Action potentials

Question 1

What is resting membrane potential

Answer 1

Difference in charge across membrane when neuron isn’t firing

-70mV

Question 2

Describe permeability of neuronal membrane

Answer 2

Sodium permeability increases rapidly whereas potassium is slower but more prolonged

Sodium permeability increases during depolarisation

Potassium permeability increases during repolarisation

Question 3

Explain function of Na+/K+ ATPase, sodium & potassium channels

Answer 3

Sodium & potassium channels allow movement of sodium & potassium in & out of neuron

More potassium moves outside neuron than in so resting potential is negative

Changing number of open ion channels changes membrane permeability & thus membrane potential

Na+/K+ ATPase pump actively pumps sodium & potassium against their concentration gradients

For every 3 Nas exported, 2Ks are pumped in

Pumps main role is to maintain Na & K gradients which give rise to membrane potentials

Question 4

Explain propagation of action potentials across unmyelinated & myelinated axons

Answer 4

In unmyelinated neurons, action potentials propagate sequentially along axon in continuous wave of depolarisation

In myelinated neurons, action potentials hop between gaps in myelin sheath called nodes of Ranvier

Results in increase in speed

Question 5

Describe Lignocaine as local anaesthetic

Answer 5

Action of lignocaine is by reversible blockade of nerve fibre propagation

Lignocaine enters nerve cells by diffusion through membranes

It then binds to sodium channels which causes conformational change that prevents transient influx of sodium & thus depolarisation

Onset of action is rapid & lasts up to 5 hours

Works more on afferent neurons (prevents signal from getting to brain

Question 6

Label the synapse

Answer 6

A. Mitochondrion
B. Synaptic vesicle
C. Synaptic cleft
D. Receptor
E. Neurotransmitters
F. Reuptake inhibitor
G. Presynaptic terminal
H. Postsynaptic neuron