Session 7

Question 1

Movement of which ion is responsible for depolarisation of a nerve cell membrane?

A: Na
B: K
C: Ca
D: Cl
E: Mg

Answer 1

A - Na

Na moves along its concentration gradient when sodium channels open, to cause a positive ion to enter the cell rapidly, causing the membrane potential to become less negative (depolarisation).

Question 2

Which of the following is involved in the repolarisation of a cell membrane?

A: Sodium channels opening
B: Na-K-ATPase
C: Calcium channels opening
D: Potassium channels opening
E: Chloride channels opening

Answer 2

D - Potassium channels opening

Opening of potassium channels allows K to leave the cell, causing the membrane to become more negative (repolarisation). The other process involved, that is not listed here, is inactivation of sodium channels. Na-K-ATPase is not directly involved in repolarisation of the action potential.

Question 3

What effect would you expect to see if a patient was given a drug blocking sodium channels e.g. lidocaine?

Answer 3

Na channel blockers slows sodium entry, therefore slowing depolarisation and conduction velocity. This can be beneficial therapeutically in preventing unwanted activity e.g. local anaesthesia and irregular heartbeats (arrhythmias).

Question 4

Which property of a membrane allows it to store charge (capacitance)?

A: Ion channels
B: Glycoproteins
C: Lipid bilayer
D: Receptor proteins
E: Transport proteins

Answer 4

C - lipid bilayer

Lipid bilayer has an ability to store charge. Ion channels contribute to resistance, rather than capacitance. The others have no significance in this context.

Question 5

What effect does demyelination have on propagation of action potentials?

Answer 5

Demyelination reduces conduction velocity. Clinically this may result in less electrical activity, which will have a variety of neurological signs and symptoms.

Question 6

Complete the process of an action potential arriving at the neuromuscular junction (NMJ):

Action potential arrives at NMJ –>
Activation of voltage-gated (A) channels –>
Intracellular (B) concentration (C) –>
This binds to synaptotagmin to form (D) –>
Neurotransmitter released from vesicle, binds to (E) receptors –>
Movement of ions causes depolarisation of muscle membrane, initiating muscle contraction

Answer 6

A: Calcium
B: Calcium
C: Increases
D: A snare complex/fusion pore
E: nACh

Question 7

What 2 things are clinically relevant about an action potential arriving at the neuromuscular junction?

Answer 7

1. Disease processes can alter this sequence e.g. myasthenia gravis altering the nACh receptors
2. Drugs can be used to block this process for therapeutic benefit e.g. succinylcholine causing muscle weakness during anaesthesia