There are 12 pairs of cranial nerves, and, each cranial nerve is designated by a number and a name.
The functional components of cranial nerves consists of 7 columns, that breaks up into smaller fragments to form nuclei of the cranial nerves.
Columns
The grey matter in the spinal cord differentiates into 2 somatic and 2 visceral functional columns. In addition, there are 2 more columns for the branchial apparatus of the head region and 1 column for the special sense.
- Somatic columns: General somatic efferent (motor or anterior horn) & General somatic afferent (sensory or posterior horn). These supply the structures derived from somites.
- Visceral columns: General visceral efferent (motor) & General visceral afferent (sensory). These are autonomic columns and supply the viscera, vessels and glands.
- Columns for Branchial apparatus: Special visceral (branchial) efferent & Special visceral afferent.
- Column for special sense: Special somatic afferent.
Nuclei
Nuclei of the cranial nerves, along with their location are as under:
General Somatic Efferent Nuclei
- Oculomotor nucleus: Midbrain at the level of superior colliculus.
- Trochlear nucleus: Midbrain at the level of inferior colliculus.
- Abducent nucleus: Lower part of pons.
- Hypoglossal nucleus: Medulla.
Special Visceral Efferent/Branchial Efferent Nuclei
- Motor nucleus of trigeminal nerve: Upper part of the pons.
- Nucleus of facial nerve: Lower part of the pons.
- Nucleus ambiguus: Medulla.
General Visceral Efferent Nuclei
- Edinger-Westphal nucleus: Midbrain in close relation to the oculomotor nucleus.
- Lacrimatory nucleus: Lower pons near the salivatory nuclei.
- Superior salivatory nucleus: Lower part of the pons.
- Inferior salivatory nucleus: Lower part of the pons.
- Dorsal nucleus of the vagus nerve: Medulla.
Nucleus of solitary tract (tractus solitarius): Medulla
- Special Visceral Afferent Nucleus (Upper part)
- General Visceral Afferent Nucleus (Lower part)
General Somatic Afferent Nuclei
- Main/Superior sensory nucleus of the trigeminal nerve: Upper part of the pons.
- Spinal nucleus of the trigeminal nerve: Descends from the main nucleus into the medulla.
- Mesencephalic nucleus of the trigeminal nerve: Extends upwards from the main sensory nucleus into the midbrain.
Special Somatic Afferent Nuclei
- Cochlear nuclei (dorsal and ventral): Junction of medulla and pons.
- Vestibular nuclei (superior, spinal, medial and lateral): Junction of medulla and pons.
Cranial Nerves
I. Olfactory nerve: Nasal cavity (Smell).
II. Optic nerve: Eye (vision).
III. Oculomotor nerve: Ciliary muscles, sphincter pupillae and extraocular muscles except superior orbital and lateral rectus.
IV. Trochlear nerve: SO muscle.
V. Abducent nerve: LR muscle.
VI. Trigeminal nerve: Sensory - face, motor - muscles of mastication.
VII. Facial nerve: Muscles of face, posterior belly of digastric, stylohyoid, auricularis muscles, stapedius and platysma.
VIII. Vestibulocochlear nerve: Cochlear (hearing), Vestibular (balance).
IX. Glossopharyngeal nerve: Taste- Posterior 1/3rd of tongue, Sensory- Tonsil, pharynx, middle ear. Motor- Stylopharyngeus, Parotid gland.
X. Vagus nerve (+ Cranial root of accessory nerve): Motor- Heart, Lungs, palate, pharynx, larynx, trachea, bronchi, and GI tract. Sensory- Heart, lungs, trachea, bronchi, larynx, pharynx, GI tract up to right 2/3rd of transverse colon and external ear.
XI. Accessory nerve (Spinal root): Sternocleidomastoid and trapezius muscles.
XII. Hypoglossal nerve: Tongue muscles, Strap muscles (C1 fibres).