The cranialnerves are twelve pairs of nerves from the central nervous system. The cranial nerves are loosely based on their functions. In this summary, we discuss the nomenclature of the cranial nerves and supply some background information that might make it easier to understand the nerves and their function.
This summary should read alongside the complete articles for each of the cranial nerves:
The cranial nerve nuclei will be covered in more detail in each cranial nerve article. A nucleus refers to a collection of neuronal cell bodies within the central nervous system and they give rise to one of seven major types of fibres (below):
GSA (general somatic afferent): receive sensory information from the skin, skeletal muscles and joints
GVA (general visceral afferent): receive sensory information from the viscera (organs)
SSA (special somatic afferent): receive sensory information from the ectodermal retina, cochlear and vestibular apparatus
SVA (special visceral afferent): receive sensory information from the endodermal nose and tongue
GSE (general somatic efferent): provide motor innervation to skeletal muscles
GVE (general visceral efferent): provide secretomotor function to smooth muscle and glands
SVE (special visceral efferent): provide motor innervation to skeletal muscles of the pharyngeal arches
Afferent fibres carry sensory information back to the brain. Efferent fibres carry motor information away from the brain.
Olfactory nerve (CN I)
CN I is the olfactory nerve. It provides special visceral afferent fibres for the sense of smell.
CN I connects to the brain (not the brainstem). It passes through the cribriform plate of the skull
Optic nerve (CN II)
CN II is the optic nerve. It provides special somatic afferent fibres for vision. It is the afferent limb for the pupillary light reflex.
CN II connects to the brain (not the brainstem). It passes through the optic canal of the skull
Oculomotor nerve (CNIII)
CN III is the oculomotor nerve. It provides general somatic efferent and general visceral efferent fibres to the extraocular muscles and pupillary constrictor muscles respectively. It is the efferent limb for the pupillary light reflex.
The muscles are the levator palpebrae superioris, inferior oblique, and superior, medial and inferior recti. CN III palsy causes a ‘down and out’ eye.
CN III connects to the midbrain. It passes through the superior orbital fissure of the skull
Trochlear nerve (CN IV)
CN IV is the trochlear nerve. It provides general somatic efferent to the extraocular superior oblique muscle. It assists in depressing and abducting the eye.
CN IV connects to the midbrain and is the only cranial nerve to leave the pontomesencephalic junction posteriorly. It passes through the superior orbital fissure of the skull.