The document discusses the action potential in nerve and muscle cells. It defines action potential as a rapid, brief change in membrane potential from negative to positive and back. The document then summarizes the four phases of the action potential: 1) Resting membrane potential, 2) Depolarization, 3) Repolarization, and 4) Hyperpolarization. It also discusses the refractory periods - the absolute refractory period when a nerve cannot respond to stimuli and the relative refractory period when a stronger than normal stimulus is needed to trigger an action potential.

1. Dr. Saif ullah Shaikh
M.B.B.S,M.Sc,Ph.D. Scholar

2.  At the end of session student should be able to :
 Define the Action Potential
 Briefly discuss the Phases of Action Potential
 Discuss the Refractory Periods

3.  Sudden, Rapid, brief, large and
spontaneous change in
membrane potential from
negative value to positive value
and again return back to its
original position is called as
Action Potential

5. RMP DEPOLARIZATION
REPOLARIZATION HYPERPOLARIZATION

6.  Is the membrane potential
before AP occurs
 Membrane is said to be
polarized (At rest)
 Its value is -70mv & in
large neurons it is-90mv

7.  Membrane is permeable
to Na ions due to Na
influx
 The polarized state of
membrane is lost
 Potential rising in positive
direction

9.  The Na channels begin to
close &
 K channels open more
than normally due to K
efflux
 Reestablishes the normal
RMP

10. Sodium channels begin to close
Potassium channels open
More than normal
Potassium EFFLUX
RE-ESTABLISHES NORMAL
NEGATIVE RMP

11.  After reaching RMP, the
potential further falls becomes
more negative
 This is after polarization or
Positive after potential
 This is due to slow opening and
closing of k channels

14. Excitable
cells
Nerve cells
Muscle cells

15. Sodium
ions
Potassium
ions

16.  Action Potential Stages: Overview

17.  Action potential in skeletal muscles is
same as that of nerves
 Only differs in some quantitative aspects
◦ RMP is -80 to -90 mv
◦ Duration of action potential is 1 to 5ms
◦ Velocity of conduction is 3 to 5m/s

20. Period during which a nerve fiber either does not
respond or responds if the strength of stimulus is
more than normal

21. Absolute
Relative
Refractory Period

22.  It is a short period during which no action
potential develop no matter how strong the
stimulus is
 A brief time when a neuron is unable to
conduct impulse (Signal)

23.  It is a short period during which the nerve
fiber shows response, if the strength of
stimulus is more than normal
 Stronger than normal stimulus is needed to
create action potential