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The Neuromuscular Junction Chapter 10 Anatomy and Physiology Mr. Knowles Liberty Senior High School
Neuromuscular Junction(NMJ) Communication b/w the nervous system & skeletal muscle fiber.
Neuromuscular Junction(NMJ) As an axon enters a muscle, it branches into a number of synaptic terminals, each of which forms a NMJ with a single muscle Fiber.
Synaptic Terminal • Contains Molecules of Acetylcholine (ACh). • ACh is a neurotransmitter, chemical released by neurons to change the membrane properties of other cells.
Synaptic Cleft • A narrow space that separates the synaptic terminal of the neuron from the sarcolemma surface. • Contains Acetylcholinesterase (AChE) which breaks down Ach.
Motor End Plate • The surface of the sarcolemma that contains membrane receptors that bind 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 ACh at the synaptic terminal.
The release of ACh • Vesicles that contain 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 • ACh molecules diffuse across the synaptic cleft & bind to AChreceptors on the motor end plate’s surface. • When ACh binding occurs, sodium ions (Na+) now can rush into the sarcoplasm.
Appearance of an action potential in the sarcolemma • The Na+ results in an action potential in the sarcolemma. • The action potential sweeps across the entire membrane surface & travels down each of the T tubules which triggers the release of Ca2+ at the terminal cisternae. • While this is occurring, AChE removes the ACh.
Return to the initial state • Even before the action potential has spread across the entire membrane, the ACh has been broken down by AChE. • This sequence of events can now be repeated, should another AP arrive at the synaptic terminal
What happens at the neuromuscular junction when exposed to botulinum toxin?