A patient has weakness of the lower face on one side. The forehead wrinkles normally on both sides. Where is the lesion? ANSWER: ABOVE the facial nerve nucleus — this is a STROKE (an upper motor neurone pattern), not a facial nerve palsy. THE ANATOMY THAT EXPLAINS IT: The part of the nucleus supplying the FOREHEAD receives input from BOTH hemispheres. The part supplying the LOWER FACE receives input from the OPPOSITE hemisphere only. So damage to one hemisphere's input weakens the lower face, while the forehead continues to work because the other hemisphere still supplies it. CONTRAST — BELL'S PALSY or any lesion of the NERVE itself: the whole side is weak and the FOREHEAD IS INVOLVED, because everything has already joined together by that point. DO NOT FORGET: check whether the EYE CLOSES. An exposed cornea ulcerates and can perforate.

A patient has a third nerve palsy. Why does the state of the pupil matter urgently? ANSWER: because the pupil-constricting fibres run on the OUTSIDE of the nerve. COMPRESSION from outside — an aneurysm, or brain pushed against the nerve by rising intracranial pressure — reaches those superficial fibres FIRST. → DILATED pupil. This is a surgical emergency until proven otherwise. SMALL-VESSEL disease affects the core of the nerve and more often SPARES the pupil. So the same palsy carries entirely different urgency depending on one sign, and the reason is the anatomical position of the fibres. OTHER FEATURES OF A COMPLETE III PALSY: the eye rests DOWN AND OUT, with PTOSIS.

Why does an infant with hydrocephalus present with an enlarging head, while an adult presents with headache and vomiting? ANSWER: because the infant skull can still EXPAND. 1. CSF production is CONTINUOUS and does not stop when flow is obstructed. 2. So fluid accumulates behind any block. 3. In an INFANT the sutures have not fused, so the skull enlarges and pressure rises more slowly — the head GROWS. 4. In an older child or adult the skull is FIXED, so the same accumulation raises pressure steeply — headache, vomiting, reduced consciousness. CLINICAL CONSEQUENCE: head circumference is measured and PLOTTED at every infant check, because it detects what a fixed skull would have announced with symptoms.

A patient has weakness affecting the LEG more than the arm, with no speech disturbance. Which artery is most likely involved? A. Middle cerebral B. Anterior cerebral C. Posterior cerebral D. Basilar ANSWER: B — anterior cerebral artery. REASONING FROM THE HOMUNCULUS: the body is mapped along the motor cortex with the LEG at the TOP and over the midline, and the face and hand at the bottom near the side. ANTERIOR cerebral supplies the MEDIAL surface, where the LEG sits → leg worse than arm MIDDLE cerebral supplies the LATERAL surface, where face and arm sit → face and arm worse than leg, plus speech disturbance if the dominant hemisphere is affected You are reading a map, not recalling a table.

A patient has a dense weakness of the face, arm and leg on one side, with normal speech and no visual field defect. Where is the lesion likely to be, and why does a small lesion cause so much weakness? ANSWER: the INTERNAL CAPSULE. WHY A SMALL LESION DOES SO MUCH: 1. Fibres leaving the cortex are spread over a WIDE surface. 2. They then converge into a NARROW band — the internal capsule. 3. Face, arm and leg fibres are packed tightly together there. 4. So a small infarct damages all three at once. WHY SPEECH AND VISION ARE SPARED: the lesion is BELOW the cortex, so the cortical language and visual areas are untouched. A cortical stroke large enough to cause the same weakness would also produce those deficits. THE GENERAL PRINCIPLE: damage depends on how tightly PACKED the fibres are, not on lesion SIZE — which is why a very small BRAINSTEM stroke can be devastating.

Why must folic acid be taken BEFORE conception rather than started at the first antenatal visit? ANSWER: because the NEURAL TUBE closes very early — often before a woman knows she is pregnant. 1. Neural tube closure occurs in the first weeks after conception. 2. Failure of closure produces spina bifida and anencephaly. 3. By the booking antenatal visit, that window has CLOSED. 4. Supplementation started then cannot prevent a defect that has already occurred. This is the anatomical reason behind a public health instruction — and it is the same logic as pre-conception care in diabetes and epilepsy, where organogenesis is complete before most women present.

Why is swallowing assessed before giving anything by mouth after a stroke? ANSWER: because cranial nerves IX and X control the palate, swallow and voice — and stroke can leave the swallow UNSAFE. 1. An unsafe swallow allows food and fluid into the AIRWAY rather than the oesophagus. 2. Aspiration causes pneumonia, which is a leading cause of death after stroke. 3. The patient may not cough — an absent cough reflex makes aspiration SILENT and therefore easy to miss. So the assessment is done BEFORE the first drink, not after the first choking episode. RELATED SIGNS OF IX/X INVOLVEMENT: a wet or gurgling voice, nasal regurgitation, and asymmetry of palate elevation.