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Cranial Nerve Review: Full Breakdown
Cranial Nerves in Order
1. Olfactory (CN I) – Smell
2. Optic (CN II) – Vision
3. Oculomotor (CN III) – Eye movement (SR, IR, MR, IO), pupil constriction, eyelid elevation
4. Trochlear (CN IV) – Eye movement (SO – superior oblique)
5. Trigeminal (CN V) – Facial sensation, mastication
6. Abducens (CN VI) – Eye movement (LR – lateral rectus)
7. Facial (CN VII) – Facial movement, taste (anterior 2/3 tongue), lacrimation, salivation (submandibular, sublingual glands)
8. Vestibulocochlear (CN VIII) – Hearing, balance
9. Glossopharyngeal (CN IX) – Taste (posterior 1/3 tongue), swallowing, salivation (parotid), carotid body/sinus reflex
10. Vagus (CN X) – Autonomic control (heart, lungs, digestion), swallowing, phonation, gag reflex
11. Accessory (CN XI) – Shoulder shrug (trapezius), head turn (SCM)
12. Hypoglossal (CN XII) – Tongue movement
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Rearranged by Function
Cranial Nerves Controlling Eye Movement
• Oculomotor (CN III): Eye movement (SR, IR, MR, IO), pupil constriction, eyelid elevation
• Trochlear (CN IV): Eye movement (SO – superior oblique)
• Abducens (CN VI): Eye movement (LR – lateral rectus)
Cranial Nerves having to do with the tongue
• Hypoglossal (CN XII): Tongue movement
• Glossopharyngeal (CN IX): Taste (posterior 1/3 of tongue), salivation (parotid)
• Facial (CN VII): Taste (anterior 2/3 of tongue), salivation (submandibular, sublingual glands)
Cranial Nerves Involved in Facial & Muscle Movements
• Facial (CN VII): Facial expression, lacrimation, salivation
• Trigeminal (CN V): Facial sensation, mastication
• Accessory (CN XI): Shoulder shrug (trapezius), head turn (SCM)
Cranial Nerves Involved in Swallowing & Speech
• Glossopharyngeal (CN IX): Swallowing, taste, salivation, carotid body reflex
• Vagus (CN X): Swallowing, phonation (voice), autonomic control (heart, lungs, digestion), gag reflex
• Hypoglossal (CN XII): Tongue movement for speech and swallowing
Cranial Nerves for Sensory Perception
• Olfactory (CN I): Smell
• Optic (CN II): Vision
• Vestibulocochlear (CN VIII): Hearing, balance
Glossopharyngeal (CN IX): Taste (posterior 1/3 of tongue), salivation (parotid)
• Facial (CN VII): Taste (anterior 2/3 of tongue), salivation (submandibular, sublingual glands)
What is the primary function of the abducens nerve (CN VI)?
Lateral eye movement (innervates the lateral rectus muscle).
A patient presents with unilateral facial weakness, inability to close the eye, and loss of forehead movement. What is the most likely diagnosis?
Bell’s palsy (CN VII dysfunction).
What test helps differentiate between sensorineural and conductive hearing loss in a patient with suspected CN VIII dysfunction?
Weber and Rinne tests.
A patient’s uvula deviates to the right when they say “ahh.” Which cranial nerve is affected, and on which side?
CN X (Vagus nerve), left side lesion.
Tongue deviation toward the right suggests a lesion in which cranial nerve, and on which side?
CN XII (Hypoglossal nerve), right side lesion.
A 45-year-old man reports difficulty seeing clearly when looking to his right. He says objects appear to overlap, and he sometimes has to turn his head to focus better. On examination, his right eye does not move past the midline when attempting to look right, but all other extraocular movements are intact. Which cranial nerve is most likely affected?
A) Oculomotor nerve (CN III)
B) Trochlear nerve (CN IV)
C) Abducens nerve (CN VI)
D) Optic nerve (CN II)
A) Oculomotor nerve (CN III) is incorrect. CN III controls most eye movements but does not primarily abduct the eye. Dysfunction would also cause ptosis and pupillary abnormalities.
B) Trochlear nerve (CN IV) is incorrect. CN IV dysfunction affects the superior oblique muscle and causes vertical misalignment, making it difficult to look down, especially when descending stairs.
C) Abducens nerve (CN VI) is correct. CN VI controls the lateral rectus muscle, which moves the eye laterally. Dysfunction leads to limited abduction, as seen in this patient.
D) Optic nerve (CN II) is incorrect. CN II is responsible for vision, not eye movement. Dysfunction would present as visual field loss or decreased acuity, not difficulty with lateral gaze.
A 32-year-old woman develops sudden-onset right-sided facial weakness. She is unable to raise her right eyebrow, close her right eye completely, or smile symmetrically. She denies limb weakness or sensory loss. There are no vesicles in her ear. What is the most appropriate initial treatment?
