Basal Ganglia

Question 1

what structures comprise the basal ganglia?

Answer 1

caudate, putamen = striatum

globus pallidus

substantia nigra

subthalamic nucleus

Question 2

ventral striatum

Answer 2

nucleus accumbens

Question 3

dorsal striatum

Answer 3

caudate and putamen

Question 4

the globus pallidus is adjacent to what two structures?

Answer 4

laterally- putamen

medially- internal capsule

Question 5

the internal capsule divides what two structures

Answer 5

caudate and putamen

also globus pallidus and thalamus

Question 6

main input to striatum

Answer 6

all areas of cortex except primary auditory and visual

Question 7

dopaminergic input to striatum

Answer 7

substantia nigra pars compacta

Question 8

output of striatum

Answer 8

globus pallidus and substantia pars reticula

external globus pallidus projects to subthalamic nucleus, which feeds back to internal globus pallidus

internal globus pallidus to VA/VL thalamus

VA/VL projects back to premotor cortex

Question 9

direct pathway of basal ganglia

Answer 9

excitement from cortex to striatum causes transient inhibition of tonically active globus pallidus internal segment

globus pallidus IS is tonically inhibitor on the VA/VL of the thalamus, so when it is inhibited by the striatum, it activates the VA/VL

the VA/VL then activates the frontal cortex

Question 10

substantia nigra pars compacta in the direct pathway

Answer 10

releases DA on D1 receptors in the striatum, exciting it and causing a net excitation of the the thalamus

Question 11

indirect pathway of the basal ganglia

Answer 11

cortex excites striatum, which inhibits the external globus pallidus

the external globus pallidus is tonically inhibiting the subthalamic nucleus. when it gets inhibited via the striatum, it releases the subthalamic nucleus, effectively activating it

the subthalamic nucleus excites the internal globus pallidus, reinforcing its tonic inhibition of the VA/VL thalamus

net effect is inhibition of the thalamus and cortex

Question 12

substantia nigra pars compacta in the indirect pathway

Answer 12

releases DA onto the D2 receptors, which is inhibitor

DA inhibits the inhibitory effect of the indirect pathway

Question 13

parallel circuits thru the basal ganglia

Answer 13

well defined projections thru basal ganglia exist for different purposes and have distinct tracts thru the cortex, striatum, pallidus, and thalamus

examples: eye movement, motor loop, limbic loop, and prefrontal loop

Question 14

convergence thru the basal ganglia

Answer 14

huge convergence occurs from cortex to striatum, and huge convergence from striatum to globus pallidus

Question 15

purpose of indirect pathway

Answer 15

inhibitory background onto which the highly focused excitatory direct pathway is superimposed

general: keep you from doing things you shouldn’t

Question 16

purpose of direct pathway

Answer 16

allow you to do the movements you should

Question 17

substantia nigra pars reticulata in eye movements

Answer 17

operates the same as the globus pallidus interna (in the direct pathway)

SNPR usually inhibits superior colliculus, inhibiting eye movements

cortex excitation releases the superior colliculus from this inhibition and allows eye movements

Question 18

there are many different types of neurons in the striatum

Answer 18

ok

Question 19

striasome

Answer 19

isolated island of specific NTs in striatum

Question 20

ventral (limbic) loop

Answer 20

similar to direct feedback loop

limbic cortex excites nucleus accumbens, which inhibits ventral pallidum, which is tonically inhibting medial dorsal portion of thalamus

additionally, D3/D4 receptors in the NA are excited by ventral tegmental area DA

all drugs of abuse increase DA release from VTA

Question 21

initiation of movement

Answer 21

before primary motor is activated, there is activity in basal ganglia to select proper motor loops and inhibiting extraneous ones