Cerebellum Flashcards
Sum up the cerebellum’s role in one sentence
Coordination, calibration, modulation, planning, learning and automating of skilled movements
How does the cerebellum calibrate movement
Compares motor command (cortex) with performance feedback (ascending proprioceptor/sensory input) to correct erorrs and make movement more successful
What are the 3 anatomical divisions of the cerebellum
Cerebrocerebellum, spinocerebellum, vestibulocerebellum
Which deep output nuclei does the spinocerebellum project to
Vermis -> Fastigial
Paravermis -> Interposed nuclei
Which deep output nuclei does the cerebrocerebellum project to
Dentate nucleus
What are the deep output nuclei of the cerebellum
Fastigial, interposed, dentate
Inside -> outside
What are the 3 major cerebellar tracts
Superior peduncle, middle peduncle, inferior peduncle
What is the superior penduncle
OUTPUT to thalamus and brainstem, comprises most output
What is the middle peduncle
INPUT from pons
What is the inferior peduncle
INPUT from vestibular nuclei, spine and inferior olive
How is the cerebellum unique to other motor areas in the brain in terms of how it works with the body
Works ipsilaterally with the body
What are the outer big sections of the cerebellum called
Lateral hemispheres
What other nuclei is important that’s not the deep nuclei
Vestibulo-cerebellum projects to the vestibular nuclei in the brainstem
What is the inner big section of the cerbellum comprised of the vermis and paravermis
Medial hemisphere
Where are each of the functional divisions of the cerebellum located
Spinocerebellum- medial hemisphere
Cerebrocerebellum- lateral hemispheres
Vestibulocerebellum- flocculonodular lobe
Input to the vestibulocerebellum
Direct sensory input from semicircular canals and otolith organs
Vestibular nuclei
Visual input from SC and visual cortex via the pons
Output from the vestibulocerebellum
Fastigial deep nucleus
Ocular motor nuclei
Medial/lateral vestibular nuclei -> Medial/lateral vestibulospinal tracts to neck and back muscles
Vestibulocerebellum functions
Balance and posture
Orientation of head and body
Eye movements
Vestibulo-ocular reflex
What is the vestibulo-ocular reflex
Maintains foveation of an object during head movements
Input to the cerebrocerebellum
Cortex -> pons -> dentate nucleus
Output from the cerebrocerebellum
From dentate nucleus-
Motor control areas and PFC via the ventrolateral thalamus
Red nucleus -> inferior olivary nucleus -> cerebellum
Functions of the cerebrocerebellum
Planning/timing/initiating precise movement
Feedback circuit to regulate cortical motor programs
Motor learning
Cognitive function
What is the function of the red nucleus -ION- cerebellar loop formed from from the cerebrocerbelleum
The red nucleus also receives input from premotor areas- loop may involve motor learning
How may the cerebrocerebellum be involved in cogntiive function
Dentate nucleus appears important in processing sensory info for tasks requiring spatial and temporal judgements
Input to the spinocerebellum
Instruction from sensory and motor cortex
Dorsal and ventral spinocerebellar tracts- neck. trunk, limbs
Inferior olivary nuclei
How does the spinocerebellum receive direct vs indirect input from the dorsal and ventral spinocerebellar tracts
Direct input from interneurons in the spinal grey matter -> mossy fibres
Indirect input via reticular formation nuclei
Output from the spinocerebellum- vermis
Via fastigial nuclei
Ventromedial brainstem descending systems- vestibulo, reticulo, and cortico-spina tracts VIA a thalamocortical relay
Output from the spinocerebellum- paravermis
Via interposed nuclei
Lateral descending systems- rubro and corticospinal tracts
Spinocerebellum functions
Control of axial and limb musculature for posture and locomotion, modulates descending motor systems through thalamocortical relay, online movement-correction, feed-forward control
How does the spinocerebellum do feedforward control
Can elaborate proprioceptive input to anticipate future body position during movement
What region of the spinocerebellum is involved in controlling eye movement together with the vertibulocerebellum
Vermis- controls saccades and smooth-pursuit eye movements
What info does the spinocerebellum receive from the dorsal vs ventral spinocerebellar tracts
Dorsal- sensory feedback from muscles following movement
Ventral- info about spinal motor neuron activity
How does the spinocerebellum do online correction of movement
Compares planned movement (from ventral spinocerebellar tract) with actual movement (dorsal cerebellar tract) to allow correction
What suggests there is a cognitive role for the cerebellum
Prefrontal connections
Expansion of cerebellar hemispheres evolved in conjunction with cerebral expansion
Cerebellar cognitive affective syndrome
Symptoms of cerebellar cognitive affective syndrome
Deficits in language, visual spatial and executive functions, disorganised through
What is the cerebellar outer cortex made up of
100 thousand million neurons (1/2 all neurons in the brain) in highly ordered repeating P-cell modules
What cells provide input to the P-cell modules
Mossy fibre input from all regions involved eg vestib, spinal, pons
Climbing fibre input from IO
What are the 3 layers of the P-cell modules
Molecular layer, Purkinje cell layer, inner granule cell layer (OUT->IN)
What cells are in the molecular layer of the P cell module
Purkinje cell dendrites, granule cell parallel fibres, climbing fibres, various interneurons
What cells are in the Purkinje cell layer of the P cell module
Purkinje cells (principal output to deep nuclei)
What cells are in the inner granule cell layer of the P cell module
Granule cells, mossy fibre inputs, Golgi interneurons
Where are the cell bodies of mossy fibres
Spinal cord, brain stem
What synapses do mossy fibres form
EXCITATORY synapses on granule cell dendrites in the granular layer
