Function: Special sensory (smell)
Innervation: Olfactory epithelium (nasal cavity)
Clinical Assessment:
Ask the patient to identify familiar odors (e.g., coffee, peppermint) with each nostril separately.
Potential Dysfunction:
Anosmia (loss of smell) – Can result from trauma, viral infections, neurodegenerative diseases (e.g., Parkinson’s, Alzheimer’s).
Function: Special sensory (vision)
Innervation: Retina of the eye
Clinical Assessment:
Visual acuity test (Snellen chart)
Visual field testing (confrontation test)
Fundoscopic exam (examine retina and optic disc)
Potential Dysfunction:
Blindness or visual field defects – Optic neuritis (multiple sclerosis), glaucoma, stroke, optic chiasm tumors (e.g., pituitary adenoma).
Function:
Somatic motor – Eye movement (superior, inferior, and medial rectus; inferior oblique; levator palpebrae superioris).
Autonomic (parasympathetic) motor – Pupil constriction (sphincter pupillae) and lens accommodation (ciliary muscle).
Clinical Assessment:
Pupil reaction to light (direct and consensual response).
Accommodation test (near response).
Extraocular movements (test all directions except lateral and downward diagonal).
Potential Dysfunction:
Ptosis (drooping eyelid), dilated pupil, impaired eye movements (down and out position) – Seen in oculomotor nerve palsy (e.g., diabetes, aneurysm, herniation).
Function: Somatic motor (superior oblique muscle – depresses and intorts the eye)
Clinical Assessment:
Have the patient look down and in (toward the nose).
Potential Dysfunction:
Vertical diplopia (double vision), head tilt to compensate – Seen in trochlear nerve palsy (e.g., trauma, congenital, stroke).
Function:
General sensory – Face, scalp, cornea, oral/nasal mucosa.
Somatic motor – Muscles of mastication (chewing).
Clinical Assessment:
Facial sensation (test ophthalmic, maxillary, mandibular branches).
Corneal reflex (blink when touching cornea).
Jaw movement (clench teeth and move jaw against resistance).
Potential Dysfunction:
Trigeminal neuralgia (severe facial pain), loss of facial sensation, weak jaw movement.
Function: Somatic motor (lateral rectus muscle – abducts the eye)
Clinical Assessment:
Test lateral eye movement.
Potential Dysfunction:
Diplopia, inability to abduct eye (eye turns inward) – Common in increased intracranial pressure, diabetes, stroke.
Function:
Somatic motor – Facial expressions.
Autonomic (parasympathetic) motor – Lacrimal, submandibular, and sublingual glands.
Special sensory – Taste (anterior 2/3 of tongue).
Clinical Assessment:
Ask patient to raise eyebrows, smile, frown, and puff cheeks.
Test taste on anterior tongue.
Potential Dysfunction:
Bell’s palsy (facial weakness, loss of taste, dry eyes/mouth, inability to close eye) – Can be due to viral infection (e.g., herpes simplex).
Function:
Special sensory (hearing) – Cochlear branch.
Special sensory (balance and equilibrium) – Vestibular branch.
Clinical Assessment:
Hearing tests (Rinne and Weber tests).
Balance and coordination tests (Romberg test).
Potential Dysfunction:
Hearing loss (sensorineural), vertigo, nystagmus, tinnitus – Common in Ménière’s disease, acoustic neuroma.
Function:
Special sensory – Taste (posterior 1/3 of tongue).
General sensory – Pharynx, tonsils, middle ear.
Autonomic motor – Parotid salivary gland.
Clinical Assessment:
Test gag reflex (along with CN X).
Potential Dysfunction:
Dysphagia (difficulty swallowing), loss of taste posterior tongue – Seen in stroke, brainstem lesions.
Function:
Somatic motor – Pharyngeal and laryngeal muscles (swallowing, voice).
Autonomic motor – Heart, lungs, digestive tract.
General sensory – External ear, larynx, pharynx.
Clinical Assessment:
Say "ahh" and observe uvula movement (should rise symmetrically).
Test gag reflex.
Potential Dysfunction:
Hoarseness, difficulty swallowing, asymmetric uvula deviation (away from lesion) – Seen in stroke, vagus nerve damage.
Function: Somatic motor (sternocleidomastoid and trapezius muscles)
Clinical Assessment:
Shrug shoulders against resistance.
Turn head against resistance.
Potential Dysfunction:
Weak shoulder shrug, weak head turning – Seen in trauma, spinal cord injury.
