Cranial Nerve Palsies

Pearls


Muscles Innervated by Cranial Nerves
Cranial Nerve	Muscle(s)	Lesion(s)
Olfactory nerve (CN I)	Sensory	Anosmia (inability to smell), hyposmia (reduced ability to smell), Dysomia, smells become mixed up
Optic nerve (CN II)	Sensory	Scotomas (blind spots) are a defect of vision in a defined area in one or both eyes. Optical neuropathologies show up as a partial or complete loss of vision
Oculomotor nerve (CN III)	Extraocular muscles innervated by CN III are superior rectus (SR) inferior rectus (IR) medial rectus (MR) inferior oblique (IO) Levator palpebrae superioris Ciliary muscle Sphincter pupillae	Diplopia Ptosis Loss of accommodation Pupillary involvement in compressive lesions the pupil becomes dilated and non-reactive in ischemic lesions (e.g., diabetes mellitus) the pupil is spared
Trochlear nerve (CN IV)	Superior oblique	Difficulty looking down Head tilt away from the side of the lesion
Mandibular branch of the trigeminal nerve (CN V3)	Muscles of mastication include masseter temporalis lateral and medial pterygoid Anterior belly of the digastric muscle Mylohyoid muscle Tensor palati Tensor tympani	Jaw deviation towards the side of the lesion
Abducens nerve (CN VI)	Lateral rectus	Horizontal diplopia
Facial nerve (CN VII)	Muscles of facial expression Posterior belly of digastric muscle Stylohyoid muscle Stapedius muscle	Bell's palsy Loss of blink reflex Hyperacusis (when the stapedius is involved)
Vestibulocochlear nerve (CN VIII)	Sensory It divides into the vestibular nerve which is responsible for balance/equilibrium and visual fixation during movement and the cochlear nerve which is responsible for hearing	Deafness, tinnitus, vertigo, dizziness, nausea, nystagmus, loss of balance and ataxia
Glossopharyngeal nerve (CN IX)	Stylopharyngeus muscle	-
Vagus nerve (CN X)	Muscles of the palate and pharynx except tensor palati muscle (CN V3) Stylopharyngeus muscle (CN IX) All muscles of the larynx	Palate droop Dysphagia Deviation of the uvula away from the side of the lesion Loss of gag reflex (the sensory component of this reflex is mostly via CN IX)
Accessory nerve (CN XI)	Sternocleidomastoid muscle Trapezius muscle	Weakness with turning of the head Shoulder droop
Hypoglossal nerve (CN XII)	Muscles of the tongue except for the palatoglossus muscles	Tongue deviation towards the side of the lesion

Osmosis

Picmonic
	There are 12 cranial nerves, which have nuclei located in the tegmentum of the brain stem. These nerves classified as either sensory, motor, or both. Play Video + Quiz
>	Cranial nerve I, also known as the olfactory nerve, is a special sensory nerve that is responsible for the smell. It travels through the olfactory tract and bulbs and exits through the foramina in the cribriform plate of the ethmoid bone. Play Video + Quiz
	CN II, also known as the optic nerve, is a special sensory nerve responsible for vision. It partially decussates in the optic chiasm and exits the cranium through the optic canal. Play Video + Quiz
	CN III, also known as the oculomotor nerve. It is a motor neuron that controls most of the eye's movements, along with accommodation, eyelid opening, and pupillary constriction. Play Video + Quiz
	CN IV, also known as the trochlear nerve. It is a motor nerve that controls the superior oblique extraocular muscle. Play Video + Quiz
	CN V, also known as the trigeminal nerve. CN V is the largest cranial nerve and has both motor and sensory functions. Play Video + Quiz
	CN VI is lso known as the abducens nerve. CN VI controls the lateral rectus extraocular muscle. Play Video + Quiz
	CN VII (Seven) is also known as the facial nerve and it has both motor and sensory functions. It's sensory functions include being responsible for taste from the anterior 2/3 of the tongue. It's motor functions include control of the muscles of facial expression, the stapedius muscle in the middle ear and closing of the eyelid Play Video + Quiz
	CN VIII is a sensory nerve that is also known as the vestibulocochlear nerve. It divides into the vestibular nerve which is responsible for balance/equilibrium and visual fixation during movement and the cochlear nerve which is responsible for hearing. Play Video + Quiz
	CN IX is also known as the glossopharyngeal nerve. It is a motor and sensory nerve that has various functions including swallowing and taste sensation for the posterior 1/3 of the tongue. It is also important for regulation of heart rate via baroreceptors in the carotid sinus and regulation of respiratory drive via chemoreceptors in the carotid body. Play Video + Quiz
	CN X is also known as the vagus nerve. it is a motor, sensory and visceral nerve with several functions such as heart rate regulation, respiratory drive regulation, palate elevation, swallowing and talking. It is clinically assessed by checking for ability to swallow, elevate the palate and maintain a midline uvula. Play Video + Quiz
	CN XI, also known as the accessory nerve. This is a motor nerve that is responsible for head-turning and shoulder shrugging via innervation of the sternocleidomastoid and trapezius muscles. Play Video + Quiz
	CN XII is also known as the hypoglossal nerve. This is a motor nerve that is responsible for tongue movement. It should be noted that unilateral damage will lead to tongue deviation TOWARD the affected side. Play Video + Quiz