MODULE 10- Modulation of Movement by the Basal Ganglia Flashcards
projections to the basal ganglia come from the ____
cerebral cortex
**striatum includes what 2 things
-caudate
-putamen
striatum includes what 3 things
-caudate + putamen (motor)
-nucleus accumbens (non-motor)
medium spiny neurons of the striatum receive input from what 3 structures
-cortex
-thalamus
-brainstem structures
striatum -> ____
pallidum
(globus pallidus (GP) and substantia nigra pars reticulata (SNpr))
subregions of stratium + pallidum have what
bilateral parts (R/L)
subregions of stratium
-caudate
-putamen
subregions of pallidum
-globus pallidus, external + internal segments
-midbrain
-substantia nigra pars compacta
-substantia nigra pars reticulata
**motor components of the basal ganglia
stratium:
-caudate
-putamen
pallidum:
-globus pallidus, external + internal segments
-midbrain
-substantia nigra pars compacta
-substantia nigra pars reticulata
caudate + putamen are what
the “input zone” or starting point of the basal ganglia
sources of input of basal ganglia (2)
-corticostriatal pathways (from nearly all regions of the cerebral cortex)
-brainstem inputs from the substantia nigra pars compacta
striatum =
caudate + putament
**GABA is excitatory/inhibitory
inhibitory
glutamate is excitatory/inhibitory
excitatory
____ is found in the stratium
GABAergic medium spiny neurons
**striatum + pallidum are GABAergic/glutamate
GABAergic
-aka inhibitory
major outputs structures of the basal ganglia (2)
-globus pallidus internal segment
-substantia nigra pars reticulata
both outputs of basal ganglia (globus pallidus internal segment + substantia nigra pars reticulata) make excitatory/inhibitory connections on their targets
inhibitory
-GABAergic
pallidum = ____ + ____
-globus pallidus
-substantia nigra pars reticulata
excitatory/inhibitory connection between the striatum + the GPi + GPe
inhibitory
excitatory/inhibitory connection between the striatum + the SNpr
inhibitory
excitatory/inhibitory connection between the GPe + the subthalamic nucleus
inhibitory
excitatory/inhibitory connections between the subthalamic nucleus onto globus pallidus + SNpr
excitatory
-this is the ONLY purely excitatory pathway among the intrinsic pathways of the basal ganglia
the direct pathways of the basal ganglia have a net excitatory/inhibitory effect on thalamic neurons
excitatory
-which in turn, the thalamic neurons make excitatory connections onto cortical neurons
direct pathways/thalamic neurons play a role in movement initiation by doing what
reducing inhibition
how do basal ganglia influence movement
by regulaing the activity of upper motor neuronal circuits
main output from the basal ganglia is excitatory/inhibitory
inhibitory (GABAergic)
inhibit an inhibitory neuron =
excitatory
____ circuit via a chain of neurons
disinhibitory
see slide 10
evidence from studies of eye movements- the basal ganglia influence movement by regulating the activity of upper motor neuronal circuits
-the basal ganglia disinhibits the generation of saccadic eye movements
-cerebral cortex excitatory input to caudate medium spiny neurons -> inhibit inhibitory (GABAergic) SNpr neurons -> superior colliculus upper motor neurons excited
-the basal ganglia initiates movement by inhibiting competing or non-synergistic motor programs that would interfere with sensory-driven or goal-directed behaviors
reduction in tonic discharge from reticulata neurons ____ upper motor neurons of the superior colliculus, allowing them to generate the burst of APs that command the saccade
disinhibits
what is the main recipient of afferents to the basal ganglia
striatum
the destination of the incoming axons from the cortex are onto dendrites of a class of cells called ____
medium spiny neurons
axons from medium spiny neurons converge on neurons in ____ + ____
-substantia nigra pars reticulata
-globus pallidus
what are the 2 major output structures of the basal ganglia
-globus pallidus internal segment (GPi)
-substantia nigra pars reticulata (SNr)
both of these structures make GABAergic, inhibitory connections on their targets
