The pyramidal system - together with the extrapyramidal system - plays a role in controlling the course of our various motor activities. There are two main routes within it, which are the cortico-nuclear pathway and the cortico-spinal pathway. What exactly is the pyramid system responsible for and what symptoms appear when it is damaged?
The pyramid system(Latinsystema pyramidale ) is responsible for controlling the course of all movements that affect the striated transverse muscles. Within the nervous system, there are many different structures that perform different functions. One of them are centers that control the course of various motor activities - we are talking about the pyramidal and extrapyramidal systems. Just as both of these work together, they have slightly different functions - the extrapyramidal system supervises movements that occur in an automated manner, the pyramid system is a structure that is responsible for free movement and posture.
Pyramid system: development
At the very beginning, it is worth mentioning that although we are of course born with a pyramidal system, it is not fully developed then - immediately after birth, some of the fibers of the pyramidal system remain unmyelinated.
The formation of the myelin sheath - which conditions, among others, the velocity of the flow of impulses in the axons - continues for some time after birth. By the age of two, most of the fibers are covered with a myelin sheath, but eventually this process can be completed around the age of 12.
The immaturity of the structures of the pyramid system is one of the factors responsible for the fact that only after some time after birth a person is able to undertake various movements depending on his will.
Pyramid layout: construction
The basic structures of the extrapyramidal system are motor neurons - their bodies are located within the motor cortex of the forebrain, as well as in the anterior horns of the spinal cord or in the nuclei of the cranial nerves. The former are sometimes referred to as central motor neurons, while the latter are called peripheral motor neurons. Both types of nerve cells mentioned are strictly connected with each otherconnections - central neurons direct their projections (i.e. axons) towards peripheral neurons.
Connections between individual elements belonging to the pyramidal system form the nerve pathways: the cortico-nuclear path and the cortico-spinal path.
The nuclear cortical pathwaybegins in the cortical centers of the forebrain, axons from these motor neurons run through the knee of the inner capsule and finally reach the midbrain, where they form the branches of the brain. The axons then travel to the pons and eventually reach the nuclei of the individual cranial nerves.
In the case ofcortico-spinal tract , axons originating from the central motor neurons run through the posterior limb of the inner capsule and continue towards the medulla and spinal cord. In a specific place - more precisely within the elongated core - the pyramid roads intersect, which will be mentioned later.
Pyramid layout: functions
Basically, the basic function of the pyramid system is to control the course of various movements - in general, this structure oversees the activity of almost all striated muscles (the only one that is not controlled by the fibers of the pyramid system is the stapes muscle).
Some muscles in the human body are innervated by fibers belonging to the cortico-nuclear pathway - such are the craniofacial muscles, the neck muscles and part of the trapezius muscle. As for the cortico-spinal pathway, the fibers belonging to it innervate all the remaining striated muscles.
The pyramid system is responsible for supervising the movements depending on our will. The impulse that is ultimately intended to stimulate the muscle cells in question to contract is initially generated in central motor neurons. Through their axons, it goes to peripheral motor neurons, and finally to effector cells. It is also mentioned that the pyramid system also has a certain influence on the maintenance of our balance and a stable body posture.
Pyramid system: causes and symptoms of damage
Damage to the pyramid system can be caused by many different factors - the cause may be:
- atherosclerosis
- neurodegenerative diseases
- multiple sclerosis
- neuropathy
It also happens that dysfunctions of the pyramidal system result from the experience of some extensive trauma or they are the result of poisoning with some toxic substances.
Considering that the function of the pyramid system is supervisionmovements, you can guess what ailments may appear in the event of its damage. First of all, it can lead to various degrees of paresis and paralysis, in addition to them, patients may also experience many other symptoms, which are collectively referred to as pyramidal symptoms.
It is worth mentioning a bit more about the crossing of fibers belonging to the pyramidal system. It is extremely important because having knowledge about it, you can - in the event of symptoms of damage to the pyramid system - infer which part of the defect occurred.
Due to the crossing of the pyramidal paths, the motor centers in the right hemisphere of the brain control the functions of the left half of the body and vice versa - the centers in the left part of the brain control the movements of the right half of the body. It is for this reason that when neurological deficits are present in the patient on the left side, the most likely damage was in the right part of the brain.
About the authorBow. Tomasz NęckiA graduate of medicine at the Medical University of Poznań. An admirer of the Polish sea (most willingly strolling along its shores with headphones in his ears), cats and books. In working with patients, he focuses on always listening to them and spending as much time as they need.