Why did Hodgkin and Huxley want to measure current instead of voltage? How does
ID: 204990 • Letter: W
Question
Why did Hodgkin and Huxley want to measure current instead of voltage? How does the voltage clamp technique work? Why is it important?
What types of current did Hodgkin and Huxley observe when the membrane was depolarized? What does the sign of the current mean?
How do the early and late currents vary over time?
How do the early and late currents vary depending on the membrane potential? Why do they vary in this way?
What experiments reveal which ions mediate the early vs. late current?
How did Hodgkin and Huxley calculate the conductance of each ion at each time?
During a voltage clamp experiment, why does the measured current for a given ion depend on both the ion conductance and the membrane potential?
How do Na+ and K+ conductance vary with depolarization and time? How do these changes explain the action potential?
Why is there a threshold for the action potential?
What does the threshold represent?
Why do action potentials have a refractory period?
Why does action potential conduction along an axon involve both passive and active flow?
Why do action potentials normally propagate in only one direction?
How does myelin increase the rate of action potential conduction?
Explanation / Answer
Why did Hodgkin and Huxley want to measure current instead of voltage?
Parent Method of voltage clamp as invented by KC Cole(later adapted by Hodgkin and Huxely), the objective was always to keep voltage constant. For this one electrode was use to measure voltage and other was use to pass the current, positive or negative, to stop the voltage to change.So the current that has been recorded was feedback current. its the feedback current to stop the cell's inward cation currents from changing the membrane potential.
How does the voltage clamp technique work?
The voltage clamp is an experimental method used by electrophysiologists to measure the ion currents through the membranes of excitable cells, such as neurons, while holding the membrane voltage at a set level. It is nothing but current generator, operates by negative feedback system.It has a voltage electrode which measures transmembrane potential and a current electrode, which passes current into cell. A holding voltage is set and negative feedback is use to maintain the cell at this voltage. The electrodes are connected to an amplifier, which measures membrane potential and feeds the signal into a feedback amplifier. This amplifier also gets an input from the signal generator that determines the command potential, and it subtracts the membrane potential from the command potential (Vcommand – Vm), magnifies any difference, and sends an output to the current electrode. Thus, the clamp circuit produces a current equal and opposite to the ionic current.
Why is it important?
The voltage-clamp allowed to record, directly, the ionic currents flowing across the axonal membrane of the giant axon without any resultant change in membrane potential. The voltage-clamp also removed the problems of capacitance and created an isopotential membrane
What types of current did Hodgkin and Huxley observe when the membrane was depolarized?
Two types of voltage dependent ionic current, outward current and inward current.
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