Membranes and cell excitation Flashcards
An electrical signal involves…
…a change in the balance of positive and negative charges
Name 5 important charged particles
Na+, K+, Cl-, Ca2+ and protein side chains
What controls ion movement inside and outside of a cell?
The membrane
What generates an electrical signal?
The transfer of ions through ion channels
What maintains gradients?
Ion pumps
Describe lipid bilayer permeability
Impermeable to most molecules, including ions
The inside of a cell contains…
….an excess of anions
What is the voltage inside the cell called?
Membrane potential (Em)
What is the membrane potential of a neurone?
-65mV
What determines membrane potential?
The balance of charges
Ion movement is…
…passive
Which ion channels are permeant?
Na+, K+, Ca2+, Cl-
Why are membrane proteins essential?
They control membrane potential
Name the three types of gated channels
Non-gated, voltage, ligand
What are non-gated channels also known as?
Leak channels
What do voltage-gated channels do?
Generate action potentials
What do ligand-gated channels do?
Generate membrane potential changes at synapses
Neurones are _____ cells
Excitable cells
Neurones have a resting membrane potential of…
…-60mV to -70mV
What factors influence ion movement across the cell membrane?
Unequal ion distribution and electrical force
What does the permeability of the membrane tell us?
How easily an ion moves across the membrane (via ion channels)
What do efflux and influx mean?
Efflux = movement out Influx = movement in
Define equilibrium
An ion is in equilibrium when chemical gradient and electrical force are in balance
What is equilibrium potential abbreviated to?
Eion
What does the Nernst equation do?
Defines the voltage at which the ion is at equilibrium
What is happening at equilibrium potential?
The amount of efflux = influx
What is different between Eion and Em
Eion is a constant, Em can vary
What is ionic driving force?
Em - Eion
Explain ionic driving force
What drives the ion across the membrane when Em is not equal to Eion
Is ionic driving force proportional?
Yes
In a neurone, what influences Em?
Na+ and K+
Em rests between what?
EK and ENa
How do we calculate Em?
The Goldman equation
What is Em dependent on?
Relative permeabilities (Pion)
Compare the relative permeabilities of Na and K
PK is 40x bigger than PNa
Why is Em closer to EK?
Because of the difference in permeabilities
What is happening at -65mV in a neurone?
Driving force acting on both Na+ and K+
Na+ influx
K+ efflux
What is making Na+ move in?
Chemical gradient and electrical force
What is making K+ move out?
Chemical gradient, but electrical force is making K+ move in
What ensures Em of -65mV is at rest?
Na+ influx = K+ efflux
Compare the driving force of Na+ and K+
Na+ = large K+ = small
Compare the permeability to Na+ and K+
Na+ = small K+ = large
Do ion pumps control Em?
No, they maintain concentration in the long term
What does the sodium-potassium pump do?
Exchanges internal Na+ for external K+
against concentration gradient
