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40 Cards in this Set
- Front
- Back
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What factors establish a bioelectric potential?
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Uneven distribution of charge in a plasma membrane
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What ionic species create a bioelectric potential?
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Na + & Cl- outside of the cell, K+ inside
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Describe the role of the lipid bilayer in developing capacitance of the membrane
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the lipid bilayer is 2 layers of ampiphathic phospholiipds, unfavorable for ions to pass through, separating the charges contributes to the electrical potential difference
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How is conductance related to resistance?
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inversely proportional
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How do ion channels contribute to membrane resistance?
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ion channels allow for ions to flow across the membrane contributing to the potential difference
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Vm = ??
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Q/Cm (Stored charge/ membrane capacitance) & Im*Rm (current times resistance)
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What is the neornal membrane capacitance?
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.9 microF/cm2
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What does the NERNST equation predict?
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the resting membrane potential
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The neuronal Vm is slightly more ___polarized than the glial Vm because ______
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depolarized, permeable to both K+ AND Na+
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What are the components of the alpha subunit of the Na+K+ATPase pump?
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intracellular Na+ and ATP binding sites, phosphorylation site, extracellular K+ and cardiac glycoside inhibitor binding sites
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How much ATP does the Na+K+ATPase use?
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about 70%
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What ionic equilibrium potential most closely matches the neuronal resting membrane potential?
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Ecl-=-70mV
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What does the glial cell goldman equation reduce to?
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the NERNST equation
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What is the relative permeabilites in a neuron membrane?
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K:Na:CL --> 1.0:.04:.45
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What distinguishes excitable cells from nonexcitable?
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Na/KATP-ase activity and expression of voltage-gated ion channels
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Where is myelin made?
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in glial cells. In CNS: oligodendrocytes and in PNS: schwann cells
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What are the types of smooth muscle cells?
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visceral and multiunit
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What is a simplified method of measuring excitability of cells?
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current clamp
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What is the dependent variable in voltage clamp?
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current - voltage is independent
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what is the measured in current clamp?
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voltage, and current is indpendent
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What is the relationships of tau with temporal summation?
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The greater the tau, the more likely temporal summation will take place (and the threshold for action potential will be reached)
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Why doesn't the apex of Ca2+ influx into the cell reach the same level as Na+?
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1) Ca2+ channels have a higher activation threshold and less rapid inactivation than Na+ channels 2)Ca2+ activates voltage gated K+ channels, and the eflux of K+ opposes the influx of Ca+ and Na+
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What is the primary cellular element responsible for the ascending phase of the action potential?
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voltage gated Na+ channels
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what is saltator conduction
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action potentials jump are propagated down an axon by jumping from node of ranvier to node
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myelin increases membrane thickness and therefore ____ Cm and ____ conduction velocity?
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DECREASES Cm and INCREASES conduction Velocity
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What is the ratio of alpha to beta subunits?
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1:01
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What part of the alpha subunit make up the pore for Na+ channels?
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transmembrane segments 5 and 6 (S5 and S6) and their intervening extracellular loop
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Where is TTX sensitivity on voltage gated Na+ channels?
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glutamate residue at 287th position in the loop beween S5 and S6
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What amino acid change can produce a considerable increase in sensitivity to the TTX toxin?
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changing glutamate to cysteine at the 387th position
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What two critical amino acid residues play critical roles in the slectivity filter of ions at the mouth of the Na+ pore?
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lysine at position 1422 of repeat III and alanine at position 1712 at repeat IV
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What/where are the residues that inactivate voltage gated Na+ channels?
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isoleucine, phenylalanine and methionine at positions 1488-1490 of cytoplasmic loop connecting repeats III and IV
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What makes up the voltage-gated K+ channel pore?
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H5 loop lines the poor, S6 and cytoplasmic loop link S4 and S5
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What is voltage-gated K+ channel's selectivity attributed to?
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a consensus sequence within the H5 loop
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What determines voltage gated K+ channel activation?
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S4 segment's voltage sensing amphipathic alpha helix
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What are the subtypes of voltage gated Ca2+ channels?
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T, L, N, P, Q & R
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what type of Ca2+ channels are blocked by dihydropydridine drugs?
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L-Type
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What type of Ca2+ channel has a low threshold and high rate of inactivation?
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T-type (T=transient!)
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What type of Ca2+ channels are antagonzed by shell fish toxins (omega-conotoxins)?
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N-Type
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What type of Ca2+ channels are antagonized by spider toxins?
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P and Q-types
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What is the structure of voltage gated Ca2+ channels?
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5 subunits in equal parts: alpha 1, alpha 2, beta, gamma and delta
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