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AN57.1-5 | Spinal Cord — Practice Quiz
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In an adult, the spinal cord (conus medullaris) normally ends at the level of:
Correct! The conus medullaris ends at the lower border of L1 (range: T12–L2) in adults. In neonates it is at L2–L3. This is why LP is safe at L3–L4 or L4–L5 in adults.
Mnemonic: Conus at L1 = "L-ONE-ly conus". Cauda equina (horse's tail) = nerve roots from L2 downward floating in the lumbar cistern. Palpating the iliac crests (Tuffier's line) = L4 spinous process = used to identify L3–L4 or L4–L5 space for LP.
Incorrect. Conus = lower border L1 in adults. LP safe below this level. In neonates, conus is at L2–L3 (use L4–L5 for LP in neonates).
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The cauda equina consists of:
Correct! Cauda equina = lumbar and sacral nerve roots (L2–Co1) that descend below the conus in the lumbar cistern, resembling a horse's tail.
Cauda equina syndrome (CES): compression of cauda equina (e.g., large central disc prolapse at L4–L5 or L5–S1) → bilateral leg weakness, perineal sensory loss (saddle anaesthesia), urinary retention (overflow incontinence). Surgical emergency. Different from conus syndrome (which affects S2–S5 directly).
Incorrect. Cauda equina = ALL nerve roots below the conus medullaris (L2–Co1) floating in CSF in the lumbar cistern. The filum terminale is a non-neural strand of pia mater running through the cauda equina.
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The lateral horn of the spinal cord grey matter, present at T1–L2, contains the cell bodies of:
Correct! The lateral horn at T1–L2 contains the intermediolateral cell column (IML) — cell bodies of preganglionic sympathetic neurons. Their axons exit via the ventral root → white rami communicantes → sympathetic chain.
Horner's syndrome (ptosis, miosis, anhidrosis) occurs when the sympathetic pathway from T1 (IML) → superior cervical ganglion → head/neck is interrupted. Common causes in India: Pancoast tumour at lung apex (T1 involvement), cervical rib, carotid artery dissection.
Incorrect. Lateral horn T1–L2 = preganglionic SYMPATHETIC neurons (IML). Preganglionic PARASYMPATHETIC = S2–S4 (sacral). Alpha motor neurons = anterior horn lamina IX.
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Fasciculus gracilis and fasciculus cuneatus in the posterior white columns of the spinal cord carry which sensory modalities?
Correct! The posterior (dorsal) columns carry fine touch, vibration, two-point discrimination, and conscious proprioception via the medial lemniscal pathway. They ascend IPSILATERAL and cross in the medulla.
Posterior column test: Romberg test (eyes closed, sway increases when proprioception removed) and vibration testing with tuning fork. In SCD (B12 deficiency), posterior columns degenerate → positive Romberg, loss of vibration sense, sensory ataxia. In Brown-Séquard, posterior column loss is IPSILATERAL to the lesion.
Incorrect. Posterior column = fine touch + vibration + proprioception + 2-point discrimination. Pain and temperature = lateral spinothalamic. Crude touch = anterior spinothalamic. Unconscious proprioception = spinocerebellar tracts.
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The lateral spinothalamic tract fibres carrying pain and temperature cross the midline in the spinal cord at which location?
Correct! Spinothalamic fibres enter the posterior horn, ascend 1–2 segments, then cross in the ANTERIOR WHITE COMMISSURE. This explains why syringomyelia (central canal expansion destroying the anterior commissure) causes bilateral cape-distribution loss of pain/temperature.
Clinically important crossing levels: Spinothalamic = anterior white commissure (1–2 segments up in cord). Posterior column = nucleus gracilis/cuneatus in medulla. Corticospinal = pyramidal decussation in medulla. This is why cord lesions produce different ipsilateral/contralateral sensory losses (Brown-Séquard).
Incorrect. Spinothalamic fibres cross in the ANTERIOR white commissure (1–2 segments above entry level). Posterior column fibres cross in the MEDULLA (not in the cord).
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A patient suffers a left-sided stab wound at T8. Examination reveals: left leg spastic paralysis with brisk reflexes; loss of proprioception and vibration in the left leg; loss of pain and temperature in the right leg below T8. This is consistent with:
Correct! Left-sided hemisection: LEFT = corticospinal (UMN → spastic paralysis) + posterior column loss (proprioception/vibration). RIGHT = spinothalamic loss (pain/temperature — these fibres crossed from right → left, so cutting left cord blocks them). Classic Brown-Séquard.
