Recall basic cranial nerve anatomy. There are 12 cranial nerves.

• CN I – Olfactory nerve – the shortest cranial nerve passes special sensory information (smell) to the forebrain, entering the skull through the cribriform plate of the ethmoid bone. Damage can lead to the loss of smell (anosmia), abnormal smell (parosmia), or loss of taste.

• CN II – Optic nerve – passes special sensory information (sight) from the retina through the optic foramen in the sphenoid bone to the optic chiasma (partial decussation), to the visual cortex. CN I and II are not associated with the brainstem.

• CN III, IV, VI – Oculomotor, Trochlear, and Abducens nerves – sends motor function through the superior orbital fissure to control ocular movement. CN III and IV emerge from the midbrain, VI from the pons. CN III contains parasympathetic (GVE) fibers that lead to pupil constriction and accommodation.

• CN VII – Facial nerve – sends motor function from the pons, through the internal auditory canal in the temporal bone and out the stylomastoid foramen, to the muscles of facial expression. There are 5 main branches (temporal, zygomatic, buccal, mandibular, cervical). Damage to the facial may cause facial (Bell’s) palsy. The nerve gives rise to chorda tympani, which supplies taste to the anterior two thirds of the tongue (joining the lingual nerve branch of V3), and synapses with the submandibular ganglion leading to parasympathetic stimulation of the submandibular and sublingual salivary glands. The greater petrosal branch provides parasympathetic innervation to several glands (nasal, palatine, lacrimal, pharyngeal) and paranasal sinuses (sphenoid, frontal, maxillary, ethmoid, nasal), and taste to the palate via the greater and lesser palatine nerves.

• CN VIII – Vestibulocochlear nerve – special sensory information (balance and hearing) from the vestibular system (vestibules and semicircular canals) and cochlea, through the internal auditory canal, to the pons. Damage can lead to vertigo and hearing loss. 

• CN IX – Glossopharyngeal nerve – transmits sensory from the upper pharynx and the posterior third of the tongue (including circumvallate papillae), through the jugular foramen, to the upper medulla. It also transmits taste from the posterior third of the tongue, and supplies motor function to the stylopharyngeus muscle. CN IX provides parasympathetic innervation of the parotid gland via the otic ganglion (tympanic branch synapses with the auriculotemporal branch of V3).

• CN X – Vagus nerve – provides sensory and parasympathetic supply to structures in the neck and also to most of the organs in the chest and abdomen. Sensory supply to the area near the epiglottis via the internal laryngeal nerve. Involved in vasovagal (reflex) syncope. Travels through the jugular foramen along with IX and XI.

• CN XII – The hypoglossal nerve – motor function,  innervates all the extrinsic and intrinsic muscles of the tongue, except for the palatoglossus which is innervated by the vagus nerve. Travels through the hypoglossal canal to the medulla. If lower motor neurons (below hypoglossal nucleus in the medulla) are damaged the tongue will deviate to the ipsilateral (affected) side when protruded. In the case of an upper motor neuron lesion (above hypoglossal nucleus in the medulla, e.g motor cortex) the tongue will deviate to the contralateral (opposite) side when protruded. Muscular atrophy will occur on the affected side. Paralysis of the genioglossus muscle will allow the tongue to fall back and potentially block the airway.