4 Explain the process and ions involved in the generation of

4) Explain the process and ions involved in the generation of action potential in both nodal and non-nodal tissue. For nodal tissue you start with the pace maker potential

Solution

Process in nodal tissue: Being the pace maker, it will be important to conclude that there doesn\'t exist any resting membrane potential as it needs to genrate action potential for the SA node to conduct electric potential to the heart causing it to beat. Another consideration in terms of difference in the ions which generate action potential is the rationale that SA node in heart are slow action potential means they will depolarize quickly. This could serve a major advantage to an organ which needs to beat without stopping. Therefore, unlike Na+ ions, we have Ca ions for generation of action potential.

Now, coming to the process...starting from the pacemaker potential is the spontaneous depolarization where upon reaching the membrane potential between -40 and -30mV, an action potential is generated. This will the follow the depolarization phase followed by repolarization of -60mV. It is during the spontaneous depolarization when the membrane potential is starting to drop to -50mV we have T- type of Ca ions opens and allows Ca ions to flow down the elctrochemical gradient. this further depolarizes the cell causing another Ca channel to open...the L-type which causes further Ca ione to move in the cell. This leads to fruther depolarization.

Finally for repolarization, the K ions open increasing the hyperpolarizing K+currents. Simultaneously the Ca ions get deactivated.

Process in non nodal tissue: as mentioned above, the first thing to include in non nodal tissue is the resting potential. This is found to be closer the equilibrium potential for K+ which is -90mV. At this stage, these channels are open meaning the K+ions are leaving the cells. this makes the membrane potential negative from inside. During this depolarization, a transient increase in Na+ channel that generate the action potential. With the two conductance changes of Na and K ions causes the potential to be positive.

consecutively, the rpeolarization is caused due to reopening of the K+ channels and to a major extent opwning of Ca+ions causing inward movement of Ca+ions to the cell. Because this movement is slow it causes a plateau phase for a short time. However, the duration of action potential is what differentiates for the much short action potentials found in nerves and skeletal muscles