2 Cerebellum Flashcards
Describe the relationship of the cerebellum to the brainstem. Be specific re: connections to rest of brain.
- lies dorsal to pons and medulla and is separated from them by 4th ventricle
a) connected to midbrain via sup cerebellar peduncle
b) connected to pons via middle cereb. ped.
c) connected to medulla via inf. cereb. ped.
How does information travel in and out of the cerebellum?
OUTPUT
-superior cereb. ped. is main output; these fibers decussates in the midbrain
INPUT
- middle cerebellar ped: input from cortex
- inferior cereb. ped: input from brainstem/spinal cord; (few outputs to brainstem nuclei)
Define the anatomical subdivisions of the cerebellum.
Two hemispheres connected by midline vermis
- primary fissure separates: anterior and posterior lobes
- posterolateral fissure separates: posterior and flocculonodular lobes
Define the functional subdivisions of the cerebellum.
- vestibulocerebellum (consists of flocculus and nodulus): receives 1° input from vestibular system; posture, balance, reflex eye mov’ts
- spinocerebellum (consists of vermis and intermediate zone
–the tissue in hemispheres just lateral to the vermis on both sides): receives most of its info from spinal cord; reg muscle tone and adjusts ongoing mov’ts
- cerebrocerebellum (consists of hemispheres lateral to the intermediate zone, see photo): input from cerebral cortex via pontine nuclei; planning and initiation of skilled mov’ts
Explain the cellular organization of the cerebellar cortex.
inner = arbor vitae (white matter) which along with the paired deep cerebellar nuclei, make up the CORE
outer = gray matter called the CEREBELLAR CORTEX which contains:
A) THREE LAYERS:
—1. Molecular layer (outer): Purkinje dendrites
—2. middle: contains PURKINJE cell bodies
—3. Granule cell layer (inner): Purkinje axons and large # granule cells’ cell bodies which project superiorly through the Purkinje layer into the Molecular layer where they form parallel fibers (“T”-shaped) that interact with the Purkinje cells
B) FIVE NEURON TYPES
–know Perkinje and Granule cells; the three other types inhibit Perkinje cells
Explain synaptic interactions between cells in the cerebellar cortex.
1. INPUT fibers are excitatory and act via two pathways:
INDIRECT PATHWAY/INHIBITORY LOOP
–MOSSY fibers (from potine nuclei vestibular nuclei and spinal cord) excite Purkinjes indirectly via granule cells which bifurcate into parallel fibers (parallel to folia) and synapse on Perks; ~100-300k synapsing on 1 Perk!
—-MOSSYS’ Parallel fibers also excite the 3 types of interneurons which all INHIB Purk cells
–CLIMBING fibers (from inf. olive of medulla) do so directly
**End result is increased firing of Purkinje cells which INHIBITS deep cerebellar nuclei
DIRECT PATHWAY/EXCITATORY LOOP
–Both Mossy and Climbing fibers excite deep cerebellar nuclei directly
2. OUTPUT is provided via deep cerebellar nuclei.
–excited directly mossy and climbing fibers
–inhibited by Purkinjes
–thus “sculpted” by cerebellar cortex to produce desired outcome
How does short-term error correction and long-term motor learning work?
- CLIMBING fibers relay msgs of motor error to PURKS and depress inappropriate PARALLEL fiber synapse onto Purkinje
- possible b/c Parallel-Purk synapses are plastic
- occurs via phosphorylation to deactivate or internalization of AMPA receptors in these synapses between Purks and Parallel Fibers
- The appropriate ones are unaffected and become enhanced leading to correction/learning
What is big picture point of cerebellum?
to modulate movement by regulating the activity of upper motor neurons (i.e. to detect motor error and provide corrections to improve performance); may also be involved in learning and memory
Which side does cerebellum affect?
ipsilateral side or bilaterally
What is the cerebellar tonsil?
The one lobule we need to know. Located just superior to the foramen magnum. Can herniate w/ incr ICP causing compressing of the respiratory centers in the medulla. (LIFE-THREATENING)
***JUST FYI: fissures shallower than the primary and posterolateral fissures separate the lobes into paried lobules *
What are the transverse folds on the cerebellum called?
folia
What is the organization of the deep cerebellar nuclei? What do they do (generally)?
medial to lateral: fastigial, interposed (globose and emboliform) and dentate
–they intergrate the output of the cerebellum before it leaves the cerebellum
What is a simple way to think about the circuitry of the cerebellum?
