cerebellum structure, circuitry

Question 1

cerebellar functions

Answer 1

motor planning, coordinates movement (compares intended movement to actual movement), maintains posture, eye movements (vestibuloocular reflex)

Question 2

Where in the cranium is the cerebellum located

Answer 2

cerebellum is located below the tentorium cerebelli in the posterior cranial fossa

it is posterior to the pons medulla and the 4th ventricle

Question 3

cerebellar peduncles

Answer 3

the cerebellum is connected to the brainstem by 3 stalks called cerebellar peduncles,

the peduncles are superior p. & inferior p. in the middle, and laterally is the middle p. (*be careful–this can be confusing)

The peduncles are white matter stalks consisting of fibers going to or coming from the cerebellum

Question 4

cerebellar lobes

Answer 4

2 lateral hemispheres and a midline vermis

midsagitally, you can see the primary fissure (very deep) that separates the anterior lobe from the posterior lobe

the small posterolateral fissure separates the very large posterior lobe from the small flocculonodular lobe (forms the floor of the 4 th ventricle)

Question 5

white and grey mater of cerebellum

Answer 5

the cortex is gray matter and is the outer layer

the white matter is on the inside

Question 6

deep cerebellar nuclei

Answer 6

buried in the deep white matter

from lateral to medial the nuclei:
Dentate (large D)
Emboliform
Globose
Fastigial 

Emboliform+globose= interposed nucleus

Question 7

Cerebellar ridges are called

Answer 7

cerebellar folia that are parallel and are seperated by fissures

Question 8

cerebellar cortex layers

Answer 8

3 layers
Outermost= molecular layer
single cell layer= Purkinje cell layer
innermost= granular layer

Question 9

purkinje cells

Answer 9

have extensive dendritic trees which extend into the molecular layer and arborize in a single plane (perpinduclar to the long axis of the folia)

dendritic trees are aligned one after another

Question 10

cerebellar circuitry

Answer 10

you might need need to draw this out:

sensory input to the cerebellum come in 2 flavors that are both excitatory

1. mossy fibers- transmit info from many areas of the NS, contact granular cells, which then contact purkinje cells via parallel fibers- granular cells are the only excitatory cell within the cerebellar cortex
2. climbing fibers- branched axons from the contralateral inferior olivary nucleus, each climbing fiber makes a single synapse with a single purkinje cell

Purkinje cells are regulated/ inhibited by basket cells and stellate cells

Golgi cells act to inhibit mossy fibers action on granule cell, rate limitors of purkinje cell activity

only output from cerbellar cortex is via purkinje cells which are inhibitory and contact the deep cerebellar nuclei

output of cerebellum as a whole is via the deep cerebellar nuclei which are excitatory- modulate the activity of other motor pathways

Question 11

cellular circuitry within a folium

Answer 11

mossy fibers and climbing fibers also excite deep cerebellar nuclei

Question 12

cerebellar functional zones

Answer 12

dentate nucleus receives input from the lateral zone

emboliform and globose aka interpose nucleus receive input from the intermediate zone

fastigial nucleus receives input from the vermis zone

vermis and intermediate hemispheres= spinocerebellum for pusture,

lateral hemishpheres= cerebrocerbellum for planning and execution of movements

flocculonodular node= vestibulocerebellum, for balance, reflexes, eye movements (nodulus and 2 lateral flocculi)

Question 13

vestibulocerebellum

Answer 13

flocculonodular lobe

balance, vestibular reflexes and facilitating eye movements

integrates senses to facilitate motor response

input via vestibular apparatus (in semicircular canals, utricle saccule) either directly to flocculonodular lobe or to vestibular nuclei then to flocculonodular lobe (inferior cerebellar peduncle)

visual cortex/superior colliculus–> pons–> flocculonodular lobe

Question 14

Vestibullaocerebellum output

Answer 14

floculonodular lobe purkinje cells –> vestibular nuclei–> spinal cord or extraocular muscles (medial longituinal fasciculus)

to spinal cord via medial and lateral vestibulospinal tracts to control axial musculature

