Essentials of Anatomy and Physiology

In the human brain the cerebral cortex is folded
extensively. The folds are called convolutions or
gyriand the grooves between them are fissuresor
sulci(you can see the folding of the cortex in the
frontal section of the brain in Fig. 8–6). This fold-
ing permits the presence of millions more neurons in
the cerebral cortex. The cerebral cortex of an animal
such as a dog or cat does not have this extensive
folding. This difference enables us to read, speak,
do long division, write poetry and songs, and do
so many other “human” things that dogs and cats can-
not do.
The cerebral cortex is divided into lobes that have
the same names as the cranial bones external to them.
Therefore, each hemisphere has a frontal lobe, pari-
etal lobe, temporal lobe, and occipital lobe (Fig. 8–8).
These lobes have been mapped; that is, certain areas
are known to be associated with specific functions. We
will discuss the functions of the cerebrum according to
these mapped areas.

Frontal Lobes

Within the frontal lobesare the motor areasthat

generate the impulses for voluntary movement. The

largest portions are for movement of the hands and

face, those areas with many muscles capable of very

fine or precise movements. It is the large size of the

motor area devoted to them that gives these muscles

their precision. The left motor area controls move-

ment on the right side of the body, and the right

motor area controls the left side of the body. This is

why a patient who has had a cerebrovascular accident,

or stroke, in the right frontal lobe will have paralysis

of muscles on the left side (see Box 8–4: Cerebrovas-

cular Accidents).

Anterior to the motor areas are the premotor

areas, which are concerned with learned motor skills

that require a sequence of movements. Tying shoe-

laces, for example, seems almost automatic to us; we

forget having learned it. It is not a reflex, however;

180 The Nervous System

Frontal lobe

Premotor area

Motor area

General sensory area

Sensory association

area

Parietal lobe

Occipital lobe

Visual area

Auditory area

Temporal lobe

Auditory

association

area

Visual association

area

Motor speech area

Orbitofrontal

cortex

Figure 8–8. Left cerebral hemisphere showing some of the functional areas that have

been mapped.

QUESTION:What sensations are felt in the general sensory area?