INPUT* –> Cerebellar Cortex –> Deep Cerebellar Nuclei –> OUTPUT**
*mostly via inferior and middle peduncles
**mostly via superior peduncle
AMPA Receptors
Present at the synapse between the Purks and the Parallel fibers of Granule Cells
–Wiki: a non-NMDA-type ionotropic transmembrane receptor for glutamate;
–mediates fast synaptic transmission in CNS.
–name b/c activated by glutamate analog “AMPA”
–most common receptor in the CNS
Where is the vestibulocerebellum again?
consists of flocculus and nodulus
What are the pathways and targets of the vesitbulocerebellum’s INPUT?
Inputs: vestib apparatus in inner ear and vestib nuclei in brainstem –> MOSSY fibers (b/c not coming from inf olive!) –> inf cereb. ped. –> project ipsilaterally to Purks via Granule Cells
What are the pathways and targets (including tracts) of the vestibulocerebellum’s OUTPUT?
**This is only cerebellar output pathway that does not project via the deep cerebellar nuclei!
Vestibulocerebellar cortex –> via Purk axons –> thru inf cereb ped. –> back to vestibular nuclei
- some fibers influence neurons of vestibulospinal tracts (posture and muscle tone)
- other fibers modulate VOR
Where is the spinocerebellum again? What’s its big picture f(x)?
The vermis and intermediate zone; regs muscle tone and movement execution
What is the first MAIN OUTPUT pathway with its targets (including tracts) of the spinocerebellum?
Two major outputs:
1st. FROM MEDIAL PART (VERMIS)
Purk axons from vermis project –>
….a) to ipsilateral fastigial nucleus (most medial) –> thru inferior peduncle –> to vestib nuc and potine/medullary reticular formation
….b) via superior cereb. peds. –> then via VL nuc of thalamus –> to contralateral motor cortex
….”thus output from the medial spinocerebellum influences descending pathways that control axial muscles (i.e. vestibulospinal, reticulospinal and ventral corticospinal tracts) and facial/tongue muscles (corticobulbar tracts)
What is the second MAIN OUTPUT pathway with its targets (including tracts) of the spinocerebellum?
2nd. FROM LATERAL PART (INTERMED ZONE)
….Purk axons from intermediate zone project –> to ipsilateral interposed nuclei –> these axons then exit through sup. cereb. ped. –> project contralaterally, decussating in sup cereb. ped in caudal midbrain though later DOUBLE-CROSSING, to:
….a) the red nucleus
….b) VL nuc of thalamus –> motor cortex
….”thus output from the lateral spinocerebellum influences descending pathways that control limb muscles (i.e. rubrospinal and lateral corticospinal tracts)
What is the MAIN OUTPUT pathway with its targets (including tracts) of the cerebrocerebellum?
Purk axons project to ipsilateral dentate nucleus –> 2° fibers cross-over in sup. cerebellar peduncle and project to:
1) via dentatothalamic fibers thru VL –> to motor cortex **affects primary and premotor cortices on contralateral side, but these will decussate therefore example of double-crossing
2) via dentatorubral fibers to parvocellular division of red nucleus –> these neurons project to ipsilateral inferior olive -> gives rise to climbing fibers –> these cross-over in medulla –>via inf. cereb. ped –> travel back to cerebellum
**Feedback loop allowing cerebellum to modulate Purk cells; part of motor learning process
Draw vestibulocerebellar pathway summary
see photo
Draw spinocerebellar pathway summary
Draw cerebrocerebellar pathway summary
What is A?
red nucelus (in the rostral midbrain)
What is B?
decussation of the superior cerebellar peduncle (in the caudal midbrain)
What is C?
superior cerebellar peduncle (in the mid-pons)
What is D?
Middle cerebellar peduncle (at mid- and caudal-pons)
What is E?
pontine nuclei and transverse pontine fibers (in mid- and caudal pons, and rostral medulla)
What is F?
vestibular nucleus (in caudal pons, rostral medulla and middle medulla)
What is G?
reticular formation (in caudal pons, rostral medulla, middle medulla)
What is H?
inferior cerebellar peduncle (in rostral and middle medulla)
What is I?
inferior olive (in rostral medulla and middle medulla)
