NMJ Steps in order

1.

Motor neuron dendrites receive stimulus

2.

Motor neuron depolarization

3.

Action potential travels down axon to NMJ

4.

AP causes Ca²⁺ ions to influx into synaptic bulb

5.

ACh is released into synaptic cleft

6.

ACh binds to receptors on muscle cell’s sarcolemma

7.

Na⁺ ion channels in sarcolemma open

8.

Na⁺ ions influx into sarcoplasma

9.

Depolarization of sarcolemma occurs

10.

AP travels down T-tubules

11.

Ca²⁺ is released from terminal cisternae

12.

Ca²⁺ binds to troponin

13.

Tropomyosin is moved on the actin fibers

14.

Myosin-binding sites on actin are exposed

15.

Myosin heads with ADP + P bind to actin to form cross bridge

16.

Myosin pulls actin filament; ADP + P leave myosin head (power stroke)

17.

ATP binds to myosin head; cross bridge is broken

18.

ATP hydrolyzes to ADP + P which cocks the myosin head

19.

Another myosin-actin cross bridge is formed to further contract sarcomere