Question

4) Click the channel which opens to bring about repolarization. Action Potential in Autorhythmic Cells 20 0 Potential (mY) -20 4.40 2-60 Membrane -80 300 150 Time ms) Sodium channel Potassium channel Calcium channel + (Na) + (Na (Na) (Na) ca (Na) + (Na) (Na be (Na)

Answer 1

Potassium channels Opens which causes efflux of K+ ,Which bring the membrane potential to Negative Value (Repolarisation)

Autorhythmic cells are the cells that are self‐excitable , that is they are able to generate an action potential without external stimulation by a nerve cell.

Example:SA Node,AV Node.

The phases in generation of action potential in cardiac autorhythmic cells (Pacemaker cells-SA node and AV node ) are-

1.Slow Depolarisation

2.Rapid Depolarisation

3.Repolarisation.

1.Slow Depolarisation.

Resting membrane potentials(RMP) of Pacemaker Cells are : -60 mV.

Slow phase of Depolarisation occurs due to Entry of Some positive ions (Na+ ions) which changes the RMP from -60 mV - -40 mV.

In this phase ,There is Closure of K+ channel(which prevents outward flow of K+ ions) & Opening of Slow NA + channels(Slow entry of Na+ channel) this changes RMP to -40 mV.

2.Rapid depolarisation.

As the RMP becomes -40 mV due to entry of Na+ channels,Ca2+ channels opens.

This -40 mV is called the threshold potential.

When RMP reaches threshold potential----Ca 2+ channels open---Entry of Ca2+ ion---Which again Converts Membrane potential to more poistive Values......This change inMembrane potential by which it loses its negative charge (-Ve resting membrane potential) is called Depolaridation.

3.Repolarisation.

Repolarisation occur when these Ca2+ channels closes & K+ channels Opens.

Now there is Efflux (Outward flow)of K+.This loss of positive ions converts the positive membrane potential back to Resting Membrane Potential (that is -60 mV)This is Known as Repolarisation(The membrane attains it Negative resting membrane Potential).