Upper motor neurons

Upper motor neurons (UMNs) are a type of motor neuron that originate in the motor region of the cerebral cortex or the brain stem. The axons of these neurons are part of the descending motor pathway for the innervation of skeletal muscles.

Anatomy

UMNs in the cerebral cortex are the primary motor neurons that send their axons to the spinal cord via the corticospinal tract to synapse on lower motor neurons, which in turn directly innervate muscles. While UMNs in the brain stem send their axons to innervate the cranial nerve nuclei in the brain stem and are involved in the control of the muscles of the face and neck.

Function

UMNs are responsible for carrying the information from the brain to the lower motor neurons, which ultimately results in muscle movement. They do not connect directly to muscles, instead, they connect to the lower motor neurons and it is these neurons that directly innervate muscles to cause movements.

Clinical significance

Damage to the UMNs often results in changes in muscle tone, known as spasticity, and muscle weakness. This is often accompanied by hyperreflexia, an exaggerated reflex response. The exact symptoms depend on where the damage to the UMN occurs.

See also

• Lower motor neuron
• Motor neuron disease
• Motor cortex
• Corticospinal tract

References

Upper motor neurons Resources
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