Chapter 1. REFLEXES, MOTION AND SYNDROMES
The motor impulses for voluntary movement are mainly generated in the precentral gyrus of the frontal lobe (primary motor cortex, Brodmann area 4) and in the adjacent cortical areas (first motor neuron). They travel in the long fiber pathways (mainly the corticonuclear and corticospinal tracts/pyramidal pathway), passing through the brainstem and down the spinal cord to the anterior horn, where they make synaptic contact with the second motor neuron - usually by way of one or more intervening interneurons. The nerve fibers emerging from area 4 and the adjacent cortical areas together make up the pyramidal tract, which is the quickest and most direct connection between the primary motor area and the motor neurons of the anterior horn. In addition, other cortical areas (especially the premotor cortex, area 6) and subcortical nuclei (especially the basal ganglia) participate in the neural control of movement. These areas form complex feedback loops with one another and with the primary motor cortex and cerebellum; they exert an influence on the anterior horn cells by way of several distinct fiber pathways in the spinal cord. Their function is mainly to modulate movement and to regulate muscle tone. Impulses generated in the second motor neurons of the motor cranial nerve nuclei and the anterior horn of the spinal cord pass through the anterior roots, the nerve plexuses (in the cervical and lumbosacral regions), and the peripheral nerves on their way to the skeletal muscles. The impulses are conveyed to the muscle cells through the motor end plates of the neuromuscular junction. Lesions of the first motor neuron in the brain or spinal cord usually produce spastic paresis, while lesions of the second motor neuron in the anterior horn, an-