On Constructing a Reality - Understanding Understanding: Essays on Cybernetics and Cognition - page 219

FIGURE 10.
The Neuron
The neuron, of which we have more than 10 billion in our brain, is a highly
specialized single cell with three anatomically distinct features (Fig. 10): (1)
the branch-like ramifications stretching up and to the side, the “dendrites”;
(2) the bulb in the center housing the cell's nucleus, the “cell body”; and
(3), the “axon,” the smooth fiber stretching downward. Its various bifurca-
tions terminate on dendrites of another (but sometimes—recursively—on
the same) neuron. The same membrane that envelops the cell body forms
also the tubular sheath for dendrites and axon, and causes the inside of the
cell to be electrically charged against the outside with about 1 / 10 of a volt.
If in the dendritic region this charge is sufficiently perturbed, the neuron
“fires” and sends this perturbation along its axon to its termination, the
synapses.
Transmission
Since these perturbations are electrical, they can be picked up by “micro-
probes,” amplified and recorded. Figure 11 shows three examples of
periodic discharges from a touch receptor under continuous stimulation,
the low frequency corresponding to a weak stimulus, the high frequency
to a strong stimulus. The magnitude of the discharge is clearly everywhere
the same, the pulse frequency representing the stimulus intensity, but the
intensity only.