The Brain as Computer: Bad at Math, Good at Everything Else
Like all the cells in the human body, a neuron normally has an electric potential of about –70 millivolts between its interior and exterior. This membrane voltage changes when a neuron receives signals from other neurons connected to it. And if the membrane voltage rises to a critical threshold, it forms a voltage pulse, or spike, with a duration of a few milliseconds and a value of about 40 mV. This spike propagates along the neuron’s axon until it reaches a synapse, the complex biochemical structure that connects the axon of one neuron to a dendrite of another. If the spike meets certain criteria, the synapse transforms it into another voltage pulse that travels down the branching dendrite structure of the receiving neuron and contributes either positively or negatively to its cell membrane voltage.