Our brain is a unique multi-complex system that simultaneously controls both sensory and vestibular apparatus, movement, thinking, speech, vision and much more.
In this article, we will talk about how the brain controls voluntary and involuntary movement. And what are the neurological abnormalities associated with damage to the pyramidal system of the brain.
The pyramidal and extrapyramidal path
The pyramidal system consists of pyramidal and extrapyramidal paths. What is their difference? The pyramidal pathway, or tractus pyramidalis, is the pathway that connects the cortical neurons responsible for motor activity with the nuclei of the spinal cord and cranial nerves. His job is to control voluntary muscle movements by transmitting CNS signals to the body. But extrapyramidal, it controls the unconscious conditioned reflexes of our body. This is an older and deeper brain structure, and its signals are not displayed in the mind.
Extrapyramidal and pyramidal - the paths are descending. And the ascending main paths are responsible for the transfer of information from the senses to the brain. These include: lateral dorsal-thalamic pathway, anterior spinal-cerebellar and posterior spinal-cerebellar.
Pyramidal pathways of the brain. Structure
They are divided into 2 types: cortical-spinal and cortical-nuclear. The cortical-spinal is responsible for the movement of the body, the cortical-nuclear controls the facial and swallowing muscles.
What is the structure of the cortical-spinal pyramidal pathway? This electrical path begins with the cerebral cortex - the area that is responsible for higher mental activity, for consciousness. The entire cortex consists of interconnected neural networks. More than 14 billion neurons are concentrated in the cortex.
In the hemispheres, the information is redistributed in this way: everything related to the work of the lower extremities is in the upper sections, and what concerns the upper ones, on the contrary, in the lower structures.
All signals from the upper and lower parts of the cortex are collected and transmitted to the inner capsule. Then, through the midbrain and through the middle part of the bridge, a bundle of nerve fibers enters the pyramids of the medulla oblongata.
Branching takes place here: most of the fibers (80%) go to the other side of the body and form the lateral spinal path. These branches “trigger” motor neurons, which then transmit signals to contract or relax directly to the muscles. A smaller part of the fiber bundle (20%) innervates the motor neurons of their “own” side.
The cortical-nuclear pyramidal pathway initially goes through the same brain structures as its “partner”, but crosses in the midbrain and goes to the facial neurons.
Anatomical features important for diagnosis
The pyramidal pathway has some features of its structure that cannot be overlooked when it is necessary to find out the localization of the pathology. What specific features do you need to know?
- A part of the nerve fibers of the cortex-spinal cord, in addition to lateral intersection, cross in the region of the white commissure of the segment of the spinal cord, where they end.
- Most of the muscles in the body are controlled by both hemispheres of the brain. This is an important defense. In the event of a stroke or stroke, those patients who are diagnosed with hemiplegia can support the body vertically.
- In the area of the brain bridge, the fibers of the cortex-spinal canal are separated by other fibers - the cerebellar path. Separated beams come out of the bridge. In this regard, motor disorders are often scattered. Whereas the pathological focus can be single.
Symptoms of the defeat of the pyramidal path are sometimes quite pronounced, as in the case of paralysis of the lower extremities, for example. But it happens that it is difficult to establish the cause. It is important to notice minor disturbances in motor skills in time and see a doctor.
Symptoms of a lesion. Levels
The clinical manifestations of a disorder of the conducting pyramidal pathway depend on in which department the damage to nerve fibers occurred. There are several levels of damage to motor activity: from complete paralysis to relatively favorable disorders.
So, neurology distinguishes the following levels of damage to the pyramidal pathway:
- Central monoparesis (paralysis). Violations are localized in the cortex (left or right).
- Central hemiparesis. The inner capsule is damaged.
- Various alternating syndromes - affected area of the brain stem.
- Paralysis of the limbs. One of the lateral cords in the spinal cord.
Central paralysis with damage to the brain capsule and cerebral hemispheres is characterized by the fact that the work of the muscles is impaired on the opposite side of the body relative to the affected area. After all, the cross of the pyramidal path works in the nervous system. That is, the fibers pass to the lateral or lateral spinal path. The simplified diagram depicts how the pyramidal path, the anatomy of which was considered above, crosses and moves on.
If the lateral cord in the spinal cord is damaged, the muscles work on the same side as the damage.
Neuropathology. Peripheral and central paralysis
Nerve fibers under the microscope are similar to the cord. Their work is extremely important for the body. If conduction is disturbed in a part of the nerve chain, muscles in some parts of the body will not be able to receive signals. This will cause paralysis. Paralysis is divided into 2 types: central and peripheral.
If one of the central motor nerves in the “network” is disrupted, then central paralysis occurs. And with a problem with the peripheral motor nerve, paralysis will be peripheral.
With peripheral paralysis, the doctor observes a decrease in muscle tone and a strong decrease in muscle mass. Tendon reflexes will also be reduced or completely disappear.
