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Questions and Answers
Which cranial nerve is responsible for the motor component of mastication?
Which cranial nerve is responsible for the motor component of mastication?
What type of reflex is tested by the corneal reflex?
What type of reflex is tested by the corneal reflex?
Which test is used to assess conduction and sensorineural hearing loss?
Which test is used to assess conduction and sensorineural hearing loss?
Which function is typically impaired in a Bell’s Palsy patient?
Which function is typically impaired in a Bell’s Palsy patient?
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What is indicated by the ability to raise eyebrows in a patient with facial weakness?
What is indicated by the ability to raise eyebrows in a patient with facial weakness?
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What is the expected finding when performing Rinne’s test on a normal patient?
What is the expected finding when performing Rinne’s test on a normal patient?
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Which cranial nerve is responsible for gag reflex and taste sensation in the posterior third of the tongue?
Which cranial nerve is responsible for gag reflex and taste sensation in the posterior third of the tongue?
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In a patient who shows uvula deviation to the left upon saying 'Ahhhh', which side is likely affected by the lesion?
In a patient who shows uvula deviation to the left upon saying 'Ahhhh', which side is likely affected by the lesion?
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What function does the Accessory nerve (XI) primarily control?
What function does the Accessory nerve (XI) primarily control?
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What clinical feature suggests a lower motor neuron lesion of the Hypoglossal nerve (XII)?
What clinical feature suggests a lower motor neuron lesion of the Hypoglossal nerve (XII)?
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Which statement about the Oculomotor nerve (III) is correct?
Which statement about the Oculomotor nerve (III) is correct?
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Which cranial nerve is most likely affected in a patient experiencing double vision due to muscle weakness?
Which cranial nerve is most likely affected in a patient experiencing double vision due to muscle weakness?
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Which cranial nerve palsy often results in a ptosis (drooping eyelid) and mydriasis (dilated pupil)?
Which cranial nerve palsy often results in a ptosis (drooping eyelid) and mydriasis (dilated pupil)?
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What is the primary function of the Oculomotor nerve?
What is the primary function of the Oculomotor nerve?
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Which cranial nerve is solely responsible for controlling the superior oblique muscle?
Which cranial nerve is solely responsible for controlling the superior oblique muscle?
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Which condition could lead to a lesion of the Abducens nerve?
Which condition could lead to a lesion of the Abducens nerve?
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What is a typical symptom of a Trochlear nerve lesion?
What is a typical symptom of a Trochlear nerve lesion?
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Which cranial nerve palsy is associated with increased intracranial pressure?
Which cranial nerve palsy is associated with increased intracranial pressure?
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Which of the following cranial nerves is involved in both sensory and motor functions?
Which of the following cranial nerves is involved in both sensory and motor functions?
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What is the primary role of the Abducens nerve?
What is the primary role of the Abducens nerve?
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Which medical condition is most commonly associated with Oculomotor nerve palsy?
Which medical condition is most commonly associated with Oculomotor nerve palsy?
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The Trochlear nerve is unique among cranial nerves because it is the only one that emerges from which part of the brain?
The Trochlear nerve is unique among cranial nerves because it is the only one that emerges from which part of the brain?
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What compensatory measure might a person take if they have a unilateral lesion of the Trochlear nerve?
What compensatory measure might a person take if they have a unilateral lesion of the Trochlear nerve?
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Which cranial nerve is primarily responsible for the sense of smell?
Which cranial nerve is primarily responsible for the sense of smell?
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Which cranial nerves have both sensory and motor functions?
Which cranial nerves have both sensory and motor functions?
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What is a common symptom of an Abducens nerve lesion?
What is a common symptom of an Abducens nerve lesion?
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What can lead to a combined lesion of cranial nerves III, IV, and VI?
What can lead to a combined lesion of cranial nerves III, IV, and VI?
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Which cranial nerve is responsible for the movement of the eye inward?
Which cranial nerve is responsible for the movement of the eye inward?
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Study Notes
Cranial Nerves
- There are 12 pairs of cranial nerves.
- The cranial nerves are numbered I to XII.
- They are named after the Roman numerals.
- They help with motor, sensory and parasympathetic functions in the head and neck.
Mnemonic Devices
- There are two common mnemonic devices to remember the cranial nerves in order:
- "On Occasion Our Trusty Truck Acts Funny, Very Good Vehicle Any How"
- "Some Say Marry Money But My Brother Says Big Brains Matter More"
Cranial Nerve I: Olfactory
- Function: Sensory - Smell.
- Location: Attached directly to the forebrain.
- Associated: Closely associated with the Limbic system.
Cranial Nerve II: Optic
- Function: Sensory- Vision.
- Location: Attached directly to the forebrain.
- Role: Transmit impulses from the retina to the brain.
- Testing:
- Visual field testing.
