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The Cerebral Cortex
The cerebral cortex is what makes us so intelligent among all the animals. The cortex is made up of 6 layers of brain cells, but these layers spell the meaning of our lives. . In general, the cerebral cortex is divided into three areas.
These areas are divided into specific areas which control our actions. The numbers on the picture below label these areas. As you read below , you will be told which number corresponds to which area. The lobes are colored blue for frontal , pink for temporal, green for parietal and yellow for occipital.
Sensory input to the cerebral cortex go mainly to the posterior half of the cerebral hemisphere and the regions behind the central sulci ( which is the back part of the cortex). In the cerebral cortex, primary sensory areas have the most direct connections with peripheral sensory receptor. These are the nerve endings on our five sense that allow us to feel pain , pressure and heat.
1) Primary somatosensory area (area 1 and 2) or general somatosensory area is located directly posterior to the central sulcus in each cerebral hemisphere in the postcentral gyrus of the parietal lobe, labelled green. The primary somatosensory area receives sensations from the cutaneous and muscular receptors in various parts of the body. Some parts of the body are represented by large areas in the primary somatosensory area. These include the lips, face and thumb. Other body parts, such as the trunk and lower limbs, are represented by relatively small areas. The amount of space given a particular part of the body determined by the functional importance of the primary somatosensory area is to localise exactly the points of the body where the sensations originate.
2) The primary visual area (area 17) is located in the occipital lobe, labelled yellow. It receives sensory impulses from the eyes and interprets shape, colour and movement.
3) The primary auditory area (area 41 and 42) located in the temporal lobe,labelled pink, interprets the basic characteristics of sound such as pitch and rhythm.
4) The primary gustatory area (area 43) is located at the base of the postcentral gyrus and interprets sensations related to taste. 5) The primary olfactory area, located in the temporal lobe,labelled pink, interprets sensations related to smell.
Just as the primary somatosensory area of the cortex has been mapped to reflect the amounts of sensory information coming from different body parts, the motor cortex has been mapped to indicate which specific areas control particular muscle groups. There is a motor cortex in both the left and the right cerebral hemispheres. The degree of representation is proportional to the precision of movement required of a particular body part. Or example, the thumb, fingers, lips, tongue and vocal cords have large representations. The trunk has a relatively small representation.
1) Primary motor area (area 4), located in the precentral gyrus of the frontal lobe, is like the primary somatosensory area. The primary motor area consists of regions that control specific muscles or groups of muscles. Stimulation of a specific point of the primary motor area results in a muscular contraction, usually on the opposite side of the body.
2) The motor speech areas (area 44) are involved in the production of speech. These areas are also known as the Broca’s area. Located in the frontal lobe, labelled blue, usually in the left one, just superior to the lateral cerebral sulcus.
The association areas of the cerebrum consist of association tracts that connect motor and sensory areas and large parts of the cerebral cortex of the occipital, parietal, and the temporal lobes and the frontal lobes anterior to the motor areas. Association areas include:
1) The somatosensory association area (area 5 and 7). Just posterior to the primary stomatosensory area, its role is to integrate and interpret sensations. This area permits you to determine the exact shape and texture of an object to another as they are felt, and to sense the relationship of one body to another.
2) The visual association area (area 18 and 19). Located in the occipital lobe , it relates present to past visual experiences with tecognition and evaluation of what is seen.
3) Auditory association area (area 22). Located below the primary auditory area in the temporal cortex, it determines if a sound is speech , music or noise. It also translates words into thoughts.
4)Gnostic area (areas 5, 7, 39, 40). This area is located among the somatosensory, visual and auditory association areas. It integrates sensory interpretations from the association areas and impulses from the other areas so that a common thought can be formed from the various sensory inputs.
5) Premotor area (area 6). Immediately in front of the primary motor area, the premotor area deals with learned motor activities of a complex and sequential nature. It generates nerve impulses that cause a specific group of muscles to contract in a specific sequence, for example, to write a word.
6)Frontal eye field area (area 8). This area in the frontal cortex controls voluntary scanning movements of the eyes - searching for a word in a dictionary for example.
7) Language areas. From Broca's area (area 44) , nerve impulses pass to the premotor regions that control the muscles of the throat, voice box and mouth. The impulses from the premotor area to the muscles result in specific, coordinated contractions that enable you to speak. Simultaneously, impulses area sent from the motor speech area to the primary motor area. From here, impulses reach your breathing muscles to regulate the proper flow of air past the vocal cords. The coordinated contractions of your speech and breathing muscles enable you to speak your thoughts.