Question 15

cerebrocerebellar input

Answer 15

via the corticopontocerebellar tract that go thru the internal capsule and then to ipsilateral pontine nucleus then to the contralateral hemisphere of cerebellum via middle peduncle

contralateral olivocerebellar tract via climbing fibers that originate in contralateral inferior olivary nucleus via inferior cerebellar peduncles

Question 16

cerebrocerebellum out put

Answer 16

lateral hemisphere to dentate nucleus to contralateral red nucleus and contralateral VPL of thalamus to the pre and primary motor cortex

influences the rubrospinal and corticospinal tracts

lesions= delays of movements timing is off

Question 17

spinocerebellum input

Answer 17

posterior spinocerebellar tract, anterior spinocerebellar tract, and cuneocerebellar tract

smooth out movements

Question 18

posterior/dorsal spinocerebellar tract

Answer 18

conveys somatosensory information from the trunk and lower limbs to maintain posture and provide feedback to the cerebellum regarding the consequences of ongoing movement

from inferior cerebellar peduncle

cell body from DRG–> synapse in the intermediate horns (T1-L2) and travel in the gracilis or cuneatus to the nucleus to the inferior peduncle

Clarks nucleus is the cell bodies in the intermediate horn

everything travels ipsilaterally terminate as mossy fibers

Question 19

anterior/ventral spinocerebellar tract

Answer 19

relays information about ongoing movements to the cerebellum by sending signals only during ACTIVE movements of lower limb

decussate at the spinal cord travel up via ventral spinocerebellar tract then all the way in the superior cerebellar peduncle and terminate as mossy fibers in the lateral hemisphere of the cerebellum

2 crossovers

Question 20

cuneocerebellar tract

Answer 20

sensory information from the upper limb

ascend via ipsilateral cuneate fasiculus then synapse in the accessory cuneate nucleus in caudal medulla then cuneocerebellar tract then to inferor cerebellar peduncle to the intermediate/vermis zone

Question 21

balance and eye movements from cerebellum

Answer 21

vermis–> fastigial nucleus–> inferior peduncle–> reticular formation and vestibular nuclei–> balance and eye movement

Question 22

intermediate hemisphere out puts

Answer 22

via the interposed nuclei –> superior peduncles–> red nucleus–> proximal muscles of upper limbs

via the interposed nuclei–> superior peduncle–> VL thalamus–> motor cortex–> distal limbs (via CST)

Question 23

cerebellar function causes…

Answer 23

hypotonia, ataxia (loss of coordination), nystagmus, dysarthria, wide stance/ ataxic gate, intention tremor

Question 24

if there is a disorder of the sensory inputs or motor system

Answer 24

vestibularr dysfunction–> nystagmus, imbalance

impaired propriocetion–> sensory ataxia

corticopontocerebellar tract dysfunction–> hypotonia

motor system–> reduced strength

Question 25

are cerebellar lesions ipsilateral or contralateral

Answer 25

IPSILATERAL! to the side of lesion

vestibular apparatus–> reciprical connections via vestibular nuclei and vestibulocerebellum to vestibulospinal tract

spinocerebellum either ipsilateral (posterior spinocerebellar) or deccussate twice (anterior) then travel down to reticulospinal and vestibulospinal tracts

cerebrocerebellum: cerebral cortex from contralateral, cerebellar out put loops back to cerebellum

Question 26

cerebellum somatotopy

Answer 26

two homunculi

mirror images with heads in the middle and arms and legs spread out

Question 27

blood supply to the cerebellum

Answer 27

superior cerebellar artery- anteriorly
AICA- posteriorly and middle

PICA- posterior

Question 28

characteristics of cerebellar dysfunction

Answer 28

HANDS Tremor

Hypotonia- reduced muscle tone
Ataxia- limb incoordination (finger to nose, heel to shin, rapid alternating movements)
Nystagmus- occular oscillations (6 primary fields of gaze)
Dysarthria- slow slurred speech hesitant (say tongue twisters)
Stance and gate- imbalace and wide, posture titubation head bobbing, tandem walk difficult
Tremor- extend upper limbs and hold against gravity

dysmetria- no heel to shin

dysdiadochokinesia- cant rapid alternating movements