Pyramidal path: structure and function
Neurology is one of the most accurate sciences of medicine. With the help of a topical diagnosis, a neurologist, using a hammer, interrogation and examination, as well as tests and various tests, can localize in some cases the lesion with high accuracy. This lesion may be located in the spinal cord or head. Previously, this was an applied science, and before that - descriptive (anatomy, too, was always related to descriptive science).
Neurology uses such concepts as "shell", "legs of the cerebellum", "water supply system" that goes deep in the brain, "fence", "hillocks of the tetrapilium" and many other formations. Their functionality has remained a mystery for a long time. The only understanding was that the components of the brain and spinal cord are gray and white substances, but this, perhaps, was the only difference. The analysis of the internal structure was not carried out, because there were no dyes that displayed neurons and proved the cellular structure of the central nervous system. These cells consist of the longest processes (about 1 meter long).
Neuroanatomy as a science did not exist. What is nerve fiber - was not known. Then Virchow's cellular theory was invented, according to which the organ's functionality depends directly on which cells it consists of. Also appeared physiology that studies neurons, their functions and differences. The nerve cell and the integrity of its work became available for understanding. Scientists Sechenov and Pavlov took the next steps.
Pyramidal path - a general concept
The pyramidal system is referred to as the “inner formation” of the central nervous system. It contributes to all motor conscious acts of a person. In the absence of a pyramidal system, we would not have the opportunity to move, and this would lead to the impossibility of the development of civilization. The human brain and hands have created a civilization, but this is all due to the pyramidal path, which provides mediation services (bringing the brain impulses to the movement to the muscles).
The pyramidal system is considered the system of efferent neurons, they are located in the cerebral cortex. The end of them is located in the motor nuclei of the nerves of the skull and the gray matter of the spinal cord.The pyramidal path consists of cortical-nuclear and cortical-spinal fibers. These are axons of the nerve cells of the cerebral cortex.
In this article we consider the pyramidal system, its functionality, as well as the scheme of the pyramidal path.
What is a pyramidal system?
Pyramidal pathways (or system) are called cortical-spinal, efferent, or descending pathways. They originate in the place where the precentral gyrus is located, or rather, in the gray matter of this gyrus. Neural bodies are located there. They produce impulses that give command to the striated (skeletal) muscles. These are conscious impulses, the pyramidal system is easily subordinated to the will of the mind.
The function of the pyramidal path is the perception of a program of voluntary movement and the carrying of impulses of the program to the stem of the brain and spinal cord. The pyramidal and extrapyramidal (unconscious) system is combined into a single system that is responsible for movement, coordination of balance and muscle tone.
Start and End Pyramid Paths
We will understand where the pyramidal path originates? Its beginning is located in the precentral gyrus.To be more precise, there is a special field in this gyrus, projecting along it from the bottom up.
This band is called Brodman’s cytoarchitecton field No. 4. The location of the giant Bez pyramidal cells is available here. (Vladimir Beze, a Russian histologist and anatomist, discovered these cells in 1874). They generate impulses with the help of which precise and targeted movements are produced.
Where does the pyramid system end? The end of the pyramidal paths is located in the spinal cord (in its front horns), while the levels vary from the neck to the sacrum. Here there is a switch to large motor neurons, the end of which is located in the neuromuscular junction. A mediator, acetylcholine, signals the muscles to contract. This is the essence of the work of the pyramidal path. Further, the anatomy and organization of the structures of the cortical-cerebrospinal pathway will be discussed in detail, with different levels described.
The neurons of the pyramidal pathway, which are located in the lower sections, are responsible for the movement of the pharynx and the reproduction of sounds. Somewhat higher are the cells that innervate facial expressions, muscles of the arms, torso and legs.
There is such a thing as "motor homunculus".Nerve cells are responsible for the hands and fingers (the subtle movements they make), as well as the vocal and facial muscles. A small number of cells is responsible for the innervation of the legs, which perform mainly stereotypical movements.
The task of cortical impulses generated by large Betz cells is to reach the muscle as quickly as possible. This is not the same as that of the autonomic nervous system, which works smoothly inside the human body. The better and faster the movements of the hands and fingers are, the better a person will be, for example, get food. Isolation of the axons of these neurons occurs "according to the highest class". Their fibers have thick myelin sheath. This is the best of all pathways; only a small number of axons from the total volume of the pyramidal system belong here. In the other part of the cerebral cortex zone, the rest of the small neurons, the sources of impulses, are located.
There are more fields, in addition to Brodman's field, which are called prematorial. They also give their impulses. This is the corticospinal path. All movements performed on the opposite side of the body are performed by the cortical structures mentioned by us.What does this mean? The left neurons generate the movement of the right side of the body, the right - the left side. The fibers create a certain cross, moving to the other half of the body. This is the structure of the pyramidal path.
