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
What is the time constant a product of?
the input resistance and the capacitance
What can graded potential be?
synaptic potentials, generator/receptor potentials, or end-plate potentials
What are the absolute refractory period vs the relative?
Absolute: Na+ channels are inactivated –> no AP possible
Relative: Na+ are closed, but Vm is lower than resting (stronger depol needed for AP)
How can the axon initial segment (AIS) control excitability?
By 1) increasing the space from the soma (less excitable the longer from the soma), and 2) by the length of the AIS (more excitable, the longer)
How does local aneasthesia work?
Targets thin unmyelinated nerves (thin pain neurons), as these are more suceptible (low resistance –> slow –> aneasthesia has more time to block)
Blocks Na_v from within (in inactivated form)
