Motor Modulation: Basal Ganglia & Cerebrebellum Flashcards
how does the basal ganglia and the cerebellum modulate motor movement?
Performing only ‘wanted’ movements, and no
‘unwanted’ movements
■ Motor ‘learning’ – improving movements with
practice
○ Coordinating timing between muscle groups to
produce fluid movements
the basal ganglia is :
-a group of nuclei which initiate a collection of relevant movements for a given task
-inhibit competing movements for that task
what is a motor program?
simple movement sequences are stored in our brains
BG accesses these stored memories and activates one and inactivates the other
does the basal ganglia initiate movement?
no it acts more like a funnel or filter for movement
what is the funnel/filter feature of the BG??
○ Funnel – receive information from many cortical areas, process it and output it to a few select structures
○ Filter – only movements appropriate to the task at hand are ‘selected
BG neurons fire _____ a movement happens
before (planning)
if you have a lesion of the BG what effect will the patient have?
disturbances in initiating movement
other than the BG what else fires during the planning phase of movement?
premotor cortex and supplementary motor area
at rest BG neurons _____ _____ the thalamus
tonically inhibit
when movement is needed what happens?
the inhibition is transiently relieved
BG acts on what?
thalamic nuclei
what is the direct BG pathway?
go signal
DISINHIBITS stimulating wanted movements
what is the indirect pathway?
stop signal
REINFORCES the inhibition stopping unwanted movement
can the indirect and direct pathway ever work together?
yes often they work together to ensure intended movements are made
what are the brain nuclei of the BG?
caudate, putamen, globus pallidus and subthalamic nucleus
what brain stem nuclei are involved with the BG?
substantia nigra
what are the input nuclei?
caudate and putamen (aka striatum)
what is the cuadate?
C shaped nucleus that curves into multiple cerebral lobes
what is the main input nucleus for motor movement?
putamen
what is the most lateral aspect of the bg?
putamen (adjacent to the lateral fissure and insula)
what is the main output for the BG?
globus pallidus
The globus pallidus has two segments:
internal and external segment
what does the internal segment of the GP do?
OUTPUTS motor info to direct and indirect pathways
what does the external segment do?
modulatory projections to the subthalamic nucleus – indirect pathway
the internal segment of the GP has high ___ activity, which has what effect?
high levels of tonic inhibitory activity acting to inhibit the thalamus in a resting state
what is a modulatory nuclei?
only communicates with other nuclei in the BG
GP, Stn, SsN
At rest for the direct pathway, the ability of the thalamus to excite the cortex
(and therefore initiate a motor program) is inhibited due to ________________
the tonic action of the GPi
for the direct pathway For a motor program to be activated, activity of the ______ must be ______
GPi must be transiently inhibited
the direct pathway ______
DISinhibits (allows)
go over the flowcharts
direct/indirect
At rest, striatal neurons are
________ and need to be __________
hyperpolarized, and need multiple excitatory inputs to reach firing threshold
what causes Parkinson’s?
associated with degeneration of dopaminergic neurons in the SN
neurodegeneration of neurons in the direct pathway causing loss of stimulation of the striatum LOSS OF GO SINGAL
what is the cardinal signs of Parkinson’s?
TRAP
tremor, rigidity, akinesia, postural change
Cortical neurons excite the:
striatum
Striatum inhibits ______________
Globus Pallidus internal segment
Thalamus (now released from GPi inhibition) can _____ and _______
can fire and excite the motor cortex
Which nuclei of the Basal Ganglia receive direct cortical input?
