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AN60.1-3 | Cerebellum — Practice Quiz
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The flocculonodular lobe of the cerebellum is primarily concerned with:
Correct! Flocculonodular lobe (vestibulocerebellum/archicerebellum) = balance, vestibulo-ocular reflex (VOR), and eye movements. Connected directly to vestibular nuclei. Damaged in posterior fossa midline tumours in children.
Vestibulocerebellum lesion: nystagmus, gait ataxia (balance-dependent), no limb ataxia. This explains why medulloblastoma (vermis + flocculonodular) → gait ataxia + nystagmus but relatively normal hand dexterity early on.
Incorrect. Flocculonodular = vestibulocerebellum = balance + eye movements. Spinocerebellum (anterior lobe + vermis) = posture/gait. Pontocerebellum (lateral hemispheres) = fine skilled movements.
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The intracerebellar deep nuclei from medial to lateral are:
Correct! Medial → lateral: Fastigial, Globosus, Emboliformis, Dentate. Mnemonic: "Feel Good Every Day". Dentate is the largest and most lateral.
Dentate nucleus is the output nucleus for the pontocerebellum (lateral hemisphere) — voluntary skilled movements. Fastigial = output for vestibulocerebellum (balance). Interposed (globosus + emboliformis) = output for spinocerebellum (posture/gait). All outputs leave via the superior cerebellar peduncle.
Incorrect. Medial → lateral: Fastigial, Globosus, Emboliformis, Dentate. "FGED" or "Feel Good Every Day". Dentate = lateral, largest.
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The main output pathway of the cerebellum (from the dentate nucleus to the thalamus and motor cortex) travels through:
Correct! The superior cerebellar peduncle (brachium conjunctivum) is the main cerebellar OUTPUT. Dentate nucleus → superior peduncle → decussates in midbrain tegmentum → red nucleus → VL thalamus → motor cortex. This decussation explains ipsilateral cerebellar signs.
Superior cerebellar peduncle decussation in midbrain + corticospinal decussation in medulla = double crossing → cerebellar hemisphere controls IPSILATERAL limb. Essential for clinical localisation: right cerebellar lesion → right limb signs.
Incorrect. Superior cerebellar peduncle = main OUTPUT (dentatorubrothalamic). Middle = INPUT only (corticopontocerebellar). Inferior = mixed (mainly input: spinocerebellar, olivocerebellar).
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Climbing fibres in the cerebellar cortex originate from the inferior olivary nucleus and carry "error signals." They synapse with:
Correct! Climbing fibres = 1:1 synapse with Purkinje cells; they wrap around the proximal Purkinje dendrites like a vine. They carry error signals from the inferior olivary nucleus and are responsible for long-term depression (LTD) of parallel fibre-Purkinje synapses — a key mechanism for motor learning.
Cerebellar motor learning: error signal (climbing fibre from inferior olive) causes LTD of the active parallel fibre-Purkinje synapse → reduced Purkinje inhibition of deep nucleus → enhanced cerebellar output → movement correction. This is the anatomical basis of motor skill acquisition and cerebellar adaptation.
Incorrect. Climbing fibres → Purkinje cells (1:1, very powerful synapse). Mossy fibres → granule cells → parallel fibres → Purkinje cells (many:1). This distinction is important for cerebellar motor learning.
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A patient with a right cerebellar hemisphere infarct would be expected to show limb ataxia and intention tremor on which side?
Correct! Cerebellar hemisphere lesions cause IPSILATERAL limb signs. The double-crossing pathway (superior cerebellar peduncle crosses in midbrain → corticospinal crosses in medulla) results in cerebellar hemisphere controlling ipsilateral limb.
Localising brainstem/cerebellar lesions: Cerebral cortex = contralateral motor/sensory. Cerebellum = ipsilateral. Brainstem = crossed (ipsilateral CN + contralateral body). This is the basis of all brainstem syndrome analysis.
Incorrect. Cerebellar lesions cause IPSILATERAL signs (opposite to cerebral cortex which causes contralateral signs). Right hemisphere → right limb ataxia.
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Intention tremor (kinetic tremor that worsens when approaching a target) is a sign of cerebellar dysfunction. It is best distinguished from resting tremor (Parkinson's) because:
Correct! Intention tremor = worsens as the limb approaches the target (dysmetria); ABSENT at rest. Resting tremor (Parkinsonian "pill-rolling") = present at rest, DECREASES or disappears on voluntary movement. Critical distinction for neurological diagnosis.
