The Cerebellum Flashcards
Where is the cerebellum located?
Located at the back of the brain under the occipital lobe, level with the brain stem.
Cerebellar stats
Comprises only 10-20% of the brains volume but contains more than 50% of its neurons.
Outline the structural organisation of the cerebellum.
Highly ordered structure with densely packed neurons and a repeating modular arrangement.
Name the 3 layers of the cerebellar cortex from outermost to innermost.
Molecular layer
Purkinje layer
Granule cell layer
Describe the structure of the folia.
Consist of outer grey matter (cerebellar cortex) as well as inner white matter that contains the deep nuclei.
Name the output nuclei of the cerebellum.
The deep nuclei
Contents of the molecular layer of the cerebellar cortex.
Granule cell axons (parallel fibres)
Stellate and basket cells
Purkinje dendritic tree
Contents of the Purkinje layer of the cerebellar cortex.
Purkinje cell bodies
Contents of the granule cell layer of the cerebellar cortex.
Granule cell bodies
Golgi cells
Cerebellar glomeruli where granule cells connect to mossy fibres
Name the 5 types of cell found in the cerebellar cortex.
Stellate cells Basket cells Golgi cells Purkinje cells Granule cells
What are the 2 inputs to the cerebellar cortex?
Climbing fibres and mossy fibres.
Does the cerebellum influence movement of the contralateral or ipsilateral side of the body, and does this involve any crossing over?
Ipsilateral body meaning there is no crossing over.
Name the three lobes of the cerebellum divided by the transverse fissures.
Anterior, posterior and flocculonodular lobe.
Name the three lobes of the cerebellum divided by the longitudinal fissures.
Vermis, intermediate and lateral zones / lobes.
Which circuit (direct or indirect) increases cerebellar output?
The DIRECT circuit.
Which circuit (direct or indirect) decreases cerebellar output?
The INDIRECT circuit.
Describe disinhibition (with example from cerebellar circuitry)
The inhibition of an inhibitory neuron eg. excitation of stellate and basket cells via excitatory input from parallel fibres. Leads to an increase in stellate / basket cells’ inhibition of the purkinje cells, decreasing PKJ cell activity.
Briefly define feedback inhibition
Inhibition of the input - when an inhibitory cell inhibits the excitatory cell from which it normally receives input.
When (excitatory) cell A activates (inhibitory) cell B, resulting in cell B inhibiting cell A (ie. when a cell inhibits the cell it normally receives input from).
Briefly define feedforward inhibition.
Inhibition of the final output.
Describe an example of feedback inhibition found in the cerebellum.
When activated, the parallel fibres (granule cell axons) excite PKJ cells. They also excite golgi cells which in turn feedback to inhibit the granule cells (ie. cells from which they had initially received input).
Describe an example of feedforward inhibition found in the cerebellum.
When activated, the parallel fibres (granule cell axons) excite PKJ cells. They also excite stellate and basket cells which in turn inhibit the activity of the recently activated PKJ cells.
Describe the effects of the general network mechanism known as feedback inhibition.
Elicits complex activity patterns (in PKJ cells) including rhythmic oscillatory activity.
Describe the effects of the general network mechanism known as feedforward inhibition.
Sets up a brief window of activity (in the PKJ cell) that is quickly shut down.
Where do climbing fibres originate from?
The inferior olive.
What cells do climbing fibres connect to in the cerebellar cortex?
Purkinje cells.
Describe the type of connection make btw climbing fibres and PKJ cells.
1 climbing fibre synapses onto 1 PKJ through wrapping around it’s cell body and dendrites.
Each single climbing fibre makes multiple connections with the single PKJ (no convergence or divergence).
Extremely powerful input called a ‘complex spike’
Describe the complex spike that occurs btw PKJ and climbing fibres.
A single AP in a climbing fibre elicits a large excitatory synaptic potential in the PKJ, resulting in a burst of APs.
What cells do the mossy fibres connect to in the cerebellar cortex?
Granule cells.
Describe the type of connection that occurs btw mossy fibres and granule cells.
The summed activity in mossy fibres triggers a single AP, a ‘simple spike’
Describe the connections btw parallel fibres and PKJ cells.
A single PKJ cell receives input from roughly 250,000 granule cells - convergence of parallel fibres.
Describe the structure of the purkinje cells.
Have a large fan-like dendritic tree that extends into the molecular layer, but only in one plane.
