Mod3-Obj10: Generation of an action potential

Question 1

Generation of an action potential

Answer 1

The generation of an action potential involves three consecutive changes in the membrane potential of an axon

1. ) Resting state
2. ) Depolarisation
3. ) Repolarisation
4. ) Hyperpolarisation

Question 2

Depolarisation

Answer 2

At threshold (-55mV), voltage-gated Na+ channels at the initial segment rapidly open

• Na+ ions rush into the ICF
• AXON INTERIOR BECOMES LESS NEGATIVE
• The membrane potential changes from -55mV to +30mV

Question 3

Repolarisation

Answer 3

At a membrane potential of +30mV

• Voltage-gated Na+ channels close and voltage-gated K+ channels open
• K+ ions rush into the ECF
• AXON INTERIOR BECOMES MORE NEGATIVE
• The membrane potential changes from +30mV to -70mV

Question 4

Hyperpolarisation

Answer 4

As the membrane potential approaches -70mV, voltage-gated channels K+ slowly close
-Excess K+ ions exit the axon and the membrane potential overshoots to -90mV
(Inside of the cell becomes more negative, causing the cell to hyperpolarise at -90mV, gated channels close)

Question 5

When both voltage-gated Na+ and K+ channels are closed…

Answer 5

leakage channels and the Na+/K+ pump, restore the resting distribution of Na+ and K+ ions and the RMP of -70mV
-The neuron can now generate another action potential

Question 6

Graded potential vs Action potentials: Origin

Answer 6

Graded=Dendrites/cell body

Action=Axon (initial segment)

Question 7

Graded potential vs Action potentials: Channel type

Answer 7

Graded=Chemically-gated or mechanically-gated

Action=Voltage-gated

Question 8

Graded potential vs Action potentials: Change in membrane potential

Answer 8

Graded=Small depolarisation or hypepolarisation, change in proportional strength of stimulus
Action potential=
1.) Depolarisation
2.) Repolarisation
3.) Hypepolarisation
Change is independent of stimulus strength

Question 9

Graded potential vs Action potentials: Distance travelled

Answer 9

Graded=Short distance

Action=Long distance (self-propagating)

Question 10

Conduction of action potential

Answer 10

If action potential are to serve as long distance communication signals, they must travel from the initial segment to the axon terminals

Question 11

Two modes of conduction of action potential

Answer 11

1. ) Continuous

2. ) Saltatory

Question 12

Continuous conduction

Answer 12

Occurs in unmyelinated axons
-A wave of action potentials are generated at the voltage-gated channels along the length of the axon
(Bringing the segments to threshold, opening the gated channel, starting membrane potential to bring signal to end)

Question 13

Saltatory conduction

Answer 13

Occurs in myelinated axons
-Action potentials are only generated at the internodes
-Signal leaps from internode to internode
(Fewer action potentials to get from one action potential to the next (due to myelin covering the membrane) cause the overall conduction to become quicker, essential in pathways such as reflex arc’s)

Question 14

A number of factors can impair the generation or propagation of an action potential

Answer 14

1. ) Local anaesthetics: Stop pain sensations by blocking voltage gated Na+ channels, preventing action potentials and inhibiting pain
2. ) Cold and pressure: Reduced pain sensations by impairing signal conduction