1. Movement

2. Endoskeletons and Exoskeletons
A. Provide support and attachment points for muscles – act as levers
B. Endo – inside body
C. Exo – shell of chitin

3. Antagonistic pairs
A. Pairs of muscle that accomplish opposite movements

4. Synovial Joints – provide movement

7. Muscle fibres (muscle cells)
Contain multiple nuclei
Plasma membrane = sarcolemma
1. Contains tunnel like extensions going into the cell called T tubules
Cytoplasm = sarcoplasm
1. Organelles that store glycogen
2. Myoglobin – like hemoglobin, stores oxygen
Myofibrils – stringy sections of a muscle cell
1. Lots of mitochondria packed between them
2. Composed of sarcomeres (contractile units)

8. V. Sarcomeres

9. VI. Steps of a Muscle Contraction https://www. youtube. com/watch

10. 1. At rest, Na+ is actively pumped out of
1. At rest, Na+ is actively pumped out of the cell and K+ is actively pumped into the cell (requires ATP).

11. 2. Neurotransmitter (chemical messenger in nervous system) called acetylcholine (Ach) is released by exocytosis at the neuromuscular junction (NMJ)

12. 3. Ach diffuses across the NMJ and attaches to receptors on the muscle cell, causing sodium gates on the sarcolemma to open and let Na+ into the cell which causes K+ to leave the cell

13. 4. If enough Ach is released, an “action potential” is generated (can’t stop once it has started) 5. At rest, actin and myosin are kept apart by troponin and tropomyosin and Ca++ is being actively transported into the SR

14. 6. Change in Na+/K+ concentrations causes the SR to release Ca++ 7
6. Change in Na+/K+ concentrations causes the SR to release Ca Ca++ attaches to troponin and tropomyosin, pulling them away from actin and exposing the myosin binding sites

16. 8. Myosin heads bind to actin and start pulling the actin inward, shortening the sarcomere (a contraction)

17. 9. As this is occurring, Ach is being broken down and its components are returning to the nerve cell 10. Once Ach is broken down, sodium gates and potassium gates close, and Na+ is actively pumped out and K+ is pumped into the muscle cell

18. 11. Return of Na+/K+ concentrations causes SR to start taking Ca++ back in Without Ca++, troponin and tropomyosin block myosin and actin from binding 13. Sarcomere relaxes