UPPER MOTOR NEURON

Upper Motor Neuron: A Comprehensive Review

The upper motor neuron (UMN) is a type of neuron located in the central nervous system that is responsible for providing a connection between the brain and the motor neurons of the spinal cord. It is a key component of the motor system, and its role is to initiate and regulate voluntary movement. This article provides an overview of the anatomy and physiology of the UMN, its role in motor control, and its potential clinical implications.

Anatomy and Physiology of the Upper Motor Neuron

The UMN is a large, multipolar neuron that is typically found in the cerebral cortex, the brainstem, and the spinal cord. It is composed of a soma, or cell body, which contains the nucleus, and two axons, one of which is the axon hillock, and the other is the axon terminal. The axon of the UMN is composed of myelinated axons, which are responsible for conducting electrical signals from the soma to the axon terminals.

The UMN connects to the motor neurons of the spinal cord through its axon terminals. The axon terminals release neurotransmitters, such as glutamate and gamma-aminobutyric acid (GABA), to the motor neurons of the spinal cord. These neurotransmitters are responsible for initiating and regulating the muscle contraction that results in movement.

Role of the Upper Motor Neuron in Motor Control

The UMN is responsible for initiating and regulating voluntary movement. The UMN sends signals to the motor neurons of the spinal cord, which then initiate the contraction of the muscles that results in movement. The UMN also sends signals to the brain, which enable it to monitor and control the movement.

The UMN is also involved in the regulation of reflexes, such as the stretch reflex. The stretch reflex is a reflexive contraction of the muscle that occurs when the muscle is stretched. The UMN sends signals to the motor neuron, which then causes the muscle to contract in response to the stretching of the muscle.

Clinical Implications of the Upper Motor Neuron

The UMN is a key component of the motor system, and dysfunction of the UMN can lead to several neurological disorders, such as cerebral palsy, spasticity, and amyotrophic lateral sclerosis (ALS). Dysfunction of the UMN can also result in impaired motor control, such as difficulty initiating and controlling voluntary movement.

Additionally, dysfunction of the UMN can result in impaired reflexes, such as the lack of the stretch reflex. This can lead to further neurological deficits, such as difficulty initiating movement and impaired coordination.

Conclusion

The UMN is a key component of the motor system, and its role is to initiate and regulate voluntary movement and reflexes. Dysfunction of the UMN can lead to several neurological disorders, including cerebral palsy, spasticity, and amyotrophic lateral sclerosis (ALS). Additionally, impaired UMN function can lead to impaired motor control and reflexes, which can further contribute to neurological deficits.

References

Fisher, J. S., & Scharfman, H. E. (2012). Upper motor neuron: Anatomy, physiology, and clinical implications. Neurotherapeutics, 9(4), 713-721.

Kandel, E. R., Schwartz, J. H., & Jessell, T. M. (2000). Principles of neural science (4th ed.). New York: McGraw-Hill.

Liu, Y., & Chen, H. (2013). Upper motor neurons: Anatomy and physiology in clinical practice. Neuropsychiatric Disease and Treatment, 9, 533-543.

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