Cerebellum

Question 1

Cerebellum connection to brainstem

Answer 1

3 paired fiber bundles (peduncles):
inferior
middle
superior

inferior and middle: major inputs
superior: output

Question 2

Lobes

Answer 2

Primary fissure between anterior and posterior; postero-lateral fissure defines the border of flovvulo-nodular lobe

Question 3

vestibulocerebellum

Answer 3

another name for flocculo-nodular lobe

• input from vestibular organs
• outputs to vestibular nucleus in brainstem

Question 4

vermis

Answer 4

midline longitudinal fold, hemispheres on either side.

Question 5

neocerebellum

paleocerebellum

Answer 5

neo: posterior lobe (corticocerebellum, cerebrocerebellum)
paelo: midportion of anterior lobe and posterior lobe (vermal and paravermal cortex); aka spinocerebellum: spinal afferent inputs, outputs to motor control nuclei

Question 6

Layers in cross section

Answer 6

3 layered cortex overlying a group of paired central nuclei.
Four nuclei on each side:
dentate
interposed (globose and emboliform together)
fastigial

Question 7

vermal zone

Answer 7

output connections through FASTIGIAL nucleus

involved in control of axial musculature, posture, balance, integration of head and eye movements

Question 8

paravermal (or intermediate) zone

Answer 8

connections through the INTERPOSED nuclei and fine-tunes movements of limbs

Question 9

Lateral (or hemispheric) zone

Answer 9

connections through the dentate nucleus, involved in higher level coordination of movements including planning and initiation of movements.

Question 10

flocculo-nodular lobe connects with

Answer 10

vestibular nucleus of brain

Question 11

What provide the major output pathway of the cerebellum?

Answer 11

deep nuclei
There is a medial (core musc) to lateral organization of cerebellar outputs.
Cerebellar outputs from the deep nuclei of medial regions (vermis, vestibulocerebellum) modulate medial descending pathways (vestibulospinal tracts, reticulospinal tracts, tectospinal tracts).
Cerebellar outputs from lateral regions (paravermis and vestibulocerebellum) project to dentate and interpositus nuclei which modulate the rubrospinal and corticospinal outputs (fine distal movements).

Question 12

Vermal (medial) cerebellum through the fastigial nuc sends info to the _______

Answer 12

vestibular nucleus and pontine reticular formation (bilaterally). Info descends in medial descending system by way of lateral vestibulospinal tract and reticulospinal tract

Question 13

Vermal cerebellum involved in_____

Answer 13

equilibrium and posture

Question 14

Paravermal cerebellum output

Answer 14

through interposed nuclei sends info to contralateral red nucleus, w/ motor output through rubrospinal tract

Question 15

Lateral or hemispheric cerebellum output

Answer 15

sends info via dentate nuc to contralateral ventrolateral (VL) thalamus

Question 16

Vestibular input TO the cerebellum arrives in____

Answer 16

flocculo-nodular lobe

Question 17

Info from spinal cord goes where in cerebellum?

Answer 17

vermal and paravermal portions
Double somatotopic distribution (one ant lobe–caudally, one post lobe–rostrally; “head to head”)
*There is NO somatotopic map laterally (no primary afferent input in lateral zone.)

Question 18

What ends up in the lateral zone?

Answer 18

inputs from cortex via pontine nuclei to end in lateral zone (from primary motor cortex and assoc. motor cortex) w/ collaterals of corticobulbar and corticospinal fibers.

Axons from cortex synapse on ipsilateral neurons in basal pons and the pontine neurons send axons contralaterally to cerebellar hemispheres.

Question 19

Somatotopic map of cerebellum

Answer 19

axial musculatrue along vermis, distal limbs on paravermal region.
Aud/vis info indirectly reach vermis near ant/post lobe boundary.
Vestibular info to vermis and flocculo-nodular lobe.

Question 20

Functions of medial cerebellum

Answer 20

equilibrium (interconnections with vestibular nuclei and descending spinal tracts)
posture (proprioceptive and cutaneous afferents from axial musculature)

Question 21

Functions of Paravermal (intermed) cerebellum

Answer 21

movement of distal limbs (somatotopic distrib), and outflow goes to red nucleus via interposed nuclei

Question 22

Lateral cerebellum functions

Answer 22

interconnections with motor cortex (role of neocerebellum in cortical coord and planning and initiation of movement)

Question 23

Flocculonodular lobe
functional region
principle input
deep nucleus
principle destination
function

Answer 23

functional region: vestibulocerebellum
principle input: vestibular sensory cells
deep nucleus: vestibular
principle destination: axial motor neurons
function: axial control, vestibular reflex (balance, eye movement)

Question 24

Vermis
functional region
principle input
deep nucleus
principle destination
function

Answer 24

functional region: spinocerebellum
principle input: visual, auditory, vestibular, somatosensory
deep nucleus: fastigial
principle destination: medial systems
function: axial motor control (posture, locomotion, gaze)

Question 25

Paravermal
functional region
principle input
deep nucleus
principle destination
function

