3: Cerebellum Flashcards
(OBJ) Describe the relationship of the cerebellum to the brainstem, and explain how information travels in and out of the cerebellum.
CEREBELLAR PEDUNCLES: tracts of white matter that join cerebellum to brainstem
- -Superior CP: cerebellum -> decussate -> midbrain [-> VL/VA of thalamus or red nucleus] (output)
- -Middle CP (aka brachium pontis): cerebral cortex -> pons -> cerebellum (input)
- -Inferior CP: medulla + spinal cord cerebellum (input and output)
(OBJ) Define the anatomical (5) subdivisions of the cerebellum.
Two hemispheres connected in midline by vermis
Folia = transverse folds; a core of white matter within a thin layer of cortex
–Arbor vitae = white matter looks like tree in sagittal view
Primary fissure = separates anterior and posterior lobes
Posterolateral fissure = separates posterior and flocculonodular lobes
Tonsil = lobule superior to the foramen magnum
(OBJ) Explain the cellular organization of the cerebellar cortex. Briefly summarize synaptic interactions.
(from surface in)
MOLECULAR LAYER: contains dendrites of Purkinje cells and axons/parallel fibers from granule cells
PURKINJE LAYER: single layer of large Purkinje cells
GRANULE CELL LAYER: contains huge numbers of tiny granule cells and their dendrites, axons of Purkinje cells, mossy fibers, & climbing fibers
Mossy fibers -!-> granule cells -!-> Purkinje cells
Climbing fibers -!!!-> Purkinje cells
List and give the function of the three functional subdivisions of the cerebellum.
Vestibulocerebellum: flocculonodular lobes
–Regulates vestibular activity, coordinates reflex eye movements
Spinocerebellum: vermis, intermediate zone of cerebellum
–Regulation of muscle tone, monitoring of execution of movement; corrects for motor error or changing circumstances of the body
Cerebrocerebellum: lateral hemispheres
–Planning, learning, and initiating complex (highly skilled) voluntary motor sequences
Briefly state the primary function of the cerebellum. How does it perform this function? Generally, what happens when it is damaged?
Modulate movement: detect motor error and provide corrections to improve performance
–Controls IPSILATERAL side of body
Acts by regulating the activity of upper motor neurons in the descending motor pathways
Damage -> clumsy and uncoordinated movement
Explain the significance of the cerebellar tonsil.
In situations of increased pressure, may herniate down through foramen magnum and compress respiratory centers in medulla and spinal cord
Why does alcohol have such a severe effect on the cerebellum?
All five types of cerebellar neurons (except granule cells) use GABA as their neurotransmitter (all are inhibitory)
(mOBJ) What are the five cell types of the cerebellum? What layer is each in?
*Purkinje cells - Purkinje layer
*Granule cells - granular layer
Golgi cells (few) - granular layer
Basket cells - molecular layer
Stellate cells - molecular layer
(mOBJ) Describe Purkinje cells.
The ONLY output from the cerebellar cortex
Cell body in Purkinje layer
Dendrites extend into molecular layer and branch extensively at right angles
Axon extends into white matter -> deep cerebellar nuclei or vestibular nucleus
(mOBJ) Describe granule cells.
Most abundant type of neuron in brain
Soma and dendrites located in granular layer
Axon -> molecular layer, then divides and spreads -> excitatory synapse on Purkinje cells
–Axons = “parallel fibers”
–TONS of parallel fibers synapse on each Purkinje cell
(mOBJ) Describe mossy fibers.
Name for the terminations of axons coming from other parts of the brain (spinocerebellar tracts, pontocerebellar tracts, etc)
Primary source of input to Purkinje cells
Synapse on granule cells in granular layer -!-> granule cells -!-> parallel fibers -!-> Purkinje cells
(mOBJ) Describe climbing fibers.
Direct source of powerfully EXCITATORY input to Purkinje cells from inferior olive
–Highly specific: one olivary neuron -> one or two Purkinje cells
Axon extends from inferior olivary nucleus -> inferior cerebellar peduncle -> Purkinje cell and wraps around it
Name the three deep cerebellar nuclei and from where each receives input. What is their significance? Which is the largest?
Fastigial nucleus (medial): input from Purkinje cells of vermis Interposed nuclei (globose & emboliform): input from intermediate zone Dentate nucleus (lateral): LARGEST, input from lateral hemispheres, output -> superior cerebellar peduncle -> decussates
Significance: most cerebellar output is integrated in the deep cerebellar nuclei before it leaves the cerebellum
Give a general overview of cerebellar circuits
Excitatory input from inferior olive -> climbing fibers -!!!-> Purkinje cells
Excitatory input from rest of brain -> mossy fibers -!-> granule cells + parallel fibers -!-> Purkinje cells
–Climbing fibers & mossy fibers -!-> deep cerebellar nucleus neurons via collaterals on their way up
Activated Purkinje cells -x-> deep cerebellar nuclei
What is inhibitory sculpting?
The manner in which excitatory output from the deep cerebellar nuclei is modified by inhibitory output of the Purkinje cells from the cerebellar cortex