LEC14: Introduction to Electrophysiology Flashcards Preview

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Flashcards in LEC14: Introduction to Electrophysiology Deck (23):

what types of membrane proteins are in the lipid bilayer of the cell membrane?

1) carrier proteins

2) channels



how do carrier proteins work?

operate in cycles 

bind solutes (i.e. their substrates), undergo conformational changes that convey the solutes across the membrane, & return to the initial conformation 

each has a characteristic Km & Vmax 


how do channels work, broadly?

allow for higher rates of movement across membranes than do carrier proteins 

do not tightly bind solutes or operate in cycles; provide a TM pore through which specific solutes can diffuse down their electrochemical gradients 



what do carrier proteins establish across cell membrane? what is return?

ion gradient 

thus ionic composition of cytoplasm of any cell is very diff from that of surrounding extracellular space 



what do ion gradients represent? what happens within/outside of cell?

represent a form of potential energy 

free energy of a system will decrease as ions move from region of high concentration to low concentration 



how is transmembrane voltage/potential generated?

ions moving through the membrane produce a transmembrane voltage/potential 

opening & closing channels that are selective for particular ions allows cells to regulate the voltage across the cell membrane 

high rates of charge transfer can produce dramatic voltage fluctuations


what are the terms, their symbol, unit for ions moving through membranes?

A image thumb

what is the membrane potential?

the inside  voltage relative to the outside 

typically = -70 mV


what are typical ion concentrations of K+, Na+, Ca2+, and Cl- inside/outside the cell?

A image thumb

which channels provide predominant membrane conductance?

K+ channels


explain the relationship between the concentration gradient and electrostatic force for K+ channel?


1) concentration gradient wants K+ to leave the cell b/c there is 150 inside and 4 mM outside, so K+ goes out per concentration gradient. The electrostatic force does not yet act bc there is no voltage gradient

2) As K+ continues to leave the cell, generate a negative force across the voltage gradient. Concentration gradient still pulling K+ out. Electrochemical gradient slightly wants it to stay in but not that strongly

3) Now if get to -91 mV gradient. Electrostatic gradient really kicks in and wants K+ ions to stay in the cell, big time! No net movement of K+ in/out of the cell - do have movement in and out but not net movement


Get to Vm, the point where electrostatic attraction and concentration gradient are equal 


A image thumb

what is the equilibrium potential?

the value of Vm where the concentration gradient and electrostatic forace are balanced 



what is Veq for Na+, K+, Ca2+, and Cl-?

Na+: +67 mV

K+: -91 mV

Ca2+: +125 mV

Cl-: -78 mV


what is "outward current"? 

what is effect on membrane?

the movement cations out of the cell

hyperpolarizes membrane


what is inward current? 

what is effect on membrane?

movement of cations into the cell

depolarizes the membrane


what is current?

what is it determined by?

rate of charge transfer from 1 point to another 


large current means that many charges (ions) are moving through the membrane per unit time 

1) electrochemical gradient for this ion 

2) ease w/ which this ion can pass through the membrane


what is the driving force of an ion?

driving force = |Vm - Veq|

changes in response to variatiosn in membrane potential 


what is conductance?

the ability of a material to carry a current 

expressed in siemens 



what is resistance?

inverse of conductance (which is ability of a material to carry a current) 

unit = ohm 

"how good a barrier a medium presents to ions/charges"



how is the resistance of biological membranes?




what is Ohm's law? 

what is its slope? 


Q image thumb

I = g*V





if there are fewer ion channels open in a membrane, will the membrane potential change be great or small in response to application of a current?

GREAT response 



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