Nerves and their functions
Everyone knows that there are muscles on the arms, legs and torso, but, in addition, it is necessary to mention the muscles of the face and head. The innervation of the extremities and the trunk is created by one bundle of fibers, and the smaller beam switches the impulses of the motor nuclei, with the help of which voluntary and conscious movements are performed.
The pyramidal path is the first bundle, the second is the cortical-nuclear or cortico-nuclear pathway. Let us consider in more detail the nerves and their work, which receive impulses from the pyramidal path:
• The oculomotor nerve (3rd pair) eyes and eyelids move.
• The block nerve (4th pair) also moves the eyes, only sideways.
• The trigeminal nerve (5th pair) performs chewing movements.
• The abducent nerve (6th pair) performs eye movements.
• Facial nerve (7th pair) creates facial movements on the face.
• The pharyngeal nerve (9th pair) is controlled by the stylopharyngeal muscle, pharyngeal constrictors.
• A moving nerve (10th pair) creates movements by the muscles of the pharynx and larynx.
• An additional nerve (11th pair) is the work of the trapezius and sternocleidomastoid muscle.
• The tongue is moved by the hypoglossal nerve (12th pair).
The work of the nuclear cortex path
Cortico-nuclear or cortical-nuclear pyramidal path serves almost all the nerves. The exception is particularly sensitive nerves - olfactory and visual. Beams that have already been divided, bend around the inner capsule with tightly lying conductors. Here the highest concentration of the brain cable network is concentrated. The inner capsule is a small band that is located in the white matter. The basal ganglia surround it. It has the so-called "thigh" and "knee." “Hips” are rejected first, then they are joined. This is the "knee." Having traveled the path to the nuclei of the cranial nerves, the impulse moves on and with the help of individual nerves goes to the muscles. Here, too, the crossing of the beams occurs, and the movements are conducted on the opposite side. But only part of them is contralateral, and the other part is ipsilateral.
The anatomy of the pyramidal tracts is unique.The main beam produces movements of the arms and legs. It goes out through the occipital foramen, and its density and thickness increase. Axons leave the inner capsule, then enter the middle of the legs of the brain, then descend into the bridge. Here they are surrounded by the cores of the bridge, fibers of the reticular formation and other formations.
After which they leave the bridge and enter the medulla. So the pyramidal tract appears visibility. These are elongated and inverted pyramids, located in symmetry from the center. Hence the name - conducting pyramidal paths of the brain.
Main ascending paths
- To the ascending posterior brain carry the posterior spinal-cerebral pathway Flexig, anterior spinal-cerebellar pathway Govers. Both cerebrospinal tract conduct unconscious impulses.
- The lateral dorsal-middle cerebral path can be attributed to the ascending middle brain.
- To the intermediate brain - lateral spinal-thalamic pathway. He conducts irritation from fever and pain. It also includes the anterior dorsal-talamic pathway, which conducts impulses of touch and touch.
The place of transition in the spinal cord
Resting against the medulla oblongata, the axons intersect. The formation of the lateral bundle. The part that did not twist was called the anterior cortical-spinal cord path.
The transition of axons to another mirror side is still carried out, but already in the part where innervation occurs. The end of this bundle is located in the region of the sacrum, where it becomes very thin.
Most of the fibers switch not to motor motor neurons in the spinal cord, but to intercalated neurons. They formed synapses, in which there are large motor neurons. Their functions are different. Inserted neurons make contact with sensory and motor nerve cells, they are autonomous. Each segment has its own polysynaptic “relay substation”. This is a kind of motor system. The pyramidal path and the extrapyramidal path of the regulation of movements differ from each other.
An extrapyramidal system operating in a completely autonomous mode does not require such a large number of bilateral ties, since it does not need arbitrary control.
Extrapyramidal system structure
Extrapyramidal system is distinguished by the following structures of the brain:
• basal ganglia;
• red core;
• interstitial nucleus;
• black substance;
• reticular formation of the bridge and the medulla;
• the nucleus of the vestibular complex;
• premotor area of the cortex;
What happens if an obstacle in the path of the pyramidal beam? If, due to injury, swelling, hemorrhage, axons break, muscle paralysis will occur. After all, the team on the movement was gone. With a partial break, partial paralysis or paresis occurs. The muscle becomes weak and hypertrophied. The death of the central neuron occurs, but the second neuron may remain intact.
This happens when you break the path. The second neuron is located in the anterior horns of the spinal cord, it is close to the muscle directly. It's just that nothing else rules them from above. This is called central paralysis. This situation is very unpleasant, so you need to be careful about your health, try to avoid injuries and other injuries.
We examined the pyramidal system, its structure, found out what nerve fiber is.