Flashcards
Ionic basis of neuronal action potentials
Cards in this deck (26)
- 1What is an equilibrium potential?The point at which a membrane which is selectively permeable to an ion has equal and opposite electrical and chemical gradients (there is no net movement of ions)
- 2write out the nernst equation at 25 degreesEa=(58/z) log10([A]out/[A]in)
z= valency - 3How would the equation change at 37 degreesthe 58 would change to 61
- 4How would a membrane only being permeable to K+ channels affect the m.p. of the cellthe m.p would decrease to the K+ equilibrium
- 5Why is the resting potential more positive than predicted?membranes are not perfectly selective for K+ therefore have to take into account Na+ euilibrium portential due to slight permeance
- 6Describe a simplified G.H.S equation to account for slight Na+ permeanceRP= (log10[Kout] + PNa /Pk [Naout})/[Ki}
- 7What determines membrane potential?Permeability of the membrane to ions
- 8Why does permeability change during action potentials?- voltage sensitive ion channels opening and closing
- this allows ions down their electrochemical gradient
- causes opening of voltage gated ion channels - 9What is AP peak height dependent ondependent on ratio of Na[out] to Na[in]
- 10Describe the technique of voltage clamp- way of controlling membrane potential to allow measurement of the flow of charged ions through the membrane
- 11Explain how the voltage clamp technique is carried outtwo leads voltage command and Vm the feedback amplifier (FBA) compares the two and then injects current to minimise difference
- 12Why is voltage clamp useful?High resolution
Gives a direct measurement of membrane current - 13How can we measure the current caused by potassium using the voltage clamp technique?- selectively block Na+ channels with tetrodotoxin
remove ECF na+ ions
make Na[in] the same as Na[out] - 14How and why does Na+ current change?Decreases due to inactivation
- 15How does increasing the voltage command change the K+ and Na+ currents?Causes a increase in current causing quicker AP upstroke due to faster opening of Na+ channels
K+ channels are slower to activate and so at a low or negative membrane potential they take a long time to open - 16Why might we express Na and K mebrane currents as changes in Na and K conductance? Write the associated equationAllows you to see the gating states of each ion
GNa = INa/(Vm-ENa)
(Driving force) - 17What shapes AP'sThe voltage and time dependent alteration in Na and K conductance
- 18Why is Na+ conductance transientDue to repolarisation dependent inactivation
- 19Why is the patch clamp technique useful?-can look at the activity for a single ion channel
- can change ECF and ICF and record effect
- can measure Popen + single channel current, amplitude + G - 20Define the term stochastic behaviour and explain how it relates to ion channelscan't be predicted precisely but can be analysed statistically
determine the probability of the channel being open Popen
whole cell behaviour results from many channels opening and closing - 21How does prolonged depolarisation affect P(Na)P(Na) decreases with prolonged depolarisation due to Na+ channel inactivation
- 22Why does absolute refractory period occur?When there is insufficient Na+ current to induce an action potential
- 23How does prolonged depolarisation affect P(K)P(K) increases causing hyperpolarisation
- 24Describe the structure of K+ channels- 80-90 genes (diverse)
- 6 alpha helical tm segments
- protein units co-assemble
- s1-s4 voltage sensing domain
-p - loop selectivity
- s5 - s6 - pore forming domain
- inner cavity - K+ blockers bind - 25Describe the structure of Na+ cahnnels- large
-4 homologous repeat domains
- repeats each have 6 alpha transmembrane segments
- intracellular linker III - IV -> inactivation gate
1 - unit = channel - 26What is the result of mutations in ion channels?Neurological diseases
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- Physiology (Physiology of excitable cells) Flashcards on Ionic basis of neuronal action potentials, created by Charlotte Pedley on 15/10/2018.
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