basal nuclei network

Question 1

what regions form the inhibitory output circuits for the basal nuclei?

Answer 1

SNr and GPi

Question 2

what region forrm the regulatory input of the basal nuclei?

Answer 2

dopaminergic input from the SNc

Question 3

what is tonic activity?

Answer 3

cells are instrincally active- producting action potentions without excitatory input

Question 4

what regions are tonically active?

Answer 4

GPe, STN, inputs from striatum to SNc and outputs from the SNr/GPi to the thalamus

Question 5

what is a convergent network?

Answer 5

takes in a lot of information to a small number of neurons

Question 6

is the basal nuclei network convergent or divergent?

Answer 6

convergent

Question 7

what neurons does the striatum contain?

Answer 7

90-95% of neurons are medium spiny neurons

Question 8

where do the MSN connect to?

Answer 8

100 MSN connect to 1 cell in the globus pallidus

Question 9

what are MSN innervated by?

Answer 9

5000 pyramidal cells (layer v) in the cortex connect to one medium spiny neuron in the striatum

Question 10

loss of somatotopy in the globus pallidus

Answer 10

high pattern of intergration of motor information from cortex to GP
lots of information so do not know where movement information comes from just by anaylsis GP activity (e.g was it right arm or left finger?)

Question 11

what are the two pathways of the basal nuclei?

Answer 11

direct pathway from striatum to thalamus
indirect pathway from striatum to thalamus

Question 12

direct basal nuclei pathway

Answer 12

excitatory input from cortex to striatum to SNr/GPi which have inhibitory output (tonically active) to thalamus
leads to reduced tonic activity to thalamus
thalamus then outputs to motor system in cortex which increases feedback to cortex
(reduced inhibition in output leads to increase in activity in thalamus- disinhibition)

Question 13

what is disinhibition?

Answer 13

inhibiting something that is already inhibitory (equivalent to already being excitatory)

Question 14

inhibitione of the motor cortex

Answer 14

when striatum is at rest then GP is tonically active thereby inhibiting the VA/VL complex so there is no excitation of the upper motor neurons in the cortex

Question 15

excitation of the motor cortex

Answer 15

when striatum is transiently excitated then the GP is transiently inhibited so the VA/VL are disinhibited so other inputs can excite it leading to excitation of upper motor neurons in the cortex

Question 16

indirect pathway of the basal nuclei

Answer 16

increased excitation in striatal-pallidal projection decreases GPe inhibition (disinhibition)
increases tonic excitation in STN so increases inhibition in SNr/GPi
leading to increased inhibition of thalamic output (reduced thalamic output)

Question 17

direct pathway overview

Answer 17

activation leads to removal of inhibitory
input to thalamus – get excitation of motor
cortex
this facilitates/initiated wanted movements

Question 18

indirect pathway output

Answer 18

activation enhances inhibitory input to
thalamus – no excitation of cortex
inhibits/suppresses unwanted movements

Question 19

STN pacemaker

Answer 19

projects back to GPe when STN is activated
this reintroduces inhibition of STN
pulsatile output from STN means the output from the GPi/SNR is not constant

Question 20

combined basal nuclei pathways

Answer 20

in the absence of cortical input, the indirect pathway dominates the direct pathway- default position of motor system is nothing (not excited)

Question 21

why is the indirect pathway more dominant than the active pathway?

Answer 21

striatal-pallidal MSNs can generate a tonic inhibitory current (indirect)
striatal-nigral
MSNs and are
quiescent at rest
and have a low
firing rate when
active (direct)

Question 22

what is the role of the nigral-striatal projection?

Answer 22

to balance the direct and indirect pathways and favour movement

Question 23

what are the two subtypes of MSN?

Answer 23

those that express the D1 dopamine receptor and those that express the D2 dopamine receptor
these control the nigral-strital projection (tonically active)

Question 24

D1 receptor role

Answer 24

positively modulatory receptor (excitatory)
enhances activity of the direct pathway

Question 25

D2 receptor role

Answer 25

negative modulatory receptor (inhibits)
supress activity of direct pathway

Question 26

effect of nigral-striatal projection balance

Answer 26

strength of input to direct/indirect will determine how far initation of movement will go
this allows smooth initation of movement

Question 27

how do the direct and indirect pathways enable movement?

Answer 27

conceptually, 3 cells in the striatum may represent 3 guitar cords based off motor cortex input
these can then be put into globus pallidus which represents the pattern of the movement needed to play a song= dircet pathway
indirect pathway will stop the playing of the cords (disable pattern)
if you want to play a specific song then you have to maintain the indirect pathway for all other songs that you know

Question 28

other parallel basal nuclei loops

Answer 28

1. oculomotor loop control of gaze
2. prefrontal and orbitofrontal loops concerned with cognition
3. limbic loop concerned with emotional and visceral functions

Question 29

impact of limbic loops

Answer 29

• may play a central role in reward learning
• involved in drug addiction mechanism
• may also be involved in diseases such as schizophrenia