Integrate and Fire

Question 1

The potential inside a neuron is _ than the potential outside.

Answer 1

Lower

Question 2

Through each cycle using Na+/K+ pump, how many Sodium ions move out of the cell?
How many Potassium ions move in to the cell?

Answer 2

3 Na out

2 K in

Question 3

If 3 Sodium ions move out of the cell and 2 potassium move in, what happens to the potential?

Answer 3

There is a net loss of one atomic charge, lowering the potnetial

Question 4

The potential difference across the membrane is called what?

Answer 4

Membrane potential

Question 5

What is the typical membrane potential value?

Answer 5

E_L=-70mV

Question 6

Where is excessive sodium found?

Where is excessive Potassium found?

Answer 6

Outside the cell

Inside the cell

Question 7

Excitatory synapses cause a _ in voltage

Answer 7

Increase

Question 8

Inhibitory synapses cause a _ in voltage

Answer 8

Decrease

Question 9

What happens if the voltage exceeds a threshold?

Answer 9

A spike occurs

Question 10

What happens after a spike?

Answer 10

Refractory period lasting about 5 ms

Question 11

what happens, there is a high concentration of potassium inside the cell and because of the random motion of particles associated with temperature, these have a tendency to diffuse, that is to increase the entropy of the situation by spreading out. It takes a force to counteract this. This is the reversal potential, EL, the voltage required for zero current even if there is some conductivity. It turns out that the normal Ohm’s law applies around the reversal potential so that the current out of the cell is proportional to V - EL.

Answer 11

..

Question 12

tau (dV/dt) = E_L-V + R_mI
This is the bucket equation for the integrate and fire model,
what are the variables?

Answer 12

V=volatge
E_L= reversal potential
R_m=1/G_m where Gm is conductance
I = usually injected current

Question 13

Non-linear effects are strongest for values of V near where a spike is produced. What is one approach to get around this?

Answer 13

Use the linear equation unless V reaches a threshold value and then add the spike by hand i.e. if v(t)>V_t:
v(t)=V_r

Question 14

tau (dV/dt) = E_L-V + R_mI
The solution to this if I is constant is equal to:
V(t)=E_L+RmI+[V(0) -E_l - RmI]exp(-t/tau)

Answer 14

No spikes for low values of the current.
Vbar=E_L + RmI
if Vbar > Vt then as V increased towards Vbar it would reach the threshold and spike.
if Vbar > VT the neuron will spike repeatedly. However if Vbar