1. Bio 449Lecture 16 - Muscle IIOct. 6, 2010 Excitation-contraction coupling Excitation Contraction Tropomyosin and troponin Cross-bridge cycling Mechanics of muscle contraction Twitch contractions Isometric Isotonic Tetanic contractions Isometric Terms to Know Transverse tubules (T-tubules) Sarcoplasm (aka myoplasm) T (Transverse) tubules Dihydropyridine receptors Ryanodine receptors (or channels) Tropomyosin Troponin Isometric contraction Isotonic contraction Twitch contraction Tetanic contraction (tetanus) Summation Latent period Contraction time 50% relaxation time Force-velocity curve Readings Lectures 15-17:Chapter 11, pages 396-401 Chapter 12 Terms to Know Motor neuron Neuromuscular junction (aka endplate) Sarcolemma

2. Length-tension curve Fig. 12-16

3. Excitation-contraction coupling

4. Neuromuscular junction Fig. 11-12 Somatic motor neuron Muscle fiber The neuromuscular junction Motor end plate Terminal bouton Mitochondria Synaptic vesicle (ACh) Presynaptic membrane Synaptic cleft Postsynaptic membrane Schwann cell sheath Axon terminal Nicotinic ACh receptors

5. Neuromuscular junction Fig. 11-13 Skeletal muscle fiber AChE Voltage-gated Ca 2+ channel Action potential ACh Ca 2+ Acetyl + choline Nicotinic receptor Motor end plate Somatic motor neuron Axon terminal K+K+ Na + K+K+ ACh Closed channel Open channel

6. T-tubules and SR Fig. 12-4 Sarcolemma Thin filament Thick filament T-tubule brings action potentials into interior of muscle fiber. Sarcoplasmic reticulum stores Ca 2+

7. Excitation-contraction coupling Axon terminal of somatic motor neuron Myosin head Myosin thick filament M line Motor end plate Sarcoplasmic reticulum ACh DHP RyR T-tubule Muscle fiber Troponin Tropomyosin Actin Z disk Na + Ca 2+ Ca 2+ released Myosin thick filament Fig. 12-11

8. Troponin and tropomyosin Fig. 12-3 Thin filaments Tropomyosin Troponin Actin chain G-actin molecule Nebulin

9. Cross-bridge cycle Fig. 12-9 ADP Actin moves Cytosolic Ca 2+ Tropomyosin shifts, exposing binding site on actin TN Power stroke Initiation of contraction Troponin G-Actin Tropomyosin blocks binding site on actin Myosin head TN Relaxed state. Myosin head cocked. Pi 1 2 3 4 5

10. Mechanics of muscle contraction

11. Twitch contractions

12. Isometric twitch

13. Isotonic twitch

14. Tetanic contractions

15. Exam 1 results Mean: 80.2 SD: 12.8 Max: 98.5