Problem 3 Flashcards
How does the Cerebellum influence movement ?
By modifying the activity patterns of the upper motor neurons
–> efferent cells don’t project directly to local circuits of brainstem + spinal cord
Organization of the cerebellum ?
Name the major division of the cerebellar hemispheres.
- Cerebrocerebellum
- Spinocerebellum
- Vestibulocerebellum
What is the primary function of the cerebellum?
To detect the difference or “motor error” between an intended movement and the actual movement
–> then reducing the error thrust its influence on upper motor neurons
Cerebrocerebellum
Regulates highly skilled movements, especially planning + execution of complex movement
–> occupies the lateral cerebellar hemispheres + receives input indirectly from many areas of the cortex
Spinocerebellum
Concerned with movements of distal (paramedian) and proximal (median (vermis)) muscles + eye movements
–> occupies the median zone of the CH + receives input directly from the Spinal cord
Vestibulocerebellum
Regulates the movements underlying posture and equilibrium + vestibule-ocular reflex
–> occupies the caudal-inferior lobes + receives input from vestibular nuclei in brainstem
The connections between the cerebellum + other parts of the NS occur by way of 3 large pathways.
Name them
- Superior cerebellar peduncle
- Middle cerebellar peduncle
- Inferior cerebellar peduncle
–> white matter tracts
Superior cerebellar peduncle
- Neurons are in the deep cerebellar nuclei
- Project to upper motor neurons of superior colliculus
- After relay in thalamus, they also project to primary motor + pre-motor areas of cortex
–> descending/efferent pathway
Middle cerebellar peduncle
- Neurons are in the base of the contralateral pons (pontine nuclei)
- Receive input from almost all areas of the cortex + superior colliculus
- Transverse pontine fibers cross its midline to enter cerebellum
–> ascending/afferent pathway
Inferior cerebellar peduncle
Smallest but most complex of them, containing multiple afferent + efferent pathways
What is the largest source of input that reaches the cerebellum ?
In addition, name the specific destination.
- Cerebral cortex
2. Cerebrocerebellum
How does the cerebellum make sure that our movements are balanced + smooth ?
- Receives info about what the actual motor plan is via afferent nerves from the respective areas in the cortex
- It receives info from muscle spindles as to where the body parts are (to compare that to the plan)
- Then it sends feedback to the motor areas which then can use this info to be better at doing their job
Cerebellar pathway
Ascending
Are destined for pre-motor + associational cortices of the FL, thus motor planning
- Closed loop
- -> project to non-motor areas, from which signals originate - Open loop
- -> get input from multiple areas; output to motor cortices
AND: both run in parallel
Spinocerebellar pathway
Ascending
Are directed to upper motor neurons, which are responsible for executing movement
- -> 1. lateral interposed nuclei
2. Superior peduncle
3. Thalamus + FL
Spinocerebellar pathway
Descending
Are directed to upper motor neurons responsible for executing movements
- -> 1. Fastigial nuclei (vermis)
2. Inferior peduncle
3. Reticular formation + vestibular complex
Vestibulocerebellar pathway
Descending
Goes from
- Inferior peduncle
- Vestibular complex
–> which governs the moment of eyes, head + neck to compensate for linear vs rotational accelerations of the head
Purkinje cells
Are the destination of afferent pathways
–> refer to huge inhibitory dendrites that receive input from parallel fibers
when we move they stop firing because they are tonically active
The cerebellum receives direct input from … ?
- Inferior Olive
- Climbing fibers
- Purkinje cells + deep nuclei
How do local circuit neurons modulate the inhibitory output of purkinje cells ?
By inhibiting them after they received the excitatory input from parallel fibers
–> involves
- Basket cells
- -> lateral inhibition that may focus the spatial distribution of purkinje cell activity - Stellate cells
How is ongoing movement coordinated by the cerebellum ?
- Neurons fire selectively for contraction vs. relaxation of specific muscles, positions of joints + direction
- Purkinje and deep nuclei cells recognise potential errors by comparing incoming patterns of activity concurrently available to both cells
- Deep nuclei send the correcting signals to upper motor neurons
Timing hypothesis
Suggests that the cerebellum is critical for sensorimotor learning because it generates predictions that are temporally precise
- cortical areas select effectors while cerebellum supplies the precise timing needed for activating these effectors
- Lesions are most disruptive to highly practiced movements, which present the greatest need for precise timing
e. g.: classical conditioning example with airpuff
State estimate
Is calculated by the brain and is a prediction of the change in motor state
–> occurs by combining sensory info about the last known position with predictions of it’s responses to recent movement commands
Forward model
Rapidly predicts whether a motor program will achieve its goal before it is carried out (thus, cerebellum)
–> accurately planning + controlling movement, where sensory consequences will signal how the movement turned out
BUT: activation of cerebellum decreases with practice showing reduction in error as skills improve
Inverse model
Inverts the information flow of the forward model by putting the desired goal of the movement into action
–> calculates motor commands that are required
Why can’t we tickle ourselves ?
Due to the sensory predictions made by the forward model
–> right anterior cerebellar cortex is selectively deactivated
e.g.: mediated by somatosensory + ACC
Cerebellar ataxia
Results in jerky + imprecise movements
Nystagmus
Difficulty of the eyes to maintain fixation
–> drifts from target then jumps back
Golgi cells
- Receives excitatory inout from parallel fibers
- Gives inhibitory output to granule cells
–> modulation
Is TMS a good method to treat cerebellar damages ?
Good method because non-invasive
–> stimulating m1 + cerebellar cortex
