Human Physiology, 14th edition (2016)

The Central Nervous System 225

8.3 Diencephalon

The diencephalon is the part of the forebrain that contains

the epithalamus, thalamus, hypothalamus, and part of the

pituitary gland. The hypothalamus performs numerous vital

functions, most of which relate directly or indirectly to the

regulation of visceral activities by way of other brain regions

and the autonomic nervous system.

7 inches long and 1¼ inches thick—was driven through his left
eye and brain and emerged through the top of his skull.
After a few minutes of convulsions, Gage got up, rode a
horse three-quarters of a mile into town, and walked up a long
flight of stairs to see a doctor. He recovered well, with no notice-
able sensory or motor deficits. His associates, however, noted
striking personality changes. Before the accident, Gage was a
responsible, capable, and financially prudent man. Afterward,
he appeared to have lost his social inhibitions; for example, he
engaged in gross profanity, which he did not do before his acci-
dent. He was impulsive, being tossed about by seemingly blind
whims. He was eventually fired from his job, and his old friends
remarked that he was “no longer Gage.”

Figure 8.18 Some brain areas involved in emotion. ( a ) The orbitofrontal area of the prefrontal cortex is shown in yellow,
and the cingulate gyrus of the limbic system is shown in blue-green (anterior portion) and green (posterior portion). ( b ) The insula of the
cortex is shown in purple, the anterior cingulate gyrus of the limbic system in blue-green, and the amygdala in red.

(a) (b)

| CHECKPOINT

3a. Describe the locations of the sensory and motor

areas of the cerebral cortex and explain how these

areas are organized.

3b. Describe the locations and functions of the basal nuclei.

Of what structures are the basal nuclei composed?

4a. Identify the structures of the limbic system and

explain the functional significance of this system.

4b. Explain the difference in function of the right and left

cerebral hemispheres.

5. Describe the functions of the brain areas involved in
   speech and language comprehension.


6. Describe the brain areas implicated in memory, and
   their possible functions.

LEARNING OUTCOME

After studying this section, you should be able to:

7. Describe the locations and functions of the thalamus
   and hypothalamus.

The diencephalon, together with the telencephalon (cere-

brum) previously discussed, constitutes the forebrain and is

almost completely surrounded by the cerebral hemispheres.

The third ventricle is a narrow midline cavity within the

diencephalon.

Thalamus and Epithalamus

The thalamus composes about four-fifths of the diencephalon

and forms most of the walls of the third ventricle ( fig.  8.19 ).

It consists of paired masses of gray matter, each positioned

immediately below the lateral ventricle of its respective cere-

bral hemisphere. The thalamus acts primarily as a relay center

through which all sensory information (except smell) passes