ACTION POTENTIALS.pptx

action potential description,physiology

1. ACTION POTENTIALS Dr.G . Reena Prasoona Asst Prof.

2. INTRODUCTION Nerve and muscle cells-excitable cells Glandular cells, macrophages,ciliated cells-local changes in membrane potentials RMP-membrane potential generated at rest Action potential-membrane potential generated during action by nerve and muscle cells

3. brief of rmp RMP of large nerve fibres -90mv Neuron -70mv Genesis of RMP- 1. potassium and sodium leak channels 2.sodium- potassium pump DIFFUSION OF POTASSIUM CONTRIBUTES MORE TO RMP

4. DEFINITION : The brief sequence of changes which occur in the Resting Membrane Potential when stimulated by a threshold stimulus . ORIGIN : Excitable cells : Nerve & muscle Cells generate Action Potentials when they are stimulated by a change in Membrane Potential. It is due to change in the conduction of ions across the cell membrane that are produced by alterations in the ion channels.

5. PHASES Of ACTION POTENTIAL : During Resting ( Polarized ) state, inside of nerve is negative and outside of nerve is positive and the RMP is -70MV 2 ) Stimulus Artifact : is a brief irregular deflection of the base line. It is due to a current leakage from the stimulating electrode to the recording electrode. 3) Latent Period : is a short Iso -electric period following the stimulus artifact . It is interval between the application of stimulus and the onset of Action potential. 4) Firing Level : Depolarization proceeds slow upto a level called the Firing Level. (-55MV) at which depolarization occurs very rapidly.

6. 6) Spike Potential : The phase of Rapid rise of potential in depolarization and a rapid fall I n repolarization phase is Spike Potential. ( 1Ms) 7) After Depolarizaton : is slow repolarization phase follows rapid fall in spike- potential and extends upto RMP level ( Negative After Potential 4 Ms). 8) After Hyperpolarization : After reachinjg the Resting Level the Potential further falls and becomes more negative (- 72MV Positive After Potential- 35-40ms ) Finally the RMP is Restored. 5) Overshoot : From the firing level the curve reaches the zero- potential rapidly and then overshoots the zero line upto +35MV

7. Genesis of action potential Voltage gated sodium channel-activation and inactivation Voltage gated potassium channel and its activation VOLTAGE CLAMP-research method for measuring the effect of voltage on opening and closing of channels-Hodgkin and Huxley –NOBLE PRIZE

8. IONIC BASES OF ACTION POTENTIAL A.P was studied Hodgkin and Huxley using the Voltage clamp technic . 1 ) Resting State ( Polarized ) : RMP inside of the membrane is negative and outside is positive. ( K + Permeability is greater. ) 2 ) Depolarization : “Na channel activation” occurs through “m”- gates. ( Positive feedback spiral – Hodgkin cycle ) 3) Repolarization : It starts with K efflux due to opening of voltage gated K + channels . 4) After Depolarization : due to slow efflux of K + . 5) After Hyper Polarization : Slow return of the K + Channels to the closed state.

9. ROLE OF OTHER IONS DURING AP Impermeable negatively charged ions inside the axons Calcium ions- Calcium pumps Calcium-sodium channels Calcium channels-slow channels-numerous in cardiac and smooth muscle Sodium channels-fast channels

10. Recording of action potential Monophasic recording-one electrode inside and other outside and connected to CRO Depolarisation Repolarisation Biphasic recording-both the electrodes outside Recording of alternate deflection [one negative below the baseline and one positive above the base line]

11. THANK U