Extrapyramidal Motor System – Structure, Function & Diseases
Extrapyramidalmotorisches System
Human motor functions are controlled by the interaction of the two pyramidal tracts and the three extrapyramidal nerve tracts in the spinal cord . In this context, the extrapyramidal or extrapyramidal motor system is primarily responsible for involuntary and automated movements. In inflammatory diseases of the central nervous system , but also in trauma , the extrapyramidal pathways can be damaged.
What is the extrapyramidal motor system?
The extrapyramidal motor or extrapyramidal system form three motor spinal cord pathways. These pathways are specifically responsible for involuntary movements of the skeletal muscles . The two pyramidal tracts, which also run through the spinal cord, must be distinguished from this.
They serve, unlike the extrapyramidal system of voluntary movement. Both motor systems belong to the somatomotor system and together enable the movements and inhibitions of the skeletal muscles. An extrapyramidal system is found almost exclusively in primates. Vertebrates, for example, don’t even have pyramidal motor tracts.
In humans, the motor spinal cord system for involuntary movements of skeletal muscles emanates from the motor cortex of the brain . These are Brodmann areas six and eight, also known as areae extrapyramidales. The motor pathways are also connected to other core areas of the brain, such as the so-called basal ganglia .
Anatomy & Structure
Unlike the pyramidal tracts, the extrapyramidal tracts are not interconnected in a pyramidal form. The extrapyramidal system includes the rubrospinal tract, the vestibulospinal tract and the reticulospinal tract. The latter itself consists of the medial reticulospinal tract and the lateral reticulospinal tract.The vestibulospinal tract runs uncrossed from the rhomboid fossa into the spinal cord. The rubrospinal tract arises from the nucleus of the brainstem and crosses into the ventral spinal cord, where it descends. The lateral reticulospinal tract of the reticulospinal tract arises from the brain area between the midbrain and the spinal cord. The medial reticulospinal tract, which runs laterally and uncrossed, originates from what is known as the bridge of the central nervous system. The pathways are each equipped with several switching points in the sense of synaptic nerve endings .
Function & Tasks
The task of the extrapyramidal system is movement control. It realizes unconscious and automated movements, such as swinging your arms while running. Movements of the torso and extremities that appear to be coarser are also initiated within the structures, such as automated holding and supporting motor functions and mass movement. The extrapyramidal system is also responsible for maintaining unconscious muscle tension.
In this context, one can speak of a network with the muscle sense. These motor pathways are also networked with the visual system, the sense of balance and the sense of one’s own position in space. In particular, the connections to the cerebellum allow the tracks to make automatic corrections to the posture and realize harmonious movements. The vestibulospinal tract is responsible for activating the motor neurons and inhibiting the flexors.
The rubrospinal tract, on the other hand, inhibits the extensors, activates the flexors and is the only extrapyramidal nerve involved in fine motor skills. Broadly speaking, the motor neurons in the muscles receive an order from the brain via the motor nerve pathways in the spinal cord. Motor neurons are efferent nerves that run throughout the muscles and are essential for movement. The connected brain regions thus take over the circuitry of the three extrapyramidal motor pathways and plan to make contact with specific motor neurons.
In the basal ganglia of the brain, for example, the selection and processing of currently required movements takes place. Here, among other things, it is planned to reach for an object in the field of vision. However, the motor pathways of the spinal cord are also involved in the inhibition of certain motor neurons, particularly that of the first motor neuron. You control the arbitrary movement of the pyramidal pathways. The exchange of information between the brain and the extrapyramidal system takes place biochemically primarily via the neurotransmitter dopamine .
Diseases
One of the most well-known disorders of the extrapyramidal system is the extrapyramidal syndrome. In this disease, the first motor neuron is no longer inhibited. Ataxia, tremor, difficulty starting and a tendency to fall are among the main symptoms of this condition. Ultimately, in this context, both greatly increased and greatly inhibited movement sequences can take place. The extrapyramidal system can also be damaged in the course of the inflammatory nervous system disease multiple sclerosis .In this case, inflammation develops in the three motor spinal cord pathways or the networked brain spheres, which in extreme cases can leave permanent damage after it has healed. When the three motor pathways become inflamed, tissue always perishes. In particular, if the inflammation persists for too long, the body can no longer compensate for the loss of this tissue. Inflammatory damage to the extrapyramidal system usually manifests itself in slower stimulus transmission and reactivity.
A loss or an increase in muscle tension can also occur as part of damage. Postural and positional reactions are sometimes also disturbed. If, instead of the extrapyramidal system, the pyramidal tracts are affected by damage, then so-called pyramidal tract signs appear. Such pyramidal signs correspond in particular to disturbed body reflexes, such as lateral foot reflexes or non-exhaustable reflexes of the hand.
The distinction between extrapyramidal symptoms and pyramidal symptoms can be of prognostic importance for the neurologist in connection with multiple sclerosis, for example. Pyramidal signs in the early years of the disease are said to be a rather unfavorable prognostic sign.
Hello! I am Lisa Newlon, and I am a medical writer and researcher with over 10 years of experience in the healthcare industry. I have a Master’s degree in Medicine, and my deep understanding of medical terminology, practices, and procedures has made me a trusted source of information in the medical world.