Chapter 3: Resting Membrane Potential Flashcards
RMP
What is the resting membrane potential, and what is it measured by?
- 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.
RMP
What is polarized, hyperpolarized, & depolarized?
- 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.
RMP
What are the two requirements for establishing a membrane potential?
- Ionic concentration gradient across the membrane
- Selective ion channels leak channels in the membrane (permeability)
Ions
What are ions and what are they responsible for?
Ions are atoms or molecules with a net electrical charge.
* Resposible for resting membrane potential.
Ions
Cations vs. Anions
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.
Ions
Describe the properties of the phospholipid bilayer
Think of Head and Tail
- 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
Ions
What are Ion channels?
Proteins that span the phospholipid bilayer that control resting & action potentials.
Leak channels and Ion Pumps
What exactly do ion channels do?
- 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.
Leak channels and Ion Pumps
What are the differences in gated channels?
- Leak channels: Always open
- Gated channels: Gates that can be opened or closed by changes in: Neurtransmitters, voltage, or mechanical forces.
Leak channels and Ion Pumps
What does leak channels do?
- Makes the neuronal membrane semipermeable (impermeable to large anions inside the cell)
- They give rise to the resting potential by always being open.
Leak channels and Ion Pumps
What are ion pumps and what do they do?
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.
Leak channels and Ion Pumps
The resting membrane potential is largely determined by which of the following channel types?
Leak channels - always open
Movement of Ions: Chemical Force
What are the two forces that govern the movement of charged particles across a permeable membrane?
-
Chemical (diffusion)
- High to low concentration
* Down the concentration gradient through ion channels
* Two requirements are permeability & concentration gradient -
Electrical
* Two requirements are permeability (ion channels) and Potential difference across membrane
Movement of Ions: Chemical Force
What is electrochemical equilibrium?
When both forces cancel each other out.
* No net movement across the membrane
The two forces are chemical diffusion and electrical btw.
Movement of Ions: Chemical Force
What is the driving force?
Ions pushed in a certain direction
Movement of Ions: Electrical Force
Describe the flow of anions and cations regarding a battery?
Anions flow toward a anode, and cations flow towards a cathode.
* Opposites attract
Movement of Ions: Electrical Force
What is current and what is its flow determined by?
**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)
Movement of Ions: Electrical Force
What is Electrical potential? V or mV
**It is a force on a charged particle **
* Seperated electrical charges have potential energy between them
* Always measured between two points
Movement of Ions: Electrical Force
What is electrical conductance? g
Measured in S or mS
**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
Movement of Ions: Electrical Force
What is resistance?
Resistance is the inabiliy of a charge to migrate.
* Measured in Ohm’s law
Movement of Ions: Electrical Force
What is Ohm’s law?
l=gV
* If conductance (g) is 0, no current will flow
* If potential difference is 0, no current will flow.
Movement of Ions: Electrical Force
Which would most strongly drive Na+ to enter a neuron permeable to Na+
High Na+ concentration outside the cell, negative charge inside the cell.
The Movement of Ions: Equilibrium Potentials
What happens with a selectively permeable membrane inside the cell?
Specifically with potassium
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
The Movement of Ions: Equilibrium Potentials
What happens when electical forces start to arise and fighting with the diffusion chemical forces?
Specifically with potassium
- 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
The Movement of Ions: Equilibrium Potentials
What are the 4 important points abt equilibrium potential?(Eion)
- Ion concentrations are** virutally unchanged **
- Net difference in electrical charge only occurs at the inside and outside surfaces of the membrane. The cytosol and extracellular fluid are electrically neutral.
- **Ionic Driving Force (Vm-Eion) **determines the direction and magnitude of ion movement.
- Each ion has its own equilibrium potential (Nernst)
The Nernst Equation & Driving Force
Describe the nernst (equilibrium) potential for an ion
- 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.
The Nernst Equation & Driving Force
Describe the driving force (Vm-Ex)
- 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.
The Nernst Equation & Driving Force
What does a negative driving force mean?
Wants to make the cell more positive
(positive ions move in and the negative ions move out)
The Nernst Equation & Driving Force
What does a positive driving force mean?
Wants to make the cell more negative
(positive ions move out and the negative ions move in)
When there is more than one ion: The Goldman Equation
What if the membrane is permeable to more than one ion?
Resting membrane potential depends on the permeability of the membrane to each of the ions»_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.
When there is more than one ion: The Goldman Equation
Why are neuronal cell membranes more permeable to k+ than to Na+?
Because they have more k+ leak channels than Na+ leak channels.
When there is more than one ion: The Goldman Equation
What is membrane protential?
A weighted average of the Nernst potentials for all the ions in the cell, weighted according to their relative permeabilities
Sodium/Potassium Pump
Describe the Sodium/Potassium Pump
- 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. **
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?
The relative permeability changed for each ions because channels might have opened up.