Function: Somatic motor (tongue muscles)
Clinical Assessment:
Stick out tongue and observe for deviation.
Potential Dysfunction:
Tongue deviates toward side of lesion – Seen in stroke, hypoglossal nerve palsy.
Case 1: Loss of Smell After Head Trauma
Symptoms: Inability to smell coffee or peppermint, no nasal congestion.
Likely Affected Nerve: Cranial Nerve I (Olfactory Nerve)
Possible Causes: Head trauma (shearing of olfactory nerve fibers), viral infection, neurodegenerative diseases (e.g., Parkinson’s, Alzheimer’s).
Case 2: Sudden Loss of Vision in One Eye
Symptoms: Blurry vision, no pupillary response in the affected eye, intact extraocular movements.
Likely Affected Nerve: Cranial Nerve II (Optic Nerve)
Possible Causes: Optic neuritis (multiple sclerosis), ischemic optic neuropathy, retinal detachment.
Case 3: Drooping Eyelid and "Down and Out" Eye
Symptoms: Ptosis (drooping eyelid), eye deviated downward and outward, pupil dilation, difficulty with accommodation.
Likely Affected Nerve: Cranial Nerve III (Oculomotor Nerve)
Possible Causes: Diabetes mellitus, aneurysm (posterior communicating artery), uncal herniation.
Case 4: Head Tilt and Vertical Diplopia (Double Vision)
Symptoms: Trouble looking down while reading, tilts head to opposite side to compensate.
Likely Affected Nerve: Cranial Nerve IV (Trochlear Nerve)
Possible Causes: Head trauma, congenital palsy, microvascular ischemia.
Case 5: Facial Numbness and Weak Jaw Movement
Symptoms: Loss of sensation on the forehead, cheek, and jaw; weak jaw movement; absent corneal reflex.
Likely Affected Nerve: Cranial Nerve V (Trigeminal Nerve)
Possible Causes: Trigeminal neuralgia, stroke, tumor (acoustic neuroma, meningioma).
Case 6: Eye Unable to Move Laterally
Symptoms: Diplopia when looking to the side, inability to abduct the affected eye.
Likely Affected Nerve: Cranial Nerve VI (Abducens Nerve)
Possible Causes: Increased intracranial pressure (hydrocephalus, brainstem tumor), stroke, diabetes.
Case 7: Facial Droop and Inability to Close Eye on One Side
Symptoms: Half of face paralyzed, inability to close eye, loss of taste on the front of the tongue, drooling.
Likely Affected Nerve: Cranial Nerve VII (Facial Nerve)
Possible Causes: Bell’s palsy (viral), stroke (if only lower face affected), parotid gland tumor.
Case 8: Hearing Loss and Ringing in One Ear
Symptoms: Progressive hearing loss in one ear, tinnitus, imbalance, dizziness.
Likely Affected Nerve: Cranial Nerve VIII (Vestibulocochlear Nerve)
Possible Causes: Acoustic neuroma (vestibular schwannoma), Ménière’s disease, ototoxic drugs.
Case 9: Difficulty Swallowing and Absent Gag Reflex
Symptoms: Trouble swallowing, choking on liquids, absent gag reflex, hoarse voice.
Likely Affected Nerve: Cranial Nerve IX (Glossopharyngeal Nerve) and Cranial Nerve X (Vagus Nerve)
Possible Causes: Stroke, brainstem lesion, Guillain-Barré syndrome.
Case 10: Hoarseness, Difficulty Swallowing, and Uvula Deviation
Symptoms: Hoarse voice, difficulty swallowing, uvula deviates away from the affected side.
Likely Affected Nerve: Cranial Nerve X (Vagus Nerve)
Possible Causes: Medullary stroke, vagus nerve damage, surgery complications.
Case 11: Weak Shoulder Shrug and Difficulty Turning Head
Symptoms: Weakness in shrugging the shoulder on one side, difficulty turning head to opposite side.
Likely Affected Nerve: Cranial Nerve XI (Accessory Nerve)
Possible Causes: Neck trauma, surgery (e.g., radical neck dissection), tumor.
Case 12: Tongue Deviation When Sticking It Out
Symptoms: Tongue deviates to one side when protruded, difficulty with speech and swallowing.
Likely Affected Nerve: Cranial Nerve XII (Hypoglossal Nerve)
Possible Causes: Stroke, brainstem tumor, ALS (amyotrophic lateral sclerosis).