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Modeling Biological Membranes with Circuit Boards and Measuring Electrical Signals in Axons: Student Laboratory Exercises
Published on: January 18, 2011
ELECTRIC IMPEDANCE OF THE SQUID GIANT AXON DURING ACTIVITY
1Department of Physiology, College of Physicians and Surgeons, Columbia University, New York, and the Marine Biological Laboratory, Woods Hole.
The Journal of General Physiology
|October 30, 2009
Summary
This study on squid giant axons reveals that nerve impulse transmission involves a significant, temporary decrease in membrane conductance. This finding is crucial for understanding the all-or-none law and nerve impulse propagation.
Area of Science:
- Neuroscience
- Biophysics
- Cellular Electrophysiology
Background:
- Nerve impulse propagation relies on changes in axonal membrane properties.
- Understanding these dynamic changes is key to explaining neuronal excitability and signaling.
Purpose of the Study:
- To investigate the electrical properties of the squid giant axon membrane during nerve impulse transmission.
- To quantify changes in membrane impedance, conductance, and capacity during an action potential.
Main Methods:
- Alternating current impedance measurements across a wide frequency range.
- Utilized a Wheatstone bridge with an amplifier and cathode ray oscillograph for precise detection.
- Stimulated the squid giant axon (Loligo pealii) and recorded impedance changes during impulse passage.
Main Results:
- Membrane phase angle remained unchanged during impulse.
- Membrane capacity decreased by approximately 2%.
- Membrane conductance dramatically decreased from 1000 ohm cm.(2) to 25 ohm cm.(2) during the impulse.
Conclusions:
- The observed decrease in membrane conductance is closely linked to changes in membrane electromotive force.
- These dynamic electrical changes are fundamental to the all-or-none law and nerve impulse initiation/propagation.
- Findings suggest similar electrical phenomena occur in other nerve fibers.
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