Brown-Séquard mnemonic: "Same-side motor/proprioception loss; opposite-side pain/temperature loss." The dissociation occurs because: posterior column and corticospinal = ipsilateral in cord → cross in medulla. Spinothalamic = crosses 1–2 segments up in cord → contralateral in cord above crossing.
Incorrect. Brown-Séquard = ipsilateral UMN + posterior column loss; contralateral spinothalamic (pain/temp) loss. Left cord cut → left UMN + proprioception loss; right pain/temp loss.
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Poliomyelitis is characterised by flaccid paralysis without sensory loss. This selective pattern occurs because the poliovirus specifically destroys:
Correct! Poliovirus selectively infects and destroys anterior horn cells (LMNs) via receptor-mediated entry (CD155/PVR). Sensory neurons and pathways are completely spared, resulting in pure LMN motor paralysis with NO sensory loss.
Polio vs GBS: Both cause acute flaccid paralysis (AFP). Polio: asymmetric, no sensory loss, fever prodrome, CSF shows neutrophilic pleocytosis initially. GBS: symmetric ascending, sensory loss + motor, post-infectious, CSF albuminocytological dissociation (high protein, normal cells). India continues AFP surveillance for wild poliovirus.
Incorrect. Polio = anterior horn cell (LMN) destruction. Pure motor paralysis, no sensory loss. Acute flaccid paralysis (AFP) surveillance in India monitors for any such presentation to detect possible poliovirus.
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A patient with a Chiari I malformation develops bilateral loss of pain and temperature in both upper limbs and trunk ("cape distribution") while position sense and touch are preserved. The pathological expansion damages which structure first?
Correct! Syringomyelia expands from the central canal outward. The anterior white commissure (carrying decussating spinothalamic fibres) is damaged first → bilateral suspended (cape) loss of pain and temperature. Posterior columns are spared initially (hence preserved fine touch and proprioception).
Suspended sensory loss = syringomyelia. "Suspended" means loss of pain/temperature at the level of the lesion (cape over shoulders/arms) with normal sensation above and below. Associated with Chiari malformation, intramedullary tumours, post-traumatic. MRI T2 = hyperintense central fluid signal. Treatment: posterior fossa decompression (if Chiari) + syringosubarachnoid shunt.
Incorrect. Syrinx expands centrally → anterior white commissure first (spinothalamic crossing fibres) → cape distribution pain/temperature loss. Posterior columns (fine touch/proprioception) are spared early.
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A strict vegetarian patient presents with spastic paraplegia, loss of vibration sense in both legs, positive Romberg test, and a serum B12 of 60 pg/mL. Which tracts are primarily degenerated?
Correct! SCD (subacute combined degeneration) of the cord from B12 deficiency: POSTERIOR columns (vibration, proprioception loss, sensory ataxia, positive Romberg) + LATERAL corticospinal tracts (spastic paraplegia, Babinski+).
SCD treatment: IM vitamin B12 (hydroxocobalamin or cyanocobalamin) initially, then monthly maintenance. Do NOT give folic acid alone in B12 deficiency — it can precipitate/worsen neurological deterioration (corrects haematological picture but not the cord lesion). Serum B12 <200 pg/mL = deficient; <100 pg/mL = severely deficient.
Incorrect. SCD = posterior columns (vibration/proprioception) + lateral corticospinal tracts (UMN). "Combined" = both columns affected. B12 deficiency is common in Indian strict vegetarians (B12 only in animal products).
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Comparing mid-cervical and mid-thoracic transverse sections of the spinal cord, the RELATIVE amount of white matter compared to grey matter is:
Correct! At cervical levels, all ascending and descending tracts are present (carrying information from the entire cord below) → lots of white matter. The grey matter is larger too (limb muscles) but white:grey ratio is greater than at lumbar levels where tracts have left the cord.
As you descend the cord: white matter DECREASES (tracts peel off at each level). Grey matter: largest at cervical (brachial plexus) and lumbosacral (lumbar plexus) enlargements; smallest in thoracic (only trunk muscles). Cervical cord = large white + large grey. Thoracic = smaller grey (no lateral horn above T1). Sacral = tiny white, relatively prominent grey.
Incorrect. White matter is greatest at cervical levels (all tracts present). At sacral levels, most tracts have already left the cord → relatively small white matter, large grey matter (for bladder/bowel control).
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