ICL 9.2: Cerebellum & Disorders

Question 1

what are the overall functions of the cerebellum?

Answer 1

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

2. muscle tone
3. stretch reflex
4. motor planning
5. execution of movement

so cerebellar lesions would result in characteristic symptoms and deficits

Question 2

what ventricle is the cerebellum related to?

Answer 2

the cerebellum forms the roof of the 4th ventricle

Question 3

how is the cerebellum connected to the brainstem?

Answer 3

cerebellum connects with brainstem to its dorsal aspect via 3 pairs of peduncles = superior, middle and inferior to the midbrain, pons and medulla, respectively

Question 4

what are the 3 lobes of the cerebellum?

Answer 4

1. anterior lobe = the region rostral to the primary fissure
2. posterior lobe = the region between the primary and dorsolateral fissure
3. 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

Question 5

which 3 arteries supply the cerebellum?

Answer 5

1. PICA = posterior inferior cerebellar arteries

supplies the dorsolateral medulla, inferior vermis and caudal hemispheres

2. AICA = anterior inferior cerebellar arteries

supplies flocculus and inner ears

3. 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

Question 6

what is the archicerebellum?**

Answer 6

it includes:

1. bilateral flocculi
2. nodulus
3. lingual

responsible for equilibrium, stance, balance and gaze control = vestibulocerebellum

parallel to the development of vestibular organs

Question 7

what is the paleocerebellum?**

Answer 7

1. anterior vermis
2. pyramids
3. uvula

responsible for propulsive and stereotypes axial motions = spinocerebellum

parallel to the development of vertebral spine

Question 8

what is the neocerebellum?**

Answer 8

1. hemispheres
2. middle vermis

responsible for fine toning and precise coordination of distal kinesis aka distal fine motion = cerebrocerebellum

parallel to the development of cerebral neocortex

Question 9

what are the 3 cellular layers of the cerebellar cortex?

Answer 9

1. molecular layer (outer)
2. purkinje cell layer = 1 cell thick (middle layer)
3. granule cell layer (inner layer)

Question 10

what are the 5 cell types found in the cerebellar cortex?

Answer 10

molecular layer:
1. stellate cell

2. 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

2. granule cell (excitatory; glutamate)

Question 11

what are purkinje cells? what NT do they release?

Answer 11

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

Question 12

what are granule cells? what NT do they release?

Answer 12

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

Question 13

what are golgi cells? what NT do they release?

Answer 13

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

Question 14

what are stellate and basket cells? what NT do they release?

Answer 14

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

Question 15

what are the 2 types of afferent fibers entering the cerebellum?

Answer 15

1. climbing fibers

2. mossy fibers

Question 16

what are climbing fibers?

Answer 16

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

Question 17

what are the mossy fibers?

Answer 17

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

Question 18

what are parallel fibers?

Answer 18

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

Question 19

what is the glomerulus?

Answer 19

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

Question 20

what are all the different fiber connections in the cerebellum?

Answer 20

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

Question 21

what are the 5 deep nuclei of the cerebellum?

Answer 21

1. dentate nucleus (the largest and most lateral cerebellar nuclei)
2. emboliform nucleus
3. globose nucleus
4. fastigal nucleus (most medial)
5. 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

Question 22

which part of the cerebellum are each of the deep nuclei of the cerebellum associated with?

Answer 22

1. fastigial nucleus = spinocerebellum
2. interposed nucleus = spinocerebellum
3. dentate nucleus = cerebrocerebellum
4. 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

Question 23

which cerebellar peduncles are incoming vs. outgoing from the cerebellum?

Answer 23

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

Question 24

what is the function of the inferior cerebellar peduncles?

Answer 24

contains mainly input fibers:
1. primary vestibular afferents

2. vestibulocerebellar projection
3. olivocerebellar tracts = climbing fibers from contralateral olivary nucleus
4. dorsal spinovestibular tracts = inputs from muscle spindles
5. 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….

Question 25

what is the function of the middle cerebellar peduncles?

Answer 25

they contain only afferent fiber projection from the contralateral pontine relaying nuclei to the neocerebellar cortices

don’t really need to know this….

Question 26

what is the function of the superior cerebellar peduncles?

Answer 26

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….

Question 27

what are the 3 cerebellum feedback loops?

Answer 27

1. triangle of Guillian-Mollaret
2. rubrospinal tract = cerebellum to the spinal cord
3. cerebrobulbar tract = cerebrum to the cerebellum loop

Question 28

what is the triangle of Guillian-Mollaret?

Answer 28

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

Question 29

what is the rubrospinal tract?

Answer 29

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

Question 30

what is the cerebrobulbar tract?

Answer 30

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

Question 31

what are the inputs and outputs of the vestibulocerebellum?

Answer 31

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

Question 32

what are the functions of the vestibulocerebellum and what would happen if there was a lesion there?

Answer 32

1. maintenance of equilibrium
2. gaze stabilization
3. 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

Question 33

what are the inputs and outputs of the spinocerebellum?

Answer 33

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

Question 34

what are the functions of the spinocerebellum and what would happen if there was a lesion there?

Answer 34

1. axial and proximal muscle tone
2. 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

Question 35

what are the inputs and outputs of the corticopontocerebellum?

Answer 35

inputs are from the corticopontocerebellar tract and olivocerebellar tract (climbing fibers)

outputs are to the dentatorubrothalamic tract

Question 36

what are the functions of the corticopontocerebellum and what would happen if there was a lesion there?

Answer 36

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

Question 37

what are the general signs and symptoms of a cerebellum problem?*

Answer 37

1. dizziness
2. vertigo
3. impaired eye control
4. gait disturbance
5. difficulty in coordination
6. nystagmus
7. ataxia
8. dysequilibirum
9. abnormal stance

Question 38

what are the different types of cerebellar disorders?

Answer 38

1. congenital malformations (chiari, dandy-walker)
2. idiopathic and hereditary diseases (friedreich’s ataxia, intension tremor)
3. trauma and vascular lesions (contusion, strokes, vascular, arterial dissection)
4. tumors
5. infections
6. paroxysmal (migraine, motion sickness)
7. neurotoxicity and adverse effects of medication (drugs, alcohol, mercury)
8. metabolic, endocrine and nutritional disorders ( thiamine or vitamin E deficiency, hypothyroidism)
9. inflammatory and autoimmune disorders (SLE, MS)
10. non-neurological causes

Question 39

what is a dandy-walker malformation?

Answer 39

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

Question 40

what is a chiari malformation?

Answer 40

the medulla and cerebellum start to slip into the cervical spinal canal

Question 41

what is machado-joseph disease?

Answer 41

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

Question 42

what is spinocerebellar ataxia type 6?

Answer 42

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

Question 43

what is Friedreich’s ataxia?

Answer 43

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