The twelve pairs of cranial nerves are numbered in Roman numerals. This numeration is in relation to a descending order of how the nerves attach to the CNS in the brain. Also deals with chewing and jaw reflexes. It deals with swallowing and gag reflexes, as well as the heart, lungs, and digestive tracts. The nerve fibers are either efferent or afferent.
Efferent fibers conduct impulses away from the spinal cord to the body.
Nerve fibers are classified by a number of criteria, including the diameter of the fiber, thickness of the myelin sheath, and speed of conduction of the impulse. Large fibers conduct impulses much more quickly, and the thicker the myelin sheath, the faster the speed of the impulse conductivity. A plexus is a network of interlacing nerves. Primary branches of nerves such as the cervical, brachial, lumbar, and sacral plexuses form some plexuses. Others include the nerves from the periphery.