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Neuroscience 🧠 > Chapter 3: Resting Membrane Potential > Flashcards

Chapter 3: Resting Membrane Potential Flashcards

1
Q

RMP

What is the resting membrane potential, and what is it measured by?

A
  • Voltage across the neuronal membrane at rest.
  • RMP is measured by electrodes that compare the inside to the outside.

*We are just measuring right outside and right inside the membrane.

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2
Q

RMP

What is polarized, hyperpolarized, & depolarized?

A
  • Polarized means the membrane is more negative on the inside. (At rest) Ex.-70mV
  • Hyperpolarized: Membrane potential is less than resting potential. Ex: -90mV
  • Depolarized: Membrane potential is greater than resting potential. Ex: 0mV

-70mV means that the inside is 70mV more NEGATIVE than the outside.

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3
Q

RMP

What are the two requirements for establishing a membrane potential?

A
  1. Ionic concentration gradient across the membrane
  2. Selective ion channels leak channels in the membrane (permeability)
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4
Q

Ions

What are ions and what are they responsible for?

A

Ions are atoms or molecules with a net electrical charge.
* Resposible for resting membrane potential.

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5
Q

Ions

Cations vs. Anions

A

Cations: Net positive charge
* Smaller, nonmetals. Ex: K+, Na+, Cl-

Anions: Net negative charge
* Bigger, metals. Ex: Ca2+

Monovalent is like a +1, -1 charge.

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6
Q

Ions

Describe the properties of the phospholipid bilayer

Think of Head and Tail

A
  • Hydrophilic compounds that dissolve in water due to uneven electrival charge (head)
  • Hydrophobic compounds that do not dissovle in water due to even electrical charge. (tails)

small non polar molecules can diffuse

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7
Q

Ions

What are Ion channels?

A

Proteins that span the phospholipid bilayer that control resting & action potentials.

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8
Q

Leak channels and Ion Pumps

What exactly do ion channels do?

A
  • Makes the membrane semipermeable so certain molecules can pass.
  • Differ in types of ions they allow to pass through the pore (selectivity).
    1. anion channels
    2. cation channels

Some channels only allow specific ions to go through.

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9
Q

Leak channels and Ion Pumps

What are the differences in gated channels?

A
  • Leak channels: Always open
  • Gated channels: Gates that can be opened or closed by changes in: Neurtransmitters, voltage, or mechanical forces.
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10
Q

Leak channels and Ion Pumps

What does leak channels do?

A
  • Makes the neuronal membrane semipermeable (impermeable to large anions inside the cell)
  • They give rise to the resting potential by always being open.
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11
Q

Leak channels and Ion Pumps

What are ion pumps and what do they do?

A

Ion pumps are membrane spanning proteins (enzymes)
* Uses ATP to transport speicifc ions across the bilayer against the concentration gradient.
Ex: Sodium-Potassium pump that establishes and maintains concentration gradient in neurons.

Against concentration gradient means from low to high concentation.

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12
Q

Leak channels and Ion Pumps

The resting membrane potential is largely determined by which of the following channel types?

A

Leak channels - always open

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13
Q

Movement of Ions: Chemical Force

What are the two forces that govern the movement of charged particles across a permeable membrane?

A
  1. Chemical (diffusion)
    - High to low concentration
    * Down the concentration gradient through ion channels
    * Two requirements are permeability & concentration gradient
  2. Electrical
    * Two requirements are permeability (ion channels) and Potential difference across membrane
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14
Q

Movement of Ions: Chemical Force

What is electrochemical equilibrium?

A

When both forces cancel each other out.
* No net movement across the membrane

The two forces are chemical diffusion and electrical btw.

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15
Q

Movement of Ions: Chemical Force

What is the driving force?

A

Ions pushed in a certain direction

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16
Q

Movement of Ions: Electrical Force

Describe the flow of anions and cations regarding a battery?

A

Anions flow toward a anode, and cations flow towards a cathode.
* Opposites attract

17
Q

Movement of Ions: Electrical Force

What is current and what is its flow determined by?

