Regulation and Integration of the Body
(pp. 447–449)
Te cerebellum consists of two hemispheres, marked by
convolutions and separated by the vermis. It is connected to the
brain stem by superior, middle, and inferior peduncles.
Te cerebellum processes and interprets impulses from the motor
cortex and sensory pathways and coordinates motor activity so
that smooth, well-timed movements occur. It also plays a poorly
understood role in cognition.
Functional Brain Systems
(pp. 449–452)
Te limbic system consists of numerous structures that encircle
the brain stem. It is the “emotional-visceral brain.” It also plays a
role in memory.
Te reticular formation is a diffuse network of neurons and nuclei
spanning the length of the brain stem. It maintains the alert state
of the cerebral cortex (RAS), and its motor nuclei serve both
somatic and visceral motor activities.
Higher Mental Functions
(pp. 452–458)
Brain Wave Patterns and the EEG
(pp. 452–453)
Patterns of electrical activity of the brain are called brain waves;
a record of this activity is an electroencephalogram (EEG). Brain
wave patterns, identified by their frequencies, include alpha, beta,
theta, and delta waves.
Epilepsy results from abnormal electrical activity of brain
neurons. Involuntary muscle contractions and sensory auras are
typical during some epileptic seizures.
(pp. 453–454)
Consciousness is described clinically on a continuum from
alertness to drowsiness to stupor and finally to coma.
Human consciousness is thought to involve holistic information
processing, which is (1) not localizable, (2) superimposed on
other types of neural activity, and (3) totally interconnected.
Fainting (syncope) is a temporary loss of consciousness that
usually reflects inadequate blood delivery to the brain. Coma
is loss of consciousness in which the victim is unresponsive to
Sleep and Sleep-Wake Cycles
(pp. 454–455)
Sleep is a state of partial consciousness from which a person can
be aroused by stimulation. Te two major types of sleep are non–
rapid eye movement (NREM) sleep and rapid eye movement
(REM) sleep.
During stages 1–4 of NREM sleep, brain wave frequency
decreases and amplitude increases until delta wave sleep (stage
4) is achieved. REM sleep is indicated by a return to alpha waves
on the EEG. During REM, the eyes move rapidly under the lids.
NREM and REM sleep alternate throughout the night.
Slow-wave sleep (stages 3 and 4 of NREM) appears to be
restorative. REM sleep is important for emotional stability.
REM occupies half of an infant’s sleep time and then declines to
about 25% of sleep time by age 10. ±ime spent in slow-wave sleep
declines steadily throughout life.
Narcolepsy is involuntary lapses into REM sleep that occur
without warning during waking periods. Insomnia is a chronic
inability to obtain the amount or quality of sleep needed to
function adequately. A person with sleep apnea stops breathing
temporarily during sleep, causing hypoxia.
Each cerebral hemisphere receives sensory impulses from, and
dispatches motor impulses to, the opposite side of the body. Te
body is represented in an upside-down fashion in the sensory and
motor cortices.
Functional areas of the cerebral cortex include (1) motor areas:
primary motor and premotor cortices of the frontal lobe,
the frontal eye field, and Broca’s area in the frontal lobe of
one hemisphere (usually the le²); (2) sensory areas: primary
somatosensory cortex and somatosensory association cortex
in the parietal lobe; visual areas in the occipital lobe; olfactory
and auditory areas in the temporal lobe; gustatory, visceral,
and vestibular areas in the insula; (3) association areas: anterior
association area in the frontal lobe, and posterior and limbic
association areas spanning several lobes.
Te cerebral hemispheres show lateralization of cortical function.
In most people, the le² hemisphere is dominant (i.e., specialized
for language and mathematical skills); the right hemisphere is
more concerned with visual-spatial skills and creative endeavors.
Fiber tracts of the cerebral white matter include commissures,
association fibers, and projection fibers.
Te paired basal nuclei (also called basal ganglia) include the
globus pallidus, putamen, and caudate nucleus. Te basal nuclei
are subcortical nuclei that help control movements. Functionally
they are closely associated with the substantia nigra of the
(pp. 441–443)
Te diencephalon includes the thalamus, hypothalamus, and
epithalamus and encloses the third ventricle.
Te thalamus is the major relay station for (1) sensory impulses
ascending to the sensory cortex, (2) inputs from subcortical
motor nuclei and the cerebellum traveling to the cerebral motor
cortex, and (3) impulses traveling to association cortices from
lower centers.
Te hypothalamus is an important control center of the
autonomic nervous system and a pivotal part of the limbic
system. It maintains water balance and regulates thirst, eating
behavior, gastrointestinal activity, body temperature, and the
activity of the anterior pituitary gland.
Te epithalamus includes the pineal gland, which secretes the
hormone melatonin.
Brain Stem
(pp. 443–447)
Te brain stem includes the midbrain, pons, and medulla
Te midbrain contains the corpora quadrigemina (visual and
auditory reflex centers), the red nucleus (subcortical motor
centers), and the substantia nigra. Te periaqueductal gray matter
is involved in pain suppression and contains the motor nuclei of
cranial nerves III and IV. Te cerebral peduncles on its ventral
face house the pyramidal fiber tracts. Te midbrain surrounds the
cerebral aqueduct.
Te pons is mainly a conduction area. Its nuclei contribute to
regulating respiration and cranial nerves V–VII.
Te pyramids (descending corticospinal tracts) form the
ventral face of the medulla oblongata. Tese fibers cross over
(decussation of the pyramids) before entering the spinal cord.
Important nuclei in the medulla regulate respiratory rhythm,
heart rate, and blood pressure and serve cranial nerves VIII–XII.
Te olivary nuclei and cough, sneezing, swallowing, and vomiting
centers are also in the medulla.
previous page 512 Human Anatomy and Physiology (9th ed ) 2012 read online next page 514 Human Anatomy and Physiology (9th ed ) 2012 read online Home Toggle text on/off