Upper motor neuron
 | This article needs additional citations for verification. (May 2010) |
| Upper motor neuron | |
|---|---|
 The motor tract | |
| Identifiers | |
| FMA | 84631 |
| Anatomical terminology | |
Upper motor neurons (UMNs) is a term introduced by
or relax. UMNs represent the major origin point for voluntary somatic movement.Upper motor neurons represent the largest pyramidal cells in the motor regions of the cerebral cortex. The major cell type of the UMNs is the Betz cells residing in layer V of the primary motor cortex, located on the precentral gyrus in the posterior frontal lobe. The cell bodies of Betz cell neurons are the largest in the brain, approaching nearly 0.1 mm in diameter. The axons of the upper motor neurons project out of the precentral gyrus travelling through to the brainstem, where they will decussate (intersect) within the lower medulla oblongata to form the lateral corticospinal tract on each side of the spinal cord. The fibers that do not decussate will pass through the medulla and continue on to form the anterior corticospinal tracts.
The upper motor neuron descends in the spinal cord to the level of the appropriate spinal nerve root. At this point, the upper motor neuron synapses with the lower motor neuron or interneurons within the ventral horn of the spinal cord, each of whose axons innervate a fiber of skeletal muscle.[1][2]
These neurons connect the
Pathways
Upper motor neurons travel in several neural pathways through the central nervous system (CNS):
| Tract | Pathway | Function |
| corticospinal tract | from the ventral horn of the spinal cord |
The major function of this pathway is fine voluntary motor control of the limbs. The pathway also controls voluntary body posture adjustments. |
| corticobulbar tract | from the motor cortex to several nuclei in the pons and medulla oblongata | Involved in control of facial and jaw musculature, swallowing and tongue movements. |
| colliculospinal tract (tectospinal tract) | from the superior colliculus to lower motor neurons | Involved in involuntary adjustment of head position in response to visual information. |
| rubrospinal tract | from red nucleus to lower motor neurons | Involved in involuntary adjustment of arm position in response to balance information; support of the body. |
| vestibulospinal tract | from vestibular nuclei, which processes stimuli from semicircular canals | It is responsible for adjusting posture to maintain balance. |
reticulospinal tract |
from reticular formation | Regulates various involuntary motor activities and assists in balance. |
Lesions
Any
See also
References
- ^ Saladin, Kenneth S. Anatomy & Physiology: The Unity of Form and Function. Dubuque: McGraw-Hill, 2010. Print.
- ^ "Frontal Lobe". Rice University Web Calendar. 26 June 2000. Web. 06 Dec. 2010. <"Frontal Lobe". Archived from the original on 2010-07-26. Retrieved 2010-12-07.>.
- ^ Purves, Dale; Augustine, George J.; Fitzpatrick, David; Katz, Lawrence C.; LaMantia, Anthony-Samuel; McNamara, James O.; Williams, S. Mark (9 May 2018). "Damage to Descending Motor Pathways: The Upper Motor Neuron Syndrome". Archived from the original on 3 May 2018. Retrieved 9 May 2018 – via www.ncbi.nlm.nih.gov.
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