Basic Neurophysiology

Basic Neurophysiology

The brain is made up of neurons, together with a range of non-nervous cells that act in support of neurons and help to maintain their survival. One of the unique properties of the living neuron is its capacity to transmit information. It does this by “firing”. This term denotes the fact that every cell periodically transmits small quantities of neurotransmitter to its neighboring neurons. All cells in the body absorb a and expel molecules. Neurons do this in a special way. Neurotransmitter molecules are expelled from the end of the axon of the neuron, into the small space separating it from the next cell, the synapse. The neurotransmitter substance is then taken up by receptors on the dendrites of neurons on the other side of the synapse. This affects the second set of neurons by increasing or decreasing the chances that they will fire. Thus, neurons are in constant communication with each other through neurotransmitters. The communication is constant. Neurons always have a base (“resting”) rate of firing; even when they are not specifically stimulated by other neurons, the fire at regular intervals. However, the action of other neurons via their neurotransmitters, modifies the base firing rate - making each neuron fire more, or less, frequently than its resting rate.

There are two general types of neurotransmitter: excitatory and inhibitory. The excitatory type (the most common) increases firing rates – or, more precisely, it increases the chances that the next neuron will fire. In increases the chances of it firing, because we are actually dealing with aggregates of large numbers of neurons firing in concert. Each neuron is influenced (via multiple neurotransmitters acting at multiple synopses) by dozens, even hundreds of thousands, of other neurons. Thus, the reception of an excitatory neurotransmitter increases the chances of the neuron firing. Similarly, an inhibitory neurotransmitter decreases the chances of that neuron firing. Because we are dealing with aggregates of neurons, it is the overall “average” outcome that will determine whether the neuron fires or not, or rather the rate at which it fires. To take a crude example, if 60% of a neuron's inputs are exciting it and 40% of them are inhibiting it, it is going to fire, but at a level not much above its base rate. If 90% are exciting it and 10% are inhibiting it, it is going to fire at a much faster rate. The complete mechanism of neurotransmission is more complex. For example, neurons are equipped with different synaptic receptors that receive, or “recognize,” different neurotransmitters – but this preliminary account conveys the essentials in sufficient detail for the purposes of this text.

So that is how neurons work. Again, it is worth noting that there is nothing mystical about these processes that “produce” the mind. They are just ordinary cellular processes. How they produce our beloved selves, with all the richness of our inner life, must involve something more than the simple facts of neurotransmission.

The Brain and the Inner World, Introduction to Basic Concepts. Mark Solms, Oliver Turnbull.

Where there is controversy, neuro-scientists can devise and execute critical experiments to test who is right and who is wrong. Typically (after some debate about whether the experiment was the correct test or not!), the losing side agrees that they were wrong. Illustration by Elena.