cerebellum Flashcards
Cerebellum damage results in what kinds of deficits
equilibrium, tone or synergy deficits (all involve coordination of motor output)
Cerebellum connects to brainstem via…
peduncles: inferior and middle peduncles carry the major inputs to the cerebellum, and the superior peduncle contains the output.
Lobes of cerebellum
The primary fissure demarcates the boundary between the anterior and posterior lobes, while the postero-lateral fissure defines the border of the flocculo-nodular lobe.
alternate names for flocculo-nodular lobe
archicerebellum (oldest phylogenetically lobe) or vestibulocerebellum (receives inputs from vestibules)
What/where is the neocerebellum
Most recent lobe evolutionarily- comprises the lateral cerebellum and is made up of mostly posterior lobe and some anterior lobe
what/where is the paleocerebellum
Midportion of the anterior and posterior lobe
List the cerebellar nuclei from medial to lateral
fastigial, 2 globose, emboliform and dentate nuclei (globose and emboliform together referred to as the interposed nucleus)
List the deep cerebellar nucleus associated with each zone of cerebellum
Vermis: fastigial nuc. Paravermis: interposed nuc. Hemisphere: dentate nuc.
list corticonuclear zones
Medial/ vermal zone, intermediate/paravermal zone, lateral/ hemispheric zone
Function of vermal zone
Has output connections through fastigial nucleus and is involved in control of axial musculature, posture and balance, and integration of head and eye movements
function of paravermal zone
Has connections through the interposed nuclei to the red nucleus and fine tunes movements of the limbs
function of lateral zone
Has connections through the dentate nucleus and is involved in higher level coordination of movements, including planning and initiation of movements
function of flocculo-nodular lobe
Has connections with vestibular nucleus of brain
Function of deep cerebellar nuclei
Provide major output pathway of the cerebellum
efferent connections of vermal cerebellum
Sends information to the vestibular nucleus and the pontine reticular formation (bilaterally) from the fastgial nucleus. From there, information descends in the medial descending system by way of the lateral vestibulospinal tract and the pontine reticulospinal tract. Some neurons in the flocculo-nodular lobe send their axons directly to cells of the vestibular nucleus without synapsing in the fastigial nucleus. vermal cerebellum is involved in motor control having to do with equilibrium and posture.
Efferent connections of paravermal cerebellum
From the interposed nuclei, info is sent to contralateral red nucleus, directing motor output through the rubrospinal tract, part of the lateral descending system
efferent connections of lateral/hemispheric cerebellum
Sends info via dentate nucleus to contralateral ventrolateral thalamus and from there influences wide areas of cortex, particularly primary motor and associated motor cortex (pre-motor)
Where do afferent fibers from spinal cord go to in the cerebellum
vermal and paravermal cerebellum- results in a somatotopic map on the vermal and paravermal cerebellum, no on lateral cerebellum
describe somatic distribution in cerebellum
a double somatotopic distribution is found (one on anterior lobe, one on posterior lobe) with axial body surface found medially at the vermis and distal limbs laterally at paravermis. The head of the map is caudal in the anterior lobe and rostral in posterior lobe, such that there is a head to head representation of the body surface
Affrent input to lateral zone of cerebellum
The lateral zone doesn’t receive any direct primary afferent input. There is no somatotopic map in the lateral hemispheres. Instead, info from the contralateral cortex (primary and associated motor cortex) comes to the lateral zones by way of the pontine nuclei (axons synapse on ipsilateral neurons in basal pons then pontine neurons send axons contralaterally).
For flocculonodular lobe: list functional region, principal input, deep nucleus, principal destination and function
vestibulocerebellum, vestibular sensory cell input, vestibular nucleus, destination is axial motor neurons, functions include axial control, vestibular reflex (balance, eye movement)
For vermis: list functional region, principal input, deep nucleus, principal destination and function
spinoocerebellum, visual, auditory, vestibular and somatosensory input, fastigial nucleus, destination is medial descending systems, functions include axial motor control (posture, locomotion, gaze)
For paravermal lobe: list functional region, principal input, deep nucleus, principal destination and function
spinoocerebellum, spinal afferent input, interposed nucleus, destination is lateral system and red nucleus, functions include distal motor control
For lateral lobe: list functional region, principal input, deep nucleus, principal destination and function
cerebrocerebellum, cortical afferent input, dentate nucleus, destination is integration areas, functions include initiation, planning, timing
cerebellar deficits are always contralateral or ipsilateral
Ipsilateral- sensory input to the cerebellum is largely uncrossed, as are descending cerebellar outputs, while tracts btw cerebellum and cortex cross.
