Muscle Contraction.

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Presentation transcript:

Muscle Contraction

I. Skeletal Muscle A. Muscle fiber 1. Sarcolemma 2. Sarcoplasm 3. Myofibrils – contractile elements a. Actin myofilament F actin strands tropomyosin troponin (T, I, C) b. Myosin myofilament

4. Sarcomere arrangement of myofibrils a. Z disk – attaches actin b. I band – actin myofilament c. A band – both actin and myosin H zone – only myosin 5. T Tubules invagination of sarcolemma 6. Sarcoplasmic Reticulum high conc. of calcium

B. Signal transmission 1. Motor neuron 2. Presynaptic terminal 3. Endplate region of skeletal fiber where synapse occurs 4. Nicotinic receptor C. Muscle Contraction 1. Action Potential -> sarcolemma ->T tubules 2. T tubules -> Sarcoplasmic Retic 3. Voltage gated Ca++ channels open 4. Ca++ -> sarcoplasm

5. Calcium binds to troponin (C) 6. Tropomyosin is deflected 7. Active sites of actin exposed 8. ATP attaches to myosin head 9. ATP is hydrolyzed (ADP & P) 10. Myosin head is phosphorylated & cocks 11. Myosin head binds to actin (cross bridge) 12. Myosin head dephosphorylates (head moves) & ADP released (power stroke)

D. Muscle relaxation Calcium pumped into Sarco Retic E. Phases of muscle movement 1. Lag Phase AP in motor neuron to exposure of active sites 2. Contraction Phase crossbridge -> power stroke 3. Relaxation Phase calcium pumped into S. R. 4. Mechanical signal measured as tension

F. Stimulus vs contraction all or none response subthreshold stimulus -> no Threshold -> AP -> contraction increase Ca++ = increase force G. Stimulus frequency no refractory period freq of AP = freq of contractions tetanus calcium not pumped back

II. Cardiac Muscle A. Contractions like skeletal striated (sarcomeres) B. Intercalated disks 1. attachment 2. Z disks 3. Gap junction III. Smooth Muscle A. Structure elongated spindle shaped no striations (no sarcomeres)

actin & myosin – loose bundles intermediate filaments noncontractile B. Contraction 1. ANS – via 2nd messenger 2. Opens Na+ and Ca++ channel 3. Depolarization 4. Muscarinic receptor ->IP3 5. IP3 -> Sarcoplasmic Retic. (Ca++ released) 6. Calcium activates calmodulin 7. Ca++/Calmod activates myosin kinase

8. Myosin kinase hydrolyzes ATP phosphorylate myosin head 9. Myosin binds to actin -> contraction 10. Relaxation – dephosphorylation (Myosin Phosphatase)