<Tr> <Th_colspan="2"> Identifiers </Th> </Tr> <Tr> <Td_colspan="2"> Anatomical terminology (edit on Wikidata) </Td> </Tr> <P> Upper motor neurons (UMNs) are motor neurons that originate either in the motor region of the cerebral cortex or in the brain stem and carry motor information down to the lower motor neurons . The main effector of motor neurons (efferent neurons) for voluntary movement lie within layer V of the primary motor cortex, and are a type of giant pyramidal cell called Betz cells . The cell bodies of these neurons are the largest in the brain, approaching nearly 0.1 mm in diameter . </P> <P> The primary motor cortex or precentral gyrus, is one of the most important areas in the frontal lobe . The precentral gyrus is the most posterior gyrus of the frontal lobe and it lies anterior to the central sulcus . The pyramidal cells of the precentral gyrus are also called upper motor neurons . The fibers of the upper motor neurons project out of the precentral gyrus ending in the brainstem, where they will decussate (intersect) within the lower medulla oblongata to form the lateral corticospinal tract on each side of the spinal cord . The fibers that do not decussate will pass through the medulla and continue on to form the anterior corticospinal tracts . The upper motor neuron descends in the spinal cord to the level of the appropriate spinal nerve root . At this point, the upper motor neuron synapses with the lower motor neuron, each of whose axons innervate a fiber of skeletal muscle . </P>

Where are the somas of upper motor neurons located