What Is the Role of the Frontal Cortex?

The cerebral cortex is the highest-level center that regulates or controls body movements. There are about 14 billion nerve cells in the human cerebral cortex, with an area of about 2200 square centimeters. They mainly contain pyramidal cells, spindle cells, astrocytes (granular cells) and nerve fibers.

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brain

Mammals develop a highly developed cerebral cortex and evolve as the nervous system evolves. Newly developed cerebral cortex is regulating

The voluntary movement of the body is only when the nervous system

Voluntary movement of the body can only occur if the nervous system's innervation of skeletal muscles remains intact, and it must be controlled by the cerebral cortex. The part of the cerebral cortex that controls body movements is called the cortical motor area.

It has been observed by electrical stimulation that certain areas of the cerebral cortex are closely related to body movements; stimulating these areas can cause muscle contraction in a certain part of the contralateral side. These areas are called exercise areas and are mainly located in the central anterior gyrus (see Figure 11-13).

The motor area also has some characteristics similar to the sensory area of the cerebral cortex:

The adjustment of the body movement is cross, but the dominance of the head and face is mainly bilateral.

There is a fine functional positioning, the arrangement of which is roughly the reflection of the body, and the arrangement inside the head and face representative area is upright.

The finer and more complex the movement of the body is, the larger the representative area is. For example, the representative areas of the hands and five fingers are large and almost the same size as the area occupied by the entire lower limb.

The muscle response obtained from the stimulation is simple, mainly the contraction of a few individual muscles.

In addition, in the cerebral cortex of monkeys and humans, motor-assisted areas can also be found using electrical stimulation; this area is in front of the lower limb movement representative area on the inner side of the cortex (the side wall of the longitudinal split of the two hemispheres). And vocal, the response is generally bilateral.

The regulation of body movement in the cerebral cortex motor area is achieved through the downward transmission of the cone system and extrapyramidal system.

The cone system generally refers to the conductive system (ie pyramidal tract, or cortical spinal tract) issued by the cerebral cortex through the medullary pyramid and then to the spinal cord. Not passing through the medullary cone should also be included in the concept of the cone system. Because the latter is functionally similar to the former, both are passed down from the cortical motor neuron (upper motor neuron) to the lower motor neuron (the spinal anterior horn motor neuron and the brain nucleus) that dominate the muscles. Neurons).

It was previously thought that the fibers transmitted down the pyramidal bundle were directly synaptic to the lower motor neurons, but now it is known that 80% to 90% of the upper and lower motor neurons are also replaced by more than one intermediate neuron. Only 10% to 20% of the connections between the upper and lower motor neurons are direct, single synaptic. Electrophysiological studies indicate that this type of single synapse is directly associated with more motor neurons in the forelimbs than in the hind limbs, and more motor neurons in the distal limbs than in the proximal muscles. It can be seen that the more delicate the muscle, the more cortical the synapses of the cerebral cortex to its motor neurons are directly connected by a single synapse.

The origin of the cerebral cortex of the cone system is relatively wide. The central anterior gyrus motor area is the main origin of the cone system, but the central posterior gyrus and other areas are also the origin of the cone system. The fibers from the fifth layer of large pyramidal cells in the central anterior gyrus motor area constitute the thicker myelinated fibers in the cone bundle, and the small cells of the third to sixth layers also emit fibers into the cone bundle; the central posterior gyrus and other areas Fibers are also involved in the composition of the cone bundle, but the descending fibers in the exercise-assist zone do not enter the cone bundle.

The extrapyramidal system is a complex concept. In anatomy, the extrapyramidal system refers to a system that regulates muscle movement without passing through the pyramidal system. Therefore, the regulating systems for muscle movements such as the basal ganglia and cerebellum belong to the extrapyramidal system. However, clinically, the extrapyramidal system refers only to the regulation system of spinal motor neurons by certain subcortical nucleuses (caudate nucleus, putamen nucleus, pale bulb, substantia nigra, red nucleus, etc.). Outside the body. Therefore, the clinical concept of extrapyramidal system is relatively narrow, and seems to have nothing to do with the cerebral cortex. However, it is now known that these nucleuses not only accept the connection of the descending fibers of the cerebral cortex, but also the connection of the ascending fibers through the thalamus to the cerebral cortex. Therefore, at present, the subcortical cortex and the subcortical nucleus (mainly referred to as the basal ganglia) are replaced to replace the conduction system that controls the spinal motor neurons, known as the extrapyramidal system of cortical origin.

In animal experiments, electrical stimulation of the neocortex can lead to changes in visceral activity, in addition to reactions such as body movements. Stimulating the medial side of the central anterior gyrus will produce changes in rectal and bladder movements; stimulating the outer side of the central anterior gyrus will produce changes in breathing and vascular movement; stimulating the bottom of the outer side of the central anterior gyrus will cause digestive tract movement and saliva Variety. These results indicate that neocortex is related to visceral activity, and that the regional distribution and the distribution of body movement representative areas are consistent. Similar results were seen with electrical stimulation of the human cerebral cortex.

The marginal lobe refers to the medial side of the cerebral hemisphere, the junction with the brain stem and the pericyclic structure next to the corpus callosum; it consists of the cingulate gyrus, hippocampal gyrus, hippocampus, and dentate gyrus. This part of the structure was once thought to be connected only to the sense of smell, and was called the olfactory brain; but it is now clear that its function is much more than that, but an important center for regulating visceral activity. Because the marginal lobe is closely related to the island lobe, temporal pole, orbital gyrus of the cerebral cortex, and the amygdala, compartment, hypothalamus, and anterior thalamic nucleus of the cortex, it is closely related. Together these structures are collectively referred to as the edge system (Figure 11-17). The function of the limbic system is more complicated, and it is related to visceral activity, emotional response, memory activity and so on.

1. The visceral regulation function of the limbic system stimulates the vegetative response caused by different parts of the limbic system. The blood pressure can be raised or lowered, the breathing can be accelerated or suppressed, the gastrointestinal movement can be strengthened or weakened, and the pupils can be enlarged or reduced. . The results of these experiments indicate that the function of the limbic system is not the same as that of the primary center; the response to the stimulation of the primary center can be more certain and consistent, and the results of stimulation of the peripheral system will vary greatly. It is conceivable that the functions of the primary center are relatively limited and the response of the activity is relatively simple. The limbic system is the regulator of many primary center activities. It can regulate or regulate the activities of more complex physiological functions by promoting or inhibiting the activities of each primary center. The response is complex and changeable.

2. The evolution of the limbic system and emotional responses of the amygdala is an ancient part, which has the function of suppressing the hypothalamic defense response area; when the hypothalamus loses control of the amygdala, animals are apt to show defensive responses, and a series of sympathetic nervous system hyperactivity It s a phenomenon of wrestling, and it s showing its fighting posture. In normal animals, the defense response area of the hypothalamus is controlled by the amygdala, and the animal becomes more tame. So the limbic system is related to emotional responses.

3. The limbic system and memory function Hippocampus and memory function may be related. Due to the need for treatment, patients who have bilaterally removed the middle temporal lobe, if the hippocampus and related structures are damaged, will cause recent loss of memory; after surgery, they will lose memory of daily encountered events. It has also been clinically observed that damage to the fornix due to surgical removal of the third ventricle cyst can also cause the patient to lose recent memory. From this perspective, the hippocampal ring activity is closely related to recent memory. This loop is: hippocampus fornix hypothalamus papillary body prethalamic nucleus cingulate gyrus hippocampus. Damage to any part of the loop can cause recent loss of memory.