1.11 Neuromuscular Junction Flashcards
What is a neuromuscular junction?
A neuromuscular junction is a specialised form of synapse, also known as a motor end plate, which refers to the flat disc shaped region in the neuromuscular junction
What incorporates acetylcholine into vesicles?
Vesicle Acetycholin transporter = VAch T
Give the 6 stages of NMJ synaptic transmission…
- An impulse causes increased permeability to calcium ions
- Release of Ach at the end of the motor end plate by exocytosis
- Ach binds to nicotinic receptors
- increase in Na input and K output in the motor end plate
- generation of end plate potential
- generation of action potential
How many nicotinic receptors are there at a motor end plate?
15-40 x 10(6) nicotinic Ach receptor per motor -end-plate
How many vesicles are released per impulse?
About 60 -200 vesicles released per impulse
How much Ach is there per vesicle?
10’000 Ach molecules vesicle
What percentage is the releasable pool and what is its firing frequency like?
20% - low firing frequency
What percentage is the reserve pool and what is its firing frequency like?
80% - high firing frequency
What is an mEPP…
Leakage - one quantum - not enough to create an AP
Define and explain QUANTUM
QUANTUM = amount of neurotransmitter in one vesicle
Where does vesicle fusion occur?
Dense bars in the active zone
What are the three SNARE proteins involved in vesicle fusion?
Synaptabrevin - vesicle
Snap25 - Membrane
Syntaxin - snap25
How many subunits is the nicotinic receptor made up of, name them…
5
2 alpha, beta, delta, gamma
Which subunits does Ach bind to?
Alpha subunits
Which subunit gets replaced when adulthood is reached and what is it replaced by?
gamma gets replaced by an epsilon
Which ions go in and which go out?
Sodium goes and potassium goes out
Is the net influx positive or negative?
Positive
Where are subjunctional folds found?
membrane of skeletal muscle
What are the top of the fold called?
Active zone
Explain what is in the ‘active zones’?
Nicotinic receptors at the top, and voltage sensitive sodium are at the base of the folds
What can be found within the folds?
Acetylecholinesterase - hydrolyse Ach
What is an EPP?
60-200 vesicles released in response to normal action potential at NMJ
Explain Myesthenia Gravis?
It is an autoimmune disorder, where antibodies destroy the Ach receptors. It is degenerative, because the antibodies increase over time. This causes EPP to not be sufficient enough to stimulate an action potential. Death usually occurs due to paralysis of respiratory muscles. Treatment through AchE inhibitors
Explain Botulin Toxin?
It is made up of a light chain and a heavy chain. The heavy chain allows protein to bind to and enter the neurone, where as the light chain cleaves vesicle docking proteins.
