Invitation to Psychology

134 Chapter 4 Neurons, Hormones, and the Brain

The Hypothalamus and the

Pituitary gland

Beneath the thalamus sits a structure called the hy-

pothalamus (hypo means “under”). It is involved in

drives associated with the survival of the individual

and the species—hunger, thirst, emotion, sex, and

reproduction. It regulates body temperature by

triggering sweating or shivering, and it controls

the complex operations of the autonomic nervous

system. It also contains the biological clock that

controls the body’s daily rhythms (see Chapter 5).

Hanging down from the hypothalamus, con-

nected to it by a short stalk, is a cherry-sized en-

docrine gland called the pituitary gland, mentioned

previously in our discussion of hormones. The

pituitary is often called the body’s “master gland”

because the hormones it secretes affect many

other endocrine glands. The master, however, is

really only a supervisor. The true boss is the hypo-

thalamus, which sends chemicals to the pituitary

that tell it when to “talk” to the other endocrine

glands. The pituitary, in turn, sends hormonal

messages out to these glands.

The hypothalamus and several other loosely

interconnected structures have often been

grouped together as the limbic system, a term from

the Latin for “border”: These structures have

been thought to form a sort of border between the

“higher” and “lower” parts of the brain. Structures

in this region are heavily involved in emotions

that we share with other animals, such as rage

and fear, so the region is also sometimes called

“the emotional brain.” But researchers now know

that these structures also have other functions,

and that other parts of the brain are also involved

in emotion. As a result, the term limbic system has

been going out of fashion.

Watch the Video Brain Stem

and Limbic System at mypsychlab

hypothalamus A brain
structure involved in
emotions and drives vital
to survival; it regulates
the autonomic nervous
system.

pituitary gland A small
endocrine gland at the
base of the brain that
releases many hormones
and regulates other endo-
crine glands.

dense network of neurons, which extends above

the brain stem into the center of the brain and has

connections with areas that are higher up, screens

incoming information and arouses the higher

centers when something happens that demands

their attention. Without the RAS, we could not

be alert or perhaps even conscious.

The Cerebellum Lo 4.10

Standing atop the brain stem and looking to-

ward the back part of the brain, we see a struc-

ture about the size of a small fist. It is the

cerebellum, or “lesser brain,” which contributes

to a sense of balance and coordinates the muscles

so that movement is smooth and precise. If your

cerebellum were damaged, you would probably

become exceedingly clumsy and uncoordinated.

You might have trouble using a pencil, thread-

ing a needle, or even walking. In addition, this

structure is involved in remembering simple skills

and acquired reflexes. But the cerebellum, which

was once considered just a motor center, is not

as “lesser” as its name implies: It is also involved

in cognitive and emotional learning (Fiez, 1996;

Timmann et al., 2010).

The Thalamus Lo 4.11

Deep in the brain’s interior, roughly at its center,

we can see the thalamus, the busy traffic officer

of the brain. As sensory messages come into the

brain—about the sight of a sunset, the sound of

a siren, the feel of a fly landing on your arm—the

thalamus directs them to higher areas in charge of

vision, sound, or touch. The only sense that com-

pletely bypasses the thalamus is the sense of smell,

which has its own private switching station, the

olfactory bulb. The olfactory bulb lies near areas in-

volved in emotion. Perhaps that is why odors, such

as the smell of fresh laundry or a steaming bowl of

chicken soup, sometimes rekindle vivid memories.

cerebellum A brain
structure that regulates
movement and balance
and is involved in some
cognitive tasks.

thalamus A brain struc-
ture that relays sensory
messages to the cerebral
cortex.

Thalamus

Olfactory bulb

Cerebellum

Reticular

activating

Medulla system

Pons