On Constructing a Reality - Understanding Understanding: Essays on Cybernetics and Cognition - page 221

FIGURE 13.
another simultaneously arriving pulse), in others a “facilitory effect”
(augmenting another pulse to fire the neuron). Consequently, the synaptic
gap can be seen as the “microenvironment” of a sensitive tip, the spine, and
with this interpretation in mind we may compare the sensitivity of the CNS
to changes of the internal environment (the sum total of all microenviron-
ments) to those of the external environment (all sensory receptors). Since
there are only 100 million sensory receptors, and about 10,000 billion
synapses in our nervous system, we are 100 thousand times more receptive
to changes in our internal than in our external environment.
The Cortex
In order that one may get at least some perspective on the organization of
the entire machinery that computes all perceptual, intellectual, and emo-
tional experiences, I have attached Figure 13, 7 which shows a magnified
section of about 2 square millimeters of a cat's cortex by a staining method
that stains only cell body and dendrites, and of those only 1% of all neurons
present. Although you have to imagine the many connections among these
neurons provided by the (invisible) axons, and a density of packing that is
100 times that shown, the computational power of even this very small part
of a brain may be sensed.
Descartes
This perspective is a far cry from that held, say, 300 years ago: 2
If the fire A is near the foot B [Fig. 14], the particles of this fire, which as you know
move with great rapidity, have the power to move the area of the skin of this foot