بسم الله الرحمن الرحيم

1. بسم الله الرحمن الرحيم ﴿و ما أوتيتم من العلم إلا قليلا﴾ صدق الله العظيم الاسراء اية 58

2. Nerve and Muscle By Dr. Abdel Aziz M. Hussein Lecturer of Medical Physiology Member of American Society of Physiology

3. Skeletal Muscle

4. Muscles • Muscles are machines which convert the stored chemicalenergy into mechanical energy (work) and heat. • Ms constitutes50% of the body weight. • There are three types of muscles

5. Skeletal ms • These ms are usually attached to the skeleton (skeletal ms) • Functions of the skeletal ms 1) Movements of the body as a whole or part of it e.g. one limb. 2) Maintenance of the body posture by their tonic contraction and ms tone. 3) Control of body temperature as; • 50% of heat production during rest is due ms activity • During ms exercise heat production is much ↑ed.

6. Functional Histology

7. Sarcotubular System

8. Sarcomere

9. Excitation Contraction Coupling(Mechanism of Sk. Ms Contraction)

10. Excitation Contraction Coupling(Mechanism of Sk. Ms Contraction) • 1) Def., • It is the process by which an action potential initiates the ms contraction. • 2) Steps: • It involves the following steps: • 1) Propagation of the AP and release of Ca ions: • Propagation of the AP in the motor nerve → production of an EPP at motor end plate → generation of AP at the adjacent areas of ms cell membrane → AP spreads on both sides of the motor end plate and spreads along the T tubules which extend deep into the ms fiber → release Ca ions from the terminal cisternae of SR.

11. Mechanism of Sk. Ms Contraction 2) Steps: 1) Propagation of the AP and release of Ca ions:

12. Mechanism of Sk. Ms Contraction • 2) Steps: • 2) Binding of the cross-bridges between myosin and actin: • The released Ca ions combine with Troponin C molecules → causes the tropomyosin to move away from its blocking position and thus exposing the binding sites present on actin molecules. • Cross bridges from the thick (myosin) filaments combine with the binding sites on the actin.

13. Mechanism of Sk. Ms Contraction 2) Steps: 3) Cycling of cross-bridges: It occurs in the following steps; a) Binding:b) Bending: c) Detachment:d) Return to original position:

14. Mechanism of Sk. Ms Contraction • 2) Steps: • 4) Relaxation: • It occurs when Ca ions are transported into the SR by an active process and Ca-ATPase. • Removal of Ca ions makes troponin to return to its original state which causes tropomyosin to move back and cover the binding sites on actin.

15. Mechanism of Sk. Ms Contraction

16. Changes that occur in the ms during contraction

17. I. Electrical Changes

18. I. Electrical Changes

19. II- Excitability changes • the excitability of the muscle fibers passes in the following phases: • Absolute refractory period (ARP): • Relative refractory period (RRP): • Supernormal phase of excitability: • Subnormal phase of excitability:

20. III. Metabolic (chemical) Changes • A) During contraction: • Energy of contraction is derived from: • 1) ATP: • It is the immediate source of energy in this process. • ATPase • ATP ADP + P (phosphoric acid) + Energy. • 2) Creatine phosphate (Cr-P): • Cr-P rapidly resynthesizes ATP from ADP by adding of phosphate group. • Creatine phosphokinase enzyme • ADP + Cr-P Creatine + ATP • The amount of Cr-P is about 10 times larger than ATP • ATP and Cr-P allow the ms to contract only 50-100 times.

