0909 - Cerebellum Flashcards
Discuss the main roles of the cerebellum in general terms.
Maintain synergy of movement, upright posture, and muscle tone. Does this by monitoring and adjusting contraction and relaxation of opponent muscle groups, intensity and duration of muscle contractions, and sequencing of contractions to execute a specific movement.
It is fed information by brainstem and proprioception to adjust the control centres, outputting to cortex via thalamus, and spinal cord via brainstem, adjusting muscle function to refine the movement.
Describe the anatomical features of the cerebellum
What are the 3 lobes of the cerebellum?
Anterior lobe (superior surface)
Primary fissure
Posterior lobe (inferior surface)
Flocculonodular lobe (very small, sits against brainstem at anterior surface).
What is the macroscopic appearance of the cerebellum
2 hemispheres plus vermis, 3 lobes and 3 peduncles. Consists of cortex, white matter, and deep nuclei, in the arbor vitae structure. Also has tonsil and nodule.
What are the three peduncles of the cerebellum?
Inferior (to/from brainstem), middle (from pons), superior (forms roof of 4th ventricle)
What are the deep nuclei of the cerebellum?
Dentate - Largest, lateral, convoluted and feeds back to motor cortical areas.
Globose and Emboliform - Collectively known as interposed - spino-cerebellar feedback
Fastigial - adjacent to midline, associated with vestibular system.
Outline the circuitry of the cerebellum.
All inputs terminate in cerebellar cortex. Neurons there project to deep cerebellar nuclei, and all outputs originate from the deep nuclei. They project to thalamus and brainstem nuclei.
What is carried in the Superior cerebellar peduncle?
Afferents are ventral spino-cerebellar tract (from mechanoreceptors in trunk and lower limb). Efferents are from dentate nucleus to primarily to ventrolateral thalamus and secondarily to red nucleus, and globose/emboliform (interposed) nucleus primarily to red nucleus and secondarily thalamus.
What would occur with a lesion of the superior cerebellar peduncle?
Loss of OUTPUTS to thalamus (cortex) and red nucleus.
Hypotonia and intention tremor, dysmetria, dysdiadochokinesia, loss of timing and control of speech.
What is carried through the Middle cerebellar peduncle?
Afferents (ponto-cerebellar)
Only afferents. Cells throughout Cx send axons through medial and lateral 1/3 of cerebral peduncle. Synapse in pontine nucleus, and become pontocerebellar fibres in MCP. Proceed to posterior cerebellar cortex, dentate nucleus, and out to thalamus/red nucleus.
What would occur with a lesion of the middle cerebellar peduncle?
Loss of pontocerebellar fibres (inputs from cortex and ION)
Hypotonia, intention tremor, dysmetria, dysdiadochokinesia, loss of timing and control of speech.
What is carried through the Inferior cerebellar peduncle?
I/L Dorsal Spino-cerebellar tract (unconsc. proprioception - lower)
I/L Cuneo-cerebellar tract (unconsc. propr. - upper)
C/L Olivocerebellar tract (Inferior Olivary Nucleus)
I/L Vestibulocerebellar tract (vestibular ganglion, vestibular N)
Efferents from fastigial N. to vestibular N.
What would occur with a lesion of the lower cerebellar peduncle
Loss of inputs from I/L DSCT, I/L CCT, C/L ION, and VCT. Loss of outputs from fastigial N - sup coll, retic form, and vestib nuclei.
Loss of proprioception from limbs - ataxic gait, clumsy movements, stagger to side of lesion
Loss of feedback when learning - intention tremor?
Ataxic stance, nystagmus
Afferents are ipsilateral dorsal spino-cerebellar and cuneo-cerebellar tracts, contralateral inferior olivary nucleus (olivocerebellar tract), and vestibular ganglion/vestibular nuclei (ves. Dorsal originate in Clarke’s column (C8-L3) with proprioceptive input from lower limbs and trunk. Cuneo is similar but from upper limbs, so from accessory cuneate nucleus above C6 (upper limbs). Also carries inputs from inferior olivary nucleus, vestibular nuclei, and brainstem reticular formation. Efferents go from fastigial nucleus, sending axons to terminate in brainstem vestibular nuclei.
Outline the
Inferior olivary nucleus
Important for learning - tweaking the movements until an error is minimised and the task is learned. Projects fibres into C/L inferior cerebellar peduncle. Only area that has “climbing fibres’ as distinct from mossy fibres.
What are the two types of input fibres for cerebellum?
Climbing - from ION - special learning component/fibres. Input comes from Red N (cerebral motor cortex and cerebellum via Red N). Climbing fibres excite a single Pj cell, and send collaterals to deep nuclei. Provides motor error to cerebellum to enable motor program to be refined and minimise error. Active during training/learning.
Mossy - all other inputs. Single mossy fibre sends collateral to deep nuclei and sends terminal axons into granular cell layer. Activate many granule cells, which in turn activate 200k Purkinje cells.
What are the cerebellar outputs
Project neurons out of the Cb from the deep nuclei. Receives excitatory inputs from mossy and climbing fibres, with activity modulated by inhibitory signals from Pj cells.
