Human Physiology, 14th edition (2016)

210 Chapter 8

located here are called upper motor neurons because of their role

in muscle regulation (chapter 12, section 12.5). The postcentral

gyrus, which is located behind the central sulcus in the parietal

lobe of each hemisphere, contains the somatosensory cortex. This

is the primary area responsible for the perception of somatesthetic

sensations —sensations arising from cutaneous, muscle, tendon,

and joint receptors. These neural pathways are described in chap-

ter 10, section 10.1.

The precentral (motor) and postcentral (sensory) gyri have

been mapped in conscious patients undergoing brain surgery.

Electrical stimulation of specific areas of the precentral gyrus

causes specific movements, and stimulation of different areas

of the postcentral gyrus evokes sensations in specific parts

called convolutions. The elevated folds of the convolutions are

called gyri, and the depressed grooves are the sulci. Each cere-

bral hemisphere is subdivided by deep sulci, or fissures, into

five lobes, four of which are visible from the surface ( fig. 8.6 ).

These lobes are the frontal, parietal, temporal, and occipi-

tal, which are visible from the surface, and the deep insula

( fig. 8.7 ), which is covered by portions of the frontal, parietal,

and temporal lobes ( table 8.1 ).

The frontal lobe is the anterior portion of each cerebral hemi-

sphere. A deep fissure, called the central sulcus, separates the fron-

tal lobe from the parietal lobe. The precentral gyrus ( figs. 8.5 and

8.6 ), involved in motor control, is located in the frontal lobe just

in front of the central sulcus. The cell bodies of the interneurons

Figure 8.5 The cerebrum. ( a ) A lateral view and ( b ) a superior view.

Superior frontal
gyrus

Superior
frontal
sulcus

Frontal
lobe

Lateral sulcus

Temporal lobe

Cerebellar

hemisphere

Occipital

lobe

Parietal lobe

Postcentral

gyrus

Central

sulcus

Precentral gyrus

(a)

Frontal poles

(b)

Longitudinal

fissure

Central

sulcus

Parietal

lobe

Superior

frontal

sulcus

Superior

frontal gyrus

Occipital poles

Central sulcus

General

interpretive area

Occipital lobe

Parietal lobe

Somatosensory cortex for

cutaneous and

proprioceptive senses

Cerebellum

Combining visual images,

visual recognition of objects

Brain stem

Frontal lobe

Motor speech area

(Broca’s area)

Lateral sulcus

Auditory area

Interpretation of sensory

experiences, memory of

visual and auditory patterns

Temporal

lobe

Primary motor cortex involved

with the control of voluntary

muscles

Figure 8.6 The lobes of the left cerebral hemisphere.

This diagram shows the principal motor and sensory areas of the

cerebral cortex.