A) Prednisone within 72 hours
B) Acyclovir and prednisone
C) MRI of the brain
D) IV ceftriaxone
• A) Prednisone within 72 hours: Correct – Bell’s palsy (peripheral CN VII dysfunction) is treated with corticosteroids if started early.
• B) Acyclovir and prednisone: Incorrect – This is used for Ramsay Hunt syndrome (herpes zoster oticus), but the absence of vesicles makes this diagnosis unlikely.
• C) MRI of the brain: Incorrect – MRI is indicated if there are red flags for central causes (e.g., forehead sparing, other neurological deficits).
• D) IV ceftriaxone: Incorrect – This is used for neuroborreliosis (Lyme disease) when facial palsy occurs with systemic symptoms, but there is no mention of tick exposure or travel to endemic areas.
A 55-year-old man complains of progressive hearing loss in his left ear over the past several months. He also notes occasional imbalance but denies vertigo or tinnitus. Weber test lateralizes to the right ear, and Rinne test shows air conduction greater than bone conduction bilaterally. What is the most likely diagnosis?
A) Meniere’s disease
B) Vestibular neuritis
C) Acoustic neuroma (vestibular schwannoma)
D) Otosclerosis
A) Meniere’s disease is incorrect. Meniere’s presents with episodic vertigo, tinnitus, and fluctuating hearing loss, none of which are described here.
B) Vestibular neuritis is incorrect. This condition typically causes acute vertigo without hearing loss. The progressive nature of the symptoms suggests a structural lesion rather than a transient vestibular dysfunction.
C) Acoustic neuroma (vestibular schwannoma) is correct. Unilateral sensorineural hearing loss with imbalance is classic for an acoustic neuroma. The slow progression and lack of vertigo support a tumor rather than an acute process.
D) Otosclerosis is incorrect. Otosclerosis causes conductive hearing loss, which would show bone conduction greater than air conduction on Rinne test. This patient has sensorineural hearing loss.
A 63-year-old man presents with difficulty swallowing and changes in his voice over the past month. He describes his voice as “hoarse” and states that he occasionally chokes on liquids. On examination, his uvula deviates to the right when he says “ahh.” Which of the following findings would most likely be present?
A) Deviation of the tongue to the right
B) Loss of the gag reflex on the left
C) Weakness of the right trapezius muscle
D) Increased deep tendon reflexes on the left
A) Deviation of the tongue to the right is incorrect. Tongue deviation occurs with hypoglossal nerve (CN XII) dysfunction. This patient’s uvula deviation suggests vagus nerve (CN X) involvement instead.
B) Loss of the gag reflex on the left is correct. The glossopharyngeal nerve (CN IX) provides sensory innervation to the gag reflex, while the vagus nerve (CN X) controls the motor response. A left-sided CN IX or X lesion would result in loss of the gag reflex on that side and uvula deviation to the right.
C) Weakness of the right trapezius muscle is incorrect. The spinal accessory nerve (CN XI) controls the trapezius and sternocleidomastoid muscles, but it does not affect the uvula or swallowing.
D) Increased deep tendon reflexes on the left is incorrect. Upper motor neuron lesions can cause hyperreflexia, but cranial nerve lesions do not directly cause asymmetric reflex changes in the limbs.
A 50-year-old woman presents with progressive difficulty speaking and swallowing over the past two months. She reports occasional choking on liquids and slurred speech. On examination, her tongue exhibits atrophy and fasciculations, and it deviates to the right when protruded. Reflexes in her upper and lower extremities are brisk, and she has mild weakness in her right hand. Which of the following is the most appropriate next step in management?
A) MRI brainstem to evaluate for stroke
B) Electromyography and nerve conduction studies
C) High-dose corticosteroids
D) Lumbar puncture for CSF analysis
A) MRI brainstem to evaluate for stroke is incorrect. While brainstem strokes can cause cranial nerve deficits, the progressive nature of symptoms over months and the presence of upper and lower motor neuron signs (hyperreflexia, atrophy, fasciculations) suggest a neurodegenerative disorder rather than an acute vascular event.
B) Electromyography and nerve conduction studies is correct. This patient’s presentation with progressive bulbar dysfunction (CN IX, X, XII involvement), tongue fasciculations, and upper motor neuron findings is highly suggestive of amyotrophic lateral sclerosis (ALS). EMG and NCS are the best next steps for confirming the diagnosis.
C) High-dose corticosteroids is incorrect. Corticosteroids are used in inflammatory conditions like Guillain-Barré syndrome or multiple sclerosis, but they are not beneficial in ALS.
D) Lumbar puncture for CSF analysis is incorrect. LP is useful in cases of suspected infection, inflammatory disorders, or Guillain-Barré syndrome, but it is not indicated in ALS diagnosis.