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LCRS - Endo and Neuro > Lecture 4 NS - Resting and Action Potentials > Flashcards

Lecture 4 NS - Resting and Action Potentials Flashcards

1
Q

How do nerve cells function to generate the behaviour of the organism?

A

Produce sophisticated electrical and chemical signals

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2
Q

What is flux?

A

The rate of transfer of molecules, so number of molecules that cross a unit area per unit of time

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3
Q

What is voltage?

A

Generated by ions to produce a charge gradient

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4
Q

What is current?

A

Movement of ions due to a potential difference

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5
Q

What is resistance?

A

Barrier that prevents the movements of ions

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6
Q

What is the zero volt level?

A

The reference electrode outside the cell

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7
Q

Why are ion channels needed?

A

The lipid cell membrane is a barrier to ion movements, separating ionic environments -> to allow ions to move across the channel

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8
Q

What is the nerve cells potential difference value when at rest?

A

-70mV

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9
Q

What type of stimuli do ion channels respond to when they need to open/close?

A

Trans-membrane voltage, presence of activating ligands or mechanical forces

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10
Q

To what can ion channels be selective for?

A

Different ions -> Na, K, Ca, Cl

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11
Q

When does movement across a membrane through an ion channel occur?

A

When there is a difference in concentration of the permanent species on one side of the membrane

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12
Q

When is electrochemical equilibrium achieved?

A

When electrical force prevents further diffusion across the membrane

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13
Q

What is the Nernst equation?

A
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14
Q

What is the composition of the main fluid compartments?

A

NB: Na and K are the most important ions for resting potential of neurons

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15
Q

What is a disadvantage of the Nernst equation?

A

Cells are not uniquely permeable to one thing, so we need to use the GHK equation

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16
Q

What is the GHK equation?

A

Describes the resting membrane potential, where P is permeability/channel open probability

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17
Q

What does increasing the permeability for Na do in the GHK eqn?

A

Makes the cell more positive

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18
Q

What are some key terms that are needed for membrane potential changes?

A
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19
Q

How is the resting potential achieved?

A

Through mainly K diffusion from inside to outside of cell

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20
Q

What is depolarisation?

A

Positive increase of the membrane potential

21
Q

What are the characteristics of graded potentials?

A

Changes in membrane potential in response to stimulation

22
Q

What is the mechanism of decremental spread of graded potentials?

A
23
Q

Where do graded potentials occur and what is their function?

A

Occur at synapses and sensory receptors and contribute to initiating or preventing action potentials

24
Q

Where do AP occur?

A

In excitable cells -> mainly neurons and muscle cells but also endocrine tissue

25
Q

What is the function of AP?

A

Allow transmission of information reliably and quickly over long distances -> central role in cell-cell communication and can activate intracellular processes

26
Q

What does the permeability of the nerve cell depend on?

A

Conformational state of the ion channel -> could be opened by membrane depolarization/inactivated by sustained depolarisation/closed by membrane hyper/repolarisation

27
Q

What happens when membrane permeability of an ion increases?

A

It crosses its membrane in direction dictated by electrochemical gradient -> changes membrane potential toward the equilibrium potential for that ion

28
Q

What does the action potential look like?

A
29
Q

What are the 5 phases of action potential?

A

1) Resting membrane potential, 2) depolarising stimulus, 3) upstroke, 4) repolarisation, 5) after-hyperpolarisation

30
Q

What occurs in the first phase of action potential - resting membrane potential?

A

Membrane permeability for potassium is a lot higher than Na, lying nearer to K electrochemical equilibrium than Na

31
Q

What occurs in the second phase of action potential - depolarising stimulus?

A

The stimulus depolarises the membrane potential and moves it in the positive direction towards the threshold

32
Q

What occurs in the third phase of action potential - upstroke?

A

Starts at threshold potential, with massive increases in Na permeability (because of VGSC opening) so membrane potential moves towards Na equilibrium potential, so Na moves into the cell down via the VGSC and K moves out of the cell (but less K than Na leaving)

33
Q

What occurs in the fourth phase of action potential - repolarisation?

A

VGSC closes (conformational change), so Na entry stops, but increased K as more VGKC open and remain open, so K leaves the cell down electrochemical gradient, so membrane potential moves toward K equilibrium potential

34
Q

What occurs in the fifth phase of action potential - after-hyperpolarisation?

A

At rest VGKC are still open, so K continues leaving the cell, moving closer to the K equilibrium -> some VGKC then close and membrane potential returns to resting potential

35
Q

What happens at the start of repolarisation?

A

Na channels inactivate as portion of structure senses the opening and blocks the channel -> called an absolute refractory period as the inactivation gate is closed and new action potential cannot be triggered even with very strong stimulus NB: K+ channels still open so cell begins to repolarise

36
Q

What happens at the end of repolarisation?

A

It enters the absolute refractory period, and both inactivation and activation gate of the Na channel is closed

37
Q

What happens during the after-hyperpolarisation?

A

Relative refractory period -> Inactivation gate (VGSC) is open, so if the stimulus is stronger than normal stimulus another AP can be evoked

38
Q

What are the changes in permeability that occur during the changes in membrane potential in an AP?

A
39
Q

What happens once the threshold potential is reached?

A

An all-or-nothing response occurs, which once triggered cannot be stopped -> only in the refractory state which is unresponsive to threshold depolarisation

40
Q

What is the loop of membrane potential?

A
41
Q

How long does the cycle of action potential increase for?

A

Continues until VGSC inactivate where the membrane remains in a refractory state until VGSC recover from inactivation

42
Q

How are ion pumps involved in action potentials?

A

They ARE NOT involved DURING the AP! To restore the electrochemical equilibrium after the AP, K and Na move through non-VGC and some ions are exchanged through pumps

43
Q

How does the AP propagate?

A

If there is a site of depolarisation, there is a decay in polarisation due to K ions moving out of the cell -> internal/membrane resistance alters propagation distance and velocity

44
Q

How is the action potential actively propagated?

A

Local current flow due to Na entering and depolarising -> the adjacent area is depolarised (may be enough to cause AP)

45
Q

How does the neuron prevent back flow of AP?

A

At this point the axon is refractory so there is no back flow of impulse

46
Q

How does the myelin sheath cause saltatory conduction?

A

It allows a more prolonged graded events of the AP until it reaches the next NoR

47
Q

What changes the conduction velocity in neurons?

A

Axon diameter and myelination (increasing both increases velocity)

48
Q

How does myelination change velocity of conduction?

A

Myelination increases speed, but reduced myelination decreases velocity

49
Q

What factors slow down conduction velocity?

A

Reduced axon diameter, reduced myelination, cold, anoxia, compression, drugs

LCRS - Endo and Neuro (22 decks)

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