2. Filaments

3. Resting state

4. Electrical impulse (Action Potential) reaches axon terminal

5. Impulse opens Calcium Channels, rapid influx of Calcium into terminal

6. Vesicles with acetylcholine (Ach) bind to cell membrane & releases Ach into synaptic cleft

7. Ach

8. Ach binds to receptors on motor end plate

9. Ach receptors opens Na+ channels, causes an influx of sodium into muscle

10. Sodium influx triggers a muscle impulse (electrical signal) in all directions of muscle fiber.

11. Electrical impulse travels across Sarcolemma, down t-tubules, and across cisternae Sarcolemma

12. Electrical impulse travels across Sarcolemma, down t-tubules, and across cisternae

13. Sarcoplasmic Reticulum releases Calcium into Sarcoplasm Sarcoplasmic Reticulum

15. Ca 2+ (Calcium) Triggers muscle contraction by binding to troponin

16. Tropomyosin moves and exposes actin filaments to cross bridges

17. Cross bridges bind to actin & pulls actin forward (ADP is released from cross bridge)

19. Videos Breakdown of ATP Synapse Transmission Action Potential Across Sarcolemma Shortening Sarcomere

20. Relaxation Calcium pumps return Calcium to Sarcoplasmic reticulum Acetylcholinesterase clears ACh from synaptic cleft ATP binds to cross bridge & myosin is released from actin * ATPase converts ATP to ADP using energy to cock cross bridge* Tropomyosin cover actin filaments * Note: ATP is required for both muscle contraction & relaxation

22. Myofibrils Actin Filaments “thin” – Anchored to z-lines (filament proteins) – I bands (light color) = actin + z-lines Myosin Filaments “thick” – A-band (dark color) = Myosin filaments + overlapping Actin filaments – H-zone (slightly lighter) = Myosin filaments between overlapping actin Sarcomere – Area between 2 z-lines – Functional unit of skeletal muscle – During contraction adjacent z-lines approach each other