Cranial Nerves: An Overview

Cranial Nerves

The 12 pairs of cranial nerves are so named because they pass through various foramina in the bones of the cranium and, with one exception, arise from the brain inside the cranial cavity.

Cranial Nerves: Naming

These nerves pass through various foramina in the bones of the cranium and, with one exception, arise from the brain inside the cranial cavity, and these numbers are ordered from anterior to posterior

Special Sensory Nerves

Three cranial nerves (I, II, and VIII) carry axons of sensory neurons that are associated with the special senses of smelling, seeing, and hearing

Motor Nerves

Five cranial nerves (III, IV, VI, XI, and XII) contain only axons of motor neurons as they leave the brainstem that innervate skeletal muscles

Motor Nerves: Types

Motor axons that innervate skeletal muscles are of two types: pharyngeal and somatic motor axons

Motor Nerves: Pharyngeal (Branchial) Motor Axons

These nerves innervate skeletal muscles that develop from the pharyngeal (branchial) arches that leave the brain through the mixed cranial nerves and the accessory nerve

Motor Nerves: Somatic Motor Axons

These nerves innervate skeletal muscles that develop from the head somites (eye muscles and tongue muscles) that leave the brain through five motor cranial nerves (III, IV, VI, XI, and XII

Motor Nerves: Somatic Motor Axons: Autonomic

Autonomic motor axons are motor axons that innervate smooth muscle, cardiac muscle, and glands that are part of the parasympathetic division

Mixed Nerves

The remaining four cranial nerves (V, VII, IX, and X) contain axons both of sensory neurons entering the brainstem and motor neurons leaving the brainstem