21. III. Metabolic (chemical) Changes A) During contraction: 3) Oxidation of glucose and free fatty acids: a) Anaerobic oxidation of glucose (or ms glycogen): Anaerobic oxidation (Glycolysis) Glucose (ms glycogen) 2ATP Anaerobic glycolysis is rapid but not economic. b) Aerobic oxidation of glucose and free acids: Aerobic oxidation (Kreb's cycle) Glucose + 6O2 6CO2+ 6H20 + 38ATP It produces great amount of ATP (38 ATP). It is economic but slow. 4) In exhausted ms: There is an emergency mechanism for the supply of ATP ADP + ADP ATP + AMP

22. III. Metabolic (chemical) Changes

23. III- Chemical changes IV- Thermal Changes

24. III. Metabolic (chemical) Changes B) During recovery: At the end of ms activity, the energy stores in the ms (ATP, Cr-P and ms glycogen) are depleted and the lactic acid is ↑ed in blood. a) Part of the lactic acid is oxidized into CO2 and H2O: The energy produced from this oxidation is used to reform ATP and by turn Cr-P. Oxidation (Kreb's cycle) Oxidation Lactic acid Pyruvic acid CO2+ H2O + ATP ATP + Creatine Cr-P + ADP

25. III. Metabolic (chemical) Changes • B) During recovery: • b) The other part of the lactic acid is converted into glucose: • Lactic acid diffuses to the blood stream and then to the liver where it is converted into blood glucose (through the Cori cycle which is the reverse of glycolysis). • Ms takes glucose from the blood stream and changes it into ms glycogen. • At the end of recovery the energy stores in the ms (ATP, Cr P and ms glycogen) are reformed again, and the lactic acid is removed.

26. III. Metabolic (chemical) Changes N.B. PH Changes in the ms during contraction: 1) At first, the pH becomes acidic due to the release of phosphoric acid. ATPase ATP ADP + Phosphoric acid + Energy 2) Then the pH becomes alkaline due to the release of creatine from the Cr-P. ADP + Cr-P ATP + creatine 3) Lastly, the pH becomes acid due to the release of lactic acid from the anaerobic oxidation of glucose. Anaerobic oxidation Glucose (ms glycogen) 2 lactic acid + 2ATP

27. IV. Thermal Changes • During contraction, heat production in the ms is about 100-1000 times during rest. • 40-50% of the energy liberated is converted into work. • 50-60% of the energy is liberated as heat at the onset of and during contraction of the muscle → so heat production occurs in two phases: • 1) Initial heat: includes: • i) Activation heat: • It is a very rapid heat production which starts before any shortening has occurred. • It results from: • Release of Ca from the terminal cisternae. • Binding of Ca to troponin protein. • Movements of cross-bridges towards the binding sites on the thin filaments.

28. IV. Thermal Changes • 1) Initial heat: • ii) Shortening heat: • It represents the heat produced by the process of shortening (cross-bridge cycling). • It is proportional to the degree of shortening. • iii) Work heat: • It occurs when the ms performs work. • It is proportional to the work done.

29. IV. Thermal Changes • 2-Delayed (recovery) heat: • It is the heat liberated from the ms after its relaxation. • It results from the metabolic reactions needed to reform the energy stores in the ms (ATP, Cr-P and ms glycogen) and to removelactic acid. • It is nearly equals to the initial heat, and continues for about 30 minutes after the end of ms contraction.

30. V. Mechanical Changes • Types of muscle contraction: • There are two types of ms contraction→ isotonic and isometric contractions.

31. V. Mechanical Changes

32. V. Mechanical Changes

33. Mechanism of isometric contraction: • In isometric contraction, the contractile components of ms shorten at the same time the elastic components (2 types, series and parallel elastic elements) are stretched to the same degree. • So the length of the ms remains constant but its tension is markedly increased. V. Mechanical Changes

34. V. Mechanical Changes • Force velocity relationship • The velocity of shortening is inverselyproportional to the weight of the load. • If the ms is unloaded, it shortens with maximum velocity. • As the weight of the load ↑es, the velocity of shortening decrease. • When the load reaches amaximum, the ms contracts without shortening i.e. contracts isometrically.

35. Length tension relationship V. Mechanical Changes • The tension developed during the isometric contractions depends on the length of the ms. • A maximum tension is obtained when the length of the ms is nearly equals to the resting length of the ms in the body (optimal length).

36. THANKS