340

24

The Nervous System

Fig. 24.1 A uniform directive correlation (Chap. 3) with focal condition FC involving four mus-

cles whose state (of excitation or inhibition) is denoted ee (see text for further explanation) (after

Sommerhoff 1950; reproduced by permission of Oxford University Press [Fig. 8, p. 121])

Fig. 24.2 The same scheme as in Fig. 24.1 except that the nerve connexions have been centralized

(within the circle), showing the great economy in the overall length of the communication channels

(see text for further explanation) (after Sommerhoff 1950; reproduced by permission of Oxford

University Press [Fig. 9, p. 131]))

centre and only the fourfold afferent and fourfold efferent connectivities are required

without. This is a way to achieve the greatest possible economy with respect to the

length of the required communication channels.

24.1

The Neuron and Neural Networks

The neuron (nerve cell) is the fundamental elementary unit of the brain. It consists

of a central body (the soma) with a single long and slender process growing out

from it—the axon, which may, however, have many branches (collaterals). Axons

impinge on receptive processes (dendrites) of other neurons or on the soma itself, the

points of impingement being called synapses, which may be excitatory or inhibitory.