Structures that form voluntary and involuntary movements

There are two main types of movements: involuntary and voluntary.

Involuntary movements are carried out due to the segmental apparatus of the spinal cord and the brain stem. They proceed according to the type of a simple reflex act.

Voluntary movements are acts of human motor behavior (praxia). They are carried out with the participation of the cerebral cortex, the extrapyramidal system and the segmental apparatus of the spinal cord. Voluntary movements are associated with the pyramidal system, which is a department of the nervous system. The central motor neuron of the motor pathway is located in the fifth layer of the cortex of the precentral gyrus of the brain and is represented by giant Betz cells. In its lower part there are neurons that innervate the muscles of the pharynx and larynx. In the middle part – neurons innervating the upper limbs, in the upper part – neurons innervating the lower limbs. Neurons in this part of the cortex control the voluntary movements of the limbs of the opposite half of the body. This is due to the intersection of nerve fibers in the lower part of the medulla oblongata. There are two ways of nerve fibers: cortical-nuclear, which ends at the nuclei of the medulla oblongata, and cortical-spinal.

The second pathway contains insertion neurons in the anterior horns of the spinal cord. Their axons end at large motor neurons located there. Their axons pass through the posterior leg of the inner capsule, then 80-85 % of the fibers cross in the lower part of the medulla oblongata. Then the fibers are directed to the insertion neurons, whose axons, in turn, are already approaching the large alpha and gamma motor neurons of the anterior horns of the spinal cord. They are peripheral motor neurons of the motor pathway. Their axons are directed to the skeletal muscles, carrying out their innervation. Large alpha-motor neurons conduct motor impulses at a speed of 60-100 m / s. This ensures fast movements that are associated with the pyramid system. Small alpha-motor neurons provide tonic muscle contraction, are associated with the extrapyramidal system. Gamma-motor neurons transmit impulses of the otoreticular formation to the muscle pro-prioreceptors.

The pyramidal pathway begins in the cerebral cortex, namely from the Betz cells located in the anterior central gyrus. The axons of these cells are directed to the segment of the spinal cord that they innervate. There they form a synapse with a large motor neuron or with the cells of the motor nuclei of the cranial nerves. Fibers from the lower third of the anterior central gyrus innervate the muscles of the face, tongue, pharynx and larynx. These fibers end at the cells of the cranial nerve nuclei. This pathway is called cortical-nuclear. The axons of the upper 2/3 of the anterior central gyrus end at large alpha-motor neurons, innervate the muscles of the trunk and limbs. This pathway is called the cortical-spinal. After leaving the anterior central gyrus, the fibers pass through the knee and the anterior 2/3 of the posterior legs of the inner capsule. Then they enter the brain stem, pass at the base of the legs of the brain. In the medulla oblongata, the fibers form pyramids.

At the border between the medulla oblongata and the spinal cord, most of the fibers cross. Then this part is located in the lateral cords of the spinal cord. The uncrossed fibers are located in the anterior cords of the spinal cord, forming a tuft of Turk. Thus, those fibers that were located laterally in the medulla oblongata become medial after the intersection.

Leave a Reply

Leave a Reply

Your email address will not be published. Required fields are marked *