Topic: descending pathways, functions of cerebellum
Question: Explain the connections and functions of cerebellum. Add a note on clinical symptoms seen in cerebellar lesions.
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The cerebellum has extensive connections with the brainstem and cerebral cortex that allow it to coordinate motor control and precision.
Connections:
– Receives input via mossy fibers and climbing fibers. Mossy fibers originate from the pons and carry information from the cortex. Climbing fibers arise directly from the inferior olivary nucleus.
– Deep cerebellar nuclei including the dentate, emboliform, globose and fastigial nuclei provide output from the cerebellum to various parts of the brain.
– Output goes mainly to the thalamus via the superior cerebellar peduncle, which then connects back to the motor cortex.
– Other connections include the vestibular nuclei and reticular formation in the brainstem.
Afferent (incoming) connections:
– Pontine nuclei → mossy fibers
– Inferior olivary nucleus → climbing fibers
– Vestibular nuclei → mossy fibers
– Spinal cord → mossy fibers
– Cerebral cortex → pontine nuclei → mossy fibers
Intrinsic connections:
– Mossy fibers → granule cells → parallel fibers
– Climbing fibers → Purkinje cells
– Deep cerebellar nuclei 
Purkinje cells, granule cells, mossy fibers
Efferent (outgoing) connections:
– Purkinje cells → deep cerebellar nuclei
– Deep cerebellar nuclei:
– Dentate nucleus → thalamus (via superior cerebellar peduncle)
– Interposed and fastigial nuclei → vestibular nuclei, reticular formation
– Vestibular nuclei → brainstem, spinal cord
– Thalamus → motor cortex
Functions:
– Coordination of voluntary movements – enables precise timing, appropriate force, range of motion.
– Maintaining posture and balance.
– Motor learning and memory – adapts movements through sensory feedback.
– Ocular motion control – vestibulo-ocular reflex.
Lesions:
Cerebellar lesions lead to characteristic neurological symptoms:
– Ataxia – impaired coordination, gait imbalance
– Dysmetria – overshooting or undershooting intended movements
– Dysdiadochokinesia – inability to perform rapid alternating movements
– Intention tremor – tremor that worsens towards end of action
– Nystagmus – jerky eye movements
– Hypotonia and weakness
– Slurred speech
Localization is based on which cerebellar peduncle or deep nucleus is involved. Stroke, tumors, infection, toxins, and degeneration can cause cerebellar damage.
