Answers to Quiz 132 · Cerebellum
Which pairing of a cerebellar peduncle with what it connects the cerebellum to is correct?
Answer: Middle peduncle – pons
Superior goes to the midbrain, middle to the pons, inferior to the medulla. The middle peduncle is the largest because it carries the corticopontocerebellar input. Revise cerebellar divisions, histology and connections
Compared with the cerebral cortex, the cerebellum has:
Answer: About 75% of its surface area but only about 10% of its weight
A sheet nearly as large as the cerebral cortex is packed into a tenth of its weight, which is why the cerebellar cortex is so deeply folded. Revise cerebellar divisions, histology and connections
The flocculonodular lobe of the cerebellum is concerned with:
Answer: Equilibrium, and learned changes in the vestibulo-ocular reflex
The flocculonodular lobe is the vestibulocerebellum, connected reciprocally with the vestibular nuclei. Posture is the vermis, skilled movement the paravermal strip, planning the hemispheres. Revise cerebellar divisions, histology and connections
The paravermal region of the spinocerebellum projects to brainstem nuclei that act on:
Answer: Distal limb muscles, so it controls skilled voluntary movement
Vermis to axial and proximal muscles, so posture; paravermal to distal muscles, so skilled movement. Getting these two the wrong way round is the commonest error in the essay. Revise cerebellar divisions, histology and connections
Which division of the cerebellum is also called the corticopontocerebellum?
Answer: Cerebrocerebellum, the two hemispheres
The cerebral cortex reaches the hemispheres after a relay in the pontine nuclei, so the neocerebellum is also named for that route. It is the division that plans and programmes movement. Revise cerebellar divisions, histology and connections
The interneurons of the molecular layer of the cerebellar cortex are:
Answer: Basket cells and stellate cells
Basket and stellate cells lie in the molecular layer and end on the Purkinje dendrites that spread into it. Granule and Golgi cells belong to the granular layer. Revise cerebellar divisions, histology and connections
Mossy fibres entering the cerebellum end mainly on:
Answer: Granule cells
Mossy fibres, the major input, relay through granule cells, whose parallel fibres then reach the Purkinje cells. Only the climbing fibres end on Purkinje cells directly. Revise cerebellar divisions, histology and connections
Climbing fibres reach the cerebellum from:
Answer: The inferior olivary nucleus, and end on Purkinje cells
The olivocerebellar tract is the only climbing fibre input, and the inferior olive first gathers proprioceptive signals from the whole body. Every other afferent tract arrives as mossy fibres. Revise cerebellar divisions, histology and connections
Which cell carries the output of the cerebellar cortex to the deep cerebellar nuclei?
Answer: The Purkinje cell
The Purkinje cell is the only cortical cell whose axon leaves the cortex, so it is the link between the cortex and the deep nuclei. The other three are interneurons acting only within the cortex. Revise cerebellar divisions, histology and connections
Nucleus interpositus is made up of which nuclei, and what feeds it?
Answer: Globose and emboliform nuclei; the paravermal spinocerebellum
Globose plus emboliform equals interpositus, and the paravermal cortex above it projects into it. The vermis projects to the fastigial nucleus and the hemispheres to the dentate. Revise cerebellar divisions, histology and connections
The signs of a cerebellar lesion appear on the same side as the lesion because:
Answer: The cerebellar outflow crosses in the midbrain and the corticospinal tract crosses again in the medulla
Two crossings return the influence to the side it came from, so a right cerebellar lesion gives right-sided signs. A capsular lesion, with only one crossing, gives contralateral signs. Revise cerebellar functions, lesions and tests
Which of these is NOT a feature of a cerebellar lesion?
Answer: Spastic paralysis with a positive Babinski sign
The cerebellum issues no command to muscle, so its lesions cause clumsiness without paralysis, and tone falls rather than rises. Spasticity with a Babinski belongs to an upper motor neuron lesion. Revise cerebellar functions, lesions and tests
A patient flexes the elbow against the examiner's pull; the pull is released suddenly and the forearm flies up and strikes his chest. This is:
Answer: The rebound phenomenon of a cerebellar lesion
The cerebellum normally checks a contracting limb the moment resistance disappears; losing that check gives the rebound, or Stewart–Holmes, sign. Revise cerebellar functions, lesions and tests
In a patient with cerebellar ataxia, Romberg's test shows:
Answer: Swaying with the eyes open that is little worse when they are closed
Romberg's sign is negative in cerebellar ataxia and positive in sensory (posterior column) ataxia, where vision is what was compensating for lost proprioception. Revise cerebellar functions, lesions and tests
A 7-year-old cannot sit or stand steadily and has nystagmus, yet coordination of the limbs is almost normal. The lesion is most likely in the:
Answer: Flocculonodular lobe and vermis
Truncal ataxia with intact limbs is the archicerebellar picture, typically a midline medulloblastoma in a child. Limb signs with intention tremor would point to a hemisphere instead. Revise cerebellar functions, lesions and tests
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