NERVOUS SYSTEM

A close look to the cerebral cortex

The cerebral cortex represent in humans a highly developed structure concerned with the most familiar functions we associate with the human brain.

It is the highly convoluted external surface of the brain. Its distinctive shape arose during evolution as the volume of the cortex increased more rapidly than the cranial volume. This differential rate of evolutionary development resulted in the convolution of the surface and the folding of the total structure of the cortex.

The convolutions consist of grooves known as sulci that separate the more elevated regions called gyri. The cortex has been divided into four lobes using certain consistently present sulci as landmarks. These lobes are named after the overlying cranial bones: frontal, parietal, temporal and occipital.




Many areas of the cerebral cortex process sensory information or coordinate motor output necessary for control of movement. These areas are divided into primary, secondary and tertiary sensory or motor areas, due to the fact that some regions are more directly involved than others with sensory or motor processing.

The primary sensory areas (visual, auditory, somatic sensory and gustatory areas) receive information from peripheral receptors with only a few synapses interposed.

The primary visual cortex is located at the caudal pole of the occipital lobe, mainly on its medial region. The primary auditory cortex lies in the temporal lobe, where it includes a portion of the lower bank of the lateral sulcus. The primary somatic sensory cortex lies on the postcentral gyrus. On the other hand the primary motor cortex lies within the precentral gyrus and contains neurons that project directly to the spinal cord. It mediates voluptuary movements of the limbs and trunk because it contains neurons that projects directly to the spinal cord to activate motor neurons.

Surrounding the primary areas are the so called higher-order secondary and tertiary sensory and motor areas. These areas integrate information coming from the primary sensory areas. In contrast Higher order motor areas send complex information required for a motor act to the primary motor cortex.

There are also three other large regions called association areas. These regions lie outside the primary, secondary and tertiary. The association areas constitute, in primates, the largest area of cortex.

The parietal-temporal-occipital association cortex occupies the interface of these three lobes. It is concerned with higher perceptual functions related to somatic sensations, hearing and vision. Information from these different sensory modalities is combined to form complex perceptions.

The prefrontal association cortex occupies most of the rostral part of the frontal lobe. An important function of this area is the planning of voluntary movement.

The limbic association cortex is devoted mainly to motivation, emotion and memory; it is located on the medial and inferior surfaces of the cerebral hemispheres in portions of the parietal temporal and frontal lobes.


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