The Neuromuscular Junction

Study Questions on the Neuromuscular Junction:

1. What causes skeletal muscle cells to contract?

2. What is a motor neuron?

3. What part of the motor neuron carries impulses to the muscle? 

4. Match the following terms to their description:

Axon terminal                                                             Synaptic Vesicles            Synaptic Cleft

Motor End Plate                                                         T Tubule                            Sarcolemma

Terminal Cisternae & Sarcoplasmic Reticulum      Sarcomere

________________________ a. Invaginations of the sarcolemma penetrating deep into the  interior of the muscle cell.

________________________ b. The space between the axon terminal and the motor end   plate.

________________________ c. The swollen distal end of the motor neuron axon.

________________________ d. The muscle cell membrane.

________________________ e. Structures within the axon terminal that contain the neurotransmitter acetylcholine.

________________________ f. The contractile unit of a muscle cell that extends from one Z line to the next.

________________________ g. Structures within skeletal muscle cells that serve as reservoirs of calcium ions.

________________________ h. A folded region of the sarcolemma at the neuromuscular junction.

5. List the following events in the order they occur:

_____ a. The motor end plate is depolarized.

_____ b. The sarcomeres contract.

_____ c. Acetylcholine is released from the axon terminal into the synaptic cleft.

_____ d. The depolarization triggers an action potential, which propagates along the sarcolemma and the T tubules.

_____ e. An action potential arrives at the axon terminal

6.  What happens at the neuromuscular junction when the action potential arrives at the axon terminal.

7.     What happens to the acetylcholine after it diffuses away from its receptor on the motor end plate?

8.  What happens as the action potential moves down the T Tubules?

9.     What happens when calcium ion is present in the cytosol of the muscle cell?

10.  Place the following events in their proper sequence:

_____ a. Acetylcholine is released into the synaptic cleft.

_____ b. Action potential propagates along the sarcolemma and down the T Tubules.

_____ c. Synaptic vesicles fuse to membrane of axon terminal.

_____ d. Motor end plate becomes depolarized.

_____ e. Action potential is initiated on the sarcolemma.

_____ f. Action potential arrives at the axon terminal.

_____ g. Calcium ions are released from the terminal cisternae.

_____ h. Acetylcholine binds to receptor sites on the motor end plate.

_____ i. The muscle cell contracts.

_____ j. Calcium ions enter the axon terminal.