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Molecular & Cellular Neuroscience > Resting Potential > Flashcards

Resting Potential Flashcards

Lecture #2

1
Q

Electric-to chemical-to electric signaling.

A

Resting state of the neuron

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2
Q

Phospholipid bilayer:

A
  • Polar phosphate group
    attached to the end
  • Long chains of carbon
    atoms bound to hydrogen
  • Consists of two layers of phospholipids
    Protects and supports the cell
    Selective permeability: allows only certain substances to pass through
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3
Q

Proteins: a brief review

A

Proteins are assembled from various combinations of 20 amino acids
An amino acid:
- Amino group (NH3+)
- carboxyl group (COO-).
- variable R group.

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4
Q

Four levels of protein structure:

A
  • Primary structure: the chain of amino acids
  • Secondary structure: the structure of the chain (for example a helix)
  • Tertiary structure: how proteins bend and fold in 3 dimensions
  • Quaternary structure: how different chains can bond together to form
    a larger molecule
    —————————————————
  • ion channels are composed of proteins.
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5
Q

The cell membrane is composed of a …

A
  • phospholipid bilayer
  • It contains ion channels composed of proteins.
  • These channels are selective: they let only certain ions through the membrane.
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6
Q

The movement of ions across the cell’s
membrane is determined by 2 forces:

A
  • Diffusion
  • Electricity
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7
Q

Diffusion

A
  • from high concentration to low concentration
  • With ion channels,
    an equilibrium is reached.
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8
Q

Concentration gradient:

A
  • difference in concentration.
  • Ions flow down their concentration gradient until an equilibrium is established.
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9
Q

Requirements for diffusion:

A
  • There are open ion channels to allow ions to flow from one side of the membrane to the other.
  • There is a concentration gradient.
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10
Q

Electricity + Electrical current

A
  • ions are electrically charged particles. Opposite charges attract. Like charges repel
  • movement of electrical charge (I) measured in amps.
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11
Q

Electrical potential or voltage =

A
  • force exerted on a charged particle (V) in volts.
  • f the voltage is increased, the force on the particles will increase and more
    current will flow
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12
Q

Electrical conductance

A
  • relative ability of a charged particle to move (g) in siemens
  • The ion channels determine the conductance.
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13
Q

Electrical resistance

A
  • the inability of a charged particle to move. (R) in ohms. R = 1/g
  • Ohm’s law: V=IR or I=gV.
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14
Q

The membrane potential + Why is the resting potential -65mV?

A
  • the voltage difference across the neuronal membrane: Vm
  • The potential difference acroiss the membrane. The inside of the membrane negative and outside positive. Inside the cell measurement means that the value is negative.
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15
Q

Electrical current needs:

A
  • An electrical potential difference across the membrane.
    Ion channels that are permeable to the ion.
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16
Q

Hypothetical cell + what happens

A
  • K+ and A- are dissolved at a higher concentration inside the cell than out.
  • No ion channels, nothing happens
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17
Q

An equilibrium is reached when …

A
  • the force of diffusion in one direction
    equals the electrical force in the opposite direction.
  • When this happens, the electrical potential difference is called the Equilibrium Potential. For K+ , in a neuron, it is -75mV.
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18
Q

Now add a K+ channel to hypothetical cell

A
  • K+ flows down the concentration gradient (brings positive charge)
  • at equilibrium, there is equal charge of K+ (After build-up of positive charge on the other side of the membrane)
19
Q

An equilibrium is reached when the force of diffusion…

A
  • in one direction equals the electrical force in the opposite direction.
  • When this happens, the electrical potential difference is called the Equilibrium Potential. For K+ , in a neuron, it is -75mV.
  • The equilibrium potential for K+ is abbreviated EK.
20
Q

EK = -75 mV

A
  • It is the membrane potential where K+ is at equilibrium.
21
Q

Start with more Na+ outside the cell…
1) Once a Na+ channel is added, in which direction will
Na+ ions flow?
2) As Na+ flows down its concentration gradient, will
the inside of the cell become positive or negative?

A
  • (inside th cell)
  • (positive)
22
Q

Forces of diffusion =

A

electrical force
- For a neuron, ENa = +58 mV. It is the membrane potential where Na+ is at equilibrium.

