The cerebellum Flashcards
Cerebellum - Prominence
Accounts for 10% of total brain volume but more than HALF of the brain’s neurons
Cerebellar cortex - Key things
1) Consists of large number of virtually identical functional units suggesting that it performs similar functional operations on different inputs
2) It receives massive input from sensory systems and from systems involved in planning and execution of movement
3) Forms loops with premotor and motor systems of cerebral cortex and brainstem that are involved in controlling movement. It also has reciprocal connections with association cortex, especially in the frontal lobes
4) Synaptic transmission in the cerebellum is subject to modification (long term depression) which is thought to be important for motor learning
Damage to cerebellum causes…
Ataxia
Intention tremors
Decomposition of movements
Ataxia
Abnormalities in execution of voluntary movements. Lack of coordination
Intention tremors
Tremors DURING movements (diff from Parkinson’s) Most noticeable at the end of a movement
Decomposition of movement
Fragmentation of complex movements that are normally carried out in a smooth coordinated fashion
Folia
Folds in cerebellum
Increase the surface area of the cerebellar cortex
Flocculonodular region
Old structure
Balance and eye movements
Flattened under cerebellum
Spinocerebellum
Intermediate hemisphere - Vermis - Intermediate hemisphere
Gets most its inputs from spinal cord
Outputs go to brainstem and down spinal cord
Coordination of limbs
Vermis
Worm
Posture control
Intermediate hemispheres
Control limbs
Lateral hemisphere
Cerebrocerebellum
Communicates with cortex
Much bigger in humans
Some cognitive functions
Cerebellar peduncles
Connect the cerebellum to the brainstem
Superior peduncle
Middle cerebellar peduncle
Inferior cerebellar peduncle
Inferior cerebellar peduncle
Inputs from spinal cord (directly and through brainsten) and vestibular nuceli
Middle cerebellar peduncle
Huge ones
Inputs from cerebral cortex by way of PONTINE (pons) nucleus
Superior cerebellar peduncle
The output of cerebellum to brainstem and thalamus
Deep nuclei
Inputs to the cerebellum project to both the cortex and the deep nuclei
Outputs from the cortex project to the deep nuclei, which, in turn, form the outputs of the cerebellum
Fastigial
Outputs from Vermis, most medial pathways, balance and posture
Interposed
Inputs from intermediate hemispheres
Outputs go for cortex and rubrospinal tract limb control
Dentate nucleus
Go back up to thalamus and then to cerebral cortex
What is between molecular layer and granule cell layer in the cerebellar cortex?
Purkinje cell layer!!
How many layers in cerebellar cortex?
3
Half the neurons in your brain are…
Cerebellar granule cells
Purkinje cell dendrites are in…
the molecular layer
5 types of neurons found in cerebellar cortex
- Purkinje cells
- Granule cell
Three inhibitory interneurons: - golgi cells
- stellate cells
- basket cells
1 mossy fiber makes connections with a few granule cells
Granule cell axon goes up to molecular layer and then head in opposite directions
Extend through dendrites of purkinje cells: these are called parallel fibers, extend half a centimeter and extend through hundreds of purkinje cells and makes excitatory synapses on all of these purkinje dendtrites
Where do mossy fibers make excitatory connections?
Granule cells
Deep cerebellar nuclei
Bundles of parallel fibers that excite the dendrites of Purkinje cells and basket cells?
Beams
Basket cell effect on Purkinje cells
Inhibit Purkinje cells on the parallel beam
Simple spikes
In Purkinje cells. Modulated by sensory stimuli and voluntary movements
Inferior olive
Source of climbing fibers
Climbing fiber
Makes direct synapse on…Purkinje cells
Results in very powerful excitation
When climbing fiber fires AP purkinje cell fires AP
Climbing fibers generate…
Complex spikes
Large prolonged depolarization caused by voltage-gated calcium channels and smaller sodium spikes
Golgi cells
Granule layer
Axons extend into molecular layer and are excited by purkinje cells
Golgi cells inhibit granule cells
Stellate cells
In molceular layers
Inhibit purkinje cells
Basket cells
molecular layer
activated by parallel fibers
Flocullonodular lobe
Input from vestibular system and visual system
balance
Spinocerebllum
Vermis
Balance and posture
Where does vermis project?
Fastigial nucleus
Involved in what? Posture
Ventral lateral nuclei of thalamus
relays cerebellar info
After the vermis projects to the fastigial nucleus, where does the fastigial nucleus project to and what tract? Mainly involved in what?
Vestibular nuclei: Vestibulospinal tract
Reticular formation: Reticulospinal tract
Mainly involved in posture
Intermediate hemispheres project to where before they go to M1?
Interposed nuclei
Magnocellular red nucleus
Magnocellular red nucleus
Rubrospinal tract
Control of limb movements
Lateral hemispheres of cerebellum form…
cerebrocerebellum
Feedback control
AFTER error has been made
Feedforward control
Anticipating that error will come, contracting
Intention tremor and cause
Have feedback control but not feedforward control
INACTIVATED DEEP NUCLEI
Efference copy comes down to cerebellum
Cerebellum gets the motor command of what you were trying to do and what you did
Long term depression - synapses that get weaker
Get weaker if active during complex spike
The hypothesis of Improvement in movement
Complex spikes, through long-term depression eliminate simple spikes that create movement errors, creating an accurate model
Complex spike spikes when incorrect and then that simple spike is eliminated
