Human Physiology, 14th edition (2016)

226 Chapter 8

Corpus callosum

Septum pellucidum

Genu of corpus

callosum

Thalamus

Anterior commissure

Hypothalamus

Optic chiasma

Infundibulum

Pituitary gland

Mammillary body

Pons

Medulla oblongata

Arbor vitae of cerebellum

Cortex of cerebellum

Corpora quadrigemina

Pineal body

Splenium of corpus callosum

Choroid plexus of third ventricle

Intermediate mass

Telencephalon

Diencephalon

Forebrain

Midbrain

Hindbrain

(b)

(a)

hormone secretion from the pituitary gland ( fig. 8.20 ). In addi-

tion, centers in the hypothalamus contribute to the regulation of

sleep, wakefulness, sexual arousal and performance, and such

emotions as anger, fear, pain, and pleasure. Acting through

its connections with the medulla oblongata of the brain stem,

the hypothalamus helps to evoke visceral responses to various

emotional states. In its regulation of emotion, the hypothala-

mus works together with the limbic system.

Regulation of the Autonomic System

Experimental stimulation of different areas of the hypothalamus

can evoke the autonomic responses characteristic of aggression,

sexual behavior, hunger, or satiety. Chronic stimulation of the

lateral hypothalamus, for example, can make an animal eat and

become obese, whereas stimulation of the medial hypothalamus

inhibits eating. Other areas contain osmoreceptors that stimu-

late thirst and the release of antidiuretic hormone (ADH) from

the posterior pituitary.

The hypothalamus is also where the body’s “thermostat”

is located. Experimental cooling of the preoptic-anterior hypo-

thalamus causes shivering (a somatic motor response) and

nonshivering thermogenesis (a sympathetic motor response).

on the way to the cerebrum. For example, the lateral genicu-

late nuclei relay visual information, and the medial genicu-

late nuclei relay auditory information, from the thalamus to

the occipital and temporal lobes, respectively, of the cerebral

cortex. The intralaminar nuclei of the thalamus are activated

by many different sensory modalities and, in turn, project to

many areas of the cerebral cortex. This is part of the system

that promotes a state of alertness and causes arousal from sleep

in response to any sufficiently strong sensory stimulus.

The epithalamus is the dorsal segment of the diencepha-

lon, containing a choroid plexus over the third ventricle where

cerebrospinal fluid is formed. The epithalamus also contains

the pineal gland (epiphysis), which secretes the hormone mela-

tonin that helps regulate circadian (daily) rhythms (chapter 11,

section 11.6).

Hypothalamus and Pituitary Gland

The hypothalamus is the most inferior portion of the dien-

cephalon. Located below the thalamus, it forms the floor and

part of the lateral walls of the third ventricle. This small but

extremely important brain region contains neural centers for

hunger and thirst; the regulation of body temperature; and

Figure 8.19 The adult brain

seen in midsagittal section. The

structures are labeled in the diagram

shown in ( a ) , and the brain regions

are indicated in the photograph in ( b ).

The diencephalon (shaded red) and

telencephalon (unshaded area) make

up the forebrain; the midbrain is shaded

purple and the hindbrain is shaded

aqua.