Head and neck
Introduit| English | Sens |
|---|---|
| cranial nerve | cranial nerve |
| vestibular schwannoma | vestibular schwannoma |
| Horner syndrome | Horner syndrome |
Twelve nerves, named holes
- Twelve cranial nerves 脑神经 leave the skull through named holes. Each nerve, and each hole, points to the site of a lesion.
- Head and neck anatomy is the purest game of "the signs name the place".
What the twelve do
- I smell, II see, III, IV and VI move the eye (VI alone turns it outwards), V feels the face and chews, VII moves the face and tastes the front of the tongue.
- VIII hears and balances, IX and X swallow and speak and supply the organs, XI shrugs the shoulders, XII moves the tongue.
Match each cranial nerve to its main job.
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Learning each nerve by one testable job turns the list into a bedside examination.
How many cranial nerves move the eye?
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III (oculomotor), IV (trochlear) and VI (abducens).
The holes they use
- II goes through the optic canal; V1 through the superior orbital fissure, V2 through foramen rotundum, V3 through foramen ovale.
- VII and VIII enter the internal acoustic meatus; IX, X and XI leave through the jugular foramen.
Which nerve leaves the skull through foramen ovale?
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V1 uses the superior orbital fissure, V2 foramen rotundum and V3 foramen ovale.
Shared holes, shared signs
- Each hole fixes what else can be caught there. VII and VIII share the internal acoustic meatus.
- So a vestibular schwannoma 前庭神经鞘瘤 there causes hearing loss and imbalance first; facial weakness, if it comes, is late.
A tumour in the internal acoustic meatus usually shows itself first by hearing loss.
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VIII shares the meatus with VII, and its hearing and balance fibres are affected first; facial weakness is late.
Worked example: forehead in or out?
- (Fictional patient) Sudden weakness of one side of the face. If the forehead is spared, the lesion is central (a stroke), because the upper face gets cortical input from both sides.
- If the forehead is weak too, the lesion is in the facial nerve itself (the Bell's palsy pattern). One test, raising the eyebrows, separates the emergency from the usually benign.
A patient has a weak lower face on one side but can wrinkle the forehead normally. Where is the lesion most likely?
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The forehead has cortical input from both sides, so a central lesion spares it; a facial nerve lesion weakens the whole side.
Worked example: a tumour at the lung tip
- (Fictional smoker) Wasting of the hand, a hoarse voice and shoulder pain. A tumour at the lung apex climbs over the top of the lung and reaches three things in turn.
- The brachial plexus (C8–T1: hand), the recurrent laryngeal nerve (hoarseness) and the sympathetic chain (a drooping eyelid and a small pupil: Horner syndrome 霍纳综合征). One corner of anatomy explains all three.
Which set of signs fits a tumour at the lung apex?
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The apex lies next to the lower brachial plexus, the recurrent laryngeal nerve and the sympathetic chain (Horner syndrome).
Three common slips
- Nerves without holes. Learn each nerve with its exit, in pairs.
- Trusting a VI palsy for location. VI has a long course inside the skull, so raised pressure anywhere can weaken it: a "false localising" sign.
- Testing IX and X apart. In the gag reflex IX carries sensation and X the movement; "aah" tests X (the uvula swings away from the weak side).
Recap
- Twelve nerves, each with a named exit; VII and VIII share the internal acoustic meatus.
- A spared forehead means a central lesion; a weak forehead means the facial nerve itself.
- The lung apex is a crossroads of the brachial plexus, recurrent laryngeal nerve and sympathetic chain.