1. Chapter 6 The Muscle Physiology

2. Nerve Stimulus to Muscles
Synaptic cleft – gap between nerve and muscle
- no contact
- filled with interstitial fluid

3. Transmission of Nerve Impulse to Muscle
1. Neurotransmitter (acetylcholine) released by nerve upon arrival of nerve impulse
2. Acetylcholine attaches to receptors on the sarcolemma
3. Sarcolemma becomes permeable to sodium (Na+)
4. Sodium rushing into the cell causes an action potential
5. Once started, muscle contraction cannot be stopped
All or None!

4. Sliding Filament Theory
Activation by nerve causes myosin crossbridges to attach to actin
then bind to the next site on actin
Myosin “slides” along actin

5. Contraction of a Skeletal Muscle
Contraction is “all or none” w/in one fiber
not all fibers may be stimulated during the same interval
Different combinations of muscle fiber contractions give different responses
Graded responses – different degrees of skeletal muscle shortening

6. Types of Graded Responses
1. Twitch
Single, brief contraction
Not a normal muscle function

7. 2. Tetanus (summing of contractions)
One contraction is immediately followed by another
The muscle does not completely return to a resting state
The effects are added

8. 2a. Unfused (incomplete) tetanus 2b. Fused (complete) tetanus
Some relaxation occurs between contractions
The results are summed
2b. Fused (complete) tetanus
No evidence of relaxation before the following contractions
The result is a sustained muscle contraction
Figure 6.9a, b

9. Tetanus can be caused by bacteria
Clostridium tetani is a bacteria that causes
tetanus in humans, also called lockjaw.
Produce toxin that affects the nerves and
controls the activity of muscles.

10. Response to Strong Stimuli
Muscle force depends upon # of fibers stimulated
More fibers contracting results in greater muscle tension
Muscles can continue to contract until they run out of energy

11. Energy for Muscle Contraction
Initially, muscles used stored ATP for energy
- ATP broken to release energy
- 4-6 sec worth of ATP stored
After this time, other pathways used to make ATP

12. Direct phosphorylation
Muscle cells contain creatine phosphate (CP)
CP is a high-energy molecule
After ATP is depleted, ADP is left
CP transfers energy to ADP, to regenerate ATP
Used up in sec
Creatine monohydrate is a precursor to creatine phosphate. By supplementing with creatine monohydrate, your muscle creatine phosphate is maximised, and more muscular work can occur due to greater energy reserves.
NOT endorsed by School!

13. Aerobic Respiration occur in the mitochondria
Glucose is broken down to carbon dioxide and water, releasing energy
slower reaction that requires oxygen
Makes the most ATP
Lasts for hours

14. Anaerobic glycolysis Reaction that breaks down glucose without oxygen
Glucose is broken down to pyruvic acid to produce 2 ATP
Lasts up to 1 min.
Muscle fatigue – no more O2 – burning due to lactic acid

15. Muscle Fatigue and Oxygen Debt
When muscle is fatigued, it can’t contract
Common reason is oxygen debt
- Oxygen needed to get rid of lactic acid
Increasing acidity (from lactic acid) and lack of ATP causes the muscle to contract less

16. Types of Muscle Contractions
1. Isotonic contractions
Myofilaments slide past each other during contractions
The muscle shortens
2. Isometric contractions
Tension in the muscles increases
The muscle does NOT shorten

17. Muscle Tone Some fibers are contracted even in a relaxed muscle
Different fibers contract at different times
Involuntary

18. Effects of Exercise on Muscle
Results of increased muscle use
- Increase size
- Increase strength
- Increase efficiency
- more fatigue resistant