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7 Cards in this Set

  • Front
  • Back

1. Brain thinks “I want to lift my right arm”

2. Nerve impulse travels from brain, down spinal cord, to cell body of a single somatic neuron in the spinal cord

3. Somatic neuron connects spinal cord to the muscle

4. Action potential generated on this neuron a. From node of Ranvier to node of Ranvier via Saltatory conduction b. Action potential carried to nerve terminal

5. Electrical potential difference at nerve terminal opens voltage-gated Calcium channels

6. Calcium enters nerve terminal

7. Interject information about Vesicle formation…a. Golgi apparatus in somatic neuron cell body forms very small vesiclesb. These empty vesicles are transported by “streaming” through the axoplasm to the c. Approximately 300,000 vesicles in the nerve terminals of one end-plated. In nerve terminal cytoplasm, Acetyl Co-A (from mitochondria) binds with choline e. Choline acetyltransferase (enzyme) makes Acetylcholine (ACH)f. ACH pumped by transport proteins into the vesicles in the axoplasm near the g. Approximately 10,000 molecules of ACH are in each vesiclenerve terminal at the tips of the nerve fibers(from recycling)nerve terminal

8. Calcium attaches to proteins on inside of membrane and outside of vesicle full of ACH

9. Vesicle drawn toward membrane and fuses with nerve terminal membrane

10. Vesicle dumps ACH molecules into the synaptic cleft

11. Fibrous protein matrix and extracellular fluid flows through here

12. ACH diffuses across synaptic cleft and bonds to ACH receptors that are located mostly on the shoulders subneural clefts of the muscle membrane

13. 2 ACH molecules attach to the each of the Alpha-Subunits of ACH receptor

14. ACH receptor opens causing large Sodium influx (little Ca in and little K out also)

15. Electrical potential difference occurs on muscle membrane

16. Ligand-gated Sodium channels (opened by attachment of ACH) continue to open furthering change in electrical potential until…

17. Voltage-gated sodium channels sense change in voltage and cause action potential (AP) and propagation of the muscle fiber in both directions

18. AP gets to T-tubules

19. AP moves down deep into the T-tubules

20. Causes release of Calcium from the sarcoplasmic reticulum into cytoplasm

21. Calcium binds to Troponin-C on double helix of 2 actin fibers that have tropomyosin wrapped in it, normally tropomyosin blocks the sites where myosin attaches to actin

22. Ca binds to Troponin-C and moves the tropomyosin out of the way and the myosin heads make contact with the actin

23. Myosin cleaves one high-energy phosphate bond from ATP to make ADP

24. Energy used to slide actin and myosin along one another and make the muscle fiber contract 25. Continuously active Ca pump moves Ca back into the sarcoplasmic reticulum

26. Calcium concentration goes down enough and Ca comes off of Troponin-C

27. This causes tropomyosin to wrap itself back around the actin and cover up active sites so the myosin can no longer bind

28. Actin and myosin separate and the muscle relaxes terminal and used to make more ACH

29. ACH attached to alpha-subunits on ligand-gated channels in NMJ will be me metabolized by acetylcholinesterase (“True” cholinesterase) into choline and acetate

30. Acetate diffused away by blood and lymph 31. Choline pumped back into the nerve

32. Muscle fiber is now ready for another action potential