1-36 Membrane Potential

Question 1

Membrane potential

Answer 1

difference in electral potential across cell membrane neurons: -70mV, RBS: -10mV Driven by K leak channels that allow K to flow and drive towards Ek (-95), but remains a little closer to positive by few Na leak channels that pull towards ENa (65) established by NA/K-ATPase: removes 3 Na+, Brings in 2 K+, hydrolyzes 1 ATP -> ADP + Pi measured by Foldman-Hodgkin-Katz equation: Em = RT/F * ln (Permeability K [K]out + etc + etc / Permeability K [K]in + etc + etc) etc for each ion of importance, usually K, Na, Cl (flip Cl cuz negative charge)

Question 2

Equilibrium potential

Answer 2

membrane potential that is just sufficient to oppose the chemical potential for a specific ion so no net movement of that ion if channels were open Eion: RT/zF * ln([Ion]out/[Ion]in) Ek: -95 mV ENa: 65mV

Question 3

Graded potentials

Answer 3

physiological stimuli can cause transient changes in membrane potential: graded potentials observed at jxns between neurons (synaptic potential) and neuron to NMJ (acetylcholic receptors, endplate potential) nervous systmem generally: graded potentials generated by stimulation NTreceptors (ligand gated ion channels), opens channel for cation to come in making the membrane less negative (depolized) or Cl- comes in and hyperpolarizes.

Types: Excitatory post-synaptic potential (EPSP) or IPSP

EPSP: activation of NTrecpet permable to Na+ or Ca+2, via ionotropic glutamate receptors

IPSP: activate NTR permable to Cl- summation happens at axon hillock: if reaches threshold potential will trigger action potential, _GABA receptors (_only adult neurons get hyperpolarized by Cl- because have mature low levels of Cl- so GABA drives Cl- in and drive Vm negative-er)

Question 4

safety factor (thresholds)

Answer 4

degree that the EPSP generated at the NMJ exceeds the threshold required for AP firing

Question 5

Action potential (neuronal)

Answer 5

dynamic, all or nothing, phasic change in membrane potential that can propagate along a neuron or surface of muscle cell

different form in different cel types (long/slow)

Events:

1. EPSP summed with drifiting up to -50mV from baby influx on Na+
2. Reach threshold and Depolarized: Voltage gated Na+ Channels open and Na+ rushes in
3. Na+ channel conformational change and close: inactivation, remains inactive until membrane is repolaried* major reason for the refractory period (absolute OR relative)
4. Repolarization: volatge gated K+ channels open in response to membrane depol by Na+ but are slower, K+ floods out of cell and often “overshoots” and causes hyperpolarization
5. K+ channels eventually close and AP ends.

Jump along myelinated nerve axon via saltatory condution

Question 6

Action potential (cardiac)

Answer 6

Cardiac action potential consists of four distinct phases (Figure 2a). In phase 0, upstroke occurs due to rapid transient influx of Na+. Later, Na+ channels are inactivated, combined with a transient efflux of K+. In phase 2, also known as the plateau phase, the efflux of K+ and the influx of Ca2+ are counterbalanced. At the end of the plateau, sustained repolarization occurs due to K+ efflux via the delayed rectifier K+ channels exceeding Ca2+ influx; this constitutes phase 3 of the action potential. Finally, as part of phase 4, resting potential in myocytes is maintained.