NMJ / Muscle Phys Flashcards
Another name for the neuromuscular junction (NMJ)
end plate
one motor unit innervating one group of muscle fibers
motor unit
What is the neuromuscular junction?
an axon making single contact with a muscle fiber
another name for the bulge of the synaptic terminal
bouton
neurotransmitter used by the presynaptic nerve in the NMJ
acetylcholine (ACh)
Postsynaptic structure at the NMJ which is responsible for increasing surface area
postjunctional folds
Where is there a meshwork of proteins and proteoglycans in the NMJ?
synaptic cleft
Region of presynaptic membrane where synaptic vesciles fuse and relase ACh
active zones
location of a high density of AChRs in the NMJ
crest of postjunctional folds
How can the current generated by an action potential in muscle contraction be measured?
Electromyography (EMG)
ACh molecules needed to open an AChR
two
Entrance of sodium ions causing current at the postsynaptic muscle of the NMJ
End-plate current (EPC)
Change in potential in the postsynaptic muscle fiber
End-Plate Potential (EPP)
Caused by a spontaneous release of trace amounts of ACh. Changes in muscle membrane potential even when the presynaptic motor neuron is not stimulated
Miniature End Plate Potentials (MEPPs)
Defined as the difference between an actual EPP and threshold potential required to generate muscle action potential
safety factor
(True/False) There will be no action potential in the event of repetitive stimulation of the (muscle) nerve, which reduces EPPs
False.
Structure of an AChR
five subunits arranged around a central pore
Differences between adult and embryonic AChR
Adult receptors have a shorter single channel mean open time and greater single channel current
Describe the communication between motor neurons and target muscles before the formation of the NMJ
Motor neurons can release ACh before making contact; likewise the muscle membrane can respond to ACh
What happens to EPPs after a motor neuron makes contact with its muscle target?
amplitude of EPPs increases
Describe the changes in AChRs before and after muscle innervation
Before innervation, AChRs pre-aggregate at the center of the developing muscle fiber. Afterwards, they become concentrated at the region of interaction
Existing, premature receptors are clustered by the protein _____ which is released from the nerve. It binds to a receptor on the muscle which activates muscle-specific kinase (MuSK)
agrin
The activation of MuSK induces clustering of AChRs by which protein?
rapsyn
Kinase required for initiating NMJ formation and for assembling other proteins found at the junction
Muscle-specific Kinase (MuSK)