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 about what neurological abnormalities are associated with damage to the pyramidal system of the brain.
Pyramidal and extrapyramidal pathways
The pyramidal system consists of pyramidal and extrapyramidal pathways. What is their difference? The pyramidal pathway, or tractus pyramidalis, is the path that connects the cortical neurons responsible for motor activity with the nuclei of the spinal cord and cranial nerves. Its 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 structure of the brain, and its signals are not displayed in consciousness.
Extrapyramidal and pyramidal - downward paths. And the ascending main pathways are responsible for the transmission 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. Building
They are divided into 2 types: cortical-spinal and cortical-nuclear. The corticospinal is responsible for the movements of the body, the corticonuclear controls the facial and swallowing muscles.
How is the cortical-spinal pyramidal tract arranged? This electrical path begins with the cerebral cortex - the area that is responsible for higher mental activity, for consciousness. The entire cortex is made up of interconnected neural networks. More than 14 billion neurons are concentrated in the cortex.
In the hemispheres, information is redistributed in this way: everything related to the work of the lower extremities is located in the upper sections, and what concerns the upper, 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.
This is where the branching occurs: most of the fibers (80%) go to the other side of the body and form the lateral spinal cord. These branches “fire” motor neurons, which then transmit signals to contract or relax directly to the muscles. Smaller partbundle of fibers (20%) innervates the motoneurons of the "own" side.
The cortical-nuclear pyramidal pathway initially passes through the same brain structures as its "partner", but crosses already in the midbrain and goes to the facial neurons.
Anatomical features important for diagnosis
The pyramidal pathway has some structural features that should not be overlooked when it is necessary to determine the location of the pathology. What exactly do you need to know?
- Part of the nerve fibers of the cortico-spinal tract, except for the lateral decussation, cross in the area of the white commissure of the spinal cord segment, where they end.
- Most of the muscles in the trunk are controlled by both hemispheres of the brain. This is an important defense. In the event of a stroke or stroke, those patients diagnosed with hemiplegia can support the body upright.
- In the region of the pons of the brain, the fibers of the cortical-spinal tract are separated by other fibers - the cerebellar tract. Separated bundles emerge from the bridge. In this regard, motor disorders are often scattered. Whereas the pathological focus can be single.
Symptoms of the defeat of the pyramidal tract are sometimes quite clear, 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 violations in motor skills in time and visit a doctor.
Symptoms of defeat. Levels
Clinical manifestations of a violation of the conductive pyramidal pathway depend on the particular department in which the damage to the nerve fibers occurred. Distinguishseveral levels of damage to motor activity: from complete paralysis to relatively benign impairments.
So, neurology identifies the following levels of damage to the pyramidal tract:
- Central monoparesis (paralysis). Violations are localized in the area of the cerebral cortex (left or right).
- Central hemiparesis. Damaged inner capsule.
- Various alternating syndromes - brainstem area affected.
- Paralysis of limbs. One of the lateral cords in the region of the spinal cord.
Central paralysis with damage to the capsule of the brain 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 intersection of the pyramidal path works in the nervous system. That is, the fibers pass to the lateral or lateral spinal cord. The simplified diagram shows how the pyramidal tract, the anatomy of which was discussed above, crosses and moves on.
When the lateral cord in the spinal cord is damaged, the work of the muscles on the same side as the damage is disrupted.
Neuropathology. Peripheral and central paralysis
Nerve fibers look like cords under a microscope. Their work is extremely important for the body. If conduction is disrupted in some part of the nerve circuit, the 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.
Ifone of the central motor nerves in the "network" is broken, then central paralysis occurs. And if there is a problem with the peripheral motor nerve, the paralysis will be peripheral.
With peripheral paralysis, the doctor observes a decrease in muscle tone and a strong decrease in muscle mass. Tendon jerks will also be reduced or disappear altogether.
It is different with central paralysis. Then hyperreflexia is observed, muscle tone is increased, sometimes there are contractures.
