15.1.9

Neuromuscular Junction

Test yourself

Neuromuscular Junction

A neuromuscular junction is a synapse between a motor neurone and a muscle cell. An action potential is transmitted across the synapse using the neurotransmitter acetylcholine. The steps involved are:

Illustrative background for Arrival at the synaptic knobIllustrative background for Arrival at the synaptic knob ?? "content

Arrival at the synaptic knob

  • An action potential arrives at the synaptic knob at the end of the motor neurone.
  • The action potential depolarises the membrane of the synaptic knob. This causes voltage-gated calcium (Ca2+) ion channels to open.
  • Ca2+ ions diffuse into the synaptic knob.
Illustrative background for Release of acetylcholine (ACh)Illustrative background for Release of acetylcholine (ACh) ?? "content

Release of acetylcholine (ACh)

  • The Ca2+ ion concentration inside the synaptic knob begins to increase.
  • This causes the synaptic vesicles to move and fuse with the presynaptic membrane.
  • Acetylcholine, the neurotransmitter inside the vesicles, is released into the synaptic cleft.
    • This process is called exocytosis.
Illustrative background for Binding to receptorsIllustrative background for Binding to receptors ?? "content

Binding to receptors

  • Acetylcholine binds to specific receptors on the postsynaptic membrane called nicotinic cholinergic receptors.
  • Binding of the neurotransmitter opens sodium ion channels in the postsynaptic muscle cell.
  • As Na+ ions diffuse into the cell, the membrane becomes depolarised.
  • If the potential difference reaches the threshold value, an action potential is generated and flows along the motor cell.
Illustrative background for Removal of acetylcholineIllustrative background for Removal of acetylcholine ?? "content

Removal of acetylcholine

  • An enzyme called acetylcholinesterase (AChE) breaks down acetylcholine in the synaptic cleft.
  • The products of the break down are reabsorbed by the presynaptic neurone and reused to synthesise more acetylcholine.
  • It is important that the acetylcholine is removed from the receptors. This stops action potentials from being continuously generated in the postsynaptic cell.

Jump to other topics

1Cell Structure

2Biological Molecules

3Enzymes

4Cell Membranes & Transport

5The Mitotic Cell Cycle

6Nucleic Acids & Protein Synthesis

7Transport in Plants

8Transport in Mammals

9Gas Exchange

10Infectious Diseases

11Immunity

12Energy & Respiration (A2 Only)

13Photosynthesis (A2 Only)

14Homeostasis (A2 Only)

15Control & Coordination (A2 Only)

16Inherited Change (A2 Only)

17Selection & Evolution (A2 Only)

18Classification & Conservation (A2 Only)

19Genetic Technology (A2 Only)

Unlock your full potential with Seneca Premium

  • Unlimited access to 10,000+ open-ended exam questions

  • Mini-mock exams based on your study history

  • Unlock 800+ premium courses & e-books

Get started with Seneca Premium