.Nerve, muscle, and certain other cell types such as the
  islet cells of the pancreas of vertebrates exhibit a special
  property called electrical excitability.As the action potential passes the recording electrode, the voltmeter or oscilloscope will
  display a characteristic pattern of membrane potential
  changes.An electrode
  called the stimulating electrode is connected to a power
  source and inserted into the axon some distance from the recording electrode (see Figure 13-3b).Alan Hodgkin and Andrew Huxley used micro electrodes and the squid giant axon to learn how action
  potentials are generated; for their work, they received a
  share of the Nobel Prize in 1963.A brief impulse
  from this stimulating electrode depolarizes the membrane
  by about 20 mV (i.e., from -60 to about -40 mV), bringing the neuron beyond the threshold potential.To understand how
  nerve cells use action potentials to transmit signals, we
  must first examine how cells generate a resting membrane
  potential and how the membrane potential changes during an action potential.This
  triggers an action potential that propagates away from the
  stimulating electrode.