulci, and fissures, but they are more delicate.

a. The cerebellum lies inferior and posterior to the cerebrum.

b. The cerebellum is the second largest brain region, constituting about 10% of its volume but more than 50% of its neurons.

5. The brainstem is at the base of the brain, and includes the thalamus, hypothalamus, midbrain, pons, and medulla oblongata.

B. Embryonic Development (p. 491; fig. 14.3; TR 484 )

1. The nervous system forms from ectoderm. By the third week, the neuroectoderm appears along the length of the embryo and forms a neural plate.

2. The neural plate sinks into a neural groove, while cells along its margin form a neural fold that eventually fuses.

3. By four weeks, a neural tube is evident, the lumen of which forms the ventricles of the brain and the central canal of the spinal cord.

4. Some cells separate from the neural tube and form the neural crest, which gives rise to some sensory neurons and other cell types (neuroglia and neurons).

5. At week four, the neural tube shows three primary vesicles, a forebrain, midbrain, and hindbrain; the forebrain then divides further into the telencephalon and diencephalon. The hindbrain divides into the metencephalon and myelencephalon. (fig. 14.4; TR 485)

II. Meninges, Ventricles, Cerebrospinal Fluid, and Blood Supply (p. 496)

A. Meninges (p. 496; fig. 14.5; TR 486, 487)

1. The meninges are three protective fibrous coverings that separate the brain and spinal cord from the skull and vertebrae.

2. The outermost meninx, the dura mater, consists of an outer periosteal layer and an inner meningeal layer.

a. In certain places, these two layers are separated by dural sinuses where blood pools.

b. In other places, the dura mater folds to separate major areas of the brain. These folds are the falx cerebri and tentorium cerebelli.

3. Within the vertebral canal, the periosteal layer of the dura is absent. The meningeal layer forms a dural sheath around the spinal cord; between the sheath and surrounding bone lies the epidural space.

4. The second meninx, the arachnoid mater, adheres to the dura and sends spiderlike extensions out to the pia mater.

5. The pia mater is highly vascular layer that closely follows the contours of the brain.

6. The dura and arachnoid are separated by a subdural space; the arachnoid and pia mater are separated by the subarachnoid space.

B. Ventricles and Cerebrospinal Fluid (p. 496; fig. 14.6; TR 488–491)

1. The brain has four internal chambers called ventricles. Each cerebral hemisphere houses a large lateral ventricle that communicates with a third ventricle through an interventricular foramen. The cerebral aqueduct connects the third with the fourth ventricle.

2. A choroid plexus within each ventricle produces cerebrospinal fluid, a clear, colorless liquid that fills the ventricles and canals of the CNS and bathes its external surface. CSF lends buoyancy, protects, removes wastes, and provides a stable chemical environment.

3. CSF circulates throughout the ventricles, and makes its way into the central canal of the spinal cord. It exits the fourth ventricle through two apertures and enters the subarachnoid space. (fig. 14.7; TR 492)

4. Hydrocephalus results from blockage of the route of CSF and its reabsorption.

C. Blood Supply and the Brain Barrier System (p. 499)

1. The brain is very metabolically active and has a high demand for oxygen and glucose. Stopping the blood supply to the brain for as little as 4 minutes can cause irreversible brain damage.

2. The CNS is protected by a blood-brain barrier that regulates substances entering the brain. Tight junctions within capillaries and astrocytes comprise this barrier.

3. The blood-brain barrier is absent in areas of the brain (called circumventricular organs) that monitor blood glucose, pH, salinity, and so forth.

III. The Spinal Cord (p. 501)

A. Functions (p. 501)

1. The spinal cord functions in conduction, locomotion, and control of reflex activity.

B. Gross Anatomy (p. 501; fig. 14.8; TR 493)

1. The spinal cord begins at the foramen magnum and ends at the first lumbar vertebra. It is divided into cervical, thoracic, lumbar, and sacral regions.

2. The spinal cord gives rise to 31 pairs of spinal nerves, each of which is connected to a segment of the spinal cord.

3. The spinal cord bears a cervical and lumbar enlargement, where nerves leading to appendages arise. The cord tapers to a point at the conus medullaris. A nerve bundle, the cauda equina, exits the bottom of the spinal cord.

C. Cross-Sectional Anatomy (p. 501; fig. 14.9; TR 494)

1. The spinal cord consists of a central area of gray matter divided into regions called horns (two dorsal horns, and two ventral horns).

a. The right and left halves are connected by the gray commissure; in the center is the central canal.

b. Sensory fibers enter the dorsal horn, sometimes synapse with an interneuron. and exit by way of the ventral root of the spinal nerve.

