WEEK 5: NERVE TRANSMISSION AND NMJ

Question 1

Describe events at NMJ.

Answer 1

1.Impulse (AP) arrives at nerve terminal

2.Opening of voltage-gated Ca2+ channels, increased permeability to Calcium

3.Calcium runs down conc. gradient into terminal

4.Induces exocytosis of acetylcholine (Ach)

5.Ach diffuses across synaptic gap

6.Ach binds with post-synaptic receptors

7.Increased permeability to small ions (K+ & Na+ esp. Na+)

8.Depolarization of post-synaptic membrane (end plate potential)

9.Local current flow takes adjacent membrane to threshold

10.Ach is broken down by Acetyl cholinesterase (AChE)

Question 2

What is Excitation-Contraction Coupling?

Answer 2

The process whereby the surface action potential results in activation of the contractile mechanism of the muscle fibre.

Question 3

Differentiate between graded and action potential.

Answer 3

Graded
1.Amplitude related to stimulus
Conducted with decrement
2.Can be summed
3.No refractory period
4.No special mechanism to return to baseline

Propagated
1.All or nothing
2.Conducted at same amplitude
3.Cannot be summed
4.Refractory period
5.Potassium permeability to baseline