n.
A motor neuron whose cell body is located in the motor area of the cerebral cortex and whose processes connect with motor nuclei in the brainstem or the anterior horn of the spinal cord.
Upper motor neuron
n.
| 5min Related Video: Upper motor neuron |
| Wikipedia: Upper motor neuron |
| Upper motor neuron | |
|---|---|
 |
|
| The motor tract | |
| Dorlands/Elsevier | motoneuron |
Upper motor neurons are motor neurons that originate in the motor region of the cerebral cortex or the brain stem and carry motor information down to the final common pathway, that is, any motor neurons that are not directly responsible for stimulating the target muscle. The main effector neurons for voluntary movement lie within layer V of the primary motor cortex and are called Betz cells. The cell bodies of these neurons are some of the largest in the brain, approaching nearly 100μm in diameter.
These neurons connect the brain to the appropriate level in the spinal cord, from which point nerve signals continue to the muscles by means of the lower motor neurons. The neurotransmitter glutamate transmits the nerve impulses from upper to lower motor neurons where it is detected by glutamatergic receptors.
Pathways
Upper motor neurons travel in several pathways through the CNS:
| Tract | Pathway | Function |
| corticospinal tract | from the motor cortex to lower motor neurons in 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. |
| tectospinal tract/colliculospinal 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
Upper motor neuron lesions are indicated by spasticity, muscle weakness, exaggerated reflexes, clonus, and an out toeing (flaring) of toes and extensor plantar response known as the Babinski sign.
External links
|
|||||||||||||||||||||||||||||||||||||||||
This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)
Learn More
 | UMN |
| clonus |
| crossed extensor reflex |
Help us answer these
 | What is upper motor neuron syndrome? |
| What is the Function of upper motor neurons? |
| What motor neurons is involved in spastic paralysis upper or lower motor neuron? |
Post a question - any question - to the WikiAnswers community:
Copyrights:
 |
 | Medical Dictionary. The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Read more |
 |
| Wikipedia. This article is licensed under the Creative Commons Attribution/Share-Alike License. It uses material from the Wikipedia article "Upper motor neuron". Read more |
Related answers
- Upper motor neuron lesion?
- What sensory neurons to motor neurons?
- What links the sensory neurons and motor neurons?
ADVERTISEMENT
