Nerve Impulses: The Neuronal Membrane at Rest(Resting Potential)

Topic 3

what is an action potential?

electrical potential that rapidly propagates down axons without degradation

cytosolic and extracellular fluid (why is water important)

uneven charge distribution allows for polar and nonpolar molecules to enter

what are ions and what do they do?

atoms/molecules with a net electrical charge, charge carriers involved in the conduction of electricity in neurons,

what are some important ions for resting potential?

K+, Na+, Ca 2+, Cl-

what are clouds of hydration and what do they do?

water molecules and ions, they insulate ions from each other

what is the phospholipid bilayer?

made up of a chain of hydrocarbons (non-polar) and a phosphate group (polar)

what are hydrocarbons and phosphate groups in relation to the phospholipids?

hydrocarbons-tails, phosphate groups-heads

what do ion channels do?

allow ions to pass through, control resting and action potentials

what do all proteins have?

alpha carbon, carboxyl group, an amine group, a hydrogen atom, and an R group

how do proteins differ?

by their R group, some R groups are hydrophobic and others are hydrophillic

why are the R groups significant in relation to the membrane?

location of hydrophobic and hydrophillic R groups determine which portion of each subunit associates with the membrane

what is ion selectivity?

how ions allow material to pass through, determined by R groups and pore diameter

what is ion gating?

some ion channels can be opened and closed, include changes in membrane potential via voltage

what is diffusion?

dissolved ions distribute evenly, ions flow down concentration gradient

what is electric current (I)

the movement of electrical charge (ions), measured in Amperes, direction degined by positive charge movement

what is electric potential? (v)

force exerted on a charged particle, reflects the difference in charge between the anode and cathode in a battery,

what is electrical conductance (g)

the ability of an electrical charge to move- this depends on the number of charge carriers and R, measured in Siemens

what is electrical resistance (R)?

resistance to the migration of charge, measured in ohms

what is the electrical resistance formula and why is it important?

R=1/g, it is the inverse of conductance- low resistance, high conductance and etc

how does electric current flow across a membrane?

only current flow is ion channels are present in the membrane, if no channels present then g=0

what is a voltmeter?

measures the electric potential difference across the membrane, it shows the difference in potential between electrode placed inside the cell and a wire placed outside

True or False, there is a net movement of ions when separated by a phospholipid membrane?

false

what happens to an equilibrium potential in the presence of a K+ channel

K+ moves outside of the cell because of a steep concentration gradient- creating a negative net charge inside the cell

how does the negative net charge affect the cell?

as the negative charge grows, an electrical force puts K+ back into the cell

what is equilibrium potential?

ion’s concentration gradient is balanced with the electric force from a membrane’s voltage- creating no net movement of an ion across the membrane

what are the two conditions needed to generate a steady electrical potential difference?

ionic concentration gradient, selective ion permeability

what are the four important points about equilibrium potentials?

large changes in Vm can be caused by very small changes in ionic concentrations, net difference in electrical charge occurs immediately inside and outside membrane surface- this can occur due to electrostatic attraction. Rate of movement of ions across the membrane can be strong or weak based on Vm-Eion. Lastly, if concentration difference of an ion is known, equilibrium potential can be calculated with the nernst equation

what is electrostatic attraction?

ions of opposite charge line up along each side of the membrane

true or false, the neuronal membrane is permeable to more than one type of ion?

true

what happens if the membrane is permeable to one type of ion?

Eion=Vm

what are the primary determinants of Vm?

K+ and Na+

what is the charge if Vm, generally?

-65mV

what is Vm more permeable to, Ek than Ena?

Ek because the membrane is more permeable to K+

how do concentration gradients arise?

ion pumps, sodium-potassium pump

what does the sodium-potassium do?

enzyme that breaks down ATP in the pressure of intracellular Na+. The energy released drives an exchange of Na+ and K+, pumps out 3 Na+ for every 2 K+ ions it pumps in, 70% of the ATP utlilized by the brain powers the pump

why is it important to regulate external potassium concentration?

neural activity produces an increase in K+, astrocytes participate in potassium spatial buffering and redistribute it away from the neuron