Invitation to Psychology

Chapter 4 Neurons, Hormones, and the Brain 133

and that you are wending your way through the

“soul’s frail dwelling house,” starting at the lower

part, just above the spine. Figure 4.8 shows the

major structures we will encounter along our tour;

you may want to refer to it as we proceed. But keep

in mind that any activity—feeling an emotion,

having a thought, performing a task— involves

many different structures working together. Our

description, therefore, is a simplification.

The Brain Stem Lo 4.9

We begin at the base of the skull with the brain

stem, which began to evolve some 500 million

years ago in segmented worms. The brain stem

looks like a stalk rising out of the spinal cord.

Pathways to and from upper areas of the brain

pass through its two main structures: the medulla

and the pons. The pons is involved in (among

other things) sleeping, waking, and dreaming. The

medulla is responsible for bodily functions that do

not have to be consciously willed, such as breath-

ing and heart rate. Hanging has long been used as

a method of execution because when it breaks the

neck, nerve pathways from the medulla are sev-

ered, stopping respiration.

Extending upward from the core of the brain

stem is the reticular activating system (raS). This

brain stem The part of

the brain at the top of the

spinal cord, consisting

of the medulla and the

pons.

pons A structure in the

brain stem involved in,

among other things,

sleeping, waking, and

dreaming.

medulla [muh-DuL-uh]

A structure in the brain

stem responsible for cer-

tain automatic functions,

such as breathing and

heart rate.

reticular activating

system (raS) A dense

network of neurons found

in the core of the brain

stem; it arouses the cor-

tex and screens incoming

information.

You are about to learn...

• the major parts of the brain and some of their
major functions.

• why it is a good thing that the outer covering of
the human brain is so wrinkled.

• how a bizarre nineteenth-century accident
illuminated the role of the frontal lobes.

a tour through

the Brain

Most modern brain theories assume that differ-
ent brain parts perform different (though greatly
overlapping) tasks. This concept, known as local-
ization of function, goes back at least to Joseph Gall
(1758–1828), an Austrian anatomist who thought
that personality traits were reflected in the devel-
opment of specific areas of the brain. Gall’s theory
led to the development of phrenology, which,
as we saw in Chapter 1, was completely wrong-
headed (so to speak). But his general notion of
specialization in the brain had merit.
To learn about what the major brain structures
do, let’s take an imaginary stroll through the brain.
Pretend that you have shrunk to a microscopic size

localization of

function Specialization

of particular brain areas

for particular functions.

Figure 4.8 Major Structures of the Human Brain
This cross section depicts the brain as if it were split in half, and shows the structures described in the text.