This presentation focuses on detail of the contraction of the contractile fibers in the muscles. short introduction to the ion channels, different potentials and phases working on the contraction of the muscles. Reference: Anatomy, Physiology & Pathophysiology by Gerard J. Tortora

1.  Graded Potential
 Action Potential

2.  Graded Potential : used for short distance communication
 Action Potential : allow communication over long distances within the
body

3.  Specific ions move across the membrane through the open ion channels,
down their electrochemical gradient.
 Electrochemical Gradient : a concentration difference plus an electrical
difference.
 As ions move, they create a flow of electrical current that can change the
membrane potential.
ION MOVEMENT
lower conc. area Higher conc. area
Cations Negatively charged area
Anions Positively charged area

4. Type
 LEAK CHANNELS
 LIGAND GATED CHANNELS
 MECHANICALLY GATED
CHANNELS
 VOLTAGE GATED CHANNELS
Description
 Randomly open and close.
 Open in response to binding of
ligand stimulus.
 Open in response to mechanical
stimulus.
 Open in response to voltage
stimulus (change in membrane
potential).

5.  The resting membrane potential exists because of a small buildup of negative ions in the
cytosol along the inside of the membrane, and an equal buildup of positive ions in the
extracellular fluid along the outside surface of the membrane.
Extracellular Fluid
equal no. of cations and anions
Resting membrane potential (-70mV)
Cytosol
equal no. of cations and anions

6.  It is a small deviation from the membrane potential that makes the
membrane either more polarized or less polarized.
 HYPERPOLARIZING GRADED POTENTIAL : when the response makes the
membrane more polarized (more -ve).
 DEPOLARIZING GRADED POTENTIAL : when the response makes the
membrane less polarized ( less –ve)

7. 1. DEPOLARIZING PHASE
 Stimulus open the Na+ channels
 Inward flow of Na+ causes the depolarizing phase of the action potential
 The changes in membrane potential : -55mV to +30mV
 i.e. the inside of the membrane is 30mV more +ve than the outside.

8. 2. REPOLARIZING PHASE
 A threshold-level depolarization opens voltage gated K+ channels.
 K+ ions move towards extracellular fluid.
 The Na+ ions movement become slow.
 Membrane potential change from +30mV to -70mV.

9. 3. AFTER-HYPERPOLARIZATION PHASE
During this phase, the voltage gated K+ channels remain open.
Membrane potential reaches to -90mV (more –ve).
K+ channels close, membrane potential returns to the resting potential i.e. -70mV.

10. MembranepotentialinmV
Time in milliseconds (msec)
After hyperpolarization PhaseStimulus
Depolarizing Phase
Repolarizing Phase
Reversal of
Polarization
Threshold
Resting Membrane
Potential
-70
-55
0
+30

11. Action Potential and Contraction of Contractile Fibers
MembranePotential(mV)
-100
-80
-60
-40
-20
0
+20
0.3 sec
Rapid depolarization due to
Na+ inflow when voltage-gated
fast Na+ channels open
1
Plateau due to Ca2+ inflow when
voltage gated slow Ca2+
channels open and K+ Outflow
when some K+ channels open
2
3
Repolarization due to closure of Ca2+
channels and K+ outflow when
additional voltage gated K+ channels
open
Depolarization Repolarization
Refractory Period
Contraction