ICL 9.2: Cerebellum & Disorders Flashcards
what are the overall functions of the cerebellum?
it’s responsible for the coordination and stability of body parts in both static and dynamic conditions
it precisely adjusts the status of muscles to ensure sufficient accuracy and stability for accomplishing discrete and skilled motor tasks
it also compares the intended action with what was actually executed to make sure they match up
cerebellar functions include:
1. equilibrium
- muscle tone
- stretch reflex
- motor planning
- execution of movement
so cerebellar lesions would result in characteristic symptoms and deficits
what ventricle is the cerebellum related to?
the cerebellum forms the roof of the 4th ventricle
how is the cerebellum connected to the brainstem?
cerebellum connects with brainstem to its dorsal aspect via 3 pairs of peduncles = superior, middle and inferior to the midbrain, pons and medulla, respectively
what are the 3 lobes of the cerebellum?
- anterior lobe = the region rostral to the primary fissure
- posterior lobe = the region between the primary and dorsolateral fissure
- flocculonodular lobe = the structures ventral to the dorsolateral fissure
folia is the tree looking part of the cerebellum and there’s also 10 lobules but you don’t need to know the specifics
which 3 arteries supply the cerebellum?
- PICA = posterior inferior cerebellar arteries
supplies the dorsolateral medulla, inferior vermis and caudal hemispheres
- AICA = anterior inferior cerebellar arteries
supplies flocculus and inner ears
- SCA = superior cerebellar arteries
supplies other parts of the cerebellum and lower midbrain
these are all branches of the vertebrobasilar arterial system
go look at slide 14 so you know which areas of the cerebellum would be effected in a stroke of a certain artery
what is the archicerebellum?**
it includes:
- bilateral flocculi
- nodulus
- lingual
responsible for equilibrium, stance, balance and gaze control = vestibulocerebellum
parallel to the development of vestibular organs
what is the paleocerebellum?**
- anterior vermis
- pyramids
- uvula
responsible for propulsive and stereotypes axial motions = spinocerebellum
parallel to the development of vertebral spine
what is the neocerebellum?**
- hemispheres
- middle vermis
responsible for fine toning and precise coordination of distal kinesis aka distal fine motion = cerebrocerebellum
parallel to the development of cerebral neocortex
what are the 3 cellular layers of the cerebellar cortex?
- molecular layer (outer)
- purkinje cell layer = 1 cell thick (middle layer)
- granule cell layer (inner layer)
what are the 5 cell types found in the cerebellar cortex?
molecular layer:
1. stellate cell
- basket cell (modulatory cells)
purkinje cell layer:
1. purkinje cell (cell body in this layer but the dendrites extend into molecular layer)
granule cell layer:
1. golgi cell
- granule cell (excitatory; glutamate)
what are purkinje cells? what NT do they release?
it’s the only cells that give out efferent projections from cerebellar cortex and it’s found in the perkinje cell layer
looks like a radish with lots and lots of roots growing out of it
they are inhibitory neurons that release GABA
what are granule cells? what NT do they release?
they’re found in the granular layer of the cerebellum
the cell bodies are compacted in the granule cell layer while the axons form the parallel fibers that travel to the molecular layer
granule cells receive excitatory inputs from mossy fibers
they are excitatory neurons that release glutamate
what are golgi cells? what NT do they release?
they’re found in the granular layer of the cerebellum
their cell bodies are found in the granule cell layer while the dendrites are found in the molecular layer
they give feedback inhibition to granule cells after being activated by them
they are inhibitory neurons that release GABA
what are stellate and basket cells? what NT do they release?
they are found in molecule cell layer
the local interneurons are in the molecular layer
they inhibit purkinje cells when activated by the parallel fibers –> so they’re inhibitory neurons that release GABA or taurine
what are the 2 types of afferent fibers entering the cerebellum?
- climbing fibers
2. mossy fibers
what are climbing fibers?
one of the two types of afferent fibers entering the cerebellum – they only account for a small proportion of afferent fibers though
they are the fibers coming from the contralateral inferior olivary nucleus –> they end at the dendrites of the Purkinje cells in the molecular layer (each purkinje cell recieves input from only one climbing fiber but each climbing fiber can stimulate 10 purkinje cells)
note: superior olivary nucleus is auditory while inferior olivary nucleus is the cerebellum
they are ALL excitatory and they have a stronger depolarization power than the mossy fibers
what are the mossy fibers?
one of the two types of afferent fibers entering the cerebellum – they account for 90% of all incoming fibers to the cerebellum!
the fibers come from the spinal cord, vestibular nerve and pontine nuclei and they end at the cell bodies of the granule cells in the granule cell layer
ALL are excitatory
what are parallel fibers?
excitatory fibers that travel longitudinally in the molecular layer
they are all the axon branches of the granule cells extending into the molecular layer!
