Sensory and Motor Cortex

65
The Central Nervous System: Making Sense of the World
Cerebral
cortex
Functional
areas
Anatomical
areas
Frontal
lobe
FIGURE
Temporal
lobe
Parietal
lobe
Occipital
lobe
Association
cortex
Motor
cortex
Somatosensory
cortex
Association
cortex
Broca’s
area
Auditory
cortex
Wernicke’s
area
Visual
cortex
2.10
The Cerebral Cortex (viewed from
the left side)
The brain’s ridges (gyri) and valleys (sulci)
are landmarks that divide the cortex into
four lobes: the frontal, parietal, occipital,
and temporal. These terms describe where
the regions are (the lobes are named for
the skull bones that cover them), but the
cortex is also divided in terms of function.
These functional areas include the motor
cortex (which controls movement), sensory
cortex (which receives information from
various senses), and association cortex
(which integrates information). Also labeled are Wernicke’s area and Broca’s
area, two regions that are found only on
the left side of the cortex and that are vital to the interpretation and production of
speech (Peña et al., 2003).
sensory cortex The part of the
cerebral cortex located in the parietal,
occipital, and temporal lobes that
receives stimulus information from the
skin, eyes, and ears, respectively.
The folds of the cerebral cortex give the surface of the human brain its wrinkled
appearance, its ridges and valleys. The ridges are called gyri (pronounced “ji-rye”), and
the valleys are known as sulci (pronounced “sulk-eye”) or fissures. As you can see in
Figure 2.10, several deep sulci divide the cortex into four areas: the frontal (front), parietal (top), occipital (back), and temporal (side) lobes. The gyri and sulci provide landmarks for describing the structure of the cortex, but the functions of the cortex do not
follow these boundaries. When divided according to function, the cortex includes areas
of sensory cortex, motor cortex, and association cortex. (“In Review: Organization of
the Brain” summarizes the major structures and functions of the brain.)
Sensory and Motor Cortex
The sensory cortex lies in the parietal, occipital, and temporal lobes. Different
regions of the sensory cortex receive information from different senses. Occipital lobe
cells called the visual cortex receive visual information. Temporal lobe cells called the
auditory cortex receive information from the ears. And information from the skin, such
as touch, pain, and temperature, is received by cells in the parietal lobe. These skinrelated areas are called the somatosensory cortex (soma is Greek for “body”). Information about skin sensations from neighboring parts of the body comes to neighboring
parts of the somatosensory cortex. It is as if the outline of a tiny person, dangling
upside down, determined the location of the information (see Figure 2.11). This pattern is called the homunculus (Latin for “little man”). The amount of sensory cortex
that responds to particular sensory stimulation can be modified by experience (Candia et al., 2003). For example, if a limb is lost, sensory cortex that had been stimulated by that limb will now be stimulated by other regions of skin. Similarly, practicing the violin will increase the number of sensory neurons that respond to touch; the
same thing happens when blind people learn to read Braille with their fingertips
(Amedi et al., 2005; Pascual-Leone & Torres, 1993).
66
in review
Chapter 2 Biology and Behavior
ORGANIZ ATION OF THE BR AIN
Major Division
Some Major Structures
Some Major Functions
Hindbrain
Medulla
Regulates breathing,
heart rate, and blood
pressure
Reticular formation (also
extends into midbrain)
Regulates arousal
and attention
Cerebellum
Controls finely
coordinated movements
and certain cognitive processes
Midbrain
Various nuclei
Relays sensory signals to
forebrain; creates
automatic responses to
certain stimuli; initiates
smooth movement
Forebrain
Thalamus
Interprets and relays
sensory information
Hypothalamus
Regulates hunger, thirst,
and sex drives
Amygdala
Connects sensations
and emotions
Hippocampus
Forms new memories
Cerebral cortex
Analyzes sensory
information; controls
voluntary movements,
abstract thinking, and
other complex cognitive
activity
Corpus callosum
Transfers information
between the two
cerebral hemispheres
?
1. The oldest part of the brain is the
.
2. Cells that operate as the body’s twenty-four-hour “time clock” are found in the
.
3. Memory problems seen in Alzheimer’s disease are related to shrinkage of the
.
motor cortex The part of the cerebral
cortex that controls voluntary
movement.
In the frontal lobe, specific neurons of the motor cortex control voluntary movements in specific parts of the body (Indovina & Sanes, 2001). The motor cortex’s
arrangement mirrors that of the somatosensory cortex. So the parts of the motor cortex that control hand movement are near parts of the sensory cortex that receive sensory information from the hands.
Seems easy, doesn’t it? You have a map of your body parts in your cerebral cortex,
and you activate cells in the hand region of the cortex if you want to move your hand.