Membrane Depolarization and the AP

What factors determine if an AP will go through?

1. Stimulus number

2. Stimulus magnitude

3. Nature

   1. EPSP

   2. IPSP

4. Where is the stimulus relative to the axon hillock

What are the two requirements for an AP?

1. NaV channels

2. Enough depolarization to activate NaV channels

How about how many vesicles do you need to cause an AP?

300

What happens to deltaV as you move further away from the stimulus?

It gets smaller

What does the length constant tell you?

How much of an area will be affected by a depolarization

If two cells receive the same stimulus which one wins out?

The one with the larger length constant

What is spatial summation?

Two zones of depolarization overlap each other increasing total depolarization

What is temporal summation?

Two depolarizations combine at the same time to cause an AP

How many NaV channels will you find per microM in the end of the dendrites?

1-10

How many NaV channels right before the soma in the dendrites?

10-100

How many NaV channels in the soma per microM?

100-1000h

How many NaV cannels per microM near the axon hillock?

1000-2000

What is electrotonic depolarization?

Change in potential with no change in conductance (no channels open)

What is the logic gate of the neuron?

Axon hillock

Where is the highest area of NaV channels?

Axon hillock

Where will you find CaV channels in a neuron?

Axon hillock

Where will you find Ca+ gated K+ channels in a neuron?

Axon hillock

What are KiR channels and what do they do?

They are Ca+ dependent K channels and they extend hyperpolarization

What is the absolute refractory period?

NaV channels cannot be stimulated (active and inactivated states)

What is the relative refractory period dependent on?

Kv channels

After hyperpolarization it requires a greater stimulus to reach threshold potential

What gives you directionality of an AP?

The absolute refractory period

How can you increase length constant?

1. Make the axon bigger

2. Insulate it with myelin