Neuromuscular Junctions

Question 1

Neuromuscular

Answer 1

Affecting or characteristic of both neural and muscular tissue

Question 2

Neuromuscular Junctions

Answer 2

Specialised synapses between neurons and muscle

Question 3

Myocyte

Answer 3

Muscle Fibre Cell Terminology

Question 4

How many NMJs exist for each muscle cell

Answer 4

Each Muscle cell has a NMJ

Question 5

Describe the structure of the muscle’s post-synaptic membrane

Answer 5

Invaginated structure

Question 6

What is associated with the protrusions of the muscular post-synaptic membrane

Answer 6

Nicotinic Receptors (Acetyl Choline) on the tips

Question 7

Describe how an action potential in the motor neuron leads to contraction of the muscle fibre (Basically what you learned at school)

Answer 7

1. Action potential in motor neuron arrives at axon terminal
2. Terminal membrane depolarises; voltage-gated calcium channels open
3. Ca2+ rushes in and Calcium-mediated exocytosis of ACh into extracellular space occurs
4. Interaction of ACh with nicotinic receptors
5. Influx of Na+ ions and efflux of K+ ions from muscle cells via nAChRs results in receptor generated potentials (RGPs)
6. If RGPs are sufficient to pass threshold, an action potential is generated
7. Action potential propagates through muscle, leading to release of Ca+ ions from sarcoplasmic reticulum leading to muscle contraction

Question 8

Compare concentration gradient of Ca2+ inside vs outside the synapse

Answer 8

Outside - 1mM

Inside - 0.01mM

Question 9

Quantal release of transmitter

Answer 9

Packets (quanta) of neurotransmitter are released as vesicles

**10^4 ACh in a vesicle

Question 10

Qualitatively compare ratio of ACh molecules to AChR proteins on motor end plate

Answer 10

Significantly more AChR proteins

Receptor Reserve

Question 11

What happens when ACh binds to nicotinic receptor

Answer 11

Conformational change to protein causing Na+ influx and K+ efflux

Question 12

Which step of synaptic transmission has the highest delay

Answer 12

Ca2+ entry into presynaptic cleft via electrochemical gradient

Question 13

How is ACh bound to receptors inactivated

Answer 13

Enzymic hydrolysis in the synaptic cleft by Acetyl Cholinesterase (AChE)

Question 14

Myasthenia Gravis

Answer 14

Autoimmune disorder of Neuromuscular transmission whereby autoantibodies directed against the nicotinic AChR are produced

Question 15

Treatment of Myasthenia Gravis

Answer 15

Increase ACh concentration in neuromuscular junction by:

• Increasing reuptake of ACh
• Inhibiting Acetyl Cholinesterase