A single motor neuron that initially stimulated 1,000 muscle cells might eventually innervate 5,000 to 10,000 cells, creating a giant motor unit.
In the Metanemertini, where the longitudinal stems lie inside the muscular body-wall, definite and metamerically placed nerve branches spring from them and divide dichotomously in the different tissues they innervate.
It then exits the canal through the infraorbital foramen to innervate the upper lip, cheek and side of the nose.
Poliomyelitis causes an overall loss of motor units; therefore, the remaining units must innervate many more muscle fibers than they did originally.
Sensory nerves supply or innervate particular regions of the body.
The action of atropine in dilating the pupil is also aided by a stimulation of the fibres from the sympathetic nervous system, which innervate the remaining muscle of the iris - the dilator pupillae.
The nervous system is represented by an oesophageal collar and a suboesophageal ganglion, whence paired nerves pass outwards to innervate the anterior extremity and backwards towards its posterior end.
The spinal cord has 31 pairs of spinal nerves attached which innervate the body and leave the vertebral canal via the intervertebral foramen.
They are, however, less excitable than are the nerve cells which innervate them.