Functions of the Cerebrum

The cerebrum provides higher brain functions: interpreting impulses from sense organs, initiating voluntary muscular movements, storing information as memory, and retrieving this information in reasoning. The cerebrum is also the seat of intelligence and personality.

Functional Regions of the Cortex

The regions of the cerebral cortex that perform specific functions have been located using a variety of techniques. Persons who have suffered brain disease or injury, such as Karen Ann Quinlan and Phineas Gage, or have had portions of their brains removed surgically, have provided clues to the functions of the impaired brain regions.

In other studies, areas of cortices have been exposed surgically and stimulated mechanically or electrically, with researchers observing the responses in certain muscles or the specific sensations that result. As a result of such investigations, researchers have divided the cerebral cortex into sections known as motor, sensory, and association areas. They overlap somewhat.

Motor Areas

The primary motor areas of the cerebral cortex lie in the frontal lobes just in front of the central sulcus (precentral gyrus) and in the anterior wall of this sulcus (fig. 11.17). The nervous tissue in these regions contains many large pyramidal cells, named for their pyramid-shaped cell bodies.

Impulses from these pyramidal cells travel downward through the brain stem and into the spinal cord on the corticospinal tracts. Most of the nerve fibers in these tracts cross over from one side of the brain to the other within the brain stem and descend as lateral corticospinal

Motor areas involved with the control of voluntary muscles

Concentration, planning, problem solving

Auditory area

Frontal lobe

Central sulcus

Motor speech area (Broca's area)

Lateral sulcus

Interpretation of sensory experiences, memory of visual and auditory patterns

Temporal lobe

Sensory areas involved with cutaneous and other senses

Motor areas involved with the control of voluntary muscles

Concentration, planning, problem solving

Central sulcus

Sensory areas involved with cutaneous and other senses

Frontal lobe

Motor speech area (Broca's area)

Sensory Input Left Parietal Lobe

Understanding speech, using words Parietal lobe

General interpretative area (Wernicke's area)

Lateral sulcus

Interpretation of sensory experiences, memory of visual and auditory patterns

Temporal lobe

Visual area Cerebellum

Brain stem

Figure 11.17

Some motor, sensory, and association areas of the left cerebral cortex.

Understanding speech, using words Parietal lobe

General interpretative area (Wernicke's area)

Occipital lobe

Combining visual images, visual recognition of objects

Visual area Cerebellum

Brain stem

Figure 11.17

Some motor, sensory, and association areas of the left cerebral cortex.

tracts. Other fibers, in the anterior corticospinal tracts, cross over at various levels of the spinal cord (see fig. 11.13).

Within the spinal cord, the corticospinal fibers synapse with motor neurons in the gray matter of the anterior horns. Axons of the motor neurons lead outward through peripheral nerves to voluntary muscles. Impulses transmitted on these pathways in special patterns and frequencies are responsible for fine movements in skeletal muscles. More specifically, as figure 11.18 shows, cells in the upper portions of the motor areas send impulses to muscles in the thighs and legs; those in the middle portions control muscles in the arms and forearms; and those in lower portions activate muscles of the head, face, and tongue.

The reticulospinal and rubrospinal tracts coordinate and control motor functions that maintain balance and posture. Many of these fibers pass into the basal ganglia on the way to the spinal cord. Some of the impulses conducted on these pathways normally inhibit muscular actions.

In addition to the primary motor areas, certain other regions of the frontal lobe control motor functions. For example, a region called Broca's area is just anterior to the primary motor cortex and superior to the lateral sul-cus (see fig. 11.17), usually in the left cerebral hemisphere. It coordinates the complex muscular actions of the mouth, tongue, and larynx, which make speech possible. A person with an injury to this area may be able to understand spoken words but may be unable to speak.

Above Broca's area is a region called the frontal eye field. The motor cortex in this area controls voluntary movements of the eyes and eyelids. Nearby is the cortex responsible for movements of the head that direct the eyes. Another region just in front of the primary motor area controls the muscular movements of the hands and fingers that make such skills as writing possible (see fig. 11.17).

An injury to the motor system may impair the ability to produce purposeful muscular movements. Such a condition that affects use of the upper and lower limbs, head, or eyes is called apraxia. When apraxia affects the speech muscles, disrupting speaking ability, it is called aphasia.

Sensory Areas

Sensory areas in several lobes of the cerebrum interpret impulses from sensory receptors, producing feelings or sensations. For example, the sensations of temperature, touch, pressure, and pain in the skin arise in the anterior portions of the parietal lobes along the central sulcus (postcentral gyrus) and in the posterior wall of this sul-cus (see fig. 11.17). The posterior parts of the occipital lobes provide vision, whereas the superior posterior portions of the temporal lobes contain the centers for hearing. The sensory areas for taste are near the bases of the

Cerebrum Centers

Frontal lobe

Frontal lobe

Motor area

Central sulcus

Sensory area

Parietal lobe

Sensory area

Parietal lobe

Figure

(a) Motor areas that control voluntary muscles (only left hemisphere shown). (b) Sensory areas involved with cutaneous and other senses (only left hemisphere shown).

central sulci along the lateral sulci, and the sense of smell arises from centers deep within the cerebrum.

Like motor fibers, sensory fibers, such as those in the fasciculus cuneatus tract, cross over in the spinal cord or the brain stem (see fig. 11.12). Thus, the centers in the right central hemisphere interpret impulses originating from the left side of the body, and vice versa. However, the sensory areas concerned with vision receive impulses from both eyes, and those concerned with hearing receive impulses from both ears.

Association Areas

Association areas are regions of the cerebral cortex that are not primarily sensory or motor in function, and interconnect with each other and with other brain structures. These areas occupy the anterior portions of the frontal lobes and are widespread in the lateral portions of the parietal, temporal, and occipital lobes. They analyze and interpret sensory experiences and help provide memory, reasoning, verbalizing, judgment, and emotions (see fig. 11.17).

The association areas of the frontal lobes provide higher intellectual processes, such as concentrating, planning, and complex problem solving. The anterior and inferior portions of these lobes (prefrontal areas) control emotional behavior and produce awareness of the possible consequences of behavior.

The parietal lobes have association areas that help interpret sensory information and aid in understanding speech and choosing words to express thoughts and feelings. Awareness of the form of objects, including one's own body parts, stems from the posterior regions of these lobes.

The association areas of the temporal lobes and the regions at the posterior ends of the lateral fissures interpret

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