Cranial Nerves
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Description
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There are 12 pairs of cranial nerves and they are numbered according to their position of where they originate in the brainstem. The names of the cranial nerves (CN) are: CN I - olfactory, CN II - optic, CN III - oculomotor, CN IV - trochlear, CN V - trigeminal, CN VI - abducens, CN VII - facial, CN VIII - vestibulocochlear, CN IX - glossopharyngeal, CN X - vagus, CN XI - accessory, and CN XII - hypoglossal. [1] Link: Introduction to Neuroanatomy
Function[edit | edit source]
The names of the cranial nerves sometimes correspond with their individual function. The cranial nerves are comprised of axons that are either sensory, motor or both. [1]
Cranial Nerve | Sensory Function | Somatic Motor Function | Autonomic (parasympathetic motor) Function |
---|---|---|---|
CN I - olfactory |
Smell (olfaction) |
- |
- |
CN II - optic |
Vision |
- |
- |
CN III - oculomotor |
- |
Innervates the inferior oblique muscle and medial, inferior, and superior rectus muscles of the eye (move the eye); levator palpebrae superioris muscle (elevate eyelid) |
Innervates the sphincter pupillae muscle (constricts the pupil), and the ciliary muscle (accomodate the eye for near vision) |
CN IV - trochlear |
- |
Innervate the superior oblique eye muscle (moves the eye inferiorly and laterally) |
- |
CN V - trigeminal |
Conducts touch, temperature and pain sensation from the face, nose, mouth, nasal and oral mucosa, anterior two-thirds of tongue, and anterior scalp; part of auricle of the ear |
Innervate the muscles of mastication, mylohyoid, digastric (anterior belly), tensor veli palatini, and tensor tympani |
- |
CN VI - abducens |
- |
Innervate the lateral rectus muscle of eye (abducts the eye) |
- |
CN VII - facial |
Taste from anterior two-thirds of tongue |
Innervate muscles of facial expression, digastric (posterior belly) and stapedius muscle |
Increase secretion from the lacrimal (tear glands) and nasal mucosal glands; submandibular and sublingual salivary glands |
CN VIII - vestibulocochlear |
Hearing (cochlear branch); linear and angular acceleration, or head position in space/equilibrium (vestibular branch) |
- |
- |
CN IX - glossopharyngeal |
Touch and taste from the posterior 1/3 of the tongue; visceral sensory from the carotid bodies |
Innervate the pharyngeal muscle |
Increase secretion from the parotid salivary gland |
CN X - vagus |
Visceral sensation (excluding pain) from heart, lungs, abdominal organs, bronchi, trachea, larynx, pharynx, gastrointestinal tract to level of descending colon General sensation from the external acoustic meatus, eardrum, and pharynx |
Innervates pharyngeal and laryngeal muscles and muscles at base of tongue |
Innervates smooth muscle an glands of the heart, lungs larynz trachea, and most abdominal organs |
CN XI - accessory |
- |
Innervates the trapezius and sternocleidomastoid muscle |
- |
CN XII - hypoglossal |
- |
Innervates intrinsic and extrinsic tongue muscles |
- |
Clinical Relevance and Assessment [3][4][edit | edit source]
Cranial Nerve |
Examination |
Involvement |
---|---|---|
CN I - olfactory |
- Test sense of smell using by closing the other nostril and using non-irritating odors like coffee, lemon oil, etc |
- Inability to detect smells (Anosmia) = frontal lobe lesions |
CN II - optic |
- Test visual acuity using a Snellen chart, test central and peripheral vision |
- Blindness, impaired vision: far (myopia) and near (presbyopia) |
CN II – optic CN III – oculomotor |
- Test pupil equality, size and shape - Test pupil constriction by shining a light in the eye |
- Absence of pupil constriction - Unequal pupils (anisocoria) - Horner’s syndrome - CN III paralysis |
