The Cerebellum

Question 1

generation of voluntary contraction begins with activation of upper motor neurons in the primary motor cortex. UMN utilize a ___ tract that descends down through brain stem and spinal cord, innervating lower motor neurons found in the ___ of the spinal cord in the ___ matter

Answer 1

generation of voluntary contraction begins with activation of upper motor neurons in the primary motor cortex. UMN utilize a CORTICOSPINAL tract that descends down through brain stem and spinal cord, innervating lower motor neurons found in the VENTRAL HORN of the spinal cord in the GRAY matter

Question 2

compare basic function of cerebellum to that of basal ganglia (nuclei)

Answer 2

cerebellum- smooth execution of movement (receives sensory input from muscle spindles/ stress receptors)

basal ganglia- initiate desire movement while also suppressing unwanted movement

Question 3

both the cerebellum and basal ganglia influence activity of UMN through connections through the ___

Answer 3

thalamus

Question 4

describe the anatomy of the cerebellum

Answer 4

vermis- midline (“vermiform”=”wormlike”)

pair of hemispheres on each side

flocculonodular lobe on the inferior surface

Question 5

vestibulocerebellum and its function

Answer 5

flocculonodular lobe and vermis of the cerebellum

maintenance of upright standing/ sitting, balance, smooth eye movement

receives input from vestibular system

Question 6

part of cerebellum involved in control of axial, proximal, and distal limb muscles

Answer 6

spinocerebellum- vermis (proximal muscles) and paravermal (distal muscles) regions

Question 7

pontocerebellum

Answer 7

largest part of each cerebellum hemisphere
motor planning and rehearsal of skilled movement (esp. involving distal limb movements- this region gets more direct information from motor cortex about motor plan)

Question 8

what portion of the cerebellum is in control of movement of forearm

Answer 8

paravermal region- smooth execution of distal limb muscles (hands, feet, forearm, legs)

Question 9

what portion of cerebellum is in control of movement of thighs and arms

Answer 9

vermis- smooth execution of axial and trunk muscles, proximal limb muscles (thighs and arms)

Question 10

why is it logical that the paravermal regions of the cerebellum, rather than the vermis, is in control of distal limb muscles?

Answer 10

paravermal regions are closer to motor planning centers. Reaching out in space and manipulating object requires more motor planning than maintaining upright standing position (axial muscles, controlled by vermis)

Question 11

name the 3 cerebellar peduncles (“ped” meaning feet of the cerebellum)

Answer 11

superior (SCP)- carry axons out from deep cerebellar nuclei (major outflow)

middle (MCP)- carry axons in from pontine nuclei (pons) that relay motor plan

inferior (ICP)- carry axons both in and out

Question 12

where do the axons of the superior cerebellar peduncle of the cerebellum go?

Answer 12

leave cerebellum, cross in the midbrain and relay through the thalamus–> influence upper motor neurons
(major outflow of cerebellum)

Question 13

the inferior olivary nucleus is the major source of input to the cerebellum, whose axons enter through the ___

Answer 13

inferior cerebellar peduncle (ICP)

Question 14

what are the three neuronal layers of the cerebellum (histologically)

Answer 14

1. molecular layer- outermost, thickest, mostly acellular (has inhibitory Basket and Stellate neurons)
2. Purkinje cells- largest neurons in brain (important), only neurons in cerebellar cortex that have axons that exit the cortex
3. granule cells- excitatory input to Purkinje cells

Question 15

the outermost molecular layer of the cerebellum is mostly acellular, but does contain the dendrites of ___ cells, axons of ___ cells, and two small inhibitory neurons, ___ and ___

Answer 15

the outermost molecular layer of the cerebellum is mostly acellular, but does contain the dendrites of PURKINJE cells, axons of GRANULE cells, and two small inhibitory neurons, BASKET and STELLATE

Question 16

which of these cells within the cerebellar cortex do NOT utilize GABA?
Purkinje
basket
Golgi
granule
stellate

Answer 16

Granule- ONLY neurons in cerebellar cortex that are excitatory. all others are inhibitory (GABA)

granule cells project axons into molecular layer, which bifurcate and form parallel fibers that synapse on dendritic branches of Purkinje cells

–> entire outflow of cerebellar cortex is inhibitory. granule cells modulate inhibitory output

Question 17

what neurons of the cerebellum actually leave the cerebellum

Answer 17

deep cerebellar nuclei, output of which is modulated by granule cells

(Purkinje axons leave the cortex but not the whole cerebellum- just influence deep cerebellar nuclei)