2. White matter consists of bundles of myelinated axons that run up and down the cord, to and from the brain. White matter is arranged into dorsal, lateral, and ventral columns.

D. Spinal Tracts (p. 503; fig. 14.10; TR 495; table 14.1)

1. Ascending tracts carry sensory information up the spinal cord; descending tracts carry motor information down it. Many of the fibers exhibit decussation.

2. Major ascending tracts include the gracile fasciculus, cuneate fasciculus, spinothalamic tract, and dorsal and ventral spinocerebellar tracts. (fig. 14.11; TR 496)

3. Descending tracts include the corticospinal tracts, tectospinal tract, lateral and medial reticulospinal tracts, and the vestibulospinal tract. (fig. 14.12; TR 497)

IV. The Hindbrain and Midbrain (p. 507)

A. The Medulla Oblongata (p. 508)

1. The medulla oblongata develops from the myelencephalon.

2. Features of the medulla include the pyramids containing nerve fibers and olives containing inferior olivary nuclei (relay centers to the cerebellum).

3. Nuclei of the medulla oblongata control coughing, sneezing, hiccuping, sweating, vomiting, and other functions.

B. The Pons and Cerebellum (p. 508; figs. 14.13, 14.14; TR 498, 499)

1. The pons and cerebellum arise from the metencephalon.

2. The gray matter of the pons contains nuclei concerned with sleep, posture, respiration, swallowing, and bladder control. Signals from the cerebrum to the cerebellum pass through the pons.

3. The cerebellum is the largest part of the hindbrain. It consists of right and left cerebellar hemispheres connected by a vermis. Three paired cerebellar peduncles connect the cerebellum to the brainstem.

4. The cerebellum modulates and coordinates voluntary movement of the limbs, maintains muscle tone and posture, coordinates eye movements, and helps in learning motor skills.

C. The Midbrain (p. 508)

1. The midbrain develops from the embryonic mesencephalon.

2. The midbrain is a short segment of the brainstem that connects the hindbrain and the forebrain.

3. Major regions of the midbrain are the cerebral peduncles, the tegmentum, the substantia nigra, the central gray matter, and the tectum. (fig. 14.15; TR 500)

D. The Reticular Formation (p. 511; fig. 14.16; TR 501)

1. The reticular formation is a group of 100 nuclei scattered throughout the medulla, midbrain, and pons that function in somatic motor control, autonomic control, arousal, and pain modulation.

V. The Forebrain (p. 512)

A. The Diencephalon (p. 513; fig. 14.17; TR 502)

1. The thalamus, which makes up four-fifths of the diencephalon, consists of an oval mass of gray matter underneath each cerebral hemisphere and a narrow intermediate mass near the third ventricle.

a. The thalamus is the "gateway to the cerebral cortex"; nearly all information heading to the cerebrum passes through the thalamus.

2. The hypothalamus forms portions of the walls of the third ventricle.

a. The hypothalamus is the major control center of the autonomic nervous system and the endocrine system, and also plays a role in homeostasis.

b. The nuclei of the hypothalamus regulate food and water intake, thermoregulation, cardiovascular regulation, sleep and waking, and emotional behavior.

3. The epithalamus consists of the pineal gland, the habenula, and a roof over the third ventricle.

B. The Cerebrum (p. 514)

1. The surface of the cerebrum is folded into gyri that give it a large surface area.

2. Each hemisphere is divided by fissures and sulci into five anatomically and functionally distinct lobes: the frontal lobe, parietal lobe, occipital lobe, temporal lobe, and insula. (fig. 14.18; TR 503)

3. The white matter of the cerebrum makes up most of the volume of the cerebrum. It houses projection tracts, commissural tracts, and association tracts. (fig. 14.19; TR 504)

4. The cerebral cortex (40% of brain mass) is a layer of gray matter, 2–3 mm thick, covering the cerebral hemispheres.

a. Two types of neurons are found in the cortex: stellate cells and pyramidal cells.

i. Stellate cells have spheroidal somas with dendrites extending in all directions. They receive sensory input and project it locally.

ii. Pyramidal cells are tall and conical, with a thick dendrite bearing many branches. These serve as the output neurons of the cerebrum.

b. Ninety percent of the cortex is a six-layered tissue called neocortex. (fig. 14.20; TR 505)

5. The basal nuclei are masses of gray matter buried deep in the cerebral hemispheres. (fig. 14.21; TR 506, 507)

a. Neuroanatomists agree that the following three brain centers are basal nuclei: the caudate nucleus, putamen, and globus pallidus.

b. The basal nuclei are involved in motor control and the thought process.

