The central nervous system is the biggest cluster of neurons in the body. There’s a billion neurons in the spinal chord and 100 billion in the brain. For our size as a species that’s an incredible amount of neurons and we have consequently got huge heads. The electrical ouput of the brain is staggering and makes sense that humans were being used as batteries in the film The Matrix. Actually each neuron has an action potential of 70mV so if the whole brain fires up at once that’s potentially millions of Volts. However the brain doesn’t operate like that but has a patterned activity depending on our interactions at any one moment.
The receptive field of a sensory neuron is a region of space in which the presence of a stimulus will alter the firing of that neuron. Receptive fields have been identified for neurons of the auditory system, the the somatosenory system, and the visual system. The concept of receptive fields can be extended to further up the neural system; if many sensory receptors all form synapses with a single cell further up, they collectively form the receptive field of that cell. For example, the receptive field of a ganglion cell in the retina of the eye is composed of input from all of the photoreceptors which synapse with it, and a group of ganglion cells in turn forms the receptive field for a cell in the brain. This process is called convergence and brings a whole array of neurons into relationship with a single neuron and back out to the array that is connected with that neuron. You can imagine multiplying this by millions to reveal the nature of the nervous system and how we can move from a relationship of the many to the one and back i.e. have a focal point in relationship to the environment.