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BIOM20002 - HSF > Lecture 3 - Membrane Potentials > Flashcards

Lecture 3 - Membrane Potentials Flashcards

0
Q

Which species can pass through a cell membrane?

A

Eg. Water
Small molecules
Lipid soluble molecules
Uncharged molecules

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1
Q

Describe the features of diffusion

A

No energy input - passive
Spontaneous
Downhill flow

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2
Q

Which species cannot pass through a cell membrane

A

Charged particles
Large proteins

Eg. Ions, insulin

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3
Q

What is tonicity?

A

Concentration of Non-penetrating solutes

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4
Q

What is osmolarity?

A

Concentration of Total solutes

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5
Q

When comparing tonicity of cells, do we call the cell or the ECF hypo/hypertonic?

A

Always the extracellular fluid

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6
Q

What are the different units for osmolarity and tonicity?

A

Osmolality: Osm

Tonicity: no unit, relative measure

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7
Q

Describe Fick’s law

A

This law dictates the rate of diffusion across a membrane, depending on various variables:

  • membrane thickness
  • membrane permeability
  • membrane surface area
  • concentration gradient
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9
Q

Is the body in chemical equilibrium?

A

No - because certain solutes will have different concentrations on either side of the cell membrane.

eg. Na extracellularly and K intracellularly

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10
Q

Is the body in osmotic equilibrium?

A

Yes - equal concentration of water on either side of the membrane
–> Water moves across the membranes to ensure this

This means that overall solute concentrations are balanced

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10
Q

What is the typical osmolarity of the body?

A

300 mOsm

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11
Q

Is the body in electrical equilibrium?

A

Whole body level: yes - neutral

Cellular level: no - neurons are negative relative to the extracellular fluid

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12
Q

Describe the dogma of neuron communication between the PNS and CNS, afferent and efferent pathways

A
  1. Afferent neurons from the PNS enters the CNS and talks to an interneuron, entirely within the CNS
  2. Integration at the interneuron
  3. Interneuron talks to the efferent neuron, originating in the CNS
  4. Efferent neuron exits the CNS to do stuff in the periphery
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13
Q

Which ions are concentrated inside the cell?

A

Potassium

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14
Q

Which ions are concentrated outside the cell?

A

Sodium
Chlorine
Calcium

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15
Q

What is the electrical equilibrium of sodium and potassium individually, and what is the overall resting membrane potential?

A

Sodium: +60 mV
Potassium: -90 mV

Overall: -70 mV

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16
Q

What is the majority of RMP due to?

What else has an influence?

A

Majority is due to movement of ions down their gradients through leak channels

Also the Na-K ATPase pump

17
Q

Why does potassium have a greater effect on the resting membrane potential (RMP)?

A

Because the membrane is more permeable to potassium, because there are more potassium leak channels

18
Q

What is the Nernst potential?

A

This is the potential that is equal in magnitude to the potential for the ion to more across the membrane.

19
Q

What does the magnitude of the Nernst potential rely on?

A

The ratio of the concentrations of the ion inside and outside the cell

21
Q

What is the role of Na-K ATPase?

A

Maintains the chemical disequilibrium across the membrane

22
Q

What are leak channels?

A

Another name for Open channels
ie not gated

They are always open for the passage of ions from ICF to ECF

23
Q

What are the two types of protein that allow movement of a substance across a membrane?

A
  1. Channel

2. Carrier

24
Q

Compare how channels are carriers move things across the membrane

A

Channel: direct connection between ICF and ECF through which things can move

Carrier: change in conformation allows movement of a molecule

25
Q

What are the two types of channel protein?

A
  1. Open / leak channels

2. Gated channels

26
Q

What are the different types of gated channels?

A

Chemically gated
Voltage gated
Mechanically gated

27
Q

Compare concentration of Na+ inside and outside the cell

A

ICF: 15 mM
ECF: 150 mM

28
Q

Compare concentration of K+ inside and outside the cell

A

ICF: 150 mM
ECF: 5 mM

29
Q

Compare concentration of Cl- inside and outside the cell

A

ICF: 10 mM
ECF: 100 mM

30
Q

Compare concentration of Ca2+ inside and outside the cell

A

ICF: 0.0001 mM
ECF: 1 mM

31
Q

What is an electrochemical gradient?

A

The combination of the cell’s chemical and electrical gradient. These gradients are often in different directions:
K+:
• Chemical gradient out of cell
• Electrical gradient into cell

32
Q

What is the equilibrium potential?

A

This is the point at which movement into and out of the cell due to chemical and electrical gradients is balanced

33
Q

What happens if Na/K ATPase is inhibited?

A
  • Na+ is no longer pumped back out
  • K is no longer pumped back in
  • RMP increases (cell more depolarised)
  • Cell more likely to fire an action potential
34
Q

What is an electrogenic pump?

A

A pump that moves ions unequally so that a potential across the cell membrane is set up

35
Q

What happens when there is a change in the membrane’s ion permeability?

A

There will be movement of ions down their concentration gradients

• Change in membrane potential

36
Q

What causes the change in a cell’s ion permeability?

A

An IPSP causes the opening of voltage gated ion channels

Voltage Gated Channels

37
Q

What happens to the membrane potential if the cell becomes more permeable to Na?

A

Cell potential decreases; cell depolarises

38
Q

What happens to the membrane potential if the cell becomes more permeable to K?

A

Cell potential increases; cell hyperpolarises

39
Q

What are the stimuli for activation of Na and K voltage gated channels?

A

Na: depolarisation to threshold
K: same

40
Q

Compare the speed of activation of Na and K voltage gated channels?

A

Na: fast
K: slow

BIOM20002 - HSF (60 decks)

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