1. 5 Rules of Skeletal Muscle Activity 1.All muscles cross at least one joint 2.Typically, the bulk of the muscle lies proximal to the joint crossed 3.Muscles can only pull, they never push. This means that most muscles must work in pairs. Muscles are arranged on the skeleton in such a way that whatever one muscle can do, another can do in reverse. 4.All muscles have at least two attachments: Origin – attachment at least moveable bone Insertion – attachment onto the moveable bone 5.During contraction, the muscle insertion moves toward the origin

2. Contraction of a Skeletal Muscle on a Whole Providing Energy for Muscle Contraction ▫ATP is stored in small amounts in muscle fibers and is quickly used up ▫ATP is regenerated by 3 routes 1.Creatine phosphate with ADP 2.Anaerobic glycolysis and lactic acid formation 3.Aerobic respiration

3. Contraction of a Skeletal Muscle on a Whole Muscle Fatigue and Oxygen Debt ▫If muscle activity is strenuous and prolonged, muscle fatigue occurs due to an accumulation of lactic acid in the muscle and a decrease in its energy (ATP) supply ▫After exercise, the oxygen debt is repaid by deep breathing

4. Contraction of a Skeletal Muscle on a Whole Muscle Tone ▫Muscle tone keeps muscles healthy and ready to react ▫It is a result of a staggered series of nerve impulses delivered to different cells within the muscle ▫If the nerve supply is destroyed, the muscle loses tone, becomes paralyzed, and atrophies

5. Contraction of a Skeletal Muscle on a Whole Effect of Exercise on Muscles ▫Inactive muscles atrophy. Muscles challenged by resistance exercise to respond beyond their ability increase in size and strength. ▫Muscles subjected to regular aerobic exercise become more efficient and stronger and can work longer without tiring.  Aerobic exercise also benefits other body systems.

6. Types of Contraction Isotonic Isometric

9. Stimulation and Contraction of a Single Skeletal Muscle Cell When the neuron releases a neurotransmitter, acetylcholine, the permeability of the sarcolemma changes, allowing sodium ions to enter the muscle cell. Fig 6.5a

10. Stimulation and Contraction of a Single Skeletal Muscle Cell This produces an electrical current, the action potential, which flows across the entire sarcolemma, resulting in release of calcium ions from the sarcoplasmic reticulum. Fig. 6.5b

11. Sliding Filament Theory Sarcomere Shortening Animation

12. Sliding Filament Theory In the contracted sarcomere, ▫the light H zone in the center of the A band has disappeared, ▫the Z lines are closer to the thick filaments, ▫ and I bands have nearly disappeared. ▫The A bands move closer together but do not change in length. Fig. 6.7

13. Sliding Filament Theory Calcium binds to regulatory proteins on the thin filaments and exposes myosin binding sites, allowing the myosin heads on the thick filaments to attach. Fig. 6.8 a, b

14. Sliding Filament Theory The attached heads pivot, sliding the thin filaments toward the center of the sarcomere, and contraction occurs. Fig. 6.8 c

15. Sliding Filament Theory ATP provides the energy for the sliding process, which continues as long as calcium is present

16. Sliding Filament Theory Video clips of sliding filament theory ▫http://www.sci.sdsu.edu/movies/actin_myosin.ht mlhttp://www.sci.sdsu.edu/movies/actin_myosin.ht ml ▫http://media.pearsoncmg.com/bc/bc_campbell_ biology_6/cipl/ins/49/HTML/source/71.htmlhttp://media.pearsoncmg.com/bc/bc_campbell_ biology_6/cipl/ins/49/HTML/source/71.html ▫http://www.wisc- online.com/objects/index_tj.asp?objID=AP2904http://www.wisc- online.com/objects/index_tj.asp?objID=AP2904