Isfahan University of Technology Advance Physiology (part 4) By: A. Riasi (PhD in Animal Nutrition & Physiology)

Muscle physiology  Three muscle types are structurally and functionally distinct.  The muscle can be classified in two different ways:  Striated or unstraited muscles  Voluntary or involuntary muscles

Skeletal Muscle

 In this section we turn our attention to the following topics:  How does cross-bridge interaction between actin and myosin bring about muscle contractions?  How does a muscle action potential trigger this contractile process?  What is the source of Ca++ that physically repositions troponin and tropomyosin to permit cross-bridge binding? Skeletal Muscle

 Acetylcholine (ACh) as neuro-transmiter  Transverse tubule (T tubule)  Action potential reach the central portion of the fiber Skeletal Muscle

Figure 3.25b Skeletal Muscle

 Three pathway supply additional ATP as needed during muscle contraction: 1.Transfer from a high energy phosphate from a phosphagen (creatine phosphate and arginine phospahte) to ADP. 2.Oxidative phosphorylation (the citric acid cycle and electron transport system) 3.Glycolysis Skeletal Muscle

 The phosphagens contain a high-energy phosphate group.  Energy and phosphate from ATP can be transferred to creatine or arginine to form the phosphate. Creatine phosphate + ADP Creatine + ATP Skeletal Muscle

 There are cardiovascular limits to the amount of O2 that can be delivered to muscle.  In this situation the muscle fibers rely increasingly on glycolysis. It has two advantages: 1- Glycolysis can form ATP in absence of O2 2- It can proceed much more rapidly than oxidative phosphorylation because fewer steps. Skeletal Muscle

 There is a disadvantage of the low efficiency of glycolysis ( 2 ATP vs 36 ATP in oxidative phosphorylation ).  The end product of anarobic glycolysis is pyruvic acid that is converted to lactic acid.  Lactic acis leads to acidosis and is believed to play a role in the onset of muscle fatigue. Skeletal Muscle

What are the reasons of muscle fatigue? 1.A local increase in inorganic phosphate resulting from the breakdown of phosphagens; 2.Accumulation of lactic acid, which (via release of H+) may inhibit key enzymes in the energy-producing pathways or the excitation contraction coupling process; 3.Depletion of energy reserves. Skeletal Muscle