Pyramidal insufficiency in newborns. Reasons
Symptoms of motor impairment in a child are strange twitches, or he may walk differently than other children - on tiptoe; or the stop position is incorrect. 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 brainstem itself is damaged, there will definitely be violations of the pyramidal pathway;
- hereditary diseases of the nervous system.
- hypoxia;
- cerebral hemorrhage after childbirth;
- an infection such as meningitis or arachnoiditis.
Treatment for adults is more often medication. But for children, it is much better to use methods such as exercise therapy, massage and taking vitamins. If there are no brain abscesses or other serious injuries, the condition improves by the first year of life.
Paresthesia and myoclonus
Disturbance in the cervical spine leads to paresthesia. This is neuropathy, which is characterized by a violation of sensitivity. Manmay either lose all sensory sensitivity of the skin, or feel tingling all over the body. Paresthesias are treated with reflexology, manual therapy or physiotherapy. And, of course, the root cause of neuropathy must be removed.
Another lesion of the pyramidal tract and, consequently, motor activity is myoclonus - involuntary twitches.
There are several types of myoclonus:
- rhythmic myoclonic contractions of a separate muscle group;
- velopalatine contractions - sudden non-rhythmic contractions of the tongue or throat;
- postural myoclonus;
- cortical;
- myoclonus in response to motor activity (in athletes).
Myoclonus or cortical myoclonus is a disease of the conduction nerve pathway, the cause of which is a violation in the motor centers of the brain. That is, at the very beginning of the pyramidal path. If there is a “failure” in the cortex, the signals to the muscles reach already distorted.
However, the causes of violations of the motor pyramidal pathway can be a lack of magnesium, and psycho-emotional or physical overwork, and many other reasons. Therefore, the diagnosis should be made by a doctor after an MRI check.
Diagnosis of violations
The descending pyramidal pathway is a projection pathway, while the ascending pathway is considered to be the one that transmits body signals through the spinal cord to the central nervous system. Downstream, on the contrary, transmits brain signals to neurons.
To determine whichit is the system that has suffered and how much, the neurologist, during examination, examines many parameters relating to 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 functioning of all facial nerves;
- measures electrical conductivity of muscles, their biopotentials;
- explores muscle strength;
- and must also check for abnormal clonic contractions.
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.
Defeat of the corticonuclear pathway
The pyramidal path is the basis of all movements not only of the muscles of the body, but also of the face. Axons of various facial motor neurons transmit signals to the muscles. Let's consider in more detail. The motor neurons of the double nucleus innervate the muscles of the pharynx, larynx, soft palate, and even the muscles of the upper esophagus. Motor neurons of the trigeminal nerve are responsible for the work of some chewing muscles and those that give a signal to contract the eardrum. Separate motor neurons contract facial muscles when we smile or frown. These are mimic neurons. Another muscle group is responsible for the movements of the eyes and eyelids.
The defeat of the leading neuron affects the work of the "subordinate" muscles. This principle is the basis of the entire pyramidalway. The neurology of the facial nerve leads to very unpleasant consequences. However, eyeball movements and swallowing are usually preserved.
It is worth noting that the complete disconnection of facial muscles 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.
Loss of the motor cortex
When the motor zones in the cortex of one of the hemispheres are damaged as a result of an injury, a person becomes paralyzed on one side. When both hemispheres are damaged, the paralysis is bilateral. If these centers are overexcited, local or centralized convulsions are caused. Frequent seizures may indicate the development of epilepsy.
Symptoms of lesions of the pyramidal tract at the level of the brainstem
Since at the level of the brainstem (medulla oblongata and pons) there is a crossover of fibers, when these structures are affected, gamiplasia occurs already on the other half of the body. This symptom is called alternating paralysis.
The pyramidal path is the foundation of fine motor skills. Even if the brainstem is slightly damaged, the small movements of the fingers suffer greatly.
There are many different syndromes that clearly and in detail characterize disorders that affect the work that the pyramidal pathway performs: Avellis, Schmidt, Wallenberg-Zakharchenko syndromes and others. From the symptoms of these syndromes, the doctor can often determine the exactlocation of conduction path disturbance prior to analysis.
