Module 2: Cerebellum Flashcards
what do lesions of the cerebellum cause
disruption of coordination of limb and eye movements, impair balance, and alter muscle tone
what is the general function of the cerebellum
paying attention to sensory stimuli that help us move more efficiently and to ignore unimportant, unhelpful stimuli
what is the hallmark of a normal cerebellum function
cerebellum output decreases
vermis
middle region of the cerebellum
spinocerebellum
the vermis plus two intermediate areas called the paravermis
cerebrocerebellum
two large lateral hemispheres on either side of the paravermis
flocculonodular lobe of the vestibulocerebellum
the smallest section of the cerebellum that looks like a bow-tie
what kind of information does the cerebellum receive
- somatosensory
- visual
- auditory
- vestibular
- proprioceptive
what kind of input does the cerebellum receive
motor cortex, somatic sensory and secondary visual cortices
where does the cortical cerebrocerebellar pathway relay and travel through?
relays in pons, goes through middle cerebellar peduncle, provides sensory info about movement
where do most cortical inputs synapse and enter the cerebellum
most synapse in the pons and enter via the middle peduncel
where do vestibular inputs to the cerebellum enter
through the inferior cerebellar peduncle and project to the vestibulocerebellum
what are the spinal inputs to the cerebellum
axons from the dorsal nucleus of Clark in the spinal cord
- receive proprioceptive input from the muscle spindles and project through the inferior cerebellar peduncle to the spinocerebellum
what inputs are referred to as mossy fibers
fibers from pons that enter the cerebellum through the middle peduncle + spinal and vestibular afferents entering through inferior peduncle
what do the pontine mossies do
relay info from the cerebral cortex
what do mossies that go through the inferior peduncle do
send sensory information from medulla, cranial nerve 8, and spinal cord
where do all mossy fibers synapse?
granule cells
where do granule cells connect
they send parallel fibers to synapse on Purkinje neurons
three layers of cerebellum
granule cell layer, purkinje cell layer, molecular layer
main function of granule cell layer
sends axons (parallel fibers) to the dendrites of the purkinje cells
characteristics of inputs from the inferior olive
they are modulatory and participate in cerebellar learning
where do climbing fibers come from
the inferior olive in the medulla
where do climbing fibers enter the cerebellum
through the inferior peduncle
where do climbing fibers synapse
directly on purkinje cells
what kind of information do climbing fibers carry
instructive information
characteristics of purkinje neurons
GABAergic, send cerebellar cortical output to the DCN
what are the two classes of excitatory inputs that innervate the cerebellar cortex
climbing fibers, and mossy fibers
characteristics of mossy fibers
synapse on DCN and on granule cells in cerebellar cortex
what are climbing fibers
inputs from inferior olive that synapse directly on Purkinjes
what are mossy fibers
sensory inputs and inputs from motor cortex that synapse on granule cell
what kind of spikes do climbing fibers display
complex spikes
what kind of spikes do parallel fibers display
simple spikes
what do mossy and climbing fibers have in common
- both send axon collaterals to the deep cerebellar nuclei and cerebellar cortex
- both are excitatory inputs
where do Purkinje cells project
deep cerebellar nuclei
where does the cerebrocerebellum project
dentate nucleu
where does the dentate nucleus project
premotor cortex (motor planning)
where does the spinocerebellum project
interposed and fastigial nuclei
where do interposed and fastigial nuclei project
motor cortex and brainstem (motor execution)
where does the vestibulocerebellum project
vestibular nuclei
where do the vestibular nuclei project
lower motor neurons in spinal cord and brainstem (balance and vestibulo-ocular regulation)
true or false: each purkinje neuron receives input from many climbing fiber
false
true or false: parallel fiber firing elicits complex spikes in the Purkinje neuron
false
true or false: a given Purkinje neuron receives either parallel fiber or climbing fiber input but not both
false
true or false: the cerebellar cortex contains multiple somatotopic maps
true
what is motor learning?
procedural/ trial-and-error learning
characteristics of procedural memories
- robust (like learning to ride a bike)
- circuits involve simple reflex pathways linking sensory input to a motor output
difference between reflex and learning
reflex = trying to stabilize yourself
learning = not getting off balance in the first place
where does input from the inferior olive enter and what are they called
enter through the inferior peduncle and are called climbing fibers; signal motor error
what is classical conditioning
a type of procedurally learned behavior
how does classical conditioning involve a reflex
an ‘unconditioned stimulus’ automatically produces an ‘unconditioned response’
how does classical conditioning involve learning
associates a new ‘conditioned stimulus’ with the unconditional stimulus
what is the conditioned response
when the conditioned stimulus triggers the response even in the absence of the unconditioned stimulus
what is the unconditioned stimulus in Pavlov’s dog
meat
what is the unconditioned response in Pavlov’s dog
salivation
what is the conditioned stimulus in Pavlov’s dog
tone
what is the conditioned response in Pavlov’s dog
the modified (learned) behavioral response to the conditioned stimulus after pairing
what do complex spikes occur in response to
climbing fiber excitation and signal error
what are simple spikes driven by
mossy fiber input and signal sensory stimuli
- mediated by AMPA receptors on the Purkinje neuron
when is motor performance bad
when a novel task is introduced
when does complex spike firing decrease
when learning is complete and there are no motor errors
what is motor error
intended motor behavior is different from the actual motor output
when are synapses candidates for removal
when sensory information coming in via simple spikes is unhelpful
what is the marr-albus theory of motor learning
that the climbing fiber activity signals that a movement has failed to meet a prediction and that corrections are then made by adjusting the effectiveness of the parallel fiber inputs to the Purkinje cell
evidence for the role of cerebellum in eyeblink conditioning
- stimulation that activates mossy or climbing fibers can be effective in conditioning
- cerebellar lesions disrupt eyeblink conditioning
how does the purkinje cell change its response
synaptic plasticity
what is long term depression caused by
internalization of the AMPA type glutamate receptor on postsynaptic neurons
what happens to AMPA receptors on Purkinje cells during learning
they are internalized at parallel fiber synapses that were active when errors occurred
what happens if a parallel fiber is active at the same time as the climbing fiber input to the post-synaptic purkinje neuron
a decrease in its ability to cause a neuron to fire will occur
when does synaptic plasticity occur
only when the climbing fibers and parallel fibers co-activate the Purkinje neuron
- long term depression occurs
what happens when there is an error
the Purkinje neuron is stimulated by both the climbing fiber and parallel fiber
- this activates 2nd messenger systems in the cell –> internalization of AMPA receptors
what does long term depression at parallel fiber synapses control
time dependent adjustments of the eyeblink reflex
what is the decline in simple spikes due to
long term depression
what carries the unconditioned stimulus
the climbing fibers
- causes complex spike in Purkinje
what carries the conditioned stimulus (tone)
the mossy –> parallel fibers (causes simple spikes)
