Neuromuscular Junction Flashcards
what is a motor end plate?
A complex of nerve fibers that invaginate the surface of a muscle fibeer but lie outside the plasma membrane. It is covered by schwann cells.
What are in an axon terminal?
mitochondria, synaptic vesicles with acetylcholine, dense bars, synaptic gutter and synaptic cleft.
What do the synaptic vesicles in an axon contain?
acetylcholine
what are dense bars?
bars that are anchored to the presynaptic membrane and associated with synaptic vesicles to which they are tethered by short filaments.
What kind of channels are on the sarcolemma?
acetyl-gated ion channels
Where are the Ach vesicles formed, and where are they transported to?
golgi; axon terminus.
Where is Ach synthesized?
cytosol of the nerve axon terminal.
What happens when an action potential arrives at the terminus of an axon?
voltage-gated calcium channels open and calcium ions enter the axon terminus.
How many Ach molecules have to bind to the ligand channel to open it?
2
What does an influx of sodium ions on the sarcolemma initiate?
an end potential
What is the end potential?
local potential created by influx of sodium ions through Ach channel (50 - 75 mV); occurs at the end plate and activates adjacent membrane space.
What appears at the axon nerve terminal after an action potential has been fired?
clathrin coated pits; they separate from the plasmalemma and are refilled as new synaptic vesicles.
What does acetylcholinesterase do?
breaks down excess acetylcholine into choline and acetate
What is reuptaken by the axon nerve terminal?
choline; it is energentically costly to make. Acetate is remade.
What is excitation-contraction coupling?
Coupling that is from an excitation in the T-tubule from an action potential; it causes a conformational change in the receptor, allowing subsequent contraction.
