The Central Nervous System
not impair muscle strength and the ability to perform the dis-
crete individual movements. For example, if the premotor area
controlling the ﬂight of your ﬁngers over a computer keyboard
were damaged, you couldn’t type with your usual speed, but you
could still make the same movements with your ﬁngers. Repro-
gramming the skill into another set of premotor neurons would
require practice, just as the initial learning process did.
Areas concerned with conscious awareness of
sensation, the sensory areas of the cortex, occur in the parietal,
insular, temporal, and occipital lobes (see Figure 12.6, dark and
light blue areas).
Primary somatosensory cortex.
resides in the postcentral gyrus of the parietal
lobe, just posterior to the primary motor cortex. Neurons
in this gyrus receive information from the general (so-
matic) sensory receptors in the skin and from propriocep-
tors (position sense receptors) in skeletal muscles, joints,
and tendons. Te neurons then identify the body region
being stimulated, an ability called
considered to be (1) present in one hemisphere only (usu-
ally the le±) and (2) a special
motor speech area
the muscles involved in speech production. However, im-
aging studies indicate that Broca’s area also becomes active
as we prepare to speak and even as we think about (plan)
many voluntary motor activities other than speech.
Frontal eye ﬁeld.
frontal eye ﬁeld
is located partially
in and anterior to the premotor cortex and superior to
Broca’s area. Tis cortical region controls voluntary move-
ment of the eyes.
Damage to localized areas of the
primary motor cortex
a stroke) paralyzes the body muscles controlled by those areas.
If the lesion is in the right hemisphere, the le± side of the body
will be paralyzed. Only
control is lost, however, as the
muscles can still contract reﬂexively.
Destruction of the
, or part of it, results in
loss of the motor skill(s) programmed by that region, but does
Motor map in
Sensory map in
Body maps in the primary motor cortex and somatosensory cortex of
The relative amount and location of cortical tissue devoted to each function is
proportional to the distorted body diagrams (homunculi).