PHYSICAL CHARACTERISTICS OF THE ACTION POTENTIAL 219 



Physical Characteristics of the Action Potential 



The present evidence supports the hypothesis that the electric response 

 is a true indication of the normal activity of the nerve and that it is not 

 an artificial effect due to the type of stimulus employed. The energy 

 manifesting itself as the nerve pulse is not obtained from the artificial 

 stimulus. This stimulus only appears to upset an equilibrated electro- 

 chemical boundary condition, which may take the form of a destruction 

 of a polarized electrical double layer and a subsequent slower repolariza- 

 tion at the expense of osmotic and chemical actions. 



40 - 



30 



= 20 



10 



t 0.2 



0.4 0.6 



Time <r=l/l000sec 



0.8 a 



Fig. VI-8. Monophasic action potential plotted to scale. In large myelinated 

 mammalian nerve fibers the phenomenon (spike) lasts about 0.4 millisecond. One 

 third of the time is taken up by the phase of development, i.e., the rising phase of this 



curve. 



If the electrical impulse is amplified and an inertialess recording instru- 

 ment, in the form of a cathode-ray oscillograph, is used to record the 

 nerve impulses, important details of nerve transmission can be observed. 



In Fig. VI-8 is shown a monophasic action potential to scale. The 

 original 40-millivolt pulse was amplified 8000 times with a 3-stage volt- 

 age amplifier, and the amplified potential changes were recorded with a 

 cathode-ray oscillograph. The electric pulse is shown moving from 

 right to left with the time recorded in milliseconds. 



It will be noticed that the start of the activity, the foot of the rising 

 phase, is not sudden or explosive. The gradual increase at the beginning 

 of the rising phase of the curve may be attributed to the fact that the 

 pick-up electrode is of finite width, so that the pulse may be considered 

 as starting at t . The subsequent rapidly rising phase of the action 



