Membrane transport and potentials Flashcards
What are the resting membrane potential determined by?
K+ and N+
What are the difinition of the membrane potential?
A weighted average of the permeable ions’ equilibrium potentials
What is the equilibrium potential dependent on, and what is the most important factor?
The chemical and the electrical forces
Most important: ion conc
How are the relative contribution from V_Na and V_K to the resting potential?
V_Na: app. 25 %
V_K: app. 75 %
How does the permeability of an ion affect the membrane potential?
The more permeable, the more effect: a change in ion permeability –> a change in membrane potential
What are the main channels responsible for the resting potential?
K+ leaky channels (+ Na/K pump: secondary by upholding the ion gradient, + Na+ leaky channels)
What is the direction an ion is moving in dependent on?
Its equilibrium potential
What makes some cell excitable?
Ion-selective and voltage-sensitive channels
What are the main energy consumper of the brain, and why?
Na/K pump: it is important to uphold the ion gradients for neural activity to work
What effect will a higher extracellular K+ conc have on the excitability of cells?
–> More positive V_eq(K+) –> more positive Vm –> Vm closer to threshold –> more excitable
What does the neurotoxin TTX do?
Inhibits the Na_V channels –> Vm decrease –> cells less excitable
Are V_eq affected by an ions permeability/conductance?
No, only by ion conc
What is the length constant?
The length down the dendrite at which the membrane depolarization is reduced to 37% of its origin
What affects the length constant?
Dendrite diameter: the bigger the diameter–> lower axial resistance –>
The ions permeability: the more open channels –> the higher the permeability –> lower membrane resistance –> lower length constant
What is the time constant?
The time it takes the Vm to rise to 63% of steady state value
