1. Muscular Contractions
Contracting and Relaxing Skeletal Muscle

2. Anatomy of a Muscle Fiber (Cell)
Sarcolemma
Myofibril
Sarcomere
Z line

3. Anatomy of a Sarcomere
Actin
Myosin

4. Contraction Overview
Lovely artwork courtesy of David Goodsell and the RCSB Protein Data Bank

5. Steps of a Muscle Contraction
Nerve causes release of acetylcholine (ACh)

6. Steps of a Muscle Contraction
Reception of ACh causes an action potential (electrical nerve signal) in muscle cell

7. Steps of a Muscle Contraction
Action potential causes release of calcium in muscle cell
Meanwhile…

8. Steps of a Muscle Contraction
Calcium binds, forming troponin complex and revealing myosin binding sites.

9. Steps of a Muscle Contraction
Sliding filament theory

11. Contraction Overview
Lovely artwork courtesy of David Goodsell and the RCSB Protein Data Bank

13. Relaxation Acetylcholinesterase breaks down Ach
Active transport prepares the muscle cell for future action potentials
Active transport removes free calcium from muscle cells
ATP breaks actin-myosin linkage

14. Relaxation

15. Interference Botox & botulism – block acetylcholine release
Rigor mortis – can’t keep calcium out of cells so muscles contract, lack of ATP prevents myosin from releasing actin