Cerebellum Flashcards
How many neurones are in the cerebellum in proportion to the rest of the brain?
- 100 billion neurones
- More than 50% of the total brain neurones
- “Little brain”
What are the functions of the cerebellum?
- Motor control
- Cognitive functions
Where is the cerebellum in the skull?
Posterior fossa
Straddling the brainstem, opposite pons
Forming the roof of the fourth ventricle
What is tentorium cerebelli?
“Tent of cerebellum”
Part of the dura matter
Separates the cerebellum from the occipital lobes
What are the cerebellar subdivisions?
- Central, worm-like structure (vermis)
- Two lateral hemispheres
- A small inferior part= Flocculonodular lobe
What divides the hemispheres?
Primary Fissure
Divides hemispheres into anterior and posterior lobes
What are the contents of the cerebellum?
- Cerebellar cortex, follia (convoluted sulcus and gyrus)
- Deep nuclei
- White matter
What are the divisions of the cerebellar based on evolutionary development?
- Vestibulocerebellum/ archicerebellum= middle, associated with vestibular function
- Spinocerebellum/ Paleocerebellum= spinal cord association
- Pontocerebellum/ Neocerebellum= communicates with brainstem
What are the deep nuclei associated with each cerebellar division?
- Vestibulocerebellum= Fastigial nucleus
- Spinocerebellum= Interposed nucleus
- Pontocerebellum= Dentate nucleus
How does the cerebellum communicate with the rest of the brain?
- Peduncles
- Contain the input and output tracts of the cerebellum
What are the names of the peduncles and what do they communicate with?
- Superior= midbrain
- Middle (biggest peduncle)= pons
- Inferior= medulla
What are the deep nuclei of the cerebellum?
- Interposed nucleus= globose, eboliform
- Dentate nucleus
- Fastigial nucleus
Describe the microscopic structure of the cerebellum
-Regular
-Ordered
-Uniform throughout
Prominently a control system so reflected in structure
What are the cerebellar cortex layers?
- Molecular layer
- Purkinje cell layer
- Granule cell layer
- White matter
What cells are in each layer (outer, middle, inner)?
- Outer= Molecular= Stellate cells, Basket cells
- Middle= Piriform= Purkinje cells
- Inner= Granular= Granule cells, Golgi cells (projections into molecular layer)
Describe the Purkinje Cells
Fan-shaped dendritic trees, extend into molecular layer
Largest dendritic trees in whole of NS
What are the inputs to the layers of cerebellar cortex?
Mossy fibres into granular layers
Climbing fibres into molecular layer
Information also goes to nuclei
What are the outputs from the layers of the cerebellar cortex?
Purkinje cells in piriform layer to central nuclei
Forms loops and circuits
=- Dendritic trees of purkinje cells extend into outer molecular layer
- Granular layer contains granular cells which also send axons up towards the molecular layer
What are inputs and outputs from the cerebellum?
Input= sensory and motor information Output= motor control (makes constant adjustments to the movements involved in actions), voluntary movement, smoothed and coordinated in relation to sensory data
What type of movement is controlled by cerebellum?
Speech and swallowing Eye Trunk Limb All voluntary movement
What are the connections and functions of each cerebellar division?
- Two-way connections= vestibular nucleus
- Spinocerebellum= spinocerebellar connections= posture and gait
- Pontocerebellum= pons and neocortex connections= uniquely large in humans, fine motor control
What are the tracts the ascend from the spinal cord into the cerebellum?
- Posterior spino-cerebellar
- Cuneocerebellar
- Anterior spinocerebellar
- Rostral spinocerebellar
What are the tracts the ascend from the head, neck and brainstem into the cerebellum?
- Olivocerebellar
- Tectocerebellar
- Pontocerebellar
- Reticulocerebellar
- Trigeminal nerve
What are the types of information that are carried in the cerebellar afferents?
- Skin sensory
- Muscle sensory
- Proprioception
- Spinal reflex arcs
- Visual
- Auditory
- Vestibular
- Sensory cortex
- Motor cortices
- Extrapyramidal system
What are the cerebellar efferents?
- Vestibular nuclei
- Reticular formation
- Red nucleus
- Ventrolateral thalamus
Describe the simplified cerebellar circuitry
Inputs= mossy fibres (spinal cord, cerebral cortex, vestibular system), climbing fibres (inferior olive)
- Cerebellar cortex
- Deep cerebellar nuclei
- Brainstem thalamus]
- Spinal cord, cerebral cortex
What are the cognitive functions of the cerebellum?
- Memory: implicit/ procedural
- Coordination of cognitive processes?
- Coordination of emotional processes?
What are the classical features of cerebellar disease?
Ataxic syndrome (incoordination of motor control) -Ataxia of upper limbs -Ataxia of lower limbs -Truncal ataxia -Gait ataxia -Dysarthria (speech) -Nystagmus (jerky movements of eyes) MAY ALSO BE DUE TO BRAINSTEM DISEASE (INPUT AND OUTPUT SYSTEMS)
Where are the defects which result in incoordination?
- Sensory and motor input
- Internal processing
- Motor output
What happens if the cerebellar disease is in the hemisphere?
Unilateral limb ataxia
Ipsilateral
What happens if the cerebellar disease is in the midline?
Trunk
Posture
Gait
What are the extended roles of the cerebellum?
- Memory problems
- Motor learning
- Autistic spectrum disorder
- Affective disorders
- Psychotic disorders
What are the cerebellar diseases?
- Neoplasia
- Multiple sclerosis
- Trauma
- Drugs and toxins
- Neurodegenerations
What are the types of hereditary and degenerative ataxias?
- Autosomal dominant cerebellar ataxia
- Spinal cerebellar ataxia
- Other