23
Q

Start with more Cl- outside the cell:
1) When you add a channel, which way will Cl- flow?
2) Will the inside of the cell become positive or negative?

A
  • inside the cell
  • negative
24
Q

Equilibrium potential:

A
  • the potential (voltage) at which there is no net
    driving force on the ion.
  • Each ion has its own equilibrium potential.
25
Q

The Nernst equation:

A
  • used to calculate the exact value of the equilibrium potential for each ion.
26
Q

Components of Nernst Equation

A
  • R = gas constant
  • T = temperature (in Kelvin)
  • F = Faraday constant
  • z = charge of the ion
  • [ion]o = concentration of the ion outside the membrane
  • [ion]i = concentration of the ion inside the membrane
27
Q

Concentration gradients are maintained by the sodium-potassium pump:

A
  • Pushes Na+ out and K+ in
  • Requires ATP
28
Q

Concentration gradients are maintained by…

A
  • astrocytes
    “potassium spatial buffering”.
  • shuttle from high concentration to low concentration
29
Q

Relative ion permeabilities at rest

A
  • In the Nernst equation, we assume that the membrane has only one type of ion channel.
  • In reality, there are many different channels (K+, Na+, Cl- etc).
  • The true resting membrane potential will depend on how permeable the membrane is to all of these ions.
30
Q

The membrane is permeable to both K+ and Na+…

A
  • Then Vm = some average of -75mV and +58mV.
31
Q

Goldman equation + components

A
  • Takes into consideration the relative permeability of the membrane to different ions
  • PK = relative permeability of K+
  • [K+]o = concentration of K+ outside the membrane
  • [K+]i = concentration of K+ inside
32
Q

Use the Nernst equation to:

A
  • What happens to the membrane potential if the membrane is permeable to one ion.
  • You can use the Nernst equation to calculate the equilibrium potential of one ion.
  • The equilibrium potential is the membrane potential where there will be no net driving force on that one ion.
33
Q

The Goldman equation shows us:

A
  • What happens to the membrane potential when the membrane is permeable to more than one ion.
  • It takes into consideration the fact that the membrane is more permeable to some ions more than others.
  • You can use the Goldman equation to calculate the membrane potential if you know the concentrations of several ions AND their relative permeabilities.
34
Q

The fact that the resting potential (-65mV) is close to the equilibrium potential for K+ (-75mV) implies that:

A

1) At rest, the membrane is more permeable to K+ than to other ions.
2) This permeability is the source of the resting membrane potential.

35
Q

Alan Hodgkin and Bernard Katz (1949)

A
  • The squid giant axon
  • Change the concentration gradient of an ion (in this case, K+) and see what happens to the membrane potential (Vm).
  • Change the concentration of K+ and measure what happens to the membrane potential of the cell.
36
Q

General set-up for recording membrane potentials in a neuron

A
  • axon
  • electrode
  • wire
  • amplifier
  • oscilloscope or computer
  • ground
37
Q

Hodgkin and Katz results:

A
  • At normal levels of K+,
    Vm = -65mV
  • and graphs differ because there are more ion channels than just K+ in the cell.
38
Q

When the concentration of K+ inside the cell = the concentration of K+ outside the cell…
What is EK?
What is Vm?

A
  • 0
  • 0
39
Q

Experimental results (for Na+):

A
  • axon
  • electrode
  • wire
  • amplifier
  • oscilloscope or computer
  • ground
  • Add Na+
40
Q

When Hodgkin and Katz added more Na+ outside the cell, what was the effect on membrane potential? Why?

A
  • No change, Na+ channels within the cell are closed
41
Q

Conclusion of Hodgkin Katz experiments

A
  • K+ channels open at rest
  • Na+ channels closed at rest
42
Q

Summary of Hodgkin and Katz:

A

The negative resting potential arises because:
1) The membrane of the resting neuron is more permeable to K+ than any of
the other ions present.
2) There is more K+ inside the neuron than outside.
3) At rest, K+ permeable channels are open.
4) At rest, Na+ permeable channels are closed.

43
Q
A
44
Q
A

Molecular & Cellular Neuroscience (8 decks)

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