Cranial nerves

Cranial nerves

The table below lists the major characteristics of the 12 cranial nerves:

Nerve	Functions	Clinical	Pathway/foramen
I (Olfactory)	Smell		Cribriform plate
II (Optic)	Sight		Optic canal
III (Oculomotor)	Eye movement (MR, IO, SR, IR) Pupil constriction Accomodation Eyelid opening	Palsy results in ptosis 'down and out' eye dilated, fixed pupil	Superior orbital fissure (SOF)
IV (Trochlear)	Eye movement (SO)	Palsy results in defective downward gaze → vertical diplopia	SOF
V (Trigeminal)	Facial sensation Mastication	Lesions may cause: trigeminal neuralgia loss of corneal reflex (afferent) loss of facial sensation paralysis of mastication muscles deviation of jaw to weak side	V1: SOF, V2: Foramen rotundum, V3: Foramen ovale
VI (Abducens)	Eye movement (LR)	Palsy results in defective abduction → horizontal diplopia	SOF
VII (Facial)	Facial movement Taste (anterior 2/3rds of tongue) Lacrimation Salivation	Lesions may result in: flaccid paralysis of upper + lower face loss of corneal reflex (efferent) loss of taste hyperacusis	Internal auditory meatus
VIII (Vestibulocochlear)	Hearing, balance	Hearing loss Vertigo, nystagmus Acoustic neuromas are Schwann cell tumours of the cochlear nerve	Internal auditory meatus
IX (Glossopharyngeal)	Taste (posterior 1/3rd of tongue) Salivation Swallowing Mediates input from carotid body & sinus	Lesions may result in; hypersensitive carotid sinus reflex loss of gag reflex (afferent)	Jugular foramen
X (Vagus)	Phonation Swallowing Innervates viscera	Lesions may result in; uvula deviates away from site of lesion loss of gag reflex (efferent)	Jugular foramen
XI (Accessory)	Head and shoulder movement	Lesions may result in; weakness turning head to contralateral side	Jugular foramen
XII (Hypoglossal)	Tongue movement	Tongue deviates towards side of lesion	Hypoglossal canal

Some cranial nerves are motor, some sensory and some are both. The most useful mnemonic is given below.

CN I ----------------------------------------------------------------------→XII

Some Say Marry Money But My Brother Says Big Brains Matter Most

S = Sensory, M = Motor, B = Both

Image sourced from Wikipedia

View from the inferior surface of the brain showing the emergence of the cranial nerves

Image sourced from Wikipedia

Diagram showing the nuclei of the cranial nerves in the brainstem

Cranial nerve reflexes

Reflex	Afferent limb	Efferent limb
Corneal	Ophthalmic nerve (V1)	Facial nerve (VII)
Jaw jerk	Mandibular nerve (V3)	Mandibular nerve (V3)
Gag	Glossopharyngeal nerve (IX)	Vagal nerve (X)
Carotid sinus	Glossopharyngeal nerve (IX)	Vagal nerve (X)
Pupillary light	Optic nerve (II)	Oculomotor nerve (III)
Lacrimation	Ophthalmic nerve (V1)	Facial nerve (VII)

Posted in: Notes : Neuroscience