The function of the human brain is to control processes throughout the body, as it is the main part of the central nervous system. It is divided into zones, each of which is responsible for a specific process. For example, for coordination of movements, muscle tone, reactions to external influences. The laws of the brain are being studied for a better understanding of the human psyche. This article will consider one of its most important parts - the bark.
Functions of the cerebral cortex
The functions of the cerebral cortex include:
- Definition of intelligence.
- Identity identification.
- Motor function.
- Planning and organizing.
- The feeling of being touched.
- Processing sensory information.
- Language processing.
A number of disorders occur as a result of damage or death of cells of the cerebral cortex. The symptoms experienced depend on the area of the cortex that is damaged. Possible consequences:
- failure to performcertain motor tasks (difficulty walking or interacting with objects);
- agraphia (inability to write);
- ataxia (discoordination);
- depressive disorders, difficulty in making decisions, problems with memory and attention.
Primary motor cortex (precentral gyrus or fourth Brodmann field)
It is an area of the brain that is located at the back of the frontal lobe. The precentral gyrus is responsible for the conscious movements of the body. It works in conjunction with other motor areas, including the premotor cortex, the parietal lobe, and several subcortical areas of the brain, to enable a person to plan and execute movements. The gyrus in question contains large neurons known as Betz cells, which, along with other cortical neurons, send impulses along long axons down the spinal cord, that is, they transmit signals to the muscular system.
Each hemisphere of the brain is responsible for the opposite side of the body. The amount of primary motor cortex destined for a body part is not proportional to the size of its surface, but corresponds to the density of cutaneous motor receptors. Thus, the human hands and face need more control of the fourth Brodmann field than the legs.
Structure
The precentral gyrus is located on the anterior wall of the central sulcus. It is bordered by the emerging lateral premotor cortex and posteriorly by the primary somatosensory cortex.
Location of primary motor cortexeasily identified in histological studies due to the presence of distinctive Betz cells. One of its layers contains giant (70-100 micrometers) pyramidal neurons. They send impulses along long axons to the motor nuclei of the cranial nerves and to the lower motor neurons in the ventral horn of the spinal cord. Axons form part of the cortico-spinal tract, where Betz cells make up about 10% of the total. But they provide clear boundaries for the precentral gyrus.
Blood supply and functions
The branches of the middle cerebral artery provide most of the arterial blood supply to the fourth Brodmann field.
Different parts of the body are displayed on the precentral gyrus in the form of the so-called homunculus (little man). The leg zone corresponds to the midline and forms a longitudinal slit in the inner sections of the motor zone. The lateral convex side is located from top to bottom in places that are responsible for the movements of the buttocks, torso, shoulders, elbows, wrists, fingers, eyelids, lips and jaws.
It is worth recalling that parts of the motor cortex are not proportional to the size of their body parts, with lips, facial features and hands (the most mobile) represented by particularly wide lobes. After amputation or paralysis, motor areas may shift to accommodate new body parts.
Betz cells
The giant pyramidal cells of the precentral gyrus are sometimes mistaken for the sole or main cortical outlet to the spinal cord. However, Betz cells make up only about 2-3% of the neurons thatconnect the cortex and spinal cord, and only about 10% of neurons that are formed in the primary motor cortex. A number of cortical regions, including premotor, supplementary motor, and even primary somatosensory, have access to the spinal cord.
Even when Betz cells are damaged, the cortex can still communicate with subcortical motor structures and control body movements. If the precentral gyrus is damaged, temporary paralysis occurs, and other areas of the cerebral cortex can obviously take over some of the lost function.
Lesions in the fourth Brodmann field lead to paralysis of the contralateral side of the body (facial paralysis, arm/leg monoparesis, hemiparesis).