Question 18

while the output of the cerebellum is inhibitory, the input to the cerebellum is excitatory, coming from these two neurons:

Answer 18

climbing fibers- direct monosynaptic excitation to Purkinje dendrites (CLIMB up dendrite)

mossy fibers- indirect, synapse with granule cells (which then bifurcate in molecular layer into parallel fibers that synapse with Purkinje dendrites)

Question 19

compare how the basket/stellate cells and Golgi cells provide inhibitory input to Purkinje cells of the cerebellum

Answer 19

basket/ stellate- direct inhibitory influence
Golgi cells- inhibit excitatory mossy fiber input to granule cells (which then form parallel fibers that synapse with Purkinje dendrites)

Question 20

T/F: deep cerebellar nuclei provide inhibitory output

Answer 20

FALSE: deep cerebellar nuclei provide excitatory output (to brain stem and thalamus, ultimately to UMN/motor cortex)

the excitatory output is modulated by GABAergic axons of Purkinje cells

Question 21

This region of the medulla oblongata is the source of climbing fibers which provide direct, monosynaptic excitatory input to Purkinje dendrites, which then replies here again with feedback. What is the ___?

Answer 21

inferior olivary nucleus (medulla oblongata)

allows climbing fibers to act as error detector for Purkinje cells- promotes motor/ procedural learning

Question 22

where are Golgi cells of cerebellum found

Answer 22

innermost granule cell layer
granule- excitatory (receive input from mossy fibers)
Golgi- GABAergic

Question 23

compare the excitation of mossy fibers and climbing fibers

Answer 23

mossy fibers- synapse on granule cells (-> parallel fibers). Purkinje dendrites contact by ~1 million parallel fibers that inform about motor plan/ give vestibular input. Steady stream of simple spikes

climbing fibers- Purkinje dendrites contacted by just one climbing fiber, but receive more complex spike

Question 24

describe the path of climbing fibers

Answer 24

inferior olivary nuclei (upper medulla)–> cross midline of medulla–> ascent through inferior cerebellar peduncle–> into contralateral (opposite side) cerebellar cortex

Question 25

describe path of mossy fibers from the pontine nuclei. where does their input originate from

Answer 25

pontine (pons) nuclei–> cross midline (contralateral)–> enter cerebellum via middle cerebellar peduncle

pontine nuclei use mossy fibers to relay input from descending premotor cortex that pass through pons

Question 26

describe how mossy fibers originate from vestibular cerebellum and spinal cord, respectively

Answer 26

both give ipsilateral input

vestibular cerebellum (flocculonodular lobe and vermis) gets ipsilateral (same side) input from vestibular nuclei–> enters cerebellum ipsilaterally via inferior cerebellar peduncle

spinal cord (from contracting muscle themselves, anterior/ventral spinocerebellar tract)- ipsilateral input from muscle spindles/ stretch and force receptors

Question 27

where is Clarke’s nucleus, what does it do

Answer 27

found in intermediolateral gray area of spinal cord (T1-L3). gives rise to dorsal/posterior spinocerebellar tract that projects to ipsilateral (same side) cerebellum

projects lower limb proprioceptive info

Question 28

the corticospinal tract send its axons through the brain stem at the pons and medulla [oblongata], which then cross at the pyramidal decussation. what side of the spinal cord do they descend down?

Answer 28

contralateral side (cross over in pyramidal decussation)–> influence lower motor neurons on opposite side

Question 29

if the cerebellum receives input from your left arm, which hemisphere will respond?

Answer 29

left- input to cerebellum is ipsilateral

this is why axons of pontine nuclei (input originating from corticospinal UMN) cross over, as well as climbing fibers from inferior olive

Question 30

the lower limb generates input to the cerebellum via Clarke’s nucleus, while the upper limb gives comparable proprioceptive information via ___

Answer 30

lateral/ external cuneate nucleus

Question 31

input about movement from your arm while you’re pitching will being generated by which on the way to the cerebellum?
Clarke’s nucleus
lateral/external cuneate nucleus

Answer 31

lateral/external cuneate nucleus- upper limbs

Clarke’s- lower limbs

Question 32

Clarke’s nucleus is found in the intermediate zone of spinal cord gray matter (T1-L3), which is [coincidently] also where what other neurons are found?

Answer 32

preganglionic sympathetic neurons

Question 33

what happens when a parallel fiber and a climbing fiber simultaneously stimulate same Purkinje cell?

