HUMAN BIOLOGY

the nerVOus system 255

What is the cerebral cortex and What does

it do?

• The cerebral cortex forms the outer layer of gray matter of each
  hemisphere. It has motor, sensory, and association areas that
  collectively govern conscious behavior.


• Each cerebral hemisphere receives and processes responses
  to sensory input mainly from the opposite side of the body.


• The left hemisphere deals mainly with speech, analytical skills,
  and mathematics. It usually dominates the right hemisphere,
  which deals more with creative activity.


• The cerebral cortex interacts with the limbic system, which
  governs emotions.

taKe-hoMe Message

sensory areas Sensory areas occur in different parts
of the cortex. In the parietal lobe, the body is spatially
mapped out in the primary somatosensory cortex. This
area is the main receiving center for sensory input from
the skin and joints. The parietal lobe also has a primary
cortical area dealing with perception of taste. At the back
of the occipital lobe is the primary visual cortex, which
receives sensory inputs from your eyes. Perception of
sounds and of odors arises in primary cortical areas in
each temporal lobe.

association areas Association areas occupy all parts
of the cortex except the primary motor and sensory
regions. Each integrates, analyzes, and responds to many
inputs. For instance, the visual association area sur-
rounds the primary visual cortex. It helps us recognize
something we see by comparing it with visual memories.
Neural activity in the most complex association area—
the prefrontal cortex—is the basis for complex learn-
ing, intellect, and personality. Without it, we would be
incapable of abstract thought, judgment, planning, and
concern for others.

the limbic system governs emotions

The limbic system circles the upper brain stem. It includes
parts of the thalamus along with the amygdala, the hypo-
thalamus, and the hippocampus (Figure 13.20). The limbic

system influences the basic body functions regulated by

the hypothalamus and brain stem and controls emotions.

It is sometimes called the “emotional brain” because it

produces emotional behaviors such as anger, pleasure,

satisfaction, fear, and sexual arousal. In all these activities

the limbic system interacts closely with the prefrontal cor-

tex. Its connections with other brain regions bring about

emotional responses such as smiling, surprise, blushing,

or laughing.

F i g u r e 13.19 The body is “mapped” in the primary motor

cortex. This diagram depicts a slice through the primary motor

cortex of the left cerebral hemisphere. The distortions to the

body draped over the diagram indicate which body parts are

controlled with the greatest precision.

eyelid and eyeball

thumb

index

middle

toes

ankle

knee

ringlittlehand hip

wristelbowshouldertrunk

face

lips

jaw

tongue

swallowing

browneck

ov

ca

liza

tio

n sa

liva

tion

ma

stica

tion

Dr. Colin Chumbley/Science Source

© Cengage Learning

(olfactory

tract) cingulate gyrus thalamus

amygdala hypothalamus

hippocampus

Figure 13.20 The limbic system operates in emotions and

some other mental activities. The amygdala and the cingulate

gyrus are especially important in emotions. The hypothalamus is

a clearinghouse for emotions and the activity of internal organs.

© iStockphoto.com/drbimages © Blend Images/Shutterstock.com

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