Topic 1: Resting membrane potential Flashcards
What does potential refer to?
Refers to separation of electrical charge across membrane.
What is having an excitable membrane mean?
Cells capable of generating and conducting AP (nerve and muscle cell)
What is it when a cell with an excitable membrane but not generating impulse?
At rest
What is the distribution of electrical charge in H20?
uneven
Is water covalently (share electron) or noncovalently bonded?
Covalently bonded
Is water polar or nonpolar?
Polar (things are different at each end)
What are atoms/molecules that have net electrical charge known as?
Ions
What bond holds 2 oppositely charged ions?
ionic bond
What are spheres of hydration?
Clouds of water that surround each ion
What are positively and negatively charged ions called, respectively?
Cations and anions
What is the building block of cell membrane?
Phospholipids
Phospholipids are long chains of…?
Non polar carbon atoms, bonded to hydrogen atoms also has polar phosphate group
What is the phospholipid “head”?
Polar group, containing phosphate, that hydrophilic
What is the phospholipid
“tail”?
Nonpolar, containing hydrocarbon that’s hydrophobic.
What’s the thickness of the neuronal membrane, and what faces outwards and inwards?
2 molecules thick. Hydrophilic head outward and hydrophobic tail inward
What is neuronal membrane called?
Phospholipid bilayer
What distinguishes neurons from other cells, in terms of protein?
Type and distribution of protein molecule
What do enzymes do?
Catalyse chemical reactions in neurons
What does the cytoskeleton do?
Give neuron its shape
What makes up proteins?
Assembled from various combinations of 20 amino acids
What are the components of amino acids
Has central carbon atom (alpha carbon) bonded to 4 molecular groups:
-Hydrogen atom
-An amino group (NH3+)
-Carboxyl group (COO-)
-And variable group called R group (R for residue)
How do difference in amino acids arise?
Differences in size and nature of R groups
What synthesizes proteins?
Ribosomes
What is the bond that connects amino acids into a chain? And how is it joined?
Peptide bond, joins amino group of one amino acid to carboxyl group of the next
Whats another name for proteins made up of a single chain of amino acids?
Polypeptides
What is the primary structure?
The sequence of amino acids in the polypeptide
What is the secondary structure?
coiling of the polypeptide, e.g., alpha helix
What is the tertiary structure
3-D folding of a polypeptide
What is quaternary structure?
Different polypeptides bonded together to form a larger protein
What is each of the different polypeptides contributing to a protein with quaternary structure called?
A subunit
Which side of phospholipid faces inwards and outward?
Hydrophobic portion facing inward, hydrophilic ends exposed to watery environment on either side
Typically, how many protein molecules for a functional ion channel?
4-6
What is ion selectivity specified by?
Diameter of pore and nature of R groups lining it
What is it called when channels open and close by changes in local microenvironment of membrane?
Gating
What is considered the energy currency of cells?
ATP (adenosine triphosphate)
What are ion pumps?
Enzymes that use the energy released by the breakdown of ATP to transport certain ions across the membrane
What influences ionic movement through channels?
Diffusion and electricity
What is diffusion?
The net movement of ions from regions of high concentration to regions of low concentration
What is the concentration gradient?
When concentration of ions higher on one side than the other therefore will flow “down” the concentration gradient
When does movement of ions across membrane by diffusion occur?
1.) The membrane has channels permeable to the ions.
2.) There is a concentration gradient across the membrane
What is electrical current and how is it represented, and measured?
Movement of electrical charge, represented by symbol I and measured in units called amperes (amps)
What is the positive direction of current by convention?
Defined by positive-charge movement, from anode to cathode
What 2 important factors determine how much current will flow?
Electrical potential and electrical conductance
What is electrical potential (voltage)?
Force exerted on a charged particle, reflects difference in charge between anode and cathode (more current will flow as this difference increases)
How is voltage represented and measure in?
V and volts
What is electrical conductance?
The relative ability of an electrical charge to migrate form one point to another
How is conductance represented and measured?
Symbol g and units called siemens (S)
What does conductance depend on?
The number of ions or electrons available to carry electrical charge.
And the ease with which these particles can travel through space
What is electrical resistance?
The relative inability of an electrical charge to migrate from one point to another
How is resistance represented and measured?
Symbol R, units ohms (Ω)
What is the inverse of conductance?
Resistance, R=1/g
What is the relationship between potential (V), conductance (g) and the amount of current (I) that will flow ?
ohm’s law, I = gV
How are concentrations of substances expressed?
Number of molecules per litre of solution
How is the number of molecules expressed?
In moles
How much is one mole?
6.02 x 10^23 molecules
A solution is said to be 1 Molar (M) if…
it has a concentration of 1 mole per litre
What is the abbreviation of concentration?
Pair of brackets, [NaCl]
What is the membrane potential?
Voltage across the neuronal membrane at any moment, Vm
How can one measure Vm?
By inserting microelectrode into the cytosol
How does microelectrode work?
Has this glass tube with extremely fine tip (0.5 micrometre), penetrate membrane of neuron, filled with electrically conductive salt solution and connected to voltmeter
What does the voltmeter connected to microelectrode do?
Measures electrical potential between the tip of this microelectrode and a wire placed outside of the cell
What is the resting potential of a typical neuron?
-65mV
What is an equilibrium potential of a given ion?
The electrical potential difference that exactly balances the concentration gradient
What happens at equilibrium?
The electrical force pulls (or pushes) ions back to counterbalance the force of diffusion, net movement across membrane ceases, happens at different potentials for different ions e.g., happens at approx. -80mV for K+ ions.
What happens to uneven charges inside and outside the neurons next to the membrane?
They line up along the membrane because of electro static attraction across very thin barrier
What is the ionic driving force?
Ions are driven across the membrane at a rate proportional to the difference between the membrane potential and the equilibrium potential (Vm - Eion)
What can we calculate using the Nernst Equation?
The equilibrium potential
What is the Nernst equation?
Eion = (RT/zF)log([iono]/[ioni])
What ions are predominantly concentrated inside and outside of neuron?
K+ more inside, Na+ and Ca2+, Cl- more outside
How do concentration gradients arise?
Established by actions of ion pumps in neuronal membrane.
What is a sodium-potassium pump (aka sodium pump)?
Enzyme that breaks down ATP in the presence of internal Na+. Uses ATP energy to exchange 3Na+ inside to outside and 2K+ from outside to inside. Pushes ions against their concentration gradient.
What is a calcium pump?
Enzyme that actively transports Ca2+ out of the cytosol across the cell membrane with energy used from ATP
What is the Goldman equation?
A mathematical formula that takes into consideration the relative permeability of the membrane to different ions, to calculate equilibrium potential
What is the molecular basis for ionic selectivity?
Arrangement of amino acid residues (R) that line the pore regions of the channels
How many subunits do most potassium channels and how are they arranged?
4, arranged like staved of a barrel to form a pore
Which parts of the potassium channel contributes to the selectivity filter and makes the channel permeable to mostly K+?
Pore loop
What is depolatization?
A change in membrane potential from normal resting value (-65mV) to less negative value
What is the blood-brain barrier
A specialization of the walls of brain capillaries that limits the movement of K+ (and other bloodborne substances) into the extracellular fluid
What do Glia, particularly astrocytes do when [K+] rises?
They take up K+
What would happen if extracellular [K+] got to high?
Depolarisations, perhaps unwanted depolarisation
What mechanism does astrocytes have to maintain extracellular K+, and what is it referred to?
Have K+ pumps that concentrate K+ in their cytosol and K+ channels -> they dissipate K+ over large area by extensive network of astrocytic process, called potassium spatial buffering.
