7 - cerebellum and control of movement Flashcards
what do LMN do and where are they?
- in spinal cord and brainstem
- innervate skeletal muscle for movement
where are UMN and what do they do?
- cerebral cortex ad brainstem
- control LMN
what does the cerebellum do?
coordinates movement
what does the basal ganglia do?
chooses appropriate movements
what do alpha motor neurons do?
innervate extrafusal muscle fibres
what do gamma motor neurons do?
- innervate intrafusal muscle fibres (stretch receptors in parallel with muscle fibres)
- control sensitivity of stretch reflex
- increase sensitivity to externally imposed stretch
what causes LMN lesions and what do they cause?
- paralysis
- loss of tendon reflex
- hypotonia, wasting, fasciculations
- motor neurone disease, polio, peripheral nerve injury
- symptoms are ipsilateral to location of lesion
what influence alpha and gamma motor neurones via descending tracts?
brainstem nuclei — vestibular, reticular, red nuclei
what pathways come from the vestibular, reticular and red nuclei and what do they control?
- vestibulospinal
- reticulospinal
- rubrospinal
control reflexes, tone and posture
overall what do brainstem nuclei excite and what are they inhibited by?
- excited by gamma motor neurones
- inhibited by cerebral cortical efferent
what UMNs come from the cortex?
corticospinal (pyramidal) and corticobulbar tracts
what do corticospinal and corticobulbar tracts do?
- innervate motor neuronal groups of spinal cord and brainstem, respectively
- control fine, skilled movements
another name for skilled movements?
fractionated movements (highly controlled by cortical effernt fibres)
where is the decussation of the pyramids?
medulla oblongata
what do the corticospinal and corticobulbar tracts travel throguh before their decussation?
internal capsule
UMN lesions are commonly caused by what?
stroke in internal capsule
symptoms of UMN lesions
- paralysis and +ve Babinski reflex
- hypertonia and hyperreflexia
- contralateral symtpoms to lesion location
what is paralysis and positive babinski reflex due to?
corticospinal tract damage
what are hypertonia and hyperreflexia due to?
loss of cortical inhibition of brainstem nuclei — increased sensitivity of stretch reflex
what are paralysis, hyperreflexia and hypertonia referred to as?
spasticity
what does the cerebellum do?
- coordinates balance and movement
- concerned with which muscles need to be activated to achieve a particular movement. timing, force
- integrates info from the cerebral cortex (what movement is intended) (via pons) and peripheral sense organs (what is going on)
- sends output to brainstem nuclei and cerebral cortex (via thalamus)
where is the cerebellum?
- in posterior fossa
- under occipital lobe
- 4th ventricle is underneath
- dorsal to pons and rostral part of medulla
how is the cerebellum attached to the brainstem?
CEREBELLAR PEDUNCLES
- superior cerebellar peduncle to midbrain
- middle cerebellar peduncle (largest) to pons
- inferior cerebellar peduncle to medulla
what is embedded in the white matter of the cerebellum?
deep cerebellar nuclei
what is the largest nucleus and what is it important in?
dentate nucleus — important in output
what are the functional divisions of the cerebellum?
- archicerebellum
- paleocerebellum
- neocerebellum
what is the oldest functional division in terms of phylogeny?
archicerebellum
which division is connected to vestibular system?
archicerebellum
what is the paleocerebellum particularly connected with?
spinocerebellar tracts
afferent to cerebellum from periphery
what is the neocerebellum particularly connected to via a relay in the pons?
cerebral cortex
which nuclei are the different divisions related to?
neo - dentate
paleo - emboliform and globose
archi - fastigial
where does the cerebellar cortex project?
cerebellar nuclei
what provides input to the cerebellum?
- spinocerebellar tracts (from spinal cord)
- vestibular nuclei (of brainstem)
- cerebral cortex (via pontine nuclei)
what are the spinocerebellar tracts lateral to in the brainstem?
trigeminal sensory nucleus
label this section at the level of the decussation of the pyramids
where are the vestibular nuclei?
in the medulla medial to the inferior cerebellar peduncles
label this medulla at the level of the inferior olivary nucleus
pontine nuclei give rise to fibres which what?
cross to other side via middle cerebellar peduncle
where are pontine nuclei?
lie in pontine tegmentum
label this pons
where does the output of the cerebellum from the deep cerebellar nuclei go?