A

**Current (l) is the movement of electrical charge measured in amps (A). **
* The direction of the movement of positive charge

The flow is determined by:
1. Electrical potential (Difference between 2 sides of a membrane)
2. Electrical conductance (ability for ions to flow)

18
Q

Movement of Ions: Electrical Force

What is Electrical potential? V or mV

A

**It is a force on a charged particle **
* Seperated electrical charges have potential energy between them
* Always measured between two points

19
Q

Movement of Ions: Electrical Force

What is electrical conductance? g

Measured in S or mS

A

**It is the relative ability of a charge to move from one point to another **
* depends on the # of ions available to carry charge
* how easy the charges travel

It is the inverse of resistance

20
Q

Movement of Ions: Electrical Force

What is resistance?

A

Resistance is the inabiliy of a charge to migrate.
* Measured in Ohm’s law

21
Q

Movement of Ions: Electrical Force

What is Ohm’s law?

A

l=gV
* If conductance (g) is 0, no current will flow
* If potential difference is 0, no current will flow.

22
Q

Movement of Ions: Electrical Force

Which would most strongly drive Na+ to enter a neuron permeable to Na+

A

High Na+ concentration outside the cell, negative charge inside the cell.

23
Q

The Movement of Ions: Equilibrium Potentials

What happens with a selectively permeable membrane inside the cell?

Specifically with potassium

A

Potassium starts to move down its cocentration gradient and the inside of the cell acquires a net negative charge.
* The membrane is losing k+ therefore the inside is getting more negative

24
Q

The Movement of Ions: Equilibrium Potentials

What happens when electical forces start to arise and fighting with the diffusion chemical forces?

Specifically with potassium

A
  • Electrical forces start to pull k+ back inside the cell.
  • When the electrical force is equal and opposite to the chemical force, equilibrium is reached and there is no net movement
25
Q

The Movement of Ions: Equilibrium Potentials

What are the 4 important points abt equilibrium potential?(Eion)

A
  1. Ion concentrations are** virutally unchanged **
  2. Net difference in electrical charge only occurs at the inside and outside surfaces of the membrane. The cytosol and extracellular fluid are electrically neutral.
  3. **Ionic Driving Force (Vm-Eion) **determines the direction and magnitude of ion movement.
  4. Each ion has its own equilibrium potential (Nernst)
26
Q

The Nernst Equation & Driving Force

Describe the nernst (equilibrium) potential for an ion

A
  • The membrane voltage where the chemical and electrical gradients are **equal and opposite in direction. **
  • An ion will work hard to try to take the membrane voltage to the value of ion’s Nernst potential.
27
Q

The Nernst Equation & Driving Force

Describe the driving force (Vm-Ex)

A
  • Difference between the actual membrane potential and the Nernst potential for an ion.
  • Moves ions across the membrane to push the membrane voltage towards the Nernst potential
  • If the cell membrane is at the Nernst potential for a particular ion then there is no net flow of ions.
28
Q

The Nernst Equation & Driving Force

What does a negative driving force mean?

A

Wants to make the cell more positive
(positive ions move in and the negative ions move out)

29
Q

The Nernst Equation & Driving Force

What does a positive driving force mean?

A

Wants to make the cell more negative
(positive ions move out and the negative ions move in)

30
Q

When there is more than one ion: The Goldman Equation

What if the membrane is permeable to more than one ion?

A

Resting membrane potential depends on the permeability of the membrane to each of the ions&raquo_space;> leak channels!
* If more than one ion present, each will tend to pull the membrane towards its Nernst potential
* The higher the relative permeability of the membrane to an ion,** the greater the effect** of that ion on the membrane potential.

31
Q

When there is more than one ion: The Goldman Equation

Why are neuronal cell membranes more permeable to k+ than to Na+?

A

Because they have more k+ leak channels than Na+ leak channels.

32
Q

When there is more than one ion: The Goldman Equation

What is membrane protential?

A

A weighted average of the Nernst potentials for all the ions in the cell, weighted according to their relative permeabilities

33
Q

Sodium/Potassium Pump

Describe the Sodium/Potassium Pump

A
  • Pumps 3 Na+ out and 2 K+ in
  • Requires ATP
  • Ensures that K+ is concentrated in the cytosol and that Na+ is concentrated in the extracellular fluid.
  • **Establishes & maintains ion concentration graidents. **
34
Q

When there is more than one ion: The Goldman Equation

Why would a neurons resting membrane potential change overtime if they are the same concentrations?

A

The relative permeability changed for each ions because channels might have opened up.

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