- Colour vision (Ishihara test).
- Visual acuity (Snellen chart).
- Papillary response.
Cranial Nerves III, IV and VI
- These cranial nerves all play a role in eye movement.
- They innervate the extrinsic muscles of the eye.
Cranial Nerve III: Oculomotor
- Function:
- Motor innervation of extrinsic eye muscles (raising eyelid).
- Parasympathetic innervation of intrinsic eye muscles (pupillary constriction and accommodation).
- Cranial III palsy:
- Uncommon.
- Risk of mortality/morbidity depends on underlying cause.
- Causes:
- Direct trauma.
- Demyelinating disease (Multiple Sclerosis - MS).
- Increased intracranial pressure (space-occupying lesion or spontaneous subarachnoid haemorrhage).
- Microvascular disease (diabetes or giant cell arteritis).
Cranial Nerve IV: Trochlear
- Function: Motor nerve.
- Role: Innervates the superior oblique muscle (lateral/inferior gaze).
- Only cranial nerve to emerge from the dorsal aspect of the brain stem.
- Single IV lesion: Rare.
- Common cause: Trauma to the orbit.
- Signs of a single IV lesion:
- Diplopia (double vision) due to weakness of downward and inward eye movement.
- Compensatory tilting of the head away from the affected side.
Cranial Nerve VI: Abducens
- Function: Motor nerve.
- Role: Movement of lateral rectus muscle (outward gaze).
- Signs of single VI lesion: Inability to look laterally.
- Causes: Multiple Sclerosis (MS) and pontine stroke (CVA).
Combined III, IV, and VI lesions
- Causes:
- Cerebrovascular accident (CVA).
- Tumors.
- Wernicke's encephalopathy.
- Aneurysms.
- Multiple Sclerosis (MS).
- Myasthenia Gravis.
- Meningitis.
- Muscular dystrophy.
- Myotonic dystrophy.
- Cavernous sinus thrombosis.
- Guillain-Barré syndrome (GBS).
- Cranial arteritis.
- Trauma and orbital pathology.
Cranial Nerve V: Trigeminal
- Function:
- Motor: Muscles of mastication (chewing).
- Sensory: Facial sensation (split into three branches).
- Motor Assessment:
- Palpate Masseter and temporalis muscles.
- Open mouth against resistance.
- Sensory Assessment:
- Sharp and dull sensation in the nerve distribution.
- Reflex Assessment:
- Corneal reflex: Blink response to light touch (cotton, tissue) of the cornea.
Cranial Nerve VII: Facial
- Function:
- Motor:
- Inspect nasolabial folds.
- Ability to raise eyebrows, close eyes tight, or blow out cheeks (forehead sparing = upper motor neuron lesion).
- Sensory: Taste in the anterior two-thirds of the tongue (tested with sugar, salt, vinegar).
- Motor:
Bell's Palsy
- Facial nerve palsy (paralysis of the facial nerve).
- Common cause: Inflammation of the facial nerve.
- Symptoms:
- Weakness or paralysis of the facial muscles on one side of the face.
- Drooping of the eyelid.
- Difficulty making facial expressions.
- Drooling.
- Dry mouth.
- Loss of taste.
- Sensitivity to sound.
Cranial Nerve VIII: Vestibulocochlear
- Function:
- Sensory: Hearing, balance and equilibrium.
- Testing:
- Simple tests of auditory acuity.
- Weber's test: Tuning fork placed on the top of the head. Conductance: Lateralized to impaired side; Sensori-neural: Lateralized to good ear; Normal: midline.
- Rinne's test: Compare air conduction to bone conduction (in normal conditions, air conduction is better than bone conduction).
Cranial Nerves IX: Glossopharyngeal and X: Vagus
- These nerves are generally assessed together.
- They control the pharynx, larynx, and swallowing.
- Testing:
- Uvula elevation: Saying "Ahhh" and observing if the uvula moves to one side (IX lesion on the opposite side).
- Vocal quality: Observe the quality of the patient's voice (Hoarseness may indicate a vagus nerve lesion.
- Gag Reflex:
- Taste: Posterior one-third of tongue.
Cranial Nerve XI: Accessory
- Function: Motor.
- Role: Innervation of the sternocleidomastoid and trapezius muscles.
- Testing:
- Shrugging: Ask the patient to shrug their shoulders against resistance.
- Head Rotation: Ask the patient to turn their head from side to side against resistance.
Cranial Nerve XII: Hypoglossal
- Function: Motor.
- Role: Tongue movement.
- Testing:
- Tongue protrusion: Ask the patient to "stick their tongue out and move it side to side" (Inspect for fasciculations - small, involuntary muscle twitches - and atrophy).
- Deviation: Tongue deviation to one side usually indicates a lesion on the side to which the tongue is deviated.
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