Task 3 Flashcards
what is the cerebellum ?
- influences movements by modifying activity patterns of the upper motor neuorns
- detects the difference between an intended movement and the actual movement (= motor errors)
-> corrects them - two main grey matter structures
-> laminated cerebellar cortex on surface
-> deep cerebellar nuclei
= main source of output - made up of three layers
-> inner granule cell layer
-> middle Purkinje cell layer
-> outer molecular layer
Of what consists the cerebellar cortex?
cerebrocerebellum
spinocerebellum
vestibulocerebellum
What is the cerebrocerebellum?
- lateral cerebellar hemisphere
- input = directly from cortex
- occupies most of the lateral hemispheres
regulation & guidance of highly skilled movements - contralateral
planning and execution of complex
movement -> speech
what is the spinocerebellum?
- median strip along the midline
- Input = directly from spinal cord
- Occupies
-> Paramedian zone
= movement of distal muscles
-> Vermis
= movement of proximal muscles & certain eye movements - ipsilateral
- fractured maps
-> each body part is presented multiple times
-> mapped topographically
what is the vestibolucerebellum?
- caudal-inferior lobes
-> flocculus + nodulus - Input = vestibular nuclei in brainstem
- Regulation of movement underlying posture & equilibrium + vestibulo-ocular reflex
- ipsilateral
what is the vestibulo-ocular reflex?
having stable vision during fast head movements
what are the cerebellar peduncles
- allow the cerebellum to communicate with the rest of the CNS
- three pathways
-> superior cerebellar peduncles
= efferent
-> middle cerebellar peduncle
= afferent
-> inferior cerebellar peduncle
= afferent & efferent
what are the superior cerebellar peduncles?
- efferent
- neurons from deep cerebellar nuclei
- ipsilateral
- their axons project to upper motor neurons in the deep layers of the superior colliculus
-> after in the dorsal thalamus, primary motor & premotor area
what are the middle cerebellar peduncles?
- afferent
- contralateral
- receives input from variety of sources
- cell bodies from pontine nuclei
what is the inferior cerebellar peduncle?
- smallest but most complex pathway
- afferent pathway
-> from vestibular nuclei, spinal cord, brain stem tegmentum
-> stay ipsilateral - efferent
-> to vestibular nuclei & reticular formation
what are inputs to the cerebellum?
- cerebellar pathway
-> cerebrocerebellum - sensory pathway
-> spinocerebellum
-> vestibulocerebellum
what is the output of the cerebellum?
- projections to deep nuclei & vestibular complex
-> projection to upper motor neurons in the brainstem & thalamic nuclei - to deep cellular nuclei
-> dentate nucleus
-> two interposed nuclei
-> fastigial nucleus
what is the ascending output? And what is the descending output ?
Ascending
- cerebrocerebellar pathway
- spinocerebellar pathway
Descending
- spinocerebellar pathways
- vestibulocerebellar pathway
what is the cerebrocerebellarpathway?
= FEEDBACK loop to the cerebellum
- from dentate nucleus
- pre motor cortex
what is the outline of the cerebellum?
- Mossy fibres
-> synapse on neurons in the deep cerebellar nuclei + on granule cells - parallel fibres
-> ascend to the molecular layer of the cerebellar cortex
-> relay excitatory input to dendric spines of Purkinje cells - Purkinje cells
-> receives input from a lot of parallel fibres + direct input from climbing fibres
-> cell body = Purkinje cell layer
-> dendrites = projecting to the molecular layer (= deep cerebellar nuclei)
-> only output of the cerebellar cortex
-> inhibitory
-climbing fibres
-> arises from the inferior olive
-> modulate parallel fibre connection with Purkinje cell
what is the deep excitatory loop?
- mossy fibres & climbing fibres collaterals excite neurons in the deep cerebellar nuclei
- input signals converge on the output stage of cerebellar processing
what is the cortical inhibitory loop?
- consists of desceding inhibitory input from the Purkinje cells
-> also driven by mossy & climbing fibres - Purkinje cells integrate inputs and invert them, by responding to excitatory input with inhibitory input
- golgi, stellate, and basket cells control the flow of information through the cerebellar cortex
-> golgi cells control how much input granule cells provide to purkinje cells
-> basket cells provide lateral inhibition to purkinje cells
How is ongoing movement coordinated?
- purkinje cell & deep cerebellar nuclei are tonically active
-> change their firing frequency as movement occurs
-> recognise potential motor errrors by comparing patterns of convergent activity - deep cerebellar nuclei sends corrective signals to the motor cortex
-> to maintain/ improve the accuracy of the movement
=> happens during the movement occurred
what is the marr-albus theory of motor learning
- climbing fibres are responsible for relying the message of a motor error to the purkinje celll
-> serve as teching signal
-> introduces a long-lasting change in strength of parallel fibre inputs - this plasticity happens when it is simultaneously active as climbing fibre input to the post-synaptic purkinje cell
- if efference copy is the same as real time information (from climbing fibres)
-> less activity in purkinje cell = no need to learn - if efference copy is not the same as real time information (from climbing fibres)
-> purkinje cells modulates its inhibitorys output
-> leads to modulated output to the deep cerebellar nuclei
what is longt-term depression in the cerebellar cortex?
- in order to induce synaptic plasticity
-> pairing stimulation of climbing fibres with stimulation of parallel fibres - activation of parallel fibres alone resulted in maller postsynaptic responses in the purkinje cells
What are consences of cerebellar lesions
errors in movement
-> always on the same side
cerebellar ataxia
= difficulties in producing smooth, well coordinated movements
= rather they are imprecise
dysmetria
= over - and underreaching impairments in highly skilled sequences of learned movements (= speech)
what is state estimation (process)?
- used to accurately plan and control movement
- combining sensory information about the last known position of body parts with predictions of their response to recent movement commands
- CNS never exactly knows the state of the motor apperatus
-> due to delays
what is the forward model?
- anticipation of sensory consequences
- after neural model has been completed, it can rapidly predict whether a motor programme will achieve its goals before it is carried out
-> can be adjusted if it seems unlikely - after movement:
model can be updated by comparing its predictions with what happened
= you can predict own movements, making it impossible to ticke oneself
what is the inverse model?
- inverts the information flow from the forwards model
- inputs the desired goal of movement and back
- calculates the motor commands rewuired to achieve gial
=> generates the program of motor commands required for movement
