Final answer:
Descending tracts excite large spinal motor neurons with long axons that extend to the skeletal muscles. These neurons, particularly multipolar motor neurons in the anterior horn, can have cell bodies hundreds of micrometers in diameter to maintain the lengthy axon required for peripheral muscle innervation.
Step-by-step explanation:
The activity in descending tracts stimulates spinal motor neurons which are pivotal in controlling skeletal muscle contraction.
The size of these motor neurons is generally quite large due to the substantial lengths of their axons, which can reach up to a meter in cases such as those traveling to the toe muscles. This physical characteristic is evident in the multipolar motor neurons found in the anterior horn of the spinal cord.
The ventral horn output of the somatic nervous system consists of these lower motor neurons, which have a significant influence over the appendicular muscles, with the lateral corticospinal tract playing a critical role. Larger cell bodies, measuring hundreds of micrometers in diameter, are necessary to maintain and support these long axonal fibers.
The diameters of these neurons illustrate the extensive capacity of the neuronal cell body required to accommodate great lengths. This is especially evident in the ventral horn of the spinal cord, where the size of the horn correlates to the number of muscles and the extent of fine motor control required.
The long axons of the motor neurons in the spinal cord are designed to carry action potentials over great distances, up to three feet long in some cases, to the muscles. These axons also collectively bundle together to form nerves.