24 : 4/ The Molecular Basis of Nerve Conduction 



447 



polarized. However, no current flows from b, c y and d to the external 

 circuit. Hence, these electrodes will not be polarized and can be used 

 for potential measurements. 



Plastic Partition 



Outer (d) and Inner (c) 

 Cylinder Electrodes 



Axon 



Cylinder Electrode e 



Rod Electrodes within Axon 

 (a) 



_b Axon 



T 



Vaseline Seal 

 Plastic Partition 



(b) 



Axon 

 Membrane 



Figu re 5. (a) Pictorial sketch of electrodes used in voltage clamp 

 experiments. The hollow cylinder electrode e is filled with 

 saline or other solution. Electrodes a and b are actually wires 

 wrapped around a glass cylinder; the wires are insulated except 

 in the region shown as electrodes in the sketch, (b) Schematic 

 arrangement of electrodes used in voltage clamp experiments. 

 The electrodes a, b, c, d, and e are all metallic. The axon is 

 sealed to the plastic insulators with vaseline. Current flows 

 from electrode a to electrode e ; potential and current measure- 

 ments are made only between the two central insulators to 

 eliminate end effects. The electrode and insulator sizes are not 

 to scale. After A. L. Hodgkin, A. F. Huxley, and B. Katz, 

 " Current- Voltage Relation in Nerve," J. Physiol. 116: 424 

 (1952). 



This experimental arrangement is useful for voltage clamp studies. 

 It also can be used to follow both the current and the potential changes, 

 if a pulse stimulus is applied. The simplest experiment of this type was 

 to apply a pulse of current between electrodes a and e and record the 



