APs Flashcards

1
Q

Changes in membrane potential from RMP that generate electrical signals (APs, synaptic potentials, receptor potentials) are caused by what?

A

Changes in the membranes relative permeability to ions.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

*The AP is generated by …

A

The flow of ions through voltage-gated channels.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Increases in Na+ conductance during depolarisation cause Na+ influx to exceed … , creating a net influx of positive charge that causes …

A

K+ efflux, creating a net influx of positive charge that causes further depolarisation.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is the increase in Na+ conductance? What does it do?

A

A regenerative positive feedback cycle. Drives membrane potential towards Na+ equilibrium potential of +55mV.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What piece of clinical evidence demonstrates the role of v-g Na+ channels in AP generation?

A

Congenital pain sensitivity is caused by mutations in the SCN9A gene which encodes the v-g sodium channel NaV1.7.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What experimental studies demonstrate the role of Na+ conductance in AP generation?

A

Voltage clamp, Hodgkin and Huxley.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

How did voltage clamp method show role of Na+ in AP generation?

A

Stepping the membrane potential from rest (-60 mV) to a depolarised level (0 mV) reveals a transient inward current, followed by a sustained outward current. Removing Na+ from the extracellular fluid eliminates the transient inward current.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

How does the voltage clamp work?

A

Permits “clamping” of membrane potential at predetermined level. Prevents changes in membrane current from influencing membrane potential. Control of membrane potential allows one to measure the effect of changes in membrane potential on the membrane conductance of individual ion species.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Who did the patch clamp method?

A

Erwin Neher and Bert Sakmann.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What did the patch clamp method find?

A

No change in ionic current through v-g isolated sodium channel at -75mV but yes at -55mV.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Why does AP peak never reach +55mV? 2 factors.

A

Because K+ leak conductance remains, continual efflux.

Also slight influx of Cl- counteracts depolarisation.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is membrane potential during AP determined by?

A

The relative permeabilities to different ions, approaching the steady-state membrane potential predicted by the GHK equation.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Why does afterhyperpolarisation occur?

A

V-g K+ channels no inactivation mechanism.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What does v-g K+ channel closure rely on?

A

The gradual reversal of the v-g conformational change that opened the channel during depolarisation.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What explains absolute refractory period?

A

Na+ conductance inactivated, so fraction available for activation insufficient to overcome K+ conductance.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is the role of the refractory period?

A

Ensures APs propagate unidirectionally.

17
Q

What is membrane resistance? What does it do to the rate of change of membrane potential?

A

How well the cell membrane resists the flow of electrical current. Reflects the permeability of the membrane to ions. Increases rate.

18
Q

Why does high membrane resistance increase propagation speed?

A

Less ion channels open at rest, reducing leakage of charge. More depolarising current flows along the axon rather than dissipating across the membrane.

19
Q

What is membrane capacitance? How is the membrane endowed with it?

A

The ability to store electric charge. Hydrophillic heads and hydrophobic tails of phospholipids give it an insulating property.

20
Q

Why does high membrane capacitance decrease propagation velocity?

A

More charge must be deposited, current requires more time to produce depolarisation.

21
Q

Why does large diameter increase propagation velocity?

A

Number of charge carriers per unit length of axon greater. More current enters, depolarised more efficiently. Lower axial resistance.

22
Q

What is Ohm’s Law? What does it mean for why low axial resistance increases CV?

A

I = V/R. Less current needed to charge up adjacent membrane segments.

23
Q

What does axial resistance decrease in proportion to? What does membrane resistance decrease in proportion to?

A

The square of the diameter. The diameter.

24
Q

What is the length constant equation? What does it determine? Why is that good for CV?

A

Squrt(Rm/Ri). How far the current can spread before decaying. Reduces the need for frequent regeneration of AP.

25
Q

What is the time constant equation? INVERSELY PROPORTIONAL.

26
Q

Using length constant equation shows the conduction velocity will increase according to …

A

The square root of the diameter.

27
Q

What adaptations have evolved to increase CV?

A

Increase in axon diameter (giant axon of squid, 1mm), myelination.

28
Q

Why no larger axon diameter than 1mm in giant squid axon?

A

Need to fit many cells in a small space.

29
Q

Why does myelination increase CV?

A

Capacitance inverse to thickness of insulation. Thus decreases T. Also decreases membrane resistance, increasing lambda.

30
Q

Why salutatory conduction required?

A

Myelin not a perfect insulator.

31
Q

Why salutatory conduction metabolically favourable?

A

Ions flow only at nodes. Less energy needed by Na+/K+ pumps to regenerate conc. gradients.

32
Q

What is a clinical example of myelination benefits/fast conduction benefits?

A

MS. Immune attacks on sheaths, slowed conduction. Leads to weakness/paralysis.