Cerebellum Flashcards
Cerebellum connection to brainstem
3 paired fiber bundles (peduncles):
inferior
middle
superior
inferior and middle: major inputs
superior: output
Lobes
Primary fissure between anterior and posterior; postero-lateral fissure defines the border of flovvulo-nodular lobe
vestibulocerebellum
another name for flocculo-nodular lobe
- input from vestibular organs
- outputs to vestibular nucleus in brainstem
vermis
midline longitudinal fold, hemispheres on either side.
neocerebellum
paleocerebellum
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
Layers in cross section
3 layered cortex overlying a group of paired central nuclei.
Four nuclei on each side:
dentate
interposed (globose and emboliform together)
fastigial
vermal zone
output connections through FASTIGIAL nucleus
involved in control of axial musculature, posture, balance, integration of head and eye movements
paravermal (or intermediate) zone
connections through the INTERPOSED nuclei and fine-tunes movements of limbs
Lateral (or hemispheric) zone
connections through the dentate nucleus, involved in higher level coordination of movements including planning and initiation of movements.
flocculo-nodular lobe connects with
vestibular nucleus of brain
What provide the major output pathway of the cerebellum?
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).
Vermal (medial) cerebellum through the fastigial nuc sends info to the _______
vestibular nucleus and pontine reticular formation (bilaterally). Info descends in medial descending system by way of lateral vestibulospinal tract and reticulospinal tract
Vermal cerebellum involved in_____
equilibrium and posture
Paravermal cerebellum output
through interposed nuclei sends info to contralateral red nucleus, w/ motor output through rubrospinal tract
Lateral or hemispheric cerebellum output
sends info via dentate nuc to contralateral ventrolateral (VL) thalamus
Vestibular input TO the cerebellum arrives in____
flocculo-nodular lobe
Info from spinal cord goes where in cerebellum?
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.)
What ends up in the lateral zone?
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.
Somatotopic map of cerebellum
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.
Functions of medial cerebellum
equilibrium (interconnections with vestibular nuclei and descending spinal tracts)
posture (proprioceptive and cutaneous afferents from axial musculature)
Functions of Paravermal (intermed) cerebellum
movement of distal limbs (somatotopic distrib), and outflow goes to red nucleus via interposed nuclei
Lateral cerebellum functions
interconnections with motor cortex (role of neocerebellum in cortical coord and planning and initiation of movement)
Flocculonodular lobe functional region principle input deep nucleus principle destination function
functional region: vestibulocerebellum
principle input: vestibular sensory cells
deep nucleus: vestibular
principle destination: axial motor neurons
function: axial control, vestibular reflex (balance, eye movement)
Vermis functional region principle input deep nucleus principle destination function
functional region: spinocerebellum
principle input: visual, auditory, vestibular, somatosensory
deep nucleus: fastigial
principle destination: medial systems
function: axial motor control (posture, locomotion, gaze)
Paravermal functional region principle input deep nucleus principle destination function
functional region: spinocerebellum principle input: spinal afferents deep nucleus: interposed principle destination: lateral system, red nucleus function: distal motor control
Lateral hemisphere (beyond paravermal) functional region principle input deep nucleus principle destination function
functional region: cerebrocerebellum principle input: cortical afferent deep nucleus: dentate principle destination: integration areas function: initiation, planning, timing
Cerebellar deficits are always ____
ipsilateral
Cerebellar lesions result in ____
loss of coordination, equilibrium (disturbed synergy–loss of coord/timing; equilib; tone)
NO LOSS of sensation or muscle strength
Dysmetria
inability to bring a limb to a desired point in space
Cerebellar deficits mnemonic
HANDS Tremor
Hypotonia (anterior lobe inj) Ataxia (dysdiadochokinesia--impaired rapid alternating movements; decomposition of movement; dysmetria) Nystagmus Dysarthria Stance and gait problems Tremor (intention)
Layers of the cerebellum
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
Info flow into cerebellar cortex via ____ (afferents)
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.
5 intrinsic cell types of cerebellar cortex
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.
Which makes more contact to separate Purkinje cells, climbing or parallel fibers?
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)
How is excitation delivered to the Purkinje cell?
- Climbing fiber input from inferior olive.
- 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.
Explain Purkinje cell inhibition
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.
Reversing prisms and VOR
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.
Motor learning
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).
2 pathways of postsynaptic purkinje cell with climbing fiber and parallel fiber activation.
- Glutamate from parallel fiber activates AMPA (depol) and metabotropic glutamate receptors (second mess cascadem producing IP3, activating PKC).
- 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.
