neuronal interconnections

The neuron is the basic operating unit of the central nervous system. Inter-neuronal information processing, involving complex neural networks, provides the nervous system with its enormous functional capacity. The human brain contains about 10^(11) neurons*, which connect, via synapses, with an average of 1000 other neurons. In total, the human brain may contain somewhere between 10^(14) and 10^(15) synaptic connections. Neurotransmitter chemicals effect the connection between neurons, when they cross the gap between neurons and interact with specific receptor proteins. More than one hundred chemicals and a much larger number of receptors have been implicated in synaptic transmission. Some neurotransmitters are the targets of drug therapies. Receptor molecules are the targets of neurotoxic venomous substances.* 10^(11) is equivalent to a 10 followed by 11 zeros = 1,000,000,000,000

Depolarization of neuronal cell membranes beyond a necessary threshold results in action potentials which propagate along the soma/axon/dendrite to the pre-synaptic terminal bulb. At the pre-synaptic terminal, the wave of depolarization results in release of vesicle-stored neurotransmitters into the synaptic cleft. Released neurotransmitters bind to specific post-synaptic receptors that open ion channels, resulting in further depolarization and post-synaptic action potentials.