Answer 33

suppression of Purkinje cell responses to parallel fibers (excitatory) and increase in strength of deep cerebellar nuclei output

enhances functionality of climbing fiber (excitatory, more complex spikes)

suppression of Purkinje cell output promotes procedural/motor learning

Question 34

in the cerebellum,
vermis controls ___
paravermal hemispheres control ___
lateral hemispheres control ___

Answer 34

vermis- axial/ proximal
paravermal- distal upper/lower
lateral- motor planning

Question 35

name the three sources of mossy fibers to the cerebellum and which are ipsa/contralateral

Answer 35

ipsilateral vestibular nuclei (brainstem)- carry balance messages
ipsilateral spinal cord- proprioceptive messages

contralateral pontine nuclei- axons cross midline of brainstem, motor planning from corticospinal tract

Question 36

Purkinje axons leave the cortex and project to deep cerebellar nuclei in a precisely topographical fashion. name these deep cerebellar nuclei from medial to lateral

Answer 36

1. vestigial nuclei (most medial)- vermis Purkinje project here
2. interposed nuclei- paravermal Purkinje project here
3. dentate nuclei (most lateral)- lateral hemisphere Purkinje project here

Question 37

vestibular nuclei (cranial nuclei for the vestibular nerve, found in the lower pons./ upper medulla of brainstem) are also considered deep cerebellar nuclei, receiving their input from ___

Answer 37

Purkinje cells in floccolonodular lobe–> only Purkinje cells that actually leave cerebellum (rather than just leave the cortex)

Purkinje cells exit via inferior cerebellar peduncle

Question 38

describe the path of the deep cerebellar nuclei? What are the two places they could synapse?

Answer 38

leave via superior cerebellar peduncle, cross midline, synapse on motor nuclei of thalamus (ventral lateral nucleus of thalamus)-> thalamus projects to UMN (corticospinal tract)

some will synapse on Red Nucleus- source of UMN, rubrospinal tract (upper limb flexors). major source of feedback to inferior olive (regulates Purkinje cells via climbing factors)

Question 39

what is the net effect of deep cerebellar nuclei and corticospinal tract both crossing over?

Answer 39

corticospinal tract crosses over to cerebellum, cerebellum crosses over to corticospinal tract–> net effect is cerebellum controls ipsilateral side of body

Question 40

where do the axons of the UMN cross over?

Answer 40

pyramidal decussation

Question 41

a patient presents with bilateral axial muscle dysfunction, including motor ataxic gait. where is a lesion likely to be found?

Answer 41

lesion of vermal region of cerebellum- maintains upright posture and balance of axial muscles and proximal limbs (thighs)

Question 42

what is a Romberg sign and what does it indicate?

Answer 42

Romberg sign- patient sways back and forth only when eyes are closed

indicates a functional cerebellum
loss of balance due to lesion of dorsal column- loss of proprioceptive input

Question 43

how will patients with dorsal column lesions or demyelinating conditions present with?

Answer 43

dorsal column- proprioception of upper and lower limbs
present with cerebellar ataxic gait called sensory ataxia because cerebellum is functional but it’s not receiving sensory proprioceptive input

Question 44

a patient who sways back and forth when their eyes or opened or closed will have a cerebellar lesion or dorsal column lesion?

Answer 44

cerebellar vermis lesion- loss of control of axial and proximal limb smooth movement

Question 45

Isolated lesions of the flocculonodular lobe and vestibular cerebellum are uncommon, but will present with two distinct symptoms other than balance problems:

Answer 45

scanning dysarthria- breaking up multi-syllabic words into individual syllables
abnormal conjugate gaze

Question 46

thiamine deficiency or alcoholism is most likely to affect which cells of the cerebellum?

Answer 46

anterior vermis Purkinje cells- patients will have motor ataxia

Question 47

a patient presents with an intention tremor. what is it, and what type of lesion do they likely have?

Answer 47

intention tremor- patient doesn’t have weakness, but has tremor with voluntary movement and smooth execution of movement is not possible

likely cerebellum hemisphere dysfunction or lesion. lesion will be ipsilateral to limb with intention tremor

Question 48

a patient presents with dysmetria (difficulty measuring), dysdiadochokinesis, and cannot complete finger to nose test. Assuming they have a brain lesion, where is it likely to be?

Answer 48

cerebellum hemisphere lesion

dysmetria- difficulty stopping movement at the proper place (measured by finger to nose test)
dysdiadochokinesis- difficulty performing rapidly alternating movements (fine motor skills)