- brainstem (vestibular, reticular and red nuclei)
- some bypass nuclei and go straight to VL thalamus
where is the red nucleus?
- in rostral part of midbrain at level of superior colliculus
- in mesencephalic tegmentum
what are the 3 histological layers of the cerebellar cortex?
- an outer, fibre-rich, molecular layer
- an intermediate Purkinje cell layer (unicellular layer)
- an inner granular layer (granule cells)
input to cerebellar cortex from spinocerebellar tracts comes in via what?
mossy fibres
where do mossy fibres terminate?
granule cells
output from Purkinje cells goes whee?
to cerebellar nuclei
describe mossy fibres
branch to supply several folia and end in the granule layer, in synaptic contact with granule cells
describe the dendrites of Purkinje cells
transverse by numerous parallel fibres from which they receive excitatory synaptic input
fibres from where wrap around the dendrites of Purkinje cells? what are these fibres called?
climbing fibres from inferior olivary nucleus
what is circled?
inferior olivary nucleus
describe the input of the archicerebellum
input comes from vestibular nerve into vestibular nuclei and from there via the inferior peduncle into the cerebellar cortex
where do the Purkinje cells of the archicerebellum project to?
fastigial nucelus
where does the fastigial nucleus project?
to the vestibular nuclei and also to the reticular nuclei of the brainstem
both of these have connections to reticulospinal and vestibulospinal tracts
what does the archicerebellum control?
posture in relation to the maintenance of equilibrium
where do they dorsal and ventral spinocerebellar tracts enter?
dorsal — inferior peduncle
ventral — superior peduncle
where do the purkinje cells in the cerebellar cortex project to in the paleocerebellum?
globose and emboliform nuclei
where do globose and emboliform nuclei project to (connections of paleocerebellum)?
throguh decussation of superior cerebellar peduncle to red nucelus in the midbrain (some fibres terminate here)
what does the red nucelus give rise to?
rubrospinal tract
where does the rubrospinal tract cross over?
ventral tegmental decussation
the paleocerebellum receives fibres from _______ and projects to _______
fibres from spinocerebellar tracts and produces to red nucleus of midbrain
what are the principle connections of the archicerebellum?
vestibular and reticular nuclei of brainstem
which part of the cerebellum controls muscle tone and posture?
paleocerebellum
describe the input to the neocerebellum
from cerebral cortex via pontine nuclei
fibres cross over after pontine nuclei and enter via the middle cerebellar peduncle and terminate in the cortex
the cortex of the neocerebellum contains purkinje cells that project where?
to the dentate nucleus
what do fibres of the dentate nucleus projects through?
superior peduncle (go through decussation of superior cerebellar peduncle)
where do fibres from dentate nucleus go?
to VL nucleus of contralateral thalamus whcih then projects to ipsilateral cerebral cortex
where does the cerebral cortex project to control muscle coordination (inc the trajectory and speed and force of movemtns)? (neocerebellum)
corticospinal tract
what does a lesion in the midline or archicerebellum cause?
loss of postural control/balance
what happens if there is a unilateral hemisphere lesion?
incoordination of arm (intention tremor) and leg causing unsteady gait. symptoms occur ipsilaterally
how can an intention tremor be demonstrated clinically?
wobbling attempt at nose pointing test — very characteristic of a cerebellar hemisphere lesion
what does a bilateral hemisphere cerebellar lesion cause?
slow, scanning speech (dysarthria), incoordination of limbs, staggering gait (when lower limbs affected) (ataxia)
what is a typical sign of cerebellar dysfunction?
nystagmus
what is ‘Charcot’s Neurological Triad’ and what is it highly diagnostic of?
nystagmus + scanning dysarthria + intention tremor = highly diagnostic of MS