The situation is different with central paralysis. Then there is hyperreflexia, muscle tone is increased, sometimes contractures are present.
Pyramidal insufficiency in newborns. Causes
Symptoms of motor failure in a child are strange twitches, or he may walk differently than other children - on tiptoe; or stop setting is wrong. The reasons for this condition in a child may be:
- underdevelopment of the brain (spinal or brain);
- birth trauma, if the parietal lobe of the brain or the brain stem itself is damaged, pyramidal path disorders will definitely be;
- hereditary diseases of the nervous system.
- hypoxia;
- cerebral hemorrhage after childbirth;
- infection such as meningitis or arachnoiditis.
Treatment for adults is often medication. But for children it is much better to use methods such as exercise therapy, massage and vitamin intake. If there are no abscesses in the brain, or other serious injuries, the condition improves by the first year of life.
Paresthesia and myoclonia
Violation of the cervical spine leads to paresthesia. This is neuropathy, which is characterized by a violation of sensitivity. A person can either completely lose the sensory sensitivity of the skin, or feel tingling sensations throughout the body. Paresthesia is treated with reflexology, manual therapy, or physiotherapy. And, of course, you need to remove the main cause of neuropathy.
Another defeat of the pyramidal pathways and, consequently, of motor activity is myoclonia - involuntary twitching.
Myoclonus is of several types:
- rhythmic myoclonic contractions of a particular muscle group;
- bicycle-palatine contractions - sudden irregular contractions of the tongue or pharynx;
- postural myoclonia;
- cortical;
- myoclonia in response to motor activity (in athletes).
Myoclonus or cortical myoclonia is a disease of the conduction nerve pathway caused by a violation in the motor centers of the brain. That is, at the very beginning of the pyramidal path. If there is a “glitch” in the cortex, the signals to the muscles reach already distorted.
However, the lack of magnesium, psychoemotional or physical overwork, and many other reasons can be the causes of disorders of the motor pyramidal path. Therefore, the doctor should make the diagnosis after checking for MRI.
Diagnosis of violations
The descending pyramidal path is projective, while the ascending path is the one that transmits body signals through the spinal cord to the central nervous system. The downstream, on the contrary, transmits brain signals to neurons.
To determine which system was affected and how much, a neurologist examines many parameters regarding muscles, joints, and nerve reflexes.
A neurologist performs the following diagnostic procedures:
- explores the range of motion of all joints;
- checks deep reflexes, looks for pathological reflexes ;
- checks the work of all facial nerves;
- measures the electrical conductivity of muscles, their biopotentials;
- explores muscle strength;
- and is also required to check if pathological clonic contractions are present.
When a neurologist checks the range of motion, he begins to examine the larger joints first, and then examines the smaller ones. That is, first examines the shoulder joint, then the elbow and wrist.
The defeat of the cortical nuclear pathway
The pyramidal path is the basis of all movements of not only the muscles of the body, but also the face. Axons of various facial motor neurons transmit signals to muscles. Let's consider in more detail. Double core motor neurons innervate the muscles of the pharynx, larynx, soft palate, and even the muscles of the upper esophagus. Trigeminal motor neurons are responsible for the functioning of some of the masticatory muscles and those that give a signal to contract the eardrum. Individual motor neurons contract the muscles of the face when we smile or frown. These are facial neurons. Another muscle group is responsible for eye and eyelid movements.
The defeat of the leading neuron is reflected in the work of the “subordinate” muscles. The whole pyramidal path is based on this principle. Neurology of the facial nerve leads to very unpleasant consequences. However, eyeball movements and swallowing are usually preserved.
It is worth noting that a complete disconnection of the muscles of the face from the controlling segment of the brain occurs only if both the right and left hemispheres are affected. Most facial neurons are controlled bilaterally, as are the muscles of the trunk. Unilateral crossed fibers go only to the lower part of the face, namely to the muscles of the tongue and lower jaw.
Damage to the motor zones of the cerebral cortex
When, as a result of an injury, motor zones in the cortex of one of the hemispheres are damaged, a person is paralyzed on one side. When both hemispheres are damaged, paralysis is bilateral. If these centers experience overexcitation, local or centralized convulsions are caused. Frequent cramps may indicate the development of epilepsy.
Symptoms of a pyramidal pathway lesion at the level of the brain stem
Since fiber crossover occurs at the level of the brain stem (oblong and varolian bridge), with the defeat of these structures, gamiplasia occurs already on the other half of the body. This symptom is called alternating paralysis.
The pyramidal path is the basis of fine motor skills. Even if the brain stem is slightly damaged, small finger movements suffer greatly.
There are many different syndromes that clearly and in detail characterize disorders that affect the work that the pyramidal path does: Avellis, Schmidt, Wallenberg-Zakharchenko syndromes and others. Based on the symptoms of these syndromes, the doctor can often determine the exact location of the pathway violation before the tests.