The Central Nervous System 239Kevin’s accident caused brain damage. His partially par-
alyzed right arm suggests involvement of motor control
areas in his left cerebral hemisphere. His aphasia also sug-
gests damage to the left hemisphere that involves Broca’s
area, because his speech, though slow and difficult, is
understandable. If it were not, damage to Wernicke’s area
would be suspected. To help him sleep, he took Ambien,
a nonbenzodiazepine that promotes GABA inhibition of
the reticular activating system. He also appears to have
suffered damage to his cerebellum, because he displays
problems with gait and coordination as well as intention
tremor. Kevin’s right foot had a Babinski reflex, demon-
strating that the corticospinal tract from the left hemisphere
was not inhibiting his toe extension.
See the additional chapter 8 Clinical Investigation on ataxia
in the Connect site for this text.Clinical Investigation SUMMARY
| CHECKPOINT
12a. Define the terms dorsal root, dorsal root ganglion,
ventral root, and mixed nerve.
12b. Describe the neural pathways and structures
involved in a reflex arc.are described together with muscle control in chapter 12, and
autonomic reflexes, involving smooth and cardiac muscle,
are described in chapter 9.
C. Particular regions of the left cerebral cortex appear to be
important in language ability; when these areas are damaged,
characteristic types of aphasias result.
1. Wernicke’s area is involved in speech comprehension,
whereas Broca’s area is required for the mechanical
performance of speech.
2. Wernicke’s area is believed to control Broca’s area by
means of the arcuate fasciculus.
3. The angular gyrus is believed to integrate different
sources of sensory information and project to
Wernicke’s area.
D. The limbic system and hypothalamus are regions of the
brain that have been implicated as centers for various
emotions.
E. Memory can be divided into short-term and long-term
categories.
1. The medial temporal lobes—in particular the
hippocampus and perhaps the amygdaloid nucleus—
appear to be required for the consolidation of short-term
memory into long-term memory.
2. Particular aspects of a memory may be stored in
numerous brain regions.
3. Long-term potentiation is a phenomenon that may be
involved in some aspects of memory.8.3 Diencephalon 225
A. The diencephalon is the region of the forebrain that includes
the thalamus, epithalamus, hypothalamus, and pituitary
gland.
1. The thalamus serves as an important relay center for
sensory information, among its other functions.Summary
8.1 Structural Organization of the Brain 207
A. During embryonic development, five regions of the brain are
formed: the telencephalon, diencephalon, mesencephalon,
metencephalon, and myelencephalon.
- The telencephalon and diencephalon constitute the
forebrain; the mesencephalon is the midbrain, and the
hindbrain is composed of the metencephalon and the
myelencephalon. - The CNS begins as a hollow tube, and thus the brain
and spinal cord are hollow. The cavities of the brain are
known as ventricles.
8.2 Cerebrum 209
A. The cerebrum consists of two hemispheres connected by a
large fiber tract called the corpus callosum.
- The outer part of the cerebrum, the cerebral cortex,
consists of gray matter. - Under the gray matter is white matter, but nuclei of gray
matter, known as the basal nuclei, lie deep within the
white matter of the cerebrum. - Synaptic potentials within the cerebral cortex produce the
electrical activity seen in an electroencephalogram (EEG).
B. The two cerebral hemispheres exhibit some specialization of
function, a phenomenon called cerebral lateralization. - In most people, the left hemisphere is dominant in
language and analytical ability, whereas the right
hemisphere is more important in pattern recognition,
musical composition, singing, and the recognition of faces. - The two hemispheres cooperate in their functions; this
cooperation is aided by communication between the two
via the corpus callosum.