MODULE 11- Modulation of Movement by the Cerebellum Flashcards
cerebellum constitutes ____% of the total brain volume
10%
-but contained more than 1/2 of the brain’s neurons
T/F: the cerebellum projects directly to the motor neurons of the spinal cord
false
what does the cerebellum do
modifies movement by regulating upper motor neurons in regions such as the motor cortex
cerebellum is mode up of a ____ and ____
-cerebellar cortex
-deep cerebellar nuclei
the cerebellum is thought to play a role in what 3 things
-motor learning
-error correctino
-sensory-motor integration
how many subdivisions of cerebellum
3
3 subdivisions of the cerebellum
-cerebrocerebellum
-spinocerebellum
-vestibulocerebellum
cerebrocerebellum receives input from
cerebral cortex (via pons)
what is cerebrocerebellum responsible for
highly skilled movements (ex: speech)
spinocerebellum receives input from
medial, directly from spinal cord
vermis
most median strip of spinocerebellum
what is the vermis (median strip) of spinocerebellum responsible for
-posture
-locomotion
-eye movements
what is the paramedian part of spinocerebellum responsible for
movements of distal muscles
vestibulocerebellum receives input from
vestibular nuclei
what is vestibulocerebellum responsible for
-balance
-vestibular reflexes
-eye movements
see slide 4 for labeled image of 3 major subdivisions (spinocerebellum, cerebrocerebellum, vestibulocerebellum)
cerebellar peduncles
thick tracts connecting the cerebellum with the rest of the CNS
deep cerebellar nuclei
project to the upper motor neurons in the motor and premotor cortices via thalamus
3 pathways between the cerebellum and other CNS
-superior
-middle
-inferior
cerebellar peduncles^
3 types of deep cerebellar nuclei
-fastigial nucleus
-interposed nuclei
-dentate nucleus
ALL output from the cerebellum is via
deep cerebellar nuclei
how many axons in cerebellum
20 million axons
how many axons in optic tract
1 million
how many axons in corticospinal
0.5 million
MCP provides input/output
input ONLY
input to middle cerebellar peduncle
pontine nuclei
output of middle cerebellar peduncle
cerebellar cortex/deep nuclei
input to inferior cerebellar peduncle
inferior olive
output of inferior cerebellar peduncle
cerebellar cortex/deep nuclei
inferior olive is responsible for
learning and memory tasks
2 sensory inputs to cerebellum
-spinal cord
-vestibular nuclei
what is the largest input to cerebellum
cerebral cortex
how does cerebral cortex travel through cerebellum
travels contralaterally through middle cerebellar peduncle
what is responsible for error signal for learning
inferior olive
how does sensory input travel through inferior cerebellar peduncle
ipsilaterally
how is the cerebellum organized
somatotopically (based on body parts)
-these maps are “fractured” with multiple representations
-see slide 9 for image
cerebellar hemispheres coordinate movement of the ipsilateral/contralateral body
ipsilateral
cerebrocerebellum goes to which deep cerebellar nuclei
dentate nucleus
-which goes to premotor cortex (motor planning and motor learning)
spinocerebellum goes to what deep cerebellar nuclei
interposed and fastigial nuclei
-which goes to motor cortex and brainstem (motor execution)
vestibulocerebellum goes to what deep cerebellar nuclei
vestibular nucleus
-which goes to lower motor neurons in spinal cord and brainstem (balance and vestibulo-ocular regulation)
what body part does superior colliculus involve
eyes
dentate and interposed axons exit cerebellum via
superior cerebellar peduncle
-and cross the midline before they synapse with the thalamus/superior colliculus
eye movement-related neurons in superior colliculus receive input from
contralateral cerebellar cortex via the upper cerebellar peduncle
superior cerebellar peduncle sends information up/down
UP
inferior cerebellar peduncle sends information up/down
to brainstem and DOWN
the gastigial nuclei project via ____ to ____
inferior cerebellar peduncle to the upper motor neurons that control axia and proximal limb muscles
inferior cerebellar peduncle primarily contains which fibers
afferents + efferents
-afferent fibers from the vestibular nuclei and spinal cord
-as well as efferents to the vestibular nuclei and reticular formation
middle cerebellar peduncle primarily contains which fibers
afferents
-afferents from the contralateral pontine nuclei
superior cerebellar peduncle primarily contains what fibers
efferent
-efferent fibers from the cerebellar nuclei to the thalamus and superior colliculus
neurons in the cerebellar cortex are organized into how many layers
3 layers
deepest layer of cerebellar cortex
granular layer
granular layer of cerebellar cortex
input layer
-deepest layer
-contains 100 billion granule cells that give rise to axons called parallel fibers that ascend to outermost molecular layer
middle layer of cerebellar cortex
