4 Networks and Populations

Question 1

For a quadratic intagrate and fire model, what are the fixed points like? (spiral/node, stable/unstable)
What are the axes for this parabola?
What position are these foxed points on this model’s parabola curve?

Answer 1

-one stable node and one unstable node
-vertical V’ and horizontal V
-stable left and unstable right because of the values of V and model is stable when V is less

Question 2

What is the equation for the Quadratic Integrate and Fire model?
What are the conditions of this equation?

Answer 2

dV/dt =b + V2
if V=Vpeak then V<-Vreset

Question 3

Summary of stages in an AP

Answer 3

rmp Na+ closed, K+ closed (inside more neg. than outside)

1depolarisation - Na+ channels open: Na+ influx
(cytosol becomes less neg.)
2repolarisation - Na+ channels inactivating, K+ channels open: K+ efflux
3hyperpolarisation - Na+ channels inactive, K+ channels open

rmp Na+ closed, K+ closed

Question 4

Which family of channels directly influences itself ?
How does the other type influence the channel?

Answer 4

-ionotropic
-metabotropic controls channels via biochemical G-protein cascade

Question 5

What are the four steps that preceed and trigger post synaptic potential (PSP)?

Answer 5

1 arrival of presynaptic spike
2 calcium influx causes NT release into synaptic cleft
3 detection of NT molecules by postynaptic receptors
4 binds to and opens NT-gated postsyaltic channels -> ion influx -> changes post synaptic membrane potential

Question 6

Which is excitatory/inhibitory: glutamate and GABA

Answer 6

glutamate=excitatory
GABA=inhibitory

Question 7

What do excitaory/inhibitory synapses do to the membrane voltage of the post synaptic neurons?

Answer 7

excitatory: increases Vm /depolarises
inhibitory: decreases Vm /hyperpolarises

Question 8

What is the IPSC?
What does it represent?

Answer 8

-inhibitory postsynaptic transmembrane current
-current responsible for causing an IPSC

Question 9

If the synaptic potential Esyn =-75 and the membrane potential of the postsynaptic neuron is -65, what will happen to the membrane potential?

Answer 9

hyperpolarise - decreases Vm

Question 10

What sort of channel receptors do GABAa and GABAb bind to?
Which ions does each GABA move thru their channels?

Answer 10

GABAa - ionotropic (exclusively Cl-)
GABAb -metabotropic (opens K+ channels)

Question 11

What is the concentrations of Na+, K+, Cl- ions relative to inside and outside the cell?

Answer 11

K+ higher inside
Na+ lower inside
Cl- higher outside

Question 12

Why does presynaptic release of GABA (a and b) cause an IPSP?

Answer 12

because both GABA a causes Cl- influx and K+ efflux on postsynaptic neuron thus Vm made more negative

Question 13

What effect does IPSP have on postsynaptic neuron?

Answer 13

suppresses AP firing

Question 14

What does the value of tau depend on in the synapse model?

Answer 14

the type of NT used

Question 15

What type of graph line does a simple model of a synapse use?

Answer 15

decreases exponentially (e-t)

Question 16

What does the double exponential synapse model allow you to adapt?

What is tau in this model?

Answer 16

-allows you to change the values of tau(decay) and tau(rise)
you can change rise and decay time constant

-time constant (of rise or decay)

Question 17

As the tau decay (decay time) increases, what happens to the gsyn conductance?

Answer 17

gradient flattens/decreases in the exponentially decreasing line

Question 18

What are the three synapse models?

Answer 18

-simple
-alpha function
-double exponential

Question 19

What is Esyn

Answer 19

reversal potential

Question 20

What is the EPSC?
What is it caused by?

Answer 20

-excitatory postsynaptic transmembrane current
-an increase in membrane voltage of postsynaptic neurons

Question 21

what are the two type of ionotropic glutamate receptors?
Excitatory or inhibitory?

Answer 21

AMPA, NMDA
excitatory

Question 22

What receptor channels are present on excitatory neurons?

Answer 22

AMPA gluatamate
NMDA glutamate

Question 23

What ions are allowed to pass thru AMPA channels?

Answer 23

Na and K

Question 24

Which is response faster ionotropic or metabotropic?

Answer 24

ionotropic

Question 25

Which ion blocks NMDA receptor? How is it removed?

Answer 25

Magnesium voltage-dependent: depolarisation causes mg2+ to go away

Question 26

Why must you use double exp. model for GABAb and NMDA receptor currents?

Answer 26

because for each NT, the rise and fall times are not the same

Question 27

Which NT is suited to which synapse model? excitatory (glutamate) AMPA NMDA inhibitoty GABAa GABAb

Answer 27

AMPA: simple NMDA: double exp. GABAa: simple GABAb: double exp.

Question 28

What is the difference between temporal summation and spatial summation on postsynaptic neuron?

Answer 28

-temporal: spaced out spiked -spatial: lots of different presynaptic inputs

Question 29

How many layers are in the cortex?

Answer 29

six layers

Question 30

If you want to model a neural network of the cortex, what percentage of excitatory and inhibitory neurons would you use? Which neuron types in cortex is responsible for excitatory and inhibitory?

Answer 30

80 % excitatory - pyramidial layer 5 20 % inhibitory - interneurons layer 4

Question 31

What are the conditions of the eqn calculating average population activity of a group of neurons?

Answer 31

○All neurons (N) are identical ○Required same external input current (Iext) ○Interaction strength (wij) is uniform

Question 32

What is the definition of average population activity of a neural network ?

Answer 32

temporal evolution of population activity in large homogenous neural populations

Question 33

Does the neural mass model calculate firing rate of neuron?

Answer 33

no calculates the average population activity

Question 34

What is the equation for leaky integrate and fire model? and the conditions of the model?

Answer 34

dV/dt= b-V if V=1 then V-> 0

Question 35

What is the connectivity of the each neuron like when using the leaky integrate and fire to model a neural NETWORK?

Answer 35

each neuron in network: all to all coupling including to itself

Question 36

What is full connectivity in neural network? What is random coupling with fixed connection probability " ? What is random coupling with fixed number of inputs " ?

Answer 36

-neurons receive input from all other neurons in the network -you decide the the probabilty and it changes depending on the N total number of neruons in network to keep probability the same -you decide number of inputs however this does not change as N changes