the net effect of the ____ inputs that reach the striatum from the cortex is to ____ the ____ inhibitory cells of the globus pallidus + sustantia nigra pars reticulata
-phasic excitatory
-disinhibit
-tonically active
2 sets of circuits of basal ganglia
-direct pathway
-indirect pathway
direct pathway serves to
release upper motoneurons from tonic inhibition
-facilitates movement
indirect pathway serves to
increase the tonic level of inhibition
-inhibits movement
direct pathway of basal ganglia system
caudate/putamen ->
GP internal segment ->
VA/VL thalamus ->
frontal cortex
indirect pathway of basal ganglia system
caudate/putamen ->
GP external segment ->
subthalamic nucleus ->
GP internal segment ->
VA/VL thalamus ->
frontal cortex
indirect + direct pathway ____
oppose each other
-EXCEPT when dopamine is released onto the striatal medium spiny neurons, results in synergistic activity
focused selection of circuits in the basal ganglia system
suppress competing motor programs that could interfere with the expression of sensory-driven or goal-directed behaviors
circuits of basal ganglia system are organized in what fashion
center-surround
-direct pathway tightly focused on GP internal segment + SNpr
-indirect pathway highly diffuse covering a broad array of functional units
what does dopamine facilitate
the expression of movement
how does dopamine modulate basal ganglia circuits
by increasing/decreasing the excitability of medium spiny neurons
striatal medium spiny neurons project to the ____
substantia nigra pars compacta (SNpc)
what does dopamine’s ability to increase or decrease excitability depend on
receptor type
-D1 or D2
excitatory inputs to the spiny cells that project to the INTERNAL GLOBUS PALLIDUS (direct pathwy) use what receptors
D1 dopamine receptors
inhibitory inputs to the spiny cells that project to the EXTERNAL GLOBUS PALLIDUS (indirect pathway) using what receptors
D2 dopamine receptors
D1 dopamine receptors = excitatory/inhibitory
excitatory
D2 dopamine receptors = excitatory/inhibitory
inhibitory
hypokinetic movement disorder
Parkinson’s disease
Parkinson’s disease
-loss of dopamine-producing neurons and transient inhibition from caudate + putamen causes failure of disinhibition
-spinal signals are not as strong causing failure of disinhibition
pathways behind Parkinson’s disease
-loss of dopamine-producing neurons in the SNpc and neighboring ventral tegmentum -> loss of nigrostriatal pathway
-loss of the transient inhibition from the caudate and putamen to the GP internal segment (direct pathway) -> decreasing thalamic excitation of the motor cortex (hypokinetic)
hypokinetic
reduction in movement
in Parkinson’s disease what degenerates
substantia nigra
substantia nigra is Latin for what
black substance
Parkinson’s disease tips the balance in favor of activity in the direct/indirect pathway
indirect
hyperkinetic movement disorder
Huntington’s disease
how is Huntingon’s disease inherited
autosomally dominant inheritance
Huntington’s disease
atrophy of primarily the caudate + putamen + secondarily, frontal + temporal cortices
Huntingon’s disease pathway
loss of D2-expressing medium spiny neurons ->
higher excitability of GP external segment ->
decreases excitation of subthalamic nucleus to the GP internal segment ->
overall decrease in inhibitory output from the basal ganglia
selective loss of striatal neurons in the indirect pathway tips the balance in favor of the direct/indirect pathway
direct pathway
reduced movement in Parkinson’s disease/Huntington’s disease
Parkinson’s disease
excessive movement in Parkinson’s disease/Huntington’s disease
Huntington’s disease
Huntington’s disease causes excessive movements in ____
hemiballismus
-damage to the subthalamic nucleus
system forms a loop that originates from
most parts of the cortex
enormous convergence in ____
basal ganglia
project back up to ____ + ____
premotor + motor cortex
how does basal ganglia regulate movement
by releasing movement via the direct pathway + focusing movements by the indirect pathway
