Upper motor neuron
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| Upper motor neuron | |
|---|---|
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| The motor tract. | |
| Dorlands/Elsevier | m_20/12542910 |
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Upper motor neurons are any neurons that originate in motor region of the cerebral cortex and/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 | Involved in involuntary maintenance of body posture. |
| 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. |
| 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 neurone lesions are indicated by spasticity, exaggerated reflexes, loss of voluntary motor control and the Babinski sign.
External links
Acknowledgement and Attribution Regarding Sources of Content
Some of the initial content on this page may be incorporated in part from copyleft sources in the public domain including wikis such as Wikipedia and AskDrWiki. Drug information for patients came from the The National Library of Medicine. Infectious disease information may have come from the Centers for Disease Control (CDC). Differential Diagnoses are drawn from clinicians as well as an amalgamation of 3 sources: 1.The Disease Database; 2. Kahan, Scott, Smith, Ellen G. In A Page: Signs and Symptoms. Malden, Massachusetts: Blackwell Publishing, 2004:3; 3. Sailer, Christian, Wasner, Susanne. Differential Diagnosis Pocket. Hermosa Beach, CA: Borm Bruckmeir Publishing LLC, 2002:7 .
