Cranial Nerves Summary

Introduction

The cranial nerves 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:

• Olfactory nerve (CN I)
• Optic nerve (CN II)
• Oculomotor nerve (CN III)
• Trochlear nerve (CN IV)
• Trigeminal nerve (CN V)
• Abducens nerve (CN VI)
• Facial nerve (CN VII)
• Vestibulocochlear nerve (CN VIII)
• Glossopharyngeal nerve (CN IX)
• Vagus nerve (CN X)
• Accessory nerve (CN XI)
• Hypoglossal nerve (CN XII)

Cranial nerve nuclei

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.

Trigeminal nerve (CN V)

CN V is the trigeminal nerve. It has three sensory nuclei:

• Mesencephalic – proprioception
• Principal – light touch and discrimination
• Spinal – pain, temperature, crude touch

It is the afferent limb of the corneal reflex; CN VII is the bilateral efferent limb.

CN V emerges from the pons. It has three divisions (ophthalmic, maxillary and mandibular).

Table 1. The three divisions of the trigeminal nerve. 

Abducens nerve (CN VI) 

CN VI is the abducens nerve. It provides general somatic efferent fibres for eye abduction. It innervates the lateral rectus muscle.

CN VI originates in the pontomedullary region. It passes through the superior orbital fissure of the skull.

Facial nerve (CN VII)

CN VII is the facial nerve. It originates in the pontomedullary region, passes through the internal auditory meatus and exits through the stylomastoid foramen.

The facial nerve loops around the abducens nucleus.

Lower motor neurone facial nerve lesions cause upper and lower facial paralysis

Upper motor neurone facial nerve lesions cause lower facial paralysis only

Table 2. Function of the facial nerve.

Vestibulocochlear nerve (CN VIII)

CN VIII is the vestibulocochlear nerve. It provides special somatic afferent fibres for hearing and balance.

CN VIII originates in the pontomedullary region. It passes through the internal auditory meatus and does not leave the skull.

The cochlea transmits sound waves to mechanical ossicle movements to electrochemical action potentials.

The vestibular apparatus detects changes in head motion.

Glossopharyngeal nerve (CN IX)

CN IX is the glossopharyngeal nerve. It originates in the medulla oblongata and passes through the jugular foramen.

It draws fibres from the solitary nucleus (taste) and nucleus ambiguus (motor).

It draws more fibres from the inferior salivatory nucleus (parotid gland) and dorsal motor nucleus (DMX; pharyngeal sensation).

Table 3. Functions of the glossopharyngeal nerve.

Vagus nerve (CN X)

CN X is the vagus nerve. It originates in the medulla oblongata and passes through the jugular foramen with CN IX and XI.

Its key role is parasympathetic innervation of the viscera

The recurrent laryngeal nerve loops under the right subclavian artery and (left) aortic arch.

Table 4. Functions of the vagus nerve.

Accessory nerve (CN XI)

CN XI is the accessory nerve. It originates in the medulla oblongata and superior cervical cord region. It exits the spinal cord in the neck and enters the skull through the foramen magnum.

It provides general somatic efferent fibres to the trapezius and sternocleidomastoid

Hypoglossal nerve (CN XII)

CN XII is the hypoglossal nerve. It provides general somatic efferent fibres for controlling tongue muscles.

It originates in the medulla oblongata and exits the skull through the hypoglossal canal.

Cranial nerve summary table 

You can download our cranial nerve summary table in PDF format here.

References

Reference texts

• Sinnatamby, C. S. (2011). Last’s Anatomy, International Edition: Regional and Applied. Elsevier Health Sciences.
• Moore, K. L., Dalley, A. F., & Agur, A. M. (2013). Clinically oriented anatomy. Lippincott Williams & Wilkins.
• Nolte, J. (2002). The human brain: an introduction to its functional anatomy.
• Snell, R. S. (2010). Clinical neuroanatomy. Lippincott Williams & Wilkins.

Reference images

1. Patrick J. Lynch, medical illustrator. License: [CC-BY]. Modified by Dr Lewis Potter.