A. Globus pallidus internal and external segments
B. Caudate and putamen
C. Substantia nigra and subthalamic nucleus
B. Caudate and putamen
Within the direct pathway, the globus pallidus internal segment provides ______ input to the ________
A. Excitatory; thalamus
B. Inhibitory; thalamus
C. Excitatory; striatum
D. Inhibitory; striatum
B. Inhibitory; thalamus
Indirect pathway reinforces _____________________
inhibitory drive to the thalamus, repressing movement – especially targeted at unwanted movement (e.g. competing motor programs)
One way to increase inhibitory drive to the thalamus is to provide ___________________
greater stimulus to the GPi, strengthening its signal
the circuitry is set up such that
the _________________ is tonically inhibiting the STN
globus pallidus external segment (GPe)
Neurons of the striatum can inhibit the ______ to release the STN and allow it to fire
GPe
in the indirect path Cortical neurons excite the _________
striatum
in the indirect path Striatum inhibits _______________ (which now cannot inhibit subthalamic nucleus)
Globus Pallidus external
what cases huntingtins disease?
degeneration of neurons in the striatum resulting in unwanted movements like chorea and rigidity
what mnemonic is used for huntingtins?
CAGE
Indirect pathway can be
modulated by neurons of the
_______________, which provide
an inhibitory signal
substantia nigra
Striatal neurons associated with direct pathway have _______ receptors that _________ in response to dopamine
D1 dopamine receptors, which depolarize a cell in response to
dopamine
Striatal neurons associated with indirect pathway have __________ receptors that _______ in response to dopamine
D2 dopamine receptors, which hyperpolarize a cell in response to dopamine
________ can both excite the direct
pathway and inhibit the indirect pathway
substantia nigra
what is the function of the cerebellum?
Coordinates timing between different muscle groups to produce fluid movement
-motor learning (improvement with practice)
-feedforward (calculating others trajectories to avoid hitting into people in a crowded path)
what happens if cerebellum becomes damaged?
loss of coordination… ATAXIA (lack of coordination between antagonist and agonist muscles, abnormal movement/trajectory)
what is the cerebellums role in movement?
modifies commands it gets from the cortices to make the movement more accurate
when does motor learning and error prediction tweaks occur?
Planning phase of movement (makes it more efficient)
when does error correction occur?
executing movement phase
what are the lobes of the cerebellum?
anterior, posterior and flocculonodular
where is cerebellar grey matter located?
–external surface folds called folia
–deep nuclei (dentate, emboliform, globose, fastigial)
what is found on the inferior and superior cerebellar peduncles?
incoming and outgoing fibers
what is found in the middle cerebellar peduncles?
incoming fibers only
what makes up the cerebellar blood supply?
-superior cerebellar artery
-anterior inferior cerebellar artery
-posterior inferior cerebellar artery
deep cerebellar nuclei are _____ structures of the cerebellum
output
what occurs at the spinocerebellum?
error correction (detects difference between motor plan and execution and reduces difference)
where does the spinocerebellum receive projections?
proprioceptors (muscle spindles and golgi tendon organs)
inferior olive
what does the paravermis and vermis control?
vermis: central body movement coordination
paravermis: distal muscles
what effect can happen from midline cerebellar damage?
loos of coordination of proximal muscles, affecting balance, posture and gait (truck ataxia and wide unsteady gait)
what happens with lateral damage to the cerebellum?
movement deficits in IPSILATERAL extremity
-loss of coordination- joints moving separately instead of smooth
-inaccuracy in range and direction of movement
-trouble with patterned movement
what does the vestibulocerebellum do?
-corrections to stability and balance, both continuous and anticipatory
-contributes to vestibular ocular reflex and smooth pursuit of eyes
where does the vestibulocerebellum receive projections?
vestibular nuclei and vestibular ganglia
-inferior olivary nucleus
what is the output for the vestibulocerebellum?
vestibular nuclei
reticular formation
(bypasses DCN)
what happens with floccular lobe syndrome?
truncal ataxia, nystagmus
where does the cerebrocerebellum receive projections?
base of pons
inferior olivary nucleus
what is the function of the cerebrocerebellum?
motor learning, adapting motor programs to make future movements more accurate especially in distal extremities
whee does the cerebrocerebellum output?
UMN of lateral movement path via VL of thalamus
how does the cerebellum error correct?
deep cerebellar nuclei (excitatory)
purkinje fibers (modulatory inhibition)
what are the layers of cell interaction in the cerebellar cortex?
incoming mossy fibers
granular cells
purkinji cells
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