Classification of cerebellar regions

Question 1

lassification from developmental (phylogenetic / ontogenic) point of view:

Answer 1

• Archicerebellum (flocculonodular lobe; oldest part )
• Paleocerebellum (anterior lobe, vermis & paravermal region; old part)
• Neocerebellum (lateral parts of the hemispheres; new part)

Question 2

Classification from functional point of view:

Answer 2

• Vestibulocerebellum (flocculonodular lobe, fastigial nuclei)
• Spinocerebellum (anterior lobe, vermis & paravermal region, interposed nuclei & fastigeal nuclei)
  Phylogeny: evolutionary history of one species, e.g. humans; ontogeny: individual history of one individual, e.g. from embryo to adulthood cerebellar hemispheres; dentate nuclei )

Question 3

Vestibulocerebellum

Answer 3

§Is the oldest part of the cerebellum (archicerebellum) and is composed of the flocculonodular lobe
§Receives projections from vestibular nuclei & vestibular nerve, thus is referred to as vestibulocerebellum
§Sends feedback to vestibular nuclei via the fastigial nuclei, primarily to influence the lateral and medial vestibulospinal tracts

Question 4

Vestibulocerebellum functions

Answer 4

§Functions (influences the activity of vestibular nuclei, e.g. for purposes of error correction of reflexes):
1. vestibulospinal reflex: keeps the body in the center of gravity (body equilibrium), by maintaining
muscle tone and activating antigravity muscles (= function of lateral vestibulospinal tracts)
2. vestibulocervical reflex: stabilizes position of the head (= function of medial vestibulospinal tracts)
3. vestibulo-ocular reflex: stabilizes gaze during head movement (= function of medial vestibular nucleus)

Question 5

Axons in the inferior cerebellar peduncle come from or exit to the medulla - Efferent input:

Answer 5

§Efferent output:

1. Cerebelloreticular tract (to reticulospinal tract)
2. Cerebelloolivary tract (to inferior olivary nucleus) 3. cerebellovestibular tract (to vestibulospinal tract)

Question 6

Axons in the inferior cerebellar peduncle come from or exit to the medulla -Afferent input:

Answer 6

1. posterior spinocerebellar tract (info: proprioception)
2. olivocerebellar tract (input from inferior olivary nucleus, the only climbing fibers)
3. Vestibulocerebellar tract (from vestibular nuclei)

Question 7

Spinocerebellum

Answer 7

§Is an old part of the cerebellum (paleocerebellum) & is composed of the anterior lobe, vermis (without the nodule), & intermediate (paravermal) hemisphere
§Receives input from ipsilateral spinal cord (spinocerebellum) mainly concerning unconscious proprioception through the posterior spinocerebellar & cuneocerebellar tracts
§Sends back information via the fastigial & interposed (globose & emboliform) nuclei to reticulospinal, rubrospinal , and vestibulospinal tracts

Question 8

Spinocerebellum function

Answer 8

§Regulates muscle tone, posture, & balance (via the medial motor pathways, e.g. reticulospinal tract)

Question 9

Dorsal (posterior) spinocerebellar and cuneocerebellar tracts

Answer 9

contain unconscious proprioceptive, but also cutaneous signals
§spinocerebellar tracts is a sensory pathways, hence 1st order neuron is located in the dorsal root ganglion
§2nd neuron: is located:
- at Clark’s nucleus of the spinal cord for dorsal spinocerebellar tract and - at accessory cuneate nucleus in the medulla for cuneocerebellar tract

Question 10

spinocerebellar tracts

Answer 10

§Dorsal (posterior) spinocerebellar tract transfers signals from lower limbs and torso. These are signals from different sensory receptors that have been integrated by Clark’s nucleus.

Question 11

cuneocerebellar tract

Answer 11

Cuneocerebellar tract transfers signals from upper limbs. These are signals from different sensory receptors that have been integrated by accessory cuneate nucleus.

Question 12

Cerebrocerebellum

Answer 12

• is a new part of the cerebellum (neocerebellum) & is composed of lateral hemispheres
• receives afferent projections primarily from contralateral neocortex (e.g. motor cortex)
• projects back via dentate nucleus to contralateral motor cortex via thalamus (VL) and red nucleus

Question 13

Cerebrocerebellum functions

Answer 13

compares intention and action of motor signals and corrects errors, especially rapid alternating and sequential movements (e.g. speaking, rapid finger [limb] movements)

Question 14

Middle cerebellar peduncle

Answer 14

§Middle cerebellar peduncle contains only afferent (arriving) axons from the pons : 1. Pontocerebellar tract (from pontine nuclei to cerebellum)

• largest afferent cerebellar input
• pontine nuclei project to contralateral cerebellum
• all pontine nuclei receive ipsilateral input from cerebral cortex, but send contralateral to cerebellum

Question 15

superior

Answer 15

§Axons that pass through the superior cerebellar peduncle come from or exit to the midbrain
§superior cerebellar peduncle contains mainly efferent (exiting) axons towards the midbrain:
1. Dentatothalamic tract (to the motor cortex via thalamus)
2. Dentatorubral tract (to the red nucleus; parvocellular part)

Question 16

Cerebellar ataxia

Answer 16

§Integration of proprioception is faulty

§Spinocerebellar & vestibulocerebellar lesions cause truncal ataxia (“A” = lack of; taxia = order

Question 17

Summary: cerebellum regulates the descending motor pathways

Answer 17

All 3 cerebellar loops coordinate sensory & motor components of ongoing movements
§The cerebellum does NOT have direct input into spinal motor neurons (LMNs), instead it influences spinal motor neurons indirectly through the descending motor pathways (pyramidal & extrapyramidal or UMNs)
§The 3 cerebellar loops regulate the descending motor pathways independent of each other