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45 Cards in this Set
- Front
- Back
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Define diffusion potential.
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Potential difference across a membrane due to a difference in ion concentration.
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What determines the size of the diffusion potential?
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Size of the concentration gradient.
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Can a diffusion potential be generated if the membrane is not permeable to the ion?
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No!
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What determines the sign of the diffusion potential?
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Charge of the diffusing ion.
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Creation of the diffusion potential requires the movement of a significant number of ions. TRUE/FALSE
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TRUE
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What facilitates the movement of ions across the membrane?
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Ion channels
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What does the conductance of an ion channel depend on?
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Probability that the channel is open.
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What controls the opening and closing of ion channels?
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Gates
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What types of gates are there?
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Voltage and ligand
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What controls the opening and closing of voltage gated channels?
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Hormones
second messengers neurotransmitters |
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Define equilibrium potential.
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Diffusion potential that exactly opposes diffusion caused by concentration difference.
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What is it called when the electrical and chemical driving forces of an ion are equally opposed?
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Electrochemical equilibrium
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What equation is used to calculate equilibrium potentials?
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Nernst equation
E= -2.3 RT log10[C1] _____________ zF [Ce] |
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What are the approximate values of the equilibrium potential for the following ions in nerves and muscles;
Na+ K+ Ca2+ Cl- |
Na+ - +65mV
K+- -85mV Ca+2 -+120mV Cl- -85mV |
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What is the resting membrane potential?
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Sum of the diffusion potentials due to the concentration differences
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Define depolarization.
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membrane potential becomes less negative(i.e., -60-- -40)
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Define hyperpolarization.
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Membrane potential becomes more negative(i.e., -60-- -90)
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What is a cell called if it is capable of producing an action potential?
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Excitable
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What do action potentials consist of?
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Rapid depolarization and repolarization
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What are the unique characteristics of action potentials?
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Stereotypical size and shape
propagation all or none events |
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What is the point after which an action potential is inevitable?
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Threshold
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What does inward or outward current charge refer to?
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Movement of positive charge into(inward) and out of (outward) the cell.
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What is the resting membrane potential for nerve cells?
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-70mV
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What ion is primarily responsible for the resting membrane potential of nerve cells?
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K+
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What signals the activation gates of the Na+ channels?
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Depolarization of the cell membrane
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What ion is responsible for the upstroke of the action potential in nerve cells?
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Na+
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Define overshoot.
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Peak of the action potential at which the membrane potential is positive.
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What signals the inactivation gates of the Na+ channels?
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Depolarization of the cell membrane.
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How can depolarization cause both activation and deactivation of Na+ channel gates?
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Inactivation occurs more slowly than activation.
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What causes repolarization of the cell membrane?
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Closure of Na+ channels and opening of K+ channels.
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What signals the opening of K+ channels?
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Depolarization of the cell membrane
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In what direction do K+ ions move during repolarization?
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Out of the cell(outward current)
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What is hyperpolarization of the afterpotential called?
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Undershoot
K+ channels stay open after the Na+ channels close |
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What types of refractory periods are there?
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Absolute
Relative |
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In what type of refractory can an action potential not be elicited?
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Absolute refractory period.
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With what does the duration of the absolute refractory period coincide?
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Nearly the entire length of the action potential.
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What produces the absolute refractory period?
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While the inactivation gates of the Na+ channels are closed, no action potential can be produced.
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How can an action potential be elicited during the relative refractory period?
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With a larger than usual stimulus to produce a larger inward current.
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What is the duration of the relative refractory period?
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Starts at the end of the absolute refractory period and lasts until the resting membrane potential is reached.
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Define accommodation.
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Cell membrane is held at a depolarization level above threshold, but no action potentials are generated.
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How do action potentials propagate?
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By spread of local currents to adjacent areas.
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How can conduction velocity be increasd?
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Increased fiber diameter and myelination.
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What type of conduction do myelinated axons demonstarte?
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Saltatory
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What type of a substance is myelin?
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Insulating
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Where are action potentials generated in myelinated axons/
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Nodes of Ranvier
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