Specific parts of the cerebral hemispheres are responsible for a certain aspect of function. In normal circumstances these functions are integrated and the patient operates as a whole. Damage to part of the cortex will result in a characteristic disturbance of function. Interruption by disease of 'connections' between one part of the cortex and another will 'disconnect' function.
Brodmann, on the basis of histological differences, divided the cortex into 47 areas. Knowledge of these areas is not practical, though they are referred to often in some texts.
Six layers can be recognised in the cerebral cortex superficial to the junction with the underlying white matter.
The relative preponderance of each layer varies in different regions of the cortex and appears to be related to function.
Molecular External granular
Internal granular Ganglionic
Each cerebral hemisphere is divided into lobes
Temporal lobe / 0c.ciPital ' ' lobe
The frontal motor cortex, dominated by pyramidal rather than granular layers, is termed the AGRANULAR CORTEX
The parietal sensory cortex, dominated by granular layers, is termed the GRANULAR CORTEX.
The largest cells of the agranular cortex are the giant cells of Betz. These give rise to some of the motor fibres of the corticospinal tract.
Unilateral brain damage reveals a difference in function between hemispheres. The left hemisphere is 'dominant' in right-handed people. In left-handed subjects the left hemisphere is dominant in the majority (up to 75%).
Hand preference may be hereditary, but in some cases disease of the left hemisphere in early life determines left-handedness.
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