NROB60 Questions and Correct AnswNROB60 Questions and Correct Answers | Latest Updateers | Latest Update
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Course
NROB60
Institution
NROB60
Action Potential
Dramatic redistribution of electrical charge across membrane. Rapid
reversal of charge across membrane such that the interior becomes
relatively positive (depolarization caused by influx of sodium)
How to determine MP
Microelectrode in cell, voltmetre used to measure...
hyperpolarization, restoration of resting potential
Length of Action Potential
~2msec
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Rising Phase
Rapid depolarization of membrane until ~40mV; Na+ rush into cell
through open Na channels
Overshoot
Section of AP where inside positively charged wrt outside; MP goes to
value close to ENa+ (greater than 0) because relative permeability of
membrane greatly favours sodium
Falling Phase
rapid repolarization (efflux of potassium) until membrane more negative
than resting potential (undershoot); result of Na+ channel inactivation, K+
channels opening, K+efflux.
Perception of Sharp Pain (thumbtack)
1. Thumbtack enters skin
2. Membrane of nerve fibres in skin stretched
3. Na+ permeable channels open, Na+ ions enter nerve fibre down [gradient]
4.entry of Na+ depolarizes membrane; depolarization reaches threshold potential; ACTION
POTENTIAL!
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"all or none"
Increasing depolarization has no effect until crossing threshold
Multiple Action Potentials: Rate and Frequency
Rate depends on magnitude of continuous depolarization
Frequency reflects magnitude of depolarization current (max: 1000Hz)
Absolute Refractory Period
~1msec; impossible to initiate another AP; Na Channels must be de -
inactivated by sufficiently negative MP
Relative Refractory Period
several msec; relatively difficult- amount of current required for
depolarization to threshold elevated (result of
hyperpolarization/undershoot)
Intracellular Recording
impale neuron w microelectrode; challenging (SIZE); goal is to measure
potential difference between intracellular electrode and grounded
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electrode; I. Electrode filled w concentrated KCl; potenti al difference
between electrode and ground displayed w oscilloscope
Extracellular Recording
Detecting sequence of ionic movements across neuronal membrane by
placing electrode near membrane; when AP arrives at recording position,
+ve charges flow away from recording electrode into neuron; as AP passes
by, +ve charges flow out across membrane towards recording electrode;
EC AP characterized by brief, alternating voltage difference between
recording electrode and ground. Voltage changes seen w oscillos cope,
heard by connecting output to loudspeaker (Popping sound)
Concentration Gradients
Na-K pumps continuous work to establish and maintain concentration
gradients; K+ efflux until inside -ve and Vm=Ek. Net movement of K+ is
electrical current (Ik); # K+ channels open proportional to electrical
conductance (gk)
Ik=gk(Vm-Ek)
Ideal Neuron
Only permeable to K+; Vm=Ek=-80mV
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