Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

ESA 2 Membranes and Receptors > Action Potentials And Its Properties (4) > Flashcards

Action Potentials And Its Properties (4) Flashcards

0
Q

What does an action potential depend on?

A
  • Ionic gradient

- Relative permeability of the membrane

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

What is an action potential?

A
  • A change in voltage across a membrane
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is the rule given to action potentials and why is this the case?

A
  • All or nothing

- An action potential will only occur if the threshold value is met.

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

Give the values of the beginning of depolarisation and the beginning of repolarisation for the following:

  • Axon
  • Skeletal
  • SAN
  • Cardiac
A
  • Axon: -70mv, +30mv
  • Skeletal: -90mv, +40mv
  • SAN: -60mv, +30mv
  • Cardiac: -90mv, +30mv
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

With reference to sodium and potassium channels describe how depolarisation and repolarisation occur.

A
  • Depolarisation: Na channels open to allow an influx of Na to increase membrane potential.
    K channels remain closed.
  • Repolarisation: Na channels become inactive no more Na influx.
    K channels open to allow an efflux of K to decrease membrane potential.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

How can Na channels reopen after repolarisation?

A
  • A negative enough potential much be reached to allow the reformation of the closed Na channels.llll
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What does the conductance for a particular ion depend on?

A
  • The number of channels for the ion that are open.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What sort of percentage change in ion concentration is required for an action potential to ‘fire’?

A
  • ~0.4%
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

How can ionic currents be measured?

A
  • Voltage clamping
  • Patch clamping enables current flowing through individual ions channels to be measured
  • Using different ionic concentrations allows contribution of specific ions to be calculated.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is an axon hillock?

A
  • Point on axon where AP is initiated.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

How does depolarisation of an AP occur?

A
  • Depolarisation to threshold: Na channels open
  • Na influx
  • Membrane depolarises
  • Positive feedback loop
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

How does repolarisation of an AP occur?

A
  • Depolarisation opens K channels and inactivates Na channels
  • K channels open causes K efflux
  • Inactivation of Na channels causes Na influx to stop
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What does ARP stand for and what occurs during this period?

A
  • Absolute refractory period
  • Can’t fire another AP
  • Nearly all Na channels are inactivated
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What does RRP stand for and what occurs during this period?

A
  • Relative refractory period
  • Na channels are recovering from inactivation, excitability returns towards normal as the number of channels in inactivated state decrease.
  • Second AP can fire in this period if signal is strong enough.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Outline how Na channels move from closed to open to inactivated.

A
  • Na channels have two voltage gates.
  • When closed the top gate is close and the bottom gate is open and the top one is closed
  • When the membrane potential is at -70mv the bottom gate opens to allow Na to influx causing the potential to increase
  • When potential has reached +30mv the Na gates become inactive, this is when the top gate remains open but the bottom gate shuts allowing Na to enter then rebound out.
  • When the potential is negative enough the bottom gate reopens and the top gate shuts, so closed.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is hyperpolarisation’s role with Na channels?

A
  • Na channels moving from inactive form to closed form.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is accommodation?

A
  • Longer the stimulus, the larger the depolarisation necessary to initiate an AP
  • Threshold becomes more positive
17
Q

What effect does accommodation have on the threshold value and the possibility of an AP firing?

A
  • Doesn’t change AP

- With accommodation no AP may be fired even if slightly over threshold value.

18
Q

To a subunit level what is a Na channel?

A
  • 4 subunits turn in to face each other.

- The ‘inactivation particle’ between subunit 3 and 4 acts as a plug for the channel.

19
Q

Give an example of an anaesthetic.

A
  • Procaine
20
Q

How do anaesthetics act on Na channels?

A
  • Bind and block Na channels thereby stopping AP generation
21
Q

In what order does anaesthetics act on axons?

A
  • Small myelinated axons (responsible for pain)
  • Non-myelinated axons
  • Large myelinated axons
22
Q

For what type of state of Na channel does anaesthetics have the greatest affinity?

A
  • Inactivated as can fit into pore with greatest ease to block.
23
Q

Which diseases are associated with AP?

A
  • CNS: - Multiple sclerosis: all CNS nerves
    - Devic’s disease: optic and spinal chord nerves only
  • Peripheral NS: - Landry-Guillian- Barre
    - Charcot-Marie tooth disease
  • Disease resulting from breakdown/damage to myelin sheaths.
24
Q

What would a graph of the reading taken from an intact membrane during an AP look like?
What would one of a damaged membrane look like?

A
  • Diphasic

- Monophasic

25
Q

How can conduction velocity be calculated?

A

Axon length (x) / time (ms)

26
Q

What is local current theory?

A
  • Injection of current into an axon will cause the resulting change to spread along the axon and cause IMMEDIATE LOCAL CHANGE in membrane potential
27
Q

What is capacitance?

A
  • The ability to store charge.
28
Q

What does membrane resistance depend on?

A
  • Depends on number of ion channels open

- The lower the resistance the more ion channels that are open.

29
Q

What does the spread of local current depend on?

A
  • Membrane’s resistance

- Membrane’s capacitance

30
Q

What does an increase in capacitance lead to?

Effect on Vmax and time

A
  • Vmax is reached over a longer period of time.
31
Q

What effect does an increase in membrane resistance lead to?

effect on how far local charge can spread

A
  • Increases the distance local charge can spread to.
32
Q

What is local currents useful for?

A
  • Propagating other AP

- Prevents the reversal of AP.

33
Q

What is used in myelination for CNS and Peripheral NS?

A
  • CNS: Schwaan cells

- Peripheral NS: Oligodendrocytes

34
Q

What does myelination do to the distribution of Na channels?

A
  • Extremely high density of Na channels in Nodes of Ranvier.
35
Q

How is the optimum conduction velocity caused in relation to myelin sheaths and axons?

A
  • D: myelin sheath & axon
  • d: axon only
  • d/D = 0.7 is optimum
36
Q

What is saltatory conduction and how does it occur?

A
  • AP jump from node to node: faster conduction velocity
  • Myelination is a good insulator, causing local circuit current to depolarise the next node to above threshold -> AP
  • Maintains AP above threshold for a greater distance
37
Q

What is conductance velocity proportional to in: myelinated and unmyelinated axons and their max speed?

A
  • Myelinated: diameter of axon. ~120m/s

- Unmyelinated: square root of diameter of axon. ~20m/s

38
Q

How does myelin sheaths improve conduction?

A
  • 100 x increase in membrane resistance
  • 100 x decrease in membrane capacitance
  • Due to these = increase length constant
  • Slight decrease in time constant
39
Q

What is conduction velocity proportional to?

A
  • Length constant / time constant
40
Q

What effect does demyelination have on transmission of AP?

A
  • Density of action current is reduced due to:
  • Resistive and capacitance shunting
  • So doesn’t reach threshold value and so no AP

ESA 2 Membranes and Receptors (11 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions