Module 2: Basal Ganglia Flashcards
what does the cortex connect to, and with what kind of connection
excitatory connection to the caudate and putamen
what connections does the caudate and putamen have
to substantia nigra pars compacta, and inhibitory connection to globus pallidus and substantia nigra pars reticulata
what connection does the substantia nigra pc have
to caudate and putamen
what connections do the globus pallidus and substantia nigra pr have
inibitory to subthalamic nucleus and inhibitory to thalamus
what connections does the subthalamic nucleus have
excitatory to globus pallidus and substantia nigra pr
what connection does the thalamus have
excitatory to cortex
how do we know that the basal ganglia is involved in motor control
postmortem exam of brains of individuals with motor diseases reveals pathology of basal ganglia nuclei
striatum components
caudate and putamen
what kind of input does the striatum receive
glutamatergic input via the corticostriatal pathway
what are the only cortical areas that do not project to the striatum?
primary auditory and visual cortex
what kind of synapses does the substantia nigra make
dopaminergic synapses at the base of spines
- this modulates the cortical input
where do inhibitory synapses occur
near cell soma
where do local circuit neurons synapse
on the cell soma of medium spiny neurons
where do cortical pyramidal neurons synapse
onto dendritic spines of striatal medium spiny neurons
are medium spiny neurons usually active or silent
silent
are the inhibitory globus pallidus and substantia nigra pr neurons usually active or inactive
usually spontaneously active
- due to persistant sodium currents, T-type calcium currents, and hyperpolarization-activated currents
what happens when medium spiny neurons aren’t silent
their inhibitory GABAergic shuts down the spontaneous firing of the palladial and SNpr neurons
what happens when striatum is at rest?
globus pallidus is tonically active and inhibiting the VA/VL complex of thalamus, which leads to no excitation of upper motor neurons in cortex
what happens when the striatum is excited
the globus pallidus is transiently inhibited and the VA/VL complex of thalamus is disinhibited so other inputs can excite it, leading to the excitation of the upper motor neurons in the cortex
what are the brain connections that encode for the disinhibition of eye movement?
the caudate and putamen have an inhibitory connection to the SNpr which has an inhibitory connection to the superior colliculus
what happens to the motor neurons in the eye when they are not scanning the environment
they are tonically inhibited
what happens to the eyes prior to a saccade
the tonic discharge of reticulata neurons drops
- opens the ‘gate’ for eyes to move
what happens if you inject muscimol to shut down the SNpr in eye movements?
it disinhibits the superior colliculus, and the eyes can no longer fixate (moving constantly)
how can you cause spontaneous irrepressible saccades
intranigral injection of muscimol to act as an agonist at GABA receptors, and is inhibitory
true or false: injecting muscimol into the SNpr mimics the action of medium spiny neuron firing
true
true or false: injecting muscimol into the SNpr mimics the action of globus pallidus neurons firing
false
true or false: injecting muscimol into the SNpr helps the eyes fixate
false
true or false: injecting muscimol into the SNpr activates the thalamus
false
what function does dopamine have
neuromodulatory
- doesn’t directly trigger a channel to open
what characteristic do DA receptors have
metabotropic
what does DA bind to
D1 and D2 type dopamine receptors on medium spiny neurons
what does DA do when bound to D1 receptors
facilitates neuronal firing
is dopamine a neurotransmitter?
no
- doesn’t directly allow ions to enter through it, but rather modulates other ion channels that do via G-proteins)
what does DA do when bound to the D2 receptor
inhibits activity
where is the D1 receptor located
on the membrane of the medium spiny neurons of the caudate/putamen
what is the main function of dopamine
facilitates activation of the direct pathway to excite the thalamus
what happens when msns projecting to the GPe fire?
they inhibit the GPe, which no longer inhibits the GPi, providing even stronger inhibition of the thalamus, decreasing movement
what is the indirect pathway modulated by
inhibitory DA input (D2 receptors) specifically to the striatal msn that project to the GPe
what happens when DA binds to D2 receptors on the MSNs that project to the GPe?
it makes it less likely that they will fire; now GPe is not inhibited; it inhibits the GPi, disinhibiting the thalamus and increasing movement
what is the net effect of DA on both pathways
to increase movement
what is the function of the indirect pathway when activated
to suppress undesired movements
what happens to the DA neurons in the SNpc in Parkinson’s
they degenerate
