Cerebellum Flashcards
Where is the cerebellum?
Back of the brain, underlying the occipital and temporal lobes of the cerebral cortex.
How much volume does the cerebellum occupy vs number of neurons.
10%, 50%.
Cerebrocerebellum location, function and inputs.
Occupies lateral hemispheres.
Motor planning, co-ordination of complex movements, cognitive functions.
Cerebral cortex via pontine nuclei.
Spinocerebellum location, function and inputs.
Includes vermis and intermediate zones of anterior and posterior lobes.
Controls muscle tone and posture.
Proprioceptive information from SC.
Vestibulocerebellum location, function and inputs.
Comprises flocculonodular lobe.
Maintains balance, eye movements.
Inputs from vestibular nuclei.
How many granule cells in granular layer?
5 x 10^10.
Where do mossy fibres originate?
Pontine nuclei, spinal cord, reticular formation, vestibular nuclei.
How are parallel fibres created?
GCs send their axons towards the cortical surface, birfurcating in the molecular later to send their collaterals in opposite directions.
The similarity of the architecture and physiology in all regions of the cerebellum implies what?
That different regions of the cerebellum perform similar computational operations on different inputs.
In what sense does the cerebellum contribute to balance and posture? What evidence?
Modulates commands to motor neurons to compensate for shifts in body position or changes in load upon muscles.
Cerebellar patients suffer from balance disorders, often develop stereotyped postural strategies to compensate e.g. wide-based stance.
Role of cerebellum in movement co-ordination is demonstrated by…
Dysmetria, dusdiadochokinesia, intention tremor.
What is dysmetria?
Inability to control distance, speed and range of motion necessary to preform smoothly co-ordinated movements.
What is dysdiadochokinesia?
Difficulty preforming rapidly alternating movements, such as hitting a surface rapidly.
What is an intention tremor?
Tremor that occurs when patient makes a movement. Believed to be due to an ‘overshoot’ in the movement, followed by rapid correction.
What does vestibulo-occular reflex allow us to do? What does it require?
Maintain gaze on an object when head is rotated.
Motor commands to eyes to be precisely calibrated with experience.
What do magnifying glasses do to VOR?
Adapt it. Cause velocity of retinal image to increase relative to head.
In what sense foes the VOR highlight the cerebellum’s role as a feedforward controller?
Refines VOR by using input from vestibular system and eye muscle proprioceptors to generate accurate compensatory eye movements.
If mismatch occurs, retinal slip serves as error signal, trial and error recalibration until movements are precisely counterbalanced.
What do mossy fibre inputs convey?
Sensory information used to evaluate the sensory context of movement: where are the body parts (proprioceptors), what are the desired movements (motor cortex).
What are the patterns of convergence and divergence in the MF pathway?
One MF connects to hundreds of GCs (divergence), which also receive inputs from many MFs (convergence).
PFs connect to the dendrites of thousands of individual PCs (divergence), and PCs receive input from hundreds of thousands of different PFs (convergence).
Divergence enables specific information to be spread to many PCs, convergence allows integration of many inputs.
Why does one CF input heavily depolarise a PC?
Each CF forms hundreds of synaptic connections with just one cell.
What is a complex spike?
Large-amplitude action potential followed by burst of high-frequency low-amplitude spikes.
Who showed complex spiking leads to LTD and how?
Ito et al (1982) showed that future excitability of PF-PC synapses concurrently active with CF inputs is reduced.
What shows that cerebellum also involved in cognition?
CCAS, deficits in language, visuospatial and executive functions. Disorganised thoughts and affective dysregulation.
Dysmetria often accompanied by difficulty in timing serial non-motor events, inability to judge distance or scale find it hard to judge the amount of time that has passed in a cognitive task or if one tone was longer than the other.
