L7 Neuronal Conduction Flashcards

1
Q

The speed of action potential gradient propagation is determined by?

A

It’s determined by how fast the next segment of membrane gets depolarized to threshold.

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2
Q

How is an action potential like a moving wave?

A

An action potential isn’t simply one event at a single point; it’s a chain reaction.

When one part of an axon’s membrane depolarizes (becomes positively charged), it triggers the depolarization of the adjacent membrane section

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3
Q

Explain continuous action potential vs saltatory Conduction

A
  • Continuous - Happens in unmyelinated axons and slow
  • Saltatory conduction - Myelinated axons, contains gaps (nodes of Ranvier) so action potential “jumps” from one node to the next, much faster
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4
Q

What 4 things influence the speed of action potential propagation?

A
  • Myelination
  • Axon diameter
  • Space constant
  • Time constant
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5
Q

What is space constant?

A

It describes how far an electrical current spreads passively along the axon

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6
Q

How does membrane resistance (Rm) affect space constant?

A

Higher membrane resistance (fewer open ion channels) allows the signal to travel further. Myelin increases membrane resistance

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7
Q

What is membrane resistance (Rm)?

A

Its a measure of much the cell membrane resists the flow of electrical current.

It prevents ions from leaking out hence the resistance

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8
Q

What is internal resistance?

A

Internal resistance is like friction inside the axon.

It means the electrical signal gets weaker as it travels down the axon because some of the electrical energy is lost overcoming the resistance of the cytoplasm inside the axon. A wider axon is like a wider hose – less internal friction, so the “water” (electrical signal) flows more easily

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9
Q

What does a higher membrane resistance mean?

A

A higher membrane resistance means that ions are less likely to leak out, allowing the eletrical signal to travel further along the axon

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10
Q

What does a lower internal resistance mean?

A

A lower internal resistance means that ions can flow more easily along the axon, allowing the electrical signal to travel faster

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11
Q

What affects time constant?

A
  • Membrane resistance (Rm): How un-leaky the hose wall is
  • Membrane Capacitance (Cm): how stretchy the hose wall is
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12
Q

Why is it better to have a lower membrane capacitance (strechiness)?

A
  • If the rubber sheet is very stretchy, it takes a lot of force (charge) to change it shape. It stores a lot of the force instead of quickly changing.
  • If the rubber sheet is stiff ( less stretchy), it takes less force to change its shape. It responds quickly to applied force -
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13
Q

What is the relationship between membrane resistance and surface area?

A

Membrane resistance is inversely proportional to the axon’s circumference of the membrane (more area, more leaks)

Circumference = 2πr

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14
Q

What is the relationship between internal resistance and cross sectional area?

A

Internal resistance is inversely proportional to the area

Area = πr²

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15
Q

What is the time constant formula?

A

Time constant = RmCm (membrane resistance X capacitance)

Rm - membrane resistance - how un-leaky is the hose wall
Cm - membrane capacitance - how stretchy is the hose wall

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16
Q

Can a cell membrane be both a resistor and a capacitor?

A

Yes - A cell membrane is both a resistor (current can pass through but not very well) and a capacitor (charge can build up on one side)

17
Q

What happens if there’s loads of Oligodendrocytes/ Schwann cells wrapped around an axon?

A

This is like wrapping a wire with insulating tape. - it increases membrane resistance.

It also increases the distance between extra and cellular solution

18
Q

What is the formula for space constant?

A

λ = / (rm / ri)

rm - membrane resistance
ri - internal resistance

19
Q

What affects does Myelin have on membrane resistance and membrane capacitance?

A

Myelin increases membrane resistance and decreases membrane capacitance

20
Q

What would happen to space + time constant if myelin increased membrane resistance and decreases membrane capacitance?

A

Myelin increases the space constant while keeping the time constant the same

21
Q

What happens in the node of ranvier?

A

Current enters through Na+ channels at a node of ranvier. This depolarisation spreads along passively down the axon

22
Q

What happens when the current reaches another node of ranvier ?

A

At the next node of ranvier, depolarisation triggers voltage - gated Na+ channels to regenerate the action potential

23
Q

How can you increase the conduction speed without myelin?

A

Without myelin, you can only increase conduction speed by widening the axon following [λ ∝ √radius]

24
Q

To increase the conduction speed by 10x, how much do you need to increase the radius and axon volume by?

A

You need to increase the radius by 100x and the axon volume by 10,000x

  • speed ∝ √radius : 10= √100
  • volume ∝ radius² : 10,000 = (100)²
25
What is a demyelinated neuron?
A demyelinated neuron is a nerve cell that has lost its myelin sheath
26
What are the 5 biological effects of demyelinated conduction?
- Decreased conduction velocity - Frequency- related block - Total conduction block - Ectopic impulse generation - Increase in mechanosensitivity
27
Name two disease caused by demyelinating.
1. Multiple sclerosis 2. Guillain - Barre syndrome
28
What does time constant mean?
Time constant is how quickly or slowly the electrical voltage across the axon’s membrane changes
29
What does a short time constant tell you?
Short time constant men’s the voltage changes quickly. The “bucket” fills up or empties fast
30
Is conducting velocity the same as space constant?
- Space constant measures **how far** a threshold change in membrane potential will passively spread along an axon - Conducting velocity describes the speed at which an action potential is propagated along the axon
31
How does widening the axon radius increase conduction speed?
Internal resistance is inversely proportional to cross-sectional area of axon therefore lower internal resistance so increased space constant use /(Rm/Ri)