Upper motor neurons are any neurons that carry motor information down to the final common pathway, that is, any 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 spinal cord, from which point nerve signals continue to the muscles by means of the lower motor neurons. Upper motor neurone lesions are indicated by spasticity, exaggerated reflexes, loss of voluntary motor control and the Babinski sign.

Somatic motor system | Efferent neurons