EXCITATORY direct synapses with target neurons in deep output nuclei
What is the neurotransmitter identity of granule cell parallel fibres in the outer molecular layer
Glutamatergic (EXCITATORY)
What input does each Purkinje cell receive from granule parallel fibres
Input from 200,000 parallel fibres firing at 50-100Hz
Input from ~200 summates
What sort of firing does input from summated granule parallel fibres elicit in Purkinje cells
Simple Na/K spikes (20-50Hz)
What modulates the frequency of simple spikes in Purkinje cells (caused by parallel granule fibres)
Sensory and motor inputs eg muscle spindles, visual input
How are P specific in their firing
P cells are tuned to particular source/type of input
Project topographically onto the body map in the deep output nuclei
What output do Purkinje cells provide
Inhibitory output to deep output nuclei
What does Purkinje inhibitory output to the deep output nuclei allow
Online calibration and optimisation of movement by correcting motor errors
What is the result of the long trajectory of granule cell parallel fibres
Allows them to contact many P cells that project along the anterior-posterior body axis in the deep output nuclei map, allowing coordinated multi-muscle movement
What info does the inferior olivary nuclei receive
Info from the spinal cord and cerebral cortex
What synapses do the climbing fibres form
Each climbing fibre winds through the dendritic tree of a Purkinje fibre, making around 300 synapses
1:1 ratio
Climbing fibre collaterals also excite the deep nuclei
What firing does APs from climbing fibres elicit in Purkinje fibres
A single AP from CFs (1-10Hz) generates a large EPSP, causing prolonged Ca2+ dependent complex spike in Purkinje fibres
What is the result of prolonged Ca2+ dependent complex spikes caused by climbing fibre input in P cells
LTD of parallel fibre- Purkinje cell synapses, reducing the efficacy of mossy fibre inputs
In what way do climbing fibres map onto Purkinje fibres
Climbing fibre terminals are arranged in a way that maintains IO topography on Purkinje fibres
What is the role of climbing fibres
Report ‘error’ to P cells (discrepancy between cerebellar motor command and sensory detection), and ‘teach’ Purkinje cells which parallel fibres they should become less responsive to
How many granule cels are in the granule cell layer
10 ^11
How many Purkinje cells are in the Purkinje cell layer
3 X 10^7
How many complex spikes does each sensory stimuli/movement generate in P cells
Only 1-2 complex spikes
What do climbing fibres allow BIG PICTURE
Cerebellum-dependent motor learning, recalibration and optimisation of movement
What 3 types of interneurons exist in the P modules
Basket cells, stellate cells, golgi cells
What input do cerebellar interneurons receive
Excitatory granule cell parallel fibre input
What do basket interneurons do
Project to neighbouring P cells forming a basket, inhibiting activity in ‘off-beam’ P cells
LATERAL INHIBITION
What do stellate interneurons do
Short-range within-beam inhibition of P cells. regulatory effect
What do Golgi interneurons do
Project back to granule cells and provide feedback inhibition, curtailing duration of excitement of GCs by mossy fibres
What is hypotonia
Diminished resistant to passive limb displacements
What is atasia
Loss of ability to maintain steady limb/body postrue across multiple joints
What is abasia
Loss of ability to maintain upright stance against gravity, often moving their legs irregularly and falling
What is ataxia
Abnormal execution of multi-jointed movements, lack of coordination
What characterises cerebellar disorders
Loss of automatic, unconscious nature of most movements, especially consisting of sequential movements
How do cerebellar lesinos affect the vestibular-ocular reflex
Inability to learn to reverse the VOR is caused by vestibulocerebellar lesions
What happens to the frequency of simple and complex spikes when first learning a new task
Learning a new task- increased frequency of complex spikes, gradual decrease in simple spikes
What happens to the frequency of simple and complex spikes when a task has been learned
Frequency of complex spikes returns to control, frequency of simple spikes remains decreased
What is dysmetria
Poor accuracy of movement
What is tremor
Low frequency high amplitude oscillations of a limb as it approaches target, overshooting/overcompensated
What is dysdiadochokinesis
Poor rapid alternating movements
What is postural ataxia
Incoordination of axial muscles, postural instability, staggering wide-based ataxic gait
What do vestibulocerebellar lesions cause
Poor balance, nystagmus (eye drift and jump)
What do spinocerebellar lesions cause
Lesions of medial zone- problems standing or walking
Lesions of intermediate zone- poor accuracy, action tremor (3-5Hz)
What do cerebrocerebellar lesions cause
Disrupts multijoint movements eg reaching and grasping objects
What does firing of climbing fibres correspond with
When stimulated, they fire single APs in temporal relation with specific sensory events- suggests they signal important events
What does firing of Purkinje fibres
Fire at up to several hundred spikes a sec during active eye, arm and face movements, due to lots of sensory info converging on the granule cells
Mossy fibre system thus encodes magnitude and direction of peripheral stimuli
Recurrent loops- thalamocortical loop?
Cerebral cortex->pons->lateral cerebellum->thalamus->cerebral cortex
Recurretnt loops- self-regulating loops
Deep cerebellar nuclei project GABAergic inhibitory neurons to the inferior olive, allowing the cerebellum to regulate its climbing fibre input
What are interal models
Interal models of the limbs within the cerebellum automatically take account of limb structure eg a dynamic arm model can convert a desired endpoint into a sequnce of commnds
Can be modulated
