Download TSM59 - The Cerebellum

TSM59: CEREBELLUM
31/10/08
LEARNING OUTCOMES
Describe the structure of the cerebellum
GROSS ANATOMY
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The cerebellum is made up of two hemispheres joined along the midline at the vermis
o Superiorly the vermis blends between the surfaces of the two hemispheres
o Inferiorly it is within a deep recess
The deep primary fissure on the superior surface of the cerebellum demarks the anterior lobe
o Posterior to this fissure, including most of the inferior surface, is the posterior lobe
The postero-lateral fissure on the inferior surface of the cerebellum demarks the flocculonodular lobe
o Small region at the caudal end comprising the central nodule and bilateral flocculus
ANATOMICAL ZONES AND FUNCTIONAL DIVISIONS
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In both the anterior and posterior lobes there are two anatomical zones:
o Intermediate (paravermal) – medial hemispheres, 1-2cm lateral to the vermis
o Lateral – lateral to the intermediate zone – makes up the majority of the posterior lobe
The cerebellum as a whole is divided into three functional zones:
o Vestibular – the flocculonodular lobe – receives ipsilateral input from the vestibular nuclei
o Spinal – the vermis and intermediate zone – receives ipsilateral input from the whole body
o Cortical – the lateral zone – receives contralateral input from the pontine nuclei
All three of the above functional zones also receive inputs from the inferior olivary nucleus
o Enter the cerebellum via the inferior cerebellar peduncle
o Fibres project contralaterally and terminate as climbing fibres
o All other cerebellar input fibres terminate as mossy fibres (more branched)
NEURONAL STRUCTURE
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The cerebellum comprises an outer layer of grey matter and an inner layer of white matter
Three bilateral pairs of deep nuclei are contained in the white matter – from medial to lateral:
o Fastigal nucleus – near the midline
o Interposed nucleus – comprising the globose and emboliform nuclei
o Dentate nucleus – prominent crumpled shape, within the cortical zone
Each nucleus gives efferent fibres which exit the cerebellum via the cerebellar peduncles
o Superior peduncle – efferent fibres from the interposed and dentate nuclei to the thalamus
o Middle peduncle – afferent fibres from the pons projecting to the cortical zone
o Inferior peduncle – efferent fibres from the fastigal nucleus to the brainstem
Note that the cerebellum does not project to the pre-frontal cortex (compare to basal ganglia)
Describe the role of the cerebellum in the control of movement
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The cerebellum modifies descending efferent motor signals to control and adjust movement
o Compares cortical (intended) signals to proprioceptive and sensory (actual) signals
o Each side of the body is controlled and represented ipsilaterally in the hemispheres
o Functions relating to postural muscles are executed in the midline
It also has roles in learning and executing complex movement sequences (‘muscle memory’)
Damage to the cerebellum is characterised by ataxia generally with muscle wasting
o Ataxic gait – clumsy, uncoordinated walking
o Past-pointing – overshooting when reaching for an object due to dysmetria
o Intention tremor – peripheral tremor during movement (absent at rest)
o Asynergy – loss of continuous smooth-flowing movement
o Dysdiadochokinesia – difficulty in repeated alternating movements e.g. flexion and extension
of the fingers, supination and pronation of the arm