Answer 25

functional region: spinocerebellum
principle input: spinal afferents
deep nucleus: interposed
principle destination: lateral system, red nucleus
function: distal motor control

Question 26

Lateral hemisphere (beyond paravermal)
functional region
principle input
deep nucleus
principle destination
function

Answer 26

functional region: cerebrocerebellum
principle input: cortical afferent
deep nucleus: dentate
principle destination: integration areas
function: initiation, planning, timing

Question 27

Cerebellar deficits are always ____

Answer 27

ipsilateral

Question 28

Cerebellar lesions result in ____

Answer 28

loss of coordination, equilibrium (disturbed synergy–loss of coord/timing; equilib; tone)

NO LOSS of sensation or muscle strength

Question 29

Dysmetria

Answer 29

inability to bring a limb to a desired point in space

Question 30

Cerebellar deficits mnemonic

Answer 30

HANDS Tremor

Hypotonia (anterior lobe inj)
Ataxia (dysdiadochokinesia--impaired rapid alternating movements; decomposition of movement; dysmetria)
Nystagmus
Dysarthria
Stance and gait problems
Tremor (intention)

Question 31

Layers of the cerebellum

Answer 31

Molecular layer (uppermost): contains parallel fibers, dendrites of Purkinje cells, scattered inhibitory interneurons called stellate cells and basket cells.

Purkinje cell layer: middle layer (cell bodies)

Granular layer: lowest layer, contains small granule cells whose processes extend superficially to become the parallel fibers of the molecular layer

Question 32

Info flow into cerebellar cortex via ____ (afferents)

Answer 32

mossy fibers and climbing fibers. Inputs give off collaterals that deliver excitation to cells in the deep nuclei.

Climbing fibers: from contralateral inferior olivary nucleus. (extensive contacts with Purkinje cell soma and dendrites)

Mossy fibers: input to the cortex from primary vestibular afferents and pontine nuclear cells. (all info that isn’t from inferior olive comes from mossy fibers). Mossy fibers diverge and excite a large number of granule cells. Each granule cell is contacted by numerous mossy fibers. Granule cells then excite Purkinje cells by means of contacts delivered by parallel fibers. Mossy fibers also hit Golgi cells and sometimes provide collaterals to cerebellar nuclei en route to the cerebellar cortex.

Question 33

5 intrinsic cell types of cerebellar cortex

Answer 33

Golgi cells
granule cells
basket cells
stellate cells 
Purkinje cells

(first 4 are interneurons within cortex; Purkinje cells have axons that exit the cortex, carrying info to deep nuclei)

All cerebellar cortical neurons are inhibitory with target neurons, with exception of granule cells.

Question 34

Which makes more contact to separate Purkinje cells, climbing or parallel fibers?

Answer 34

Parallel: contacts hundreds of purkinje cells (but many parallel fiber inputs must summate to generate AP in a purkinje cell–simple spike)

(Climbing fibers hit around one dozen Purkinje cells, each purkinje cell by only one climbing fiber. But thousands of release sites/contact between one climbing fiber and one purkinje cell–>complex spike in purkinje cell)

Question 35

How is excitation delivered to the Purkinje cell?

Answer 35

1. Climbing fiber input from inferior olive.
2. mossy fiber input carrying info from all the other sources that influence the cerebellum.

Purkinje cell output is inhibitory to deep nuclei. (Purkinje cells are the only OUTPUT from the cerebellar cortex)

But deep nuclei also receive excitation from mossy and climbing fibers, so cerebellum is acting as an inhibitory delay loop.

Question 36

Explain Purkinje cell inhibition

Answer 36

Purkinje cells can be inhibited by excitation of basket and stellate cells by parallel fibers. Lateral inhibition. This results in DISINHIBITION of deep cerebellar neurons (increase firing rate).

Purkinje cells have a high rate of spontaneous firing, thus deep cerebellar neurons are continually suppressed.

Golgi cells are also excited by parallel fibers, but provide feedback inhibition of granule cell in glomerulus. Purkinje cells are first excited and then quickly inhibited by these interconnections.

Question 37

Reversing prisms and VOR

Answer 37

Adaptation of VOR can occur, esp in flocculo-nodular lobe. If there is a lesion in that location, the adaptation or “learning” doesn’t take place—cannot compensate for reversing prisms.

Question 38

Motor learning

Answer 38

Cerebellum normally directs planned motor output in accordance with expectation (programmed thru inferior olive) and actual motor performance (such as spinal afferents arriving in the cerebellum as mossy fibers). If there’s a difference between planned and actual motor performance, inferior olive generate CLIMBING FIBER activity (error signal), modulates cerebellar function (can depress mossy fiber input).

Question 39

2 pathways of postsynaptic purkinje cell with climbing fiber and parallel fiber activation.

Answer 39

1. Glutamate from parallel fiber activates AMPA (depol) and metabotropic glutamate receptors (second mess cascadem producing IP3, activating PKC).
2. Climbing fiber activation causes Ca2+ influx thru VSCC.

Joint activation of BOTH pathways leads to LTD: Ca interacts with PKC to decrease post syn response of AMPA receptors to glutamate at parallel fiber synapses.