Tremor types in Indian neurology: (1) Resting = Parkinson's disease (pill-rolling, suppressed by movement). (2) Intention/kinetic = cerebellar (worsens near target). (3) Postural = essential tremor (most common in India, autosomal dominant, present with arms outstretched, improves with alcohol). (4) Flapping (asterixis) = hepatic/metabolic encephalopathy.
Incorrect. Intention tremor = worsens approaching target, absent at rest. Resting tremor = present at rest (Parkinson's), suppressed by movement. Opposite patterns.
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Dysdiadochokinesia is a sign of cerebellar hemisphere dysfunction. It is tested by asking the patient to:
Correct! Dysdiadochokinesia = inability to perform rapid alternating movements. Tested by asking rapid pronation/supination of the forearm or alternate tapping. It reflects failure of agonist-antagonist muscle coordination.
Cerebellar examination: (1) Dysdiadochokinesia = rapid alternating movements (pronation/supination, alternating hand tapping). (2) Dysmetria = finger-nose test (past-pointing + intention tremor). (3) Gait ataxia = wide-based, staggering, falls ipsilaterally. (4) Heel-shin test for lower limb coordination. All tests map to specific cerebellar pathways.
Incorrect. Dysdiadochokinesia = rapid alternating movements (pronation/supination). Finger-nose = tests for intention tremor/dysmetria. Tandem walking = gait ataxia. Romberg = sensory ataxia.
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Purkinje cells in the cerebellar cortex are:
Correct! Purkinje cells = ONLY output neurons of cerebellar cortex. They are INHIBITORY (GABAergic) → tonically inhibit the intracerebellar deep nuclei (especially dentate). When Purkinje cells are less active, deep nuclei become more active → increased cerebellar output to thalamus/motor cortex.
Cerebellar circuit logic: Purkinje cells are tonically INHIBITORY. Input (mossy/climbing fibres) → granule cells → parallel fibres → activate Purkinje cells → inhibit deep nuclei. Purkinje cells also have "pause" — when inhibited by basket/stellate cells, deep nuclei become active. This inhibitory-disinhibitory circuit underlies cerebellar timing and coordination.
Incorrect. Purkinje = only cortical output, INHIBITORY (GABA) → intracerebellar nuclei. Most numerous neurons in cerebellum = granule cells (most numerous neurons in the ENTIRE BRAIN!).
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The inferior olivary nucleus sends climbing fibre inputs to the cerebellum via which peduncle?
Correct! Olivocerebellar fibres from the inferior olivary nucleus enter the cerebellum via the INFERIOR cerebellar peduncle. The inferior olive is the source of all climbing fibres (one olivary neuron → one Purkinje cell).
Inferior cerebellar peduncle contents: (1) Olivocerebellar (from inferior olive — error signals, motor learning). (2) Posterior spinocerebellar (from Clarke's column — proprioception). (3) Vestibulocerebellar (balance). (4) Arcuatocerebellar. Output: cerebellovestibular (fastigial → vestibular nuclei).
Incorrect. Olivocerebellar fibres = inferior cerebellar peduncle. Superior = cerebellar OUTPUT (dentatorubrothalamic). Middle = corticopontocerebellar INPUT from contralateral cortex via pons.
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In alcoholic cerebellar degeneration, selective degeneration of the anterior lobe of the cerebellum preferentially affects which functional zone, leading to predominant gait ataxia with relatively preserved upper limb coordination?
Correct! Alcoholic cerebellar degeneration selectively affects the ANTERIOR LOBE VERMIS (spinocerebellum responsible for trunk, posture, and gait). This causes gait ataxia and truncal ataxia with relatively preserved upper limb coordination (which is controlled by lateral hemispheres).
Alcoholic cerebellar degeneration: caused by thiamine (B1) deficiency + direct alcohol toxicity. Selective anterior vermis degeneration. Pattern: severe gait ataxia, stance ataxia (truncal), mild arm involvement. Compare with paraneoplastic cerebellar degeneration (pan-cerebellar involvement) and hereditary ataxia (Friedreich's, spinocerebellar ataxias).
Incorrect. Alcohol preferentially damages the anterior lobe (spinocerebellum/vermis) → gait ataxia. Lateral hemispheres (pontocerebellum) are more spared → arm coordination relatively preserved. This is a classic pattern on examination.
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