CN III – oculomotor CN IV – trochlea CN VI - abducens |
- Test extraocular movements - Observe eye position, presence of strabismus (loss of ocular alignment) or ptosis of eyelid - Test pursuit eye movement without head movement |
- Strabismus and impaired eye movement - CN III: Ptosis, pupil dilation - CN IV: Eye cannot look down when adducted - CN VI: Eye pulled inward, eye cannot look out |
CN V - trigeminal |
- Pain and light touch sensation of face (forehead, cheeks, jaw) - Open and close jaw against resistance - Test corneal and jaw jerk reflex |
- Loss of facial sensation and numbness - Loss of ipsilateral corneal reflex - Weakness and wasting of mastication muscles - Jaw deviation when opened to ipsilateral side |
CN VII - facial |
- Test motor function of the facial muscles and look for asymmetry: raise eyebrows, frown, smile, close eyes tightly, puff cheeks, etc. |
- Ipsilateral paralysis of facial muscles: unable to close eye, mouth corner droops, difficulty with speech articulation = peripheral nerve injury (PNI) Bell’s Palsy (CN VII); or facial paralysis due to stroke |
CN VIII - vestibulocochlear |
- Test balance - Gaze instability with head rotations - Test auditory acuity with a tuning fork placed in the middle on top of the head and check if the sound is equal or louder in one ear (Weber’s test) - Vibrating tuning fork place on mastoid bone, then near the ear canal and note hearing acuity (Rinne’s test) |
- Vertigo and disequilibrium - Nystagmus - Deafness, tinnitus and hearing loss - Unilateral conductive loss - Sensorineural loss: sound heard in good ear - Conductive loss: sound heard through bone is longer or equal than air - Sensorineural loss: sound heard longer through air |
CN IX – glossopharyngeal CN X - vagus |
- Listen to voice quality - Test for difficulty swallowing - Let the patient say “ah” and observe the soft palate elevating and that the uvula remain in midline - Examine the gag reflex |
- Dysphonia - Dysphagia - With paralysis the palate does not elevate (lesion CN V), unilateral paralysis there is asymmetrical elevation - Absent gag reflex (lesion CN IX, possibly X) |
CN XI - accessory |
- Examine muscle bulk - Test Trapezius and Sternocleidomastoid muscles against resistance |
- Atrophy, fasciculations, weakness PNI: shoulder droops and unable to shrug ipsilateral shoulder - Unable to turn the head to the contralateral side |
CN XII - hypoglossal |
- Examine protruded tongue: rapid side-to-side movements - Examine the tongue’s resting position - Listen to the patient’s word articulations |
- Movement impairment: deviation to weak side - Atrophy or tongue fasciculations - Dysartrhia (CN X or XII lesions) |
See also[edit | edit source]
- Moebius Syndrome
- Temporomandibular Disorders
- Acoustic Neuroma
- Migraine Headache
- Ramsay Hunt Syndrome
- Trigeminal Neuralgia
- Cervicogenic Headache
- Sturge-Weber Syndrome
- Synkinesis
References[edit | edit source]
- ↑ 1.0 1.1 1.2 McKinley M, O'Loughlin VD. Human Anatomy. 2nd ed. New York: McGraw-Hill, 2008fckLRfckLRHill C. Practical guidelines for cystic fibrosis care. Edinburgh: Churchill Livingstone, 1998.
- ↑ Fuller KS, Introduction to Central Nervous System Disorders. Goodman CC, Fuller KS. Pathology: implications for the physical therapist. Elsevier Health Sciences; 2014. p1371-1404
- ↑ O'Sullivan SB, Neuromuscular Physical Therapy. In: O'Sullivan SB, Siegman RP. National Physical Therapy Examination Review & Study Guide. 19th edit. Evanston: TherapyEd, 2016. p121-184
- ↑ Chui KK, Schmitz TJ. Examination in Sensory Function. In: Physical Rehabilitation. 6th Edit. Philadelphia: O’Sullivan SB, Schmitz TJ, Fulk GD F.A. Davis Company, 2014. P87-121