The peripheral nerves may contain four different types of fibers:
Somatomotor (efferent)fibers(A1)for striated muscles
Somatosensory (afferent)fibers(A2) for skin sensibility
Visceromotor fibers (A3) for smooth muscles
Viscerosensory fibers (A4) for inner organs
The spinal nerves usually contain several types of fibers; they are mixed nerves. The different fibers have the following path-ways. The somatomotor fibers pass from the anterior horn cells (A5) through the anterior root (A6); the somatosensory and viscerosensory fibers originate from the nerve cells of the spinal ganglia (A7); and the visceromotor fibers of the lateral horn cells (A8) pass mostly through the anterior root. Anterior and posterior roots (A9) join to form the spinal nerve (A10), which con- tains all types of fibers. This short nerve trunk then divides into four branches:
The meningeal branch (A11), a recurrent sensory branch extending to the spinal meninges
The posterior branch (A12)
The anterior branch (A13)
The communicating branch (A14)
The posterior branch supplies motor fibers to the deep (autochthonous) muscles of the back and sensory fibers to the skin areas on both sides of the vertebral column.
The anterior branch supplies motor fibers to the muscles of the anterior and lateral walls of the trunk and to the muscles of the limbs; it also supplies sensory fibers to the corre- sponding skin areas. The communicating branch connects with the sympathetic chain ganglion (A15) (autonomic nervous system, p. 292). It usually forms two independentcommunicating branches, the white com- municating branch (A16) (myelinated) and the gray communicating branch (A17) (un- myelinated). The visceromotor fibers pass via the white branch to the sympathetic chain ganglion, where they are relayed to the spinal nerve as postganglionic fibers via the gray branch.