Upper motor neuron

Overview
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 100&mu;m 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:

Lesions
Upper motor neurone lesions are indicated by spasticity, exaggerated reflexes, loss of voluntary motor control and the Babinski sign.