Action Potential

Question 1

Be able to label and draw and fully understand action potential graph

Answer 1

Question 2

Electrical signals are sent through neurons by ion movement across membranes
two possible directions which are what

Answer 2

influx- movement of ions (Na+) in- from ECF into cytosol
efflux- movement of ions (K+) from in to out

Question 3

ion movement is driven by what

Answer 3

concentration gradient

Question 4

are action potentials all or nothing? what does this mean?

Answer 4

yes they are
once an action potential beings it proceeds through the entire length of the axon

Question 5

explain phase 1 of action potential
Resting potential

Answer 5

near -70 mv
leakage and active transport rates are approx matching
leak channels: Allow flow down concentration gradient (Na+ into cell K+ out of cell)
Na-K-ATPase: (actively pump against concentration gradient) Na+ out of cell and K+ into cell

Question 6

explain phase 2 of action potential
Graded Potential

Answer 6

graded potentials are small changes in membrane potential that may trigger or inhibit action potential. If the net graded potential exceeds -55 which is threshold potential an action potential will begin

Question 7

explain phase 3 of action potential
Depolarization

Answer 7

After threshold potential is reached 2 types of voltage gated channels open 1) voltage gated Na channels which are faster 2) voltage gated K channels which are slower.
Na+ rushed into the cell causing the membrane potential to become more positive
Peak membrane potential: +30 mV

Question 8

explain phase 4 of action potential
Repolarization

Answer 8

As the membrane potential crosses 0 mV the voltage gated Na+ channels begin to close. This allows the efflux of K+ to counteract the influx of Na+. Remember that the Na+ and K+ channels open at the same time but the K+ channels are much slower. K+ rushed out of the cell causing the membrane potential to become more negative bc positive ions are flowing out. This process returns membrane potential to -70 mV but the voltage gated K+ channels close at -70 mV.

Question 9

explain phase 5 of action potential
Hyperpolarization

Answer 9

As the membrane potential crosses -70 mV the voltage gated K+ channels begin to close since K+ channels are slow, K+ continues to leave the cell.
This causes the membrane potential to become more negative than the resting potential. At the end of this phase, membrane potential returns to -70 mV.

Question 10

During the action potential refractory period occur
What are the names of the 2 and what is a refractory period

Answer 10

Absolute
Relative
A refractory period is where cell doesn’t respond to stimulus

Question 11

What is a absolute refractory period

Answer 11

another action potential cannot occur
exists while voltage gated channels are open

Question 12

what is a relative refractory period

Answer 12

an action potential can occur but a larger graded potential is needed. Exists during hyperpolarization

Question 13

Conduction of action potential through the axon depends on what?

Answer 13

passive electrotonic current
the passage of electrical energy is adjacent regions of the axon membrane

Question 14

what factors influence conduction speed

Answer 14

axon diameter (larger is faster)
myelination- presence of myelination allows saltatory conduction to occur which increases action potential transfer speed.