Question

Arrange the following events at the Neuromuscular Junction in the correct sequence:
(1) AChase splits apart ACh
(2) exocytosis of ACh
(3) ligand-gated Na+ channels open in muscle cell
(4) voltage-gated Ca+2 channels open in synaptic knob
(5) Action Potential in MUSCLE cell
(6) activation of Ach Receptor Sites on muscle cell
(7) muscle cell contracts
The correct sequence should read:

A. 1, 3, 2, 4, 6, 5, 7
B. 2, 3, 5, 4, 6, 7, 1
C. 2, 4, 6, 3, 5, 7, 1
D. 2, 6, 3, 5, 4, 7, 1
E. 3, 2, 4, 6, 5, 7, 1
F. 4, 1, 2, 6, 3, 5, 7
G. 4, 1, 6, 3, 5, 2, 7
H. 4, 2, 6, 3, 5, 7, 1
I. 4, 5, 6, 2, 3, 7, 1
J. 5, 2, 6, 3, 4, 7, 1
K. 5, 2, 6, 4, 3, 7, 1
L. 6, 3, 4, 2, 5, 7, 1
M. 6, 7, 5, 4, 3, 1, 2

Answer 1

Ans- H. 4,2,6,3,5,7,1

The correct order of events at neuromuscular junction are-

4. Voltage gated calcium channels open in synaptic knob- First step is arriving of action potential in the axon terminal of the nerve. This leads to opening of voltage gated calcium channels and release of calcium ions.

2. exocytosis of ACh- when calcium ions are released, the synaptic vesicles break and release of acetylcholine is there which diffuses to the synaptic cleft.

6. activation of ACh receptor sites on muscle cells- When acetylcholine is released in the synaptic cleft, after this it reaches the postsynaptic membrane where it binds to receptors. There is activation of acetylcholine receptor sites on the muscle cells for its binding.

3. ligand gated Na+ channels open in muscle cells- Now after this there is opening of ligand gated Na+ channels and release of Na+ ions causing depolarization.

5. Action potential in muscle cells- Due to the development of depolarization in the muscle cells, there is now development of action potential which will initiate the process of muscle contraction.

7. muscle cell contracts- after action potential and all the events, the muscle cells will finally contract.

1. AChase splits apart ACh- After the end of all the process, now ACh will break into its components which are later recycled for all the steps in the presence of an enzyme acetycholinestrase.