Question

Phase	Name of Phase	gNa or gKhigher?	V-gated Na+ channel state (open, opening, closing, closed, inactivated)	V-gated K+ channel state (open, opening, closing, closed, inactivated)
1	Resting Potential	?	?	?
2	Threshold	?	?	?
3	Rising Phase	?	?	?
4	Falling Phase	?	?	?
5	Undershoot	?	?	?

2. Does resting membrane potential and equilibrium potential of sodium both change during an action potential?

3. How is the action potential affected with a defect in the Na+/K+ pump and a deleterious mutation in the leak channels?

Answer 1

Phase	Name of Phase	gNa or gK higher	V gated Na+ channel state	V gated K+ channel state
1	Resting potential	gK is higher	closed	Closed
2	Threshold	gNa higher	open	Slow opening
3	Rising phase	gNa higher	open	open
4.	Falling phase	gK higher	Inactive	open
	Undershoopt	gK higher	Inactive	open

2.The resting membrane potential depends on the ion channels that are open and ion concentrations in extracellular and intracellular fluids. Its typically between -50mV—75mV.The equilibrium potential of a cell membrane is the electrical potential difference that balances the concentration gradient of ions. Its value for sodium ions is approximately +60mV.The equilibrium potential of Na+ does not change during the action potential or after an action potential. The resting membrane potential changes during action potentials because it depends on the ion concentrations. The voltage difference across the cell membrane changes during the action potential and it causes sodium channels to open and close as the membrane voltage raises and reduces by affecting the cell membrane permeability. This changes in permeability causes movement of ions across the cell. When sodium cahnnels are open then Na+ ions are pushed into the neuron.

3)The leak channels allow the movement of ions across the cell. When this is mutated the sodium channels are depolarized as explained earlier and potassium channels open and the concentration gradient is affected. This causes prolonged action potentials and can cause LQT syndrome, QT syndrome etc.Also the regulation of insulin secretion can be affected because K+ channels are responsible for maintaining the resting potentials and mutations can cause changes in ATP to ADP ratios and insulin secretion may be inhibited. Mutations in K+ channels increases the activity of some K+ channels like for example BK channel in Central Nervous system and this is associated with epilepsy. Mutations in Na+ channels may cause excess depolarization resulting in impaired muscle activities. The cardiac action potential is resulted from a complex activities through ion channels.Mutations  causes acetylcholine receptor deficiency and a myasthenic syndrome .Depolarization at the motor endplate activates voltage gated Na+ channels, resulting in an action potential, calcium release and involuntary contractions of muscle.All these shows that action potential is affected with mutations in ion channels.