purkinje cell layer
purkinje cell layer of cerebellar cortex
output layer
-middle layer
-dendrites of purkinje cells extend upward into the molecular layer where they receive input from a large number of parallel fibers
output of purkinje cells is to
deep cerebellar nuclei
outermost layer of cerebellar cortex
molecular layer
molecular layer of cerebellar cortex
outmost layer
-important processing layer
processing layer of cerebellar cortex
molecular layer
output layer of cerebellar cortex
purkinje cell layer
input layer of cerebellar cortex
granule cell layer
5 cell types in cerebellar cortex
-granule (+)
-golgi (-)
-purkinje (-)
-stellate (-)
-basket (-)
circuits wtihin the cerebellum
-purkinje neuron
-mossy fibers
-granule cells
-climbing fibers
-basket, stellate, golgi cells
purkinje neuron
ultimate afferent destination for cerebellar cortex
mossy fibers
a major source of input from brainstem and spinal cord
granule cells give rise to
parallel fibers
climbing fibers of inferior olive synapse onto
purkinje cells
basket, stellate, and golgi cells are all inhibitiory/excitatory input to purkinje
inhibitiory
2 inputs to cerebellum
-mossy fibers
-climbing fibers
mossy fibers
-arise from cell bodies in the pontine nuclei, brainstem, and spinal cord
-synapse (excitatory) onto granule cells, which give rise to parallel fibers which have excitatory synapses onto the dendritic spines of the purkinje cells
-highly convergent- each purkinje neuron is contacted by 200,000 to 1 million granule cells
climbing fibers
-arise from inferior olive
-contact purkinje cells directly; also excite the deep nuclei
-excitatory synapses onto purkinje cells
-each purkinje cell receives numerous synaptic contacts from 1 single climbing fiber
where do purkinje cells project to
deep cerebellar nuclei
-these are the ONLY output cells of the cerebellar cortex
what output from purkinje cells
GABAergic inhibitory output
in the deep cerebellar nuclei, inhibitory inputs from purkinje cells converge with
excitatory inputs from mossy + climbing fibers
how does cerebellum coordinate ongoing movement
by reducing motor error
cerebellar circuitry and coordination of ongoing movement
-deep cerebellar cells and purkinje cells recognize potential errors by comparing convergent activity concurrently available to both cell types
-the potential for making errors can be experimentally induced
-ex: partial cutting of lateral rectus muscle in monkey eye -> cover the normal eye -> weak eye initially hypometric -> then, overtime, becomes hypermetric
hypometric
person undershoots movement
hypermetric
overshoots movements
eyes and head move in what direction
opposite
learned changes in vestibulo-ocular reflex in monkeys
normal vesitbulo-ocular reflex (VOR):
-head and eyes move in coordinated manner to keep image on retina
VOR out of register:
-eyes move too far in relation to image movement on the retina when the head moves
after several hours…
VOR gain reset:
-eyes move smaller distances in relation to head movement to compensate
if cerebellum is damaged, does VOR adapt
no VOR adaptation if cerebellum is damaged
what do lesions of cerbellum do
do not paralyze movement but result in large movement errors
damage to cerebrocerebellum
deficits in coordination and visuomotor integration
damage to vestibulocerebellum
impairs ability to stand upright and maintain direction of gaze
damage to spinocerebellum
difficulty walking
3 other signs of damage to cerebellum
-dysmetria
-action or intention tremors
-speech deficits
dysmetria
over or under reaching a target
motor + non-motor consequences of cerebellar lesions
chronic alcohol use can eventually degenerate the vermis ->
difficulty walking (wide and staggered gait)
movement errors are on what side of the body relative to damage to cerebellum
same side
dymetria
movement inaccuracy
dysdiadochokinesia
difficulty performing rapid alternating movements
3 typical defects observed in cerebellar diseases
- A lesion in the left cerebellar hemisphere delays the initiation of movement. The patient is told to clench both hands at the same time on a “go” signal. The left hand is clenched later than the right, as is evident in the recordings from a pressure bulb transducer squeezed by the patient.
- A patient moving his arm from a raised position to touch the tip of his nose exhibits inaccuracy in range and direction (dysmetria) and moves his shoulder and elbow separately (decomposition of movement). Tremor increases as the finger approaches the nose.
- A subject was asked to alternately pronate and supinate the forearm while flexing and extending at the elbow as rapidly as possible. Position traces of the hand and forearm show the normal pattern of alternating movements and the irregular pattern typical of cerebellar disorder.
ataxia
difficulty producing smooth, well-coordinated movement