these fibers connect with multiple purkinje cells and activate a bunch of them
what is the glomerulus?
a bulbous expansion of distal mossy fiber forms excitatory synapses to the surrounding granule cell dendrites which are also postsynaptic to the inhibitory terminals of Golgi cells
so it’s a small, intertwined mass of nerve fiber terminals in the granular layer of the cerebellar cortex – it consists of post-synaptic granule cell dendrites and pre-synaptic Golgi cell axon terminals surrounding the pre-synaptic terminals of mossy fibers
so it’s a modulatory effect on the mossy fibersbecause granular cells are excitatory while golgi cells are inhibitory
what are all the different fiber connections in the cerebellum?
the climbing fibers excite the purkinje cells and then the purkinje cells inhibit one of the central nuclei of he cerebellum or the golgi cell
mossy fibers excite the granular cells and then the granular cells excite the purkinje fibers
the golgi cells inhibit the granular cells
what are the 5 deep nuclei of the cerebellum?
- dentate nucleus (the largest and most lateral cerebellar nuclei)
- emboliform nucleus
- globose nucleus
- fastigal nucleus (most medial)
- vestibular nuclei
these nuclei are the major synapsing points of the purkinje fibers
the emboliform nucleus, globose nucleus and festival nucleus are the medial nuclei associated with the vermis while the dentate is the lateral nuclei associated with the cerebellar hemispheres
interposed nucleus = globose + emboliform nuclei
which part of the cerebellum are each of the deep nuclei of the cerebellum associated with?
- fastigial nucleus = spinocerebellum
- interposed nucleus = spinocerebellum
- dentate nucleus = cerebrocerebellum
- vestibular nuclei = vestibulocerebellum
spinocerebellum is the middle part of the cerebellum, cerebrocerebellum is the lateral parts of the cerebellum and the vestibulocerebellum is the floculonodulous
which cerebellar peduncles are incoming vs. outgoing from the cerebellum?
the inferior and middle cerebellar peduncles are incoming (except the cerebellobulbar tract from the inferior cerebellar peduncles)
the superior cerebellar peduncle fibers are all outgoing except the ventral spinocerebellar tract
what is the function of the inferior cerebellar peduncles?
contains mainly input fibers:
1. primary vestibular afferents
- vestibulocerebellar projection
- olivocerebellar tracts = climbing fibers from contralateral olivary nucleus
- dorsal spinovestibular tracts = inputs from muscle spindles
- afferents from brainstem reticular formation
contains a small amount of output fibers from the cerebellobulbar tract which go to the ipsilateral vestibular nucleus
don’t really need to know this….
what is the function of the middle cerebellar peduncles?
they contain only afferent fiber projection from the contralateral pontine relaying nuclei to the neocerebellar cortices
don’t really need to know this….
what is the function of the superior cerebellar peduncles?
they contain mainly outputs so it contains all the cerebellar outgoing fibers except for the cerebellobulbar tract which is in the inferior cerebellar peduncle
they contain a small amount of input projections from the ventral spinocerebellar tract so it carries inputs from the golgi tendon organs
don’t really need to know this….
what are the 3 cerebellum feedback loops?
- triangle of Guillian-Mollaret
- rubrospinal tract = cerebellum to the spinal cord
- cerebrobulbar tract = cerebrum to the cerebellum loop
what is the triangle of Guillian-Mollaret?
it’s one of the cerebellar feedback loops
cerebellum perkinje fibers –> dentate nucleus –> –> red nucleus –> inferior olive –> –> cerebellum perkinje fibers
the purkinje cell fibers go to the dentate nucleus which then go to the *contralateral red nucleus in the tegmentum of the midbrain
then the red nucleus sends descending fibers to the inferior olive also on the contralateral side via the “central tegmental tract”
then from the contralateral inferior olivary nucleus, climbing fibers are sent back across the midline back to the cerebellum = double crossing!
this is why cerebellum lesions are ipsilateral due to the double crossing!
slide 33
what is the rubrospinal tract?
it’s one of the cerebellar feedback loops that connects the cerebellum to the spinal cord
cerebellum –> dentate nucleus –> red nucleus –> spinal cord –> cerebellum
fibers in the cerebellum cross the midline to the contralateral red nucleus
then the fibers from the red nucleus descend ipsilaterally to the spinal cord via the rubrospinal tract –> this tract controls the muscle tone of the flexors!
then in the spinal cord, the fibers cross midline again to effect contralateral gamma neurons down in the spinal cord –> then spinal cord information travels ipsilaterally back to the cerebellum = again this is a double crossing!
slide 34
what is the cerebrobulbar tract?
it’s one of the cerebellar feedback loops that helps the cerebellum communicate with the cerebrum
cerebrum –> pons –> cerebellum –> dentate nucleus –> VMP thalamus –> cerebrum
when the cerebral cortex is trying to initiate movement, the intention goes through the cerebrobulbar tract to the ipsilateral pontine nucleus –> then the fibers cross the midline via the middle cerebellar peduncle to the contralateral dentate nucleus
then the cerebellum sends information to the contralateral VMP thalamus and then to the cerebral cortex telling the brain that it’s ready or not ready to initiate movement – this loop happens really quickly before a movement even happens
slide 35
what are the inputs and outputs of the vestibulocerebellum?
inputs are from the primary and secondary vestibular inputs
outputs from the vestibulocerebellum are from the purkinje cells to the bilateral vestibular nuclei, contralateral cerebellum, and brainstem reticular formation
what are the functions of the vestibulocerebellum and what would happen if there was a lesion there?
