What is the pyramid train?
The pyramidal tract is part of the central nervous system and extends from the spinal cord to the brain. It is calculated as the motor system. As an efferent trajectory to the motocortex, it sends impulses from the central nervous system to the alpha motor neurons. From there, the action potentials are transferred to the muscles of the skeletal muscle. Thus, the pyramidal track is an important switching point for movements of voluntary and reflex motor skills.
The pyramidal tract is also the longest descending pathway of the human nervous system and belongs to the pyramidal system. The pyramidal system is the motor neuron and its nerve processes, which converge in the pyramidal tract. The pyramidal system is particularly strong in humans and in primates. Together with the extrapyramidal system, it controls all motor functions in the human organism. A clear separation of the two systems is considered critical by many sources.
Anatomy & Construction
The Pyramidenbahn consists in the broadest sense of two different fiber webs. The corticospinal tract meets the corticonuclear tract in its anatomical structure. Both tracts are motor nerve tracts of the central nervous system. The pyramidal tract lies on both sides of the lower myelencephalon and is recognizable as a pyramidal longitudinal ridge. Between the Nachhirn and the spinal cord lies the so-called pyramid cross.
A large part of the neurites cross at this point as the corticospinal tract lateralis on the opposite side of the pathway. The corticospinalis anterior paramedian tract consists of the remaining ten to 30 percent of the neurites. This lane runs in the spinal cord anterior and crosses in segments into the spinal cord front horn. A few lanes are not involved in the intersection. Because the corticonuclear tract is connected to the cranial nerve nuclei by individual fibers and thus does not pass through the pyramidal structure of the myelencephalon, it belongs only in the broadest sense to the pyramidal tract.
Function & Tasks
The pyramidal tract belongs to the somatomotor system of humans and most mammals. This anatomical structure controls the voluntary movement and thus the skeletal musculature responsible for these movements. The heart muscles are not controlled somatomotorically. It is under the control of an independent and involuntary system, also known as the autonomic nervous system.
Also for the control of the digestive organs is not the somatomotor, but the enteric nervous system responsible. As part of the somatomotor system, the pyramidal tract is primarily responsible for voluntary movement. It performs this function especially as part of the pyramidal-motor structures, whereby the extrapyramidal-motor system is also counted as a somatomotor system. Not all movements in the human body are controlled arbitrarily. While the voluntary motor function depends on the pyramidal tract, the involuntary part of the motor system depends on the extrapyramidal system. In the pyramidal system, fine motor skills are controlled in addition to voluntary motor skills. The primary motor cortex of the cerebrum performs important tasks in this context. The cell bodies of central motor neurons are anchored here.
Histologically, these cells are also referred to as pyramidal cells. The pyramidal system consists primarily of small pyramidal cells originating from the motor cortex. From the cerebral cortex, the axonal fibers of the central motor neurons pass through the spinal cord, reaching the lower motoneuron, which lies in the anterior horn of the spinal cord. Movement commands are passed on from the brain to the success organs via the first and second motor neuron. As alpha neurons, the upper and lower motoneurons transmit momentum very quickly. As connecting pieces between the two motor neurons, the pyramidal track is an irreplaceable part of the motor system.
In the context of lesions of the pyramidal tract, the concept of the Babinski group plays a role clinically. Symptoms from this group are also called pyramidal tract signs. These are reflex motor movements that are physiological in infants but of pathological value in adults. In the neurological reflex test, the neurologist checks his patients by default for pyramidal tract signs because they can be an indication of damage to the central motor neurons.
In addition to the diagnostic value of pyramidal tract signs, they also have prognostic value in diseases such as multiple sclerosis. Pyramidal tract signs and thus damage to the central motoneurons or the pyramidal tract can be caused by inflammation as well as by degenerative processes or circulatory disorders. A lesion of the pyramidal tract inside the brain usually manifests itself in flaccid paralysis or impaired fine motor skills. The flaccid paralysis will eventually become a spastic paralysis with increased muscle tone. In this context, disturbed blood flow is the most common cause of injury.
In degenerative diseases such as ALS, on the other hand, the motor nervous system breaks down. In contrast, inflammation in the brain and spinal cord is present in the autoimmune disease MS. When these inflammations affect the pyramidal tracts, an average less favorable prognosis for the course of the disease is given. Meanwhile, the presence of pyramidal tract signs is considered a rather uncertain diagnostic tool. Nonetheless, it is still one of the few means of suspected motor neuronal damage to the nervous system.