The neuromuscular junction (NMJ) is a specialized synapse between a motor neuron and a muscle fiber. It's essential for muscle contraction and involves several key players like neurotransmitters, receptors, and ion channels. When an action potential reaches the NMJ, it triggers the release of acetylcholine, which binds to receptors on the muscle fiber, leading to depolarization and ultimately muscle contraction.

1. Neuromuscular Junction
Yashaaswini. N
BPT 2nd year

2. Neuromuscular junction
• Neuromuscular junction : the synapse between
motor neuron and muscle fiber is called the
neuromuscular junction.

3. Physiologic anatomy of NMJ
• As axon approaches muscle , it divides into many
terminal branches and loses its myelin sheath .
• Each of these axon terminal forms special junction ,a
neuromuscular junction with one or more muscle fiber.

5. Physiologic anatomy of N.M junction
• The axon terminal is enlarged into a knoblike structure ,the
terminal button, which fits into shallow depression in
underlying muscle fiber.

7. Action potentials arriving at the presynaptic
terminal cause voltage-gated Ca2+ channels to
open.

8. Ca2+ uptake into the terminal causes release of the
neurotransmitter acetylcholine into synaptic cleft , which has
been synthesized and stored into synaptic vesicles .

9. Ach travels across the synaptic cleft to postsynaptic membrane which
is also known as motor end plate.

10. Sequence Of Events At
Neuromuscular Junction
• Motor end plate contains receptors for Ach , which are ligand gated
ion channels
• Ach binds to the alpha subunits of receptors and causes
conformational change.
• When conformational changes occurs ,the central core of channels
opens & permeability of motor end plate to Na+ increases.

13. Agents & disease that alters the function
of N.M junction
Myasthenia gravis
• A disease involving N.M junction is characterized by the extreme
muscular weakness (myasthenia=muscular & gravis=severe)
• It is an auto immune condition (auto immune means immunity against self)
in which the body erroneously produces antibodies against its own motor
end plate ach receptors.

14. • Black widow spider venom.
• Botulinum toxin : botulinum toxin exerts its
lethal effect by blocking the release of Ach .

15. Thank you