- maintenance of equilibrium
- gaze stabilization
- posture control
if there was a lesion in the vestibulocerebellum the patient would have distorted equilibrium such as astasia, abasia, ataxia, nystagmus, and tendency of falling or nystagmus, impaired gaze holding, distorted posture and stance
what are the inputs and outputs of the spinocerebellum?
inputs are from the dorsal and ventral spinocerebellar tracts, cuneocerebellar tract (Ia fibers from Golgi organs and muscle spindles)
there’s also auditory, visual, vestibular and cerebral inputs
outputs are from the purkinje cells of the vermis –> fastigial nucleus –> lateral vestibular nucleus –> contralateral ventrolateral thalamus and brainstem reticular formation
or
outputs can be from the purkinje cells of the paravermian hemispheres –> interposed nuclei –> contralateral red nucleus and the contralateral ventrolateral thalamus
what are the functions of the spinocerebellum and what would happen if there was a lesion there?
- axial and proximal muscle tone
- control stretch reflexes
if there was a lesion on the spinocerebellum there would be ipsilateral truncal and limb ataxia, gait disturbance, asynergia, hypotonia, altered tendon reflex and scanning speech
what are the inputs and outputs of the corticopontocerebellum?
inputs are from the corticopontocerebellar tract and olivocerebellar tract (climbing fibers)
outputs are to the dentatorubrothalamic tract
what are the functions of the corticopontocerebellum and what would happen if there was a lesion there?
the function of the corticopontocerebellum is to receive cerebral planning about voluntary movement in advance, compares planned and actual motion, and modulates pyramidal and extrapyramidal actions to ensure the precision and smoothness of complex motion
if there was a corticopontocerebellum lesion the patient would experience distal ataxia, dysmetria, asynergia, dysdiadochokinesia, intention tremor, hypotonia, delay in initiation of motor task, inability to estimate weight
what are the general signs and symptoms of a cerebellum problem?*
- dizziness
- vertigo
- impaired eye control
- gait disturbance
- difficulty in coordination
- nystagmus
- ataxia
- dysequilibirum
- abnormal stance
what are the different types of cerebellar disorders?
- congenital malformations (chiari, dandy-walker)
- idiopathic and hereditary diseases (friedreich’s ataxia, intension tremor)
- trauma and vascular lesions (contusion, strokes, vascular, arterial dissection)
- tumors
- infections
- paroxysmal (migraine, motion sickness)
- neurotoxicity and adverse effects of medication (drugs, alcohol, mercury)
- metabolic, endocrine and nutritional disorders ( thiamine or vitamin E deficiency, hypothyroidism)
- inflammatory and autoimmune disorders (SLE, MS)
- non-neurological causes
what is a dandy-walker malformation?
a congenital malformation involving the cerebellum where there is agenesis or hypoplasia of the cerebellar vermis, cystic dilatation of the fourth ventricle, and enlargement of the posterior fossa
so with a small/nonexistent vermis, the patient will have equilibrium, stance, balance and gaze control problems
what is a chiari malformation?
the medulla and cerebellum start to slip into the cervical spinal canal
what is machado-joseph disease?
aka spinocerebellar ataxia type 3
a rare autosomal dominantly inherited neurodegenerative disease that causes progressive cerebellar ataxia which results in a lack of muscle control and coordination of the upper and lower extremities
it’s an AD hereditary problem where there are CAG repeat expansions in chromosome 14 on the ataxin-3 protein gene
what is spinocerebellar ataxia type 6?
an AD condition with CAG repeats on chromosome 19 on the CACNA1A gene coding for alpha1A voltage-dependent P/Q type calcium channel subunit
patient will experience late onset and progressive ataxia, nystagmus, large fiber neuropathy, pyramidal signs
there is SEVERE loss of purkinje cells
what is Friedreich’s ataxia?
it’s GAA repeats in the intron of the FRDA gene coding for frataxin which is a mitochondrial protein in the brain, heart and pancreas
the disease presents in kids and patients will have kyphoscoliosis, progressive cerebellar ataxia due to loss of purkinje cells and dentate neurons, sensory ataxia etc.
patients will also have cardiomegaly and many develop DM2 – ultimately most die from arrhythmias and heart failure