Cerebellar lesions have what effect on muscles
Loss of coordination and equilibrium, but NOT loss of sensation or strength
Which regions of cerebellum are most resistant to obvious motor effects when damaged
Lesions of cerebellar cortex have little obvious motor effect. To have a visible deficit, it must involve large regions of cortex, or lesions of underlying deep nuclei
Ataxia
loss of coordination or timing of involved muscles. Symptoms include past-pointing (aka dysmetria, patients inability to bring a limg to a required or desired point in space), decomposition of movement (aka dysdiadochokinesia), intention tremors perpendicular to direction of limb motion, nystagmus, slurred speech
Cerebellar cortex layers and cells found in these layers
- Molecular layer (uppermost)- contains parallel fibers from granule cells, dendrites of purkinje cells and scattered inhibitory interneurons called stellate cells and basket cells. 2. Purkinje layer (middle)- purkinje cell bodies. 3. Granular layer (inner layer)- granule cell bodies
Info comes to cerebellar cortex through what fibers
mossy fibers (from wide variety of sources such as primary vestibular afferents and pontine nuclear cells), and climbing fibers (from contralateral inferior olivary nucleus) - both give off collaterals that excite cells in deep nuclei too
Describe pontine nuclei tract pathway
axons from pontine nucle on one side immediately cross midline to enter the middle cerebellar peduncle of the opposite side. The fibers of the middle cerebellar peduncle then enter the cerebellum to end as mossy fibers
Middle cerebellar peduncle contains what kinds of fibers
consists nearly entirely of axons going to the cerebellum from the pontine nuclei.
Describe flow of info via mossy fibers
Mossy fibers diverge extensively to excite a large number of granule cells, and each granule cell is contacted by numerous mossy fibers. Granule cells then excite purkinje cells via their parallel fibers. Each parallel fiber may contact hundreds of purkinje cells, and each purkinje cell is contacted by >200,000 parallel fibers
Distribution of climbing fibers
More discrete than mossy fibers- each climbing fibers contacts as few as a dozen purkinje cells, and each purkinje cell is contacted by only one climbing fiber. All parts of cerebellar cortex receiving climbing fiber input
climbing fibers tract pathway
Axons from inferior olive cross the midline immediately and enter the contralateral inferior cerebellar peduncle
What fibers are found in inferior cerebellar peduncle
Majority are fibers going to the cerebellum, but also contains fibers going from the cerebellum to the vestibular nucle
Compare complex to simple spikes
Climbing fibers form powerful synaptic contacts with purkinje fibers, such that single AP in a climbing fiber gives rise to a burst of spikes in Purkinje cell (called a complex spike). On the other hand, many parallel fiber inputs must sum to generate a single action potential in a Purkinje cell (called a simple spike)
What do Purkinje cells do
When activated, Purkinje cells are inhibitory onto cells of deep nuclei, turning them off. They are the only output from the cerebellar cortex. They also have a high rate of spontaneous activity, generating AP’s without excitatory input. Thus they are continually suppressing activity of deep cerebellar neurons
Function of basket and stellate cells
Inhibitory interneurons. Parallel fibers excite these cells, which in turn inhibit Purkinje cells. This form of lateral inhibition results in DISinhibition of the deep cerebellar neurons, thus increasing their firing rate
Function of golgi cells
Inhibitory interneuron. Provide feedback inhibition of granule cell in glomerulus. Are excited by parallel fibers
- Which cells of the cerebellar cortex have inhibitory actions?
basket cells, stellate cell, golgi cells,
Describe use of mossy fibers vs climbing fibers in motor learning
Purkinje fibers fire simple spikes arising from mossy fiber activity in synchrony with a trained movement. When that movement changes (ie, increased load), the Purkinje fiber fires complex spikes arising from climbing fiber activity. After a while, the complex spikes stop and simple spikes occur again at lower frequency than before. This occurs because the inferior olive generates climbing fiber activity (an error signal) when there is a discrepancy btw planned and actual motor performance. This leads to long term depression of sensitivity to mossy fiber input.
superior cerebellar peduncle contains what?
output from deep cerebellar nuclei (95%) and small amount of sensory info input
superior cerebellar peduncle pathway
axons cross midline in brainstem to reach red nucleus and VA/VL
pontine nucleus projections and inputs
Pontine nuclei project to contralateral cerebellum ending as mossy fibers and receive input from ipsilateral cerebral cortex, esp. motor and premotor cortex
Lesion in the cerebral peduncle would cause what
contralateral spastic paralysis in the entire trunk and extremities as well as contralateral weakness in the lower half of the face due to denervation of upper motor neuron input to the facial nucleus
