The pyramidal tract is the longest nerve pathway in the body and transmits motor impulses from the first motoneuron in the brain to the second motoneuron in the spinal cord. Thus, it plays a high role in voluntary motor function and is part of the pyramidal system. Damage to the pyramidal pathway causes spastic and flaccid paralysis.
What is the pyramidal tract?
The pyramidal tract is part of the central nervous system and extends from the spinal cord to the brain. It is considered part of the motor system. As the efferent pathway system to the motocortex, it transmits impulses from the central nervous system to the alpha motoneurons. From there, action potentials are transmitted to the muscles of the skeletal musculature. Thus, the pyramidal tract is an important switching point for movements of the voluntary and reflex motor systems. The pyramidal tract is also the longest descending tract of the human nervous system and is part of the pyramidal system. The pyramidal system refers to the motor neurons and their nerve processes that converge in the pyramidal tract. The pyramidal system is particularly developed in humans and primates. Together with the extrapyramidal system, it controls all motor functions in the human organism. Many sources judge a clear separation of the two systems to be critical.
Anatomy and structure
In the broadest sense, the pyramidal tract consists of two distinct fiber tracts. The tractus corticospinalis meets the tractus corticonuclearis in anatomic structure. Both tracts are motor neural pathways of the central nervous system. The pyramidal tract abuts the inferior myelencephalon on both sides, where it is recognizable as a pyramidal longitudinal bulge. Between the afterbrain and the spinal cord lies the so-called pyramidal crossing. A large part of the neurites crosses at this point as tractus corticospinalis lateralis to the opposite side of the pathway in each case. The tractus corticospinalis anterior paramedian consists of the remaining ten to 30 percent of the neurites. This tract runs in the anterior cord and crosses into the anterior horn of the spinal cord in segments. A few tracts are not involved in the crossing. Because the tractus corticonuclearis is connected to the cranial nerve nuclei by single fibers and thus does not run through the pyramidal structure of the myelencephalon, it belongs to the pyramidal tract only in the broadest sense.
Function and Tasks
The pyramidal tract is part of the somatomotor system in humans and most mammals. This anatomical structure controls voluntary movement and thus the skeletal muscles responsible for these movements. The cardiac musculature is not controlled somatomotorly. It is subject to the control of an independent and involuntary system also known as the autonomic nervous system. The enteric nervous system, rather than the somatomotor system, is also responsible for the control of the digestive organs. As part of the somatomotor system, the pyramidal pathway is primarily responsible for voluntary motor function. It performs this function specifically as a portion of the pyramidal motor structures, although the extrapyramidal motor system is also included in the somatomotor system. Not all movements in the human body are controlled voluntarily. While voluntary motor activity depends on the pyramidal pathway, the involuntary portion of motor activity 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 called pyramidal cells. The pyramidal system consists primarily of small pyramidal cells that originate from the motor cortex. From the cortex, the axon fibers of the central motor neurons pass through the spinal cord to reach the lower motor neuron, which is located in the anterior horn of the spinal cord. Movement commands are thus transmitted from the brain to the organs of success via the first and second motoneurons. As alpha neurons, the upper and lower motoneuron transmit impulse particularly fast. As connectors between the two motoneurons, the pyramidal tract is an irreplaceable part of motor control.
Diseases
In the context of lesions of the pyramidal pathway, the term Babinski group plays the most important role clinically. Symptoms from this group are also called pyramidal tract signs.These are motor reflex movements that are physiological in infants but have pathological value in adults. In neurological reflex testing, the neurologist checks his patients for pyramidal tract signs as a standard procedure because they can be an indication of damage to the central motor neurons. In addition to the diagnostic value of pyramidal pathway signs, they also have prognostic value in diseases such as multiple sclerosis. Pyramidal tract signs and thus damage to the central motor neurons or the pyramidal tract can be caused by inflammation, degenerative processes or circulatory disorders. A lesion of the pyramidal tract inside the brain usually manifests as flaccid paralysis or impaired fine motor skills. Flaccid paralysis becomes spastic paralysis with increased muscle tone over time. In this context, impaired blood flow is the most common cause of damage. In degenerative diseases such as ALS, on the other hand, the motor nervous system degrades. Inflammations in the brain and spinal cord, on the other hand, are present in the autoimmune disease MS. When these inflammations affect the pyramidal tracts, the prognosis for the course of the disease is on average less favorable. Meanwhile, the presence of pyramidal tract signs is considered a rather uncertain diagnostic tool. Nonetheless, it has been one of a few means of suspected diagnosis of motoneuronal damage to the nervous system.
