Membrane potential

Question 1

What is Nernst potential?

Answer 1

Diffusion potential level across a membrane that exactly opposes the net diffusion of a particular ion through the membrane.
It measures the potential for one type of ion at the time
E= (2.3RT/F) log(Co/Ci)
EMF= z (61.5) log ( [ion]outside/[ion] inside)

Question 2

Assumptions for Nernst Equation

Answer 2

Equation can only be used for one ion at a time
Membrane must be completely permeable to that ion
Ion must be at equilibrium

Question 3

Action potential characteristic

Answer 3

All or none
Self propagating
Non decremental

Question 4

Voltage gated sodium channels

Answer 4

Has 2 gates: Activation and Inactivation gates
-90 mV—>Activation gate closed, inactivation opened
-90 mV to +35 mV—> both gates are opened
Activation gates open as voltage reaches -70 mV to -50 mV
+35 mV to -90 mV inactivation gate is closed

Question 5

Channel leak potassium

Answer 5

Potassium channels too small for hydrated potassium or hydrated sodium
Form a selectivity filter
Bound to carbonyl oxygens
“naked” potassium pass through channels

Question 6

Potassium gated channels

Answer 6

Have a single gate

Slow activation opens the gate from +35 mV to -90 mV

Question 7

Speed of an action potential

Answer 7

Can be increased by:

• Increasing diameter of axon
• Increasing membrane resistance (myelination)

Question 8

What is threshold?

Answer 8

Point at which a local potential will elicit an action potential

Question 9

Direction of propagation

Answer 9

-Orthodomic direction–>towards distal end of the axon
Due to hyperpolarization and refractionary period

-antidromic direction–>opposite direction towards axon hillock

Question 10

Myelination

Answer 10

Sphingomyelin–>principal lipid in myelin sheath
Schwann cells are cells that form myelin sheaths in peripheral axons
Nodes of Ranvier are unmyelinated junction between Schwann cells
Requires little energy for repolarization

Question 11

Refractory period mechanisms

Answer 11

Inactivation gate closed and will not reopened until the membrane is close to the resting potential
have 2 types:
Absolute refractory period
Relative refractory period

Question 12

Absolute refractory period

Answer 12

Period during which a second action potential cannot be elicited even with a strong stimulus
Most fast sodium channels are either open or in the inactivated state

Question 13

Relative refractory period

Answer 13

Stronger than normal stimulus can cause action potential

Question 14

What is diffusion potential?

Answer 14

It is caused by ion concentration difference on either side of a membrane