Because each nerve and each root and branch (dendrites and axons) can participate in numerous different pathways, the number of possible pathways through the net is unimaginably vast: more pathways than there are atoms in the universe!

Every junction between a nerve branch (axon) and a root (dendrite) is a complex chemical soup (synapse) which carries or blocks the signal from a branch of one nerve on up to the root of another. If enough of its roots are receiving input, a threshold is crossed, and an electrotonicic pulse passes up the trunk of the nerve to ALL its branches, which connect to the roots of other nerves. Each nerve receives signals through its roots from numerous other nerves, 'polls' them, and passes on a signal to numerous further nerves' roots, or blocks the signal if insufficient of its roots are receiving input. Thus the whole system continuously processes the flow of input.

An afferent (incoming) signal starting at a fingertip will travel along a nerve till it reaches (say) the knuckle. There it may jump the gap ƒ the synapse ƒ to a root of a new nerve, combine with a signal from another finger (say), which has similarly jumped another synapse to another root of the new nerve. The combination will trigger a pulse in the new nerve's trunk, which will take the signal as far (say) as the wrist. There it will cross other synapses to trigger other nerves which will take the signal on up to the elbow.

Eventually, passing up the chain, it will reach the brain, where it will be processed (combined and compared with other current and previous input and amplified or attenuated) eventually to emerge as a pattern of efferent (out-going) signals which passes down another chain of nerves to trigger various muscular contractions in the neck and eye which will move the head and focus the eyes upon the fingers.

Every synaptic junction between a nerve branch (axon) and another nerve's root (dendrite) transmits or blocks the signal depending on the concentration of the neuro-transmitters, which are degraded by the act of transmission: the synapse will transmit a specific limited number of signals before it is 'worn out' ƒ the chemical neuro-transmitters in the soup have broken down ƒ and there follows a refractory period while the synapse recovers, when the signals are blocked.

After 'resting', the neuro-transmitters re-combine and the synapse will again transmit a certain number of signals before needing another refractory period.

Thus the synapse is constantly in a delicate and dynamic state of balance between assembly and dissolution of the neuro-transmitters.

Narcotics (ethanol, nicotine, heroin, cocaine) shift the balance towards breakdown of the neuro-transmitters so that fewer signals jump across from nerve to nerve, while psychedelics (cannabis, mushrooms, LSD) shift the balance towards assembly of the transmitting substances, so that more signals pass.