cb cvmb fjgkh fgjh,h, fjngmh, fggg

1. PHY 3.8
Action potential and it’s properties in different muscle
types

2. Objectives
• Mechanism of development of Action potential in a skeletal muscle
• Distinguish between end plate potential and action potential
• Difference between action potential in skeletal muscle and neuron
• Types of action potential in smooth muscle
• Difference between action potential in smooth and skeletal muscle
• Properties of skeletal muscle
• Contractile response of skeletal muscle to single and multiple
stimulus

3. Action potential in skeletal muscle

4. Ionic Basis of Action Potential in skeletal muscle

5. ENDPLATE POTENTIAL
• Change in resting membrane potential when an impulse reaches the
neuromuscular junction.
• When sodium ions enter inside, slight depolarization occurs up to –60 mV, which
is called endplate potential.

6. Event Nerve fiber Skeletal muscle
fiber
Resting membrane
potential
–70 mV –90 mV
Firing level –55 mV –75 mV
End of
depolarization
+35 mV +55 mV

7. Action potential smooth muscle fibers
Three types :
1. Spike potential
2. Spike potential initiated by slow-wave rhythm
3. Action potential with plateau.

8. Different type of Action Potential in Smooth muscle

9. IONIC BASIS OF ACTION POTENTIAL in smooth muscle and
skeletal muscle
• The important difference between action potential in skeletal muscle
and smooth muscle lies in the ionic basis of depolarization.
• In skeletal muscle, the depolarization occurs due to opening of
sodium channels.
• But in smooth muscle, the depolarization is due to entry of calcium
ions.
• Unlike the fast sodium channels, the calcium channels open and close
slowly. It is responsible for the prolonged action potential with plateau
in smooth muscle

10. PROPERTIES OF SKELETAL MUSCLE
The important properties of skeletal muscle are:
1. Contractility
2. Excitability
3. Fatigability
4. Summation of contraction
5. Staircase phenomenon
6. Tetanization
7. Post-tetanic potentiation
8. Length-tension relationship
9. Load-velocity relationship

11. The Muscle Twitch
• A single action potential causes a brief contraction followed by
relaxation.
• This response is called a muscle twitch.
• The twitch starts about 2 ms after the start of depolarization of the
membrane, before repolarization is complete.

12. Simple muscle twitch
LP: Latent period; CT: Contraction time; RT: Relaxation time

13. Contractile response of skeletal muscle to multiple stimuli
The following may happen if multiple stimuli are given to a skeletal
muscle fibre
1. Summation of contraction
2. Staircase phenomenon
3. Tetanization

14. Summation of contraction
• Isometric tension developed in a single fiber or a muscle depends on
the frequency of the stimulus applied to it.

15. Summation of contraction

16. Staircase Phenomenon
• If a skeletal muscle is stimulated rapidly (but below the tetanizing
frequency) with a maximal stimulus
• There is a progressive increase in the force of contraction for the first
few contractions
• until a maximum uniform tension per contraction is reached.
• This is the staircase phenomenon or treppe

17. Tetanization
• Muscle stimulated repeatedly at a very high frequency
• Continuous activation of the contractile mechanism occurs without any
relaxation
• Resulting in a sustained contraction known as tetanus (tetanic
contraction).

18. 1. Complete/fused tetanus - no relaxation between the contraction phases.
2. Clonus or incomplete or unfused tetanus- periods of incomplete relaxation
between the maintained contractions
3. While the frequency of the action potentials progressively increases to tetanizing
frequency, the tension generated in the muscle gradually rises and summated
until a maximal tetanic tension is reached.
Beyond this, tension does not increase further with increase in
frequency of the action potentials.
Tetanization

19. A = staircase B & C = clonus or partial tetanization D = tetanization

20. Load-velocity relationship

21. Length–tension relationship