Direct / indirect pathways from basal ganglia

Question 1

what is the main outcome of the direct pathway

Answer 1

results in strengthening / vigor / speed fo motor commands from M1 and premotor areas

Question 2

what is the main outcome of the indirect pathway

Answer 2

inhibit thalamic neurons that project to M1 and premotor areas blocking unwanted mvmts
inhibits antagonist muscel to desired mvmts
decreased interference with desired motor mvmts

Question 3

explain the direct pathway

Answer 3

• motor and premotor areas become active and send excitatory inputs to the striatum
• excitation of striatum leads to increase in inhibitory inputs to GPi
• inhibition of GPi leads to reduction in GPi output
• reduction in release of inhibitory NT
• causes excitation of neurons in the thalamus which excites M1 and premotor areas in prep to launch a specific mvmt

Question 4

what is the state of the direct pathway at rest

Answer 4

output nuclei of the basal ganglia send tonic inhibitory signals to the thalamus

Question 5

why is the inhibitory baseline in the direct pathway important

Answer 5

keeps the motor system in check and allows cortical representation of possible mvmts to become activities without engaging muscles

Question 6

how is a motor mvmt launched from the direct pathway

Answer 6

• as a specific motor plan becomes strengthened (increased cortical activity from M1) the inhibitory signal is reduced
• excitatory signals from cortex enter the basal ganglia via the putamen and SNc
• mvmt is launched

Question 7

what type of dopaminergic projections are used in the direct pathway

Answer 7

excitatory dopaminergic projections

Question 8

what is the state of the indirect pathway at rest

Answer 8

output nuclei of the basal ganglia send tonic inhibitory signals to the thalamus
(same as direct pathway)

Question 9

what occurs in the indirect pathway when a motor plan is strengthened

Answer 9

as the specific motor plan is strengthened (increased cortical activity)
- motor plans for other undesired mvmts and antagonist muscels are inhibited

Question 10

what occurs during the reduction of inhibitory inputs in the indirect pathway

Answer 10

excitation of STN - which excites GPi
inhibits thalamic nuclei and cortex

Question 11

explain the indirect pathway

Answer 11

• motor and premotor areas send excitatory inputs to the striatum (putamen)
• excitation of putamen = increase in inhibition of GPe
• reduces inhibition on STN
• therefore excitation of STN = increased inhibition from the GPi to the thalamus
  = inhibition of thalamic neurons to block unwanted mvmts and inhibit antagonist muscles