6. The limbic system is a loop of cortical structures that surrounds the corpus callosum and thalamus and contains nuclei called the amygdala and the hippocampus. (fig. 14.22; TR 508)

a. The amygdala is important in emotion.

b. The hippocampus is important in memory.

c. Some neuroanatomists now argue that the limbic system’s diverse components do not qualify it as a "system."

VI. Anatomical Checklist for the Brain (see pp. 530–31; table 14.2)

VII. Higher Brain Functions (p. 519)

A. Brain Waves and Sleep (p. 519)

1. Brain waves are rhythmic voltage changes resulting from synchronized postsynaptic potentials in the cerebral cortex. They can be recorded as an electroencephalogram (EEG). The absence of brain waves on an EEG is often used as a legal criterion for death. (fig. 14.23; TR 509, 510)

2. Brain waves are classified as alpha, beta, theta, and delta waves.

a. Alpha waves are seen when the subject is awake and resting, but with eyes closed and mind wandering.

b. Beta waves are seen during mental activity and sensory perception.

c. Theta waves are normal in children and sleeping adults, but signal brain disorders and emotional stress in awake adults.

d. Delta waves are present in awake infants and in deeply sleeping adults. If present in awake adults, they indicate brain damage.

3. Sleep is a temporary state of unconsciousness from which the person can be aroused, whereas a coma is a state of unconsciousness from which the person cannot be aroused.

4. The biological clock that regulates sleep-wake cycles is the suprachiasmatic nucleus of the hypothalamus. The hypothalamus and brainstem control sleep.

5. We pass through four stages of brain activity after falling asleep. (fig. 14.24; TR 511)

a. Stage 1 sleep occurs after first falling asleep; alpha waves are dominant, and the person is easily aroused.

b. Stage 2 sleep is characterized by brain waves called sleep spindles and an irregular EEG.

c. During stage 3, sleep deepens, vital signs decline, and theta waves appear.

d. Stage 4 (slow-wave sleep) is dominated by delta waves. The person is deeply asleep.

e. Several times per night, the sleeper "backtracks" to stage 1 and enters rapid eye movement (REM) sleep. It is also called paradoxical sleep because of the difficulty with which a sleeper can be aroused. Most dreams occur during this period. As sleep continues, periods of REM sleep get longer.

B. Cognition (p. 520)

1. Seventy-five percent of brain tissue consists of association areas dedicated to the processes of awareness, thinking, knowledge, and memory.

2. Lesions to the parietal, temporal, and frontal lobes can have serious effects on these processes.

C. Memory (p. 522)

1. The hippocampus of the limbic system is essential to memory consolidation, the process of organizing diverse experiences into unified long-term memory.

2. Lesions of the hippocampus can cause anterograde amnesia, the inability to store new information.

3. Retrograde amnesia is the inability to recall things the person knew before.

D. Emotion (p. 523)

1. The prefrontal cortex is the seat of judgment, intent, and control of emotions, but the feelings themselves and emotional memories form in the hypothalamus and amygdala.

2. Much behavior is shaped by learned associations between stimuli, our responses, and the subsequent reward or punishment.

E. Sensation (p. 523)

1. Sensory functions are of two types: somesthetic senses and special senses.

2. The postcentral gyrus functions as the primary sensory area. Here neurons receive sensory information. This gyrus also exhibits somatotropy.

3. Located in various regions of the cerebral cortex are the primary sensory areas for taste, smell, vision, hearing, and equilibrium. (figs. 14.25, 14.26; TR 512, 513)

F. Motor Control (p. 525; figs. 14.27, 14.28; TR 514, 515)

1. Voluntary muscle contractions are initiated in the motor association (premotor) area of the frontal lobes. The impulse is then sent to the precentral gyrus (primary motor area), which exhibits a somatotopy.

G. Language (p. 526; fig. 14.29; TR 516)

1. Language includes several abilities and is assigned to different regions of the cerebral cortex.

a. Wernicke's area is responsible for the recognition of spoken and written language and formulation of phrases; it lies just posterior to the lateral sulcus, usually in the left hemisphere.

b. Broca's area generates a motor program to produce speech and is located in the inferior prefrontal cortex in the same hemisphere.

H. Cerebral Lateralization (p. 528; fig. 14.30; TR 517)

1. Cerebral lateralization is the assignment of different tasks to different hemispheres and is correlated with handedness.

a. Most Americans are right-handed, and 96% of them have the left hemisphere as the categorical one.

b. Males show more lateralization than females.

I. Disorders of the Central Nervous System (p. 531; table 14.3)