action potential ,nerve muscle 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

6. 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.

8. PHASES Of ACTION POTENTIAL :
1) 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.

9. 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

10. 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

12. 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.

14. 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

15. 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]

17. THANK U