Lecture 11.2 main points Flashcards
describe excitable cells in their resting state. What are ions, what do opposite charges do? what do some charges do?
excitable cells in their resting state have a negative charge on the inside of the membrane (-70mV is the average for neurons) compared to the outside (0mV)
Ions are charged atoms, or molecules, that have lost or gained electrons
opposite charges attract
like charges repel
define electric potential
separated electrical charges of opposite sign have the potential to do work if they are allowed to come together
define membrane potential
voltage of the intracellular region of the membrane compared to the extracellular
what does it mean for the membrane voltage to increase/ decrease membrane potential
increasing the membrane potential - excite the call - makes it more positive
decrease the membrane potential - inhibit the cell - make it more negative
define potential difference
the difference in potential (charge) between the outside of the cell and the inside
what does it mean for the membrane voltage to increase/ decrease potential difference
increasing the potential difference of a resting membrane voltage - make it more negative
decrease the potential difference - make it more positive
define conductance? what is the shorthand?
the permeability of the membrane to an ion
represented by the lowercase g
gK= conductance of potassium
can charge/polar chemicals pass easily directly through the membrane
the plasma membrane is relatively impermeable to charge atoms and molecules
how is the membrane conductance for charged or polar chemicals altered?
ions must travel through transmembrane protein, when more are open, the greater the conductance for that ion
define current? what is the shorthand representation?
current is the actual movement (flow) of ions through membrane channels
represented by a capital I
INa= current for sodium
IK= current for potassium
what does it mean to increase/ decrease current
increase current means high flow of ions across the membrane
what does it mean to have positive/negative current
positive current means ions flowing out of the cell
negative current means ions flowing into the cell
sodium concentration inside v outside
cation, higher outside the cell
chloride concentration inside v outside
an anion, higher concentration outside
calcium concentration inside v outside
cation, higher outside
potassium concentration inside v outside
cation, higher concentration inside the cell
phosphate concentration inside v outside
polyatomic ion, higher inside the cell
majority of phosphate bound to proteins and ATO
shorthand representation for concentration of intracellular/ extracellular potassium, sodium?
[K]o or [K]e for extracellular
[K]I for intracellular
describe concentration differences intra vs extracellular K and Na
intracellular K > intracellular Na
extracellular Na > extracellular K
define diffusion
movement of an atom or molecule from a region of high concentration to a region of low concentration
where does sodium want to go? inside or outside the cell? does it flow up or down its concentration gradient
sodium wants to flow into the cell, down its concentration gradient
describe the charge of the extracellular region by the membrane vs intracellular region by the membrane
extracellular region is more positive than intracellular region
why would sodium want to flow into the cell at typical neuronal resting membrane potential
sodium wants to flow from the positive extracellular into the negative intracellular at resting membrane voltage
when sodium flows from a positive region to a more negative one, it is said to flow up or down its concentration gradient
down its concentration gradient
define the equilibrium potential (Nernst value)
the voltage at which the electrical gradient cancels the chemical gradient
specific for each ion based on intracellular and extracellular concentration
with respect to a particular chemical, what does it mean for the chemical and electrical forces when the Vm is at the Nernst value
there is no net movement (current) of ions across the membrane
the electrical repulsion force cancels out the diffusion force (they oppose each other with equal force)
if intracellular v extracellular concentration for a particular ion changes, is the nersnt affected? why?
Yes, because there will be a net movement of ions up or down the concentration gradient
what is the value for ENa listed in the powerpoints? describe the effect on sodium’s want to flow into the cell if the Vm is at the sodium Nernst?
roughly +55mV
this means that the intracellular membrane voltage is so positive that it will repel the positive sodium on the outside and keeps it from entering the cell despite Na wanting to flow into the cell down its concentration gradient
what is the value of EK listed in the powerpoints? Describe the effect on potassium’s want to flow out of the cell if the Vm is at the potassium Nernst
roughly -78mV
means that inside of the cell is so negative that the potassium is repelled from wanting to leave the cell
despite wanting to flow out of the cell down its concentration gradient
specifically describe driving force
how much, or how badly, something wants to go across the membrane
for ions - depends on concentration and electrical gradients
how does concentration affect driving force
greater concentration difference across the membrane, greater the driving force of that ion
how do charges and magnitude affect driving force
greater the electrical gradient across the membrane, the greater the driving force for that ion
what is the shorthand representation for resting membrane potential
RMP or Vrm
how is resting membrane potential created by cells? how does lipid bilayer play an important role in this?
created using ion gradients and variety of ion channels that open or close in response to specific stimuli
because the lipid bilayer of the plasma membrane is a good insulator, ions must flow through these channels
where can ion channels be found in the body ? where are they especially prominent?
present in the plasma membrane of all cells in the body
especially prominent component of the nervous system
ligande - gated channels
respond to specific chemical stimulus and are mainly concentrated at the synapse
neurotransmitters, hormones, and some ions can open or close these channels
-nicotinic ACh recepotors are an example
voltage gated channels
respond to changes in the transmembrane electrical potential and are mainly located along the neuronal axon
participate in the generation and conduction of AP
-voltage gated Ca channels are an example
mechanically - gated channels
respond to mechanical deformation (ex. applying pressure to, or stretching, a receptor)
-ryanodine receptors are an example
leakage channels
randomly alternate between open and closed states
allow ions to “leak” across the membrane
when is a neurons RMP measured
at rest, not conducting a nerve impulse
how is the difference in concentrations created and maintained in the RMP
by transport proteins in the cell’s plasma membrane
is the buildup of charge only close to the membrane, or is it found throughout the entire cell?
only very close to the membrane, the cytosol everywhere else in the cell is electrically neutral
