The Neuromuscular Junction

Chapter 10

Anatomy and Physiology

Mr. Knowles

Liberty Senior High School

Neuromuscular Junction

(NMJ)Communication b/w the nervoussystem & skeletal muscle fiber.

Soma

Soma

Neuromuscular Junction

(NMJ)As an axon enters a muscle, it branches into a number of synaptic terminalssynaptic terminals, each of whichforms a NMJ with a single muscleFiber.

Synaptic Terminal

•Contains Molecules of Acetylcholine (ACh).Acetylcholine (ACh).

•AChACh is a neurotransmitter, chemical released by neurons to change the membrane properties of other cells.

Synaptic Cleft•A narrow spacenarrow space that

separates the synaptic terminal of the neuron from the sarcolemma surface.

•Contains Acetylcholinesterase (AChE)(AChE) which breaks down AchAch.

Motor End Plate•The surface of the sarcolemma that contains membrane receptors that bind ACh.ACh.

When a neuron stimulates a muscle fiber, Heeeeere’s what happens . . .

The arrival of an action potential

•Sudden change in the transmembrane potential along the axon.

•This stimulates the release of AChACh at the synaptic terminal.

The release of ACh•Vesicles that contain ACh,ACh, in the synaptic terminal, fuse with the membrane of the neuron & are released by exocytosis into the synaptic cleft.

ACh binding at the motor end plate

•AChACh molecules diffuse across the synaptic cleft & bind to AChACh receptorsreceptors on the motor end plate’s surface.

•When AChACh binding occurs, sodium ions (Na(Na++)) now can rush into the sarcoplasm.

Appearance of an action potential in the

sarcolemma• The NaNa++ results in an action potential in the sarcolemma.

• The action potential sweeps across the entire membrane surface & travels down each of the T tubulesT tubules which triggers the release of CaCa2+2+ at the terminal cisternae.terminal cisternae.

• While this is occurring, AChE AChE removes the ACh.ACh.

Return to the initial state

• Even before the action potential has spread across the entire membrane, the AChACh has been broken down by AChEAChE.

• This sequence of events can now be repeated, should another AP arrive at the synaptic terminal

Normal

Show me the action! Potential, that is!

What happens at the neuromuscular junction

when exposed to botulinum toxin?

Effects of a Nerve Agent

Atropine Antidote

What is myasthenia gravis?