CRANIAL NERVES – BASIC OVERVIEW WITH THEIR FUNCTION

The cranial nerves are those nerves which emerge directly from the brain and brainstem. There are twelve pairs of cranial nerves. They serve as crucial links between the brain and various parts of the body, primarily head and neck regions. They are responsible for essential functions such as vision, taste, hearing, smell, facial sensation and movement.

The cranial nerves emerge from the central nervous system above the level of the first vertebra. They are named and numbered in a cranio-caudal sequence with respect to their attachment to the brain. They are designated with roman numerals ( I – XII ). Cranial nerves I and II emerge from the cerebrum and rest ten pairs emerge from the brainstem.

NAMES OF CRANIAL NERVES

• I – OLFACTORY
• II – OPTIC
• III – OCULOMOTOR
• IV – TROCHLEAR
• V – TRIGEMINAL
• VI – ABDUCENT
• VII – FACIAL
• VIII – VESTIBULOCOCHLEAR
• IX – GLOSSOPHARYNGEAL
• X – VAGUS
• XI – ACCESSORY
• XII – HYPOGLOSSAL

Motor – III, IV, VI, XI and XII.

Sensory – I, II and VIII.

Mixed – V, VII, IX and X.

NUCLEI OF CRANIAL NERVES

• Midbrain – Has nuclei of cranial nerves III and IV.
• Pons – Has nuclei of cranial nerves V, VI, VII and VIII.
• Medulla – Has nuclei of cranial nerves IX, X, XI and XII.

Cranial nerves I and II lack nuclei. The first cranial nerve arises from olfactory bulb and second from the lateral colliculus.

CRANIAL NERVES EXIT FROM THE SKULL

• I – Cribriform plate
• II – Optic foramen
• III, IV, VI and ophthalmic division of V – Superior orbital fissure
• Maxillary division of V – Foramen rotundum
• Mandibular division of V – Foramen ovale
• VII – Stylomastoid foramen
• VIII – Internal auditory canal
• IX, X, XI – Jugular foramen
• XII – Hypoglossal canal

FUNCTIONS OF CRANIAL NERVES

CRANIAL NERVE	SENSORY FUNCTION	MOTOR FUNCTION	AUTONOMIC FUNCTION	FUNCTION
I – Olfactory	Smell	–	–	Sensory
II – Optic	Vision	–	–	Sensory
III – Oculomotor	–	Facilitates movement of eyeball. (Innervates inferior oblique, medial rectus, superior rectus, inferior rectus). It also innervates levator palpebrae superioris muscle which elevates eyelid.	Supplies sphincter pupillae muscle causing constriction of pupil and ciliary muscle which helps in accomodation of eye in near vision	Motor
IV – Trochlear	–	Innervates superior oblique muscle of eye responsible for ocular movement	–	Motor
V – Trigeminal	Carries sensation of touch, temperature and pain from face, mouth, nose, nasal mucosa, oral mucosa, anterior two-thirds of tongue, anterior scalp and part of auricle of ear.	Innervates the muscles of mastication, mylohyoid, anterior belly of digastric, tensor veli palatini and tensor tympani.	–	Both sensory and motor
VI – Abducens	–	Supplies lateral rectus muscle which abducts the eye,	–	Motor
VII – Facial	Carries sensation of taste from anterior two-thirds of tongue.	Innervates muscles of facial expression, posterior belly of digastric, stylohyoid and stapedius muscle.	Provides secretory fibers to lacrimal gland, nasal mucosal glands, submandibular and sublingual glands.	Both sensory and motor.
VIII – Vestibulocochlear	Sense of hearing (cochlear branch); maintenance of equilibrium (vestibular branch).	–	–	Sensory
IX – Glossopharyngeal	Carries sensation of touch and taste from posterior one-third of tongue. Visceral sensory from carotid sinus and bodies.	Innervates stylopharyngeus	Increases secretion from parotid salivary gland.	Both sensory and motor
X – Vagus	Visceral sensation (except pain) from heart, lungs, abdominal organs, trachea, bronchi, larynx, pharynx and gastrointestinal tract to the level of descending colon. General sensation from external auditory canal, eardrum and pharynx. Taste from posterior most part of tongue.	Innervates muscles of pharynx, larynx and muscles at base of tongue.	Supplies smooth muscles and glands of heart, lungs, larynx, trachea and most abdominal organs.	Both sensory and motor.
XI – Accessory	–	Supplies trapezius and sternocleidomasto-id muscle.	–	Motor
XII – Hypoglossal	–	Innervates intrinsic and extrinsic muscles of tongue.	–	Motor