Neuromuscular junctions

Question 1

What is the first system of muscle weakness

Answer 1

Droopy eyes

Question 2

what is myasthenia gravis

Answer 2

Disorder of neuromuscular transmission

Question 3

Key features of a synapse

Answer 3

• Unidirectional
• Irreversible delay
• Chemical

Question 4

How many muscle fibers does a single axon connect to in the eye
-In the biceps?

Answer 4

One

-Many

Question 5

HOW many neuromuscular junctions are there per muscle fibre

Answer 5

Only ever 1

Question 6

What are the events that occur during transmission at a neuromuscular junction

Answer 6

1) Action potential in motor neuron arrives at axon terminal
2) Terminal membrane depolarizes, voltage-gated calcium channels open
3) Ca2+ enter via ecg
4) Exocytosis of ACh which then binds to receptor (nAChR)
5) Na+ enter and K+ exit muscle cell via nAChR’s which results in receptor generated potential
6) If RGP passes threshold, action potential generated
7) AP propagates through muscle which leads to release of calcium ions from SR leading to contraction

Question 7

What happens when there is release of acetylcholine from a single synaptic vesicle

Answer 7

Small membrane depolarisation

Question 8

What is the aCh nicotinic receptor

-what happens when ach binds

Answer 8

Ionotropic (an ionic channel complex)

-ACh binds, conformational change and opens channel which allows na and k to pass in/out

Question 9

What happens when an action potential arises a presynaptic bouton (how I end plate potential created)

Answer 9

1) AP
2) open ca2+ channel (voltage gated) and so calcium ions enter
3) Exocytosis of ach
4) ach binds to nicotinic receptor
5) conformational change
6) na influx and k+ efflux
7) depolarization
8) END PLATE POTENTIAL

Question 10

What happens when an end pate potential is created

Answer 10

• end plate potential
• propagated action potential
• spreads in muscle
• contraction

Question 11

how do action potentials trigger muscle contraction

Answer 11

If sufficient ach released, end plate potential occurs. If end plate potential is big enough, causes opening of Na+ voltage channels which propagates AP in myocyte
-AP then travels through sarcolemma and down T Tubules and binds to receptors etc

Question 12

Terminate ach action by?

Answer 12

AchE converts ACh to acetate and choline

Question 13

How to treat myasthenia gravis

Answer 13

Use drugs which prevent the metabolism of ach (stopping action of achE)