1. Module 1

1.55. Page 4

Lesson 8

Module 1—The Nervous System

Neuromuscular Junctions

 

Now you know how messages are communicated from neuron to neuron through the nervous system. However, when you try to talk, how do the muscles in your mouth “get the message” from the neurons?

 

A diagram shows three muscle fibres lying horizontally. Lying along the length of the surface of two of the fibres are Schwann cells at the end of a motor neuron. A diagram shows a motor nerve connecting to three muscle fibres. The structures shown from the far end of the motor neuron to the muscle fibre are: dendrites, nucleus, axon, along the length of the axon are many Schwann cells and the nucleus of one Schwann cell is labeled. A gap between two Schwann cells is labelled as the node of Ranvier. The connection between the nerve and the muscle fibres is labelled as the neuromuscular junction. An arrow indicates that the direction of the nerve impulse is along the axon from the nucleus toward the muscle fibres.

 

Read

 

When you read pages 380 to 382 in your textbook, you learned the details of the event that occur at the tiny gap located between the axon terminal and the muscle cell. You should choose to do one of the following to include this information in your course folder:

  • Make summary notes for your course folder.
  • Prepare a fully labelled diagram that outlines the process that occurs at the synaptic gap.
  • Prepare a flow chart that outlines the events at the synaptic gap.

Make sure that your work addresses the following questions:

  • What causes the synaptic vesicles to move toward the presynaptic membrane and fuse with it?
  • What does the neurotransmitter that is released do?
  • What does the fusion of the neurotransmitter, in this case acetylcholine, with the protein receptor do?
  • What event does this initiate?

Please note that the figure incorrectly labels the sarcolemma as the neural membrane, when in fact the sarcolemma is a muscle cell membrane.

 

Try This

 

neuromuscular junction: a tiny gap located between an axon terminal and a muscle cell

Interruption of neuromuscular transmission can have deadly effects on the body, particularly if the breathing muscles, such as the diaphragm, are affected. Research the following neurotoxins that act directly on neuromuscular junctions.

 

TR 1. The native tribes of South America apply a plant extract called curare to the tips of their arrows. Research how curare specifically affects neuromuscular junctions and why it is such an effective poison for the tribesmen.

 

TR 2. Botulism is a dreaded food poisoning that can be contracted by eating improperly canned foods. The neurotoxin involved in botulism is also the main ingredient in wrinkle-reduction injections called Botox. Research botulism to discover how the toxin specifically affects neuromuscular junctions. What is the result of this toxin on the body? Is there an antidote? How does botulism in the form of Botox injections reduce wrinkles?