Building Blocks of the Brain
The fundamental building block of the human brain, like that of nervous systems throughout the animal kingdom, is the neuron or nerve cell. Neurons are cells with unique characteristics. The neuron conducts signals by means of an axon, a long fiber which extends out from the cell body like a single long arm. Axons may reach a short distance, a few millimeters, or longer distances, stretching across the brain or even from the spinal cord all the way down the leg to the foot. Most neurons' axons are sheathed in myelin, a fatty substance operating as an insulator that helps speed signals along. Numerous shorter arms called dendrites ("little branches") conduct signals back to the cell body. They serve as the receiving area. The site of communication between any two neurons is not direct, with one neuron touching another. Instead there is a small space between the cells called a cleft across which signals are transmitted. 10
Because neurons do not touch one another, the signal has to leap from one to the next in a connection called a synapse. A neuron could receive signals from one other neuron or it could be connecting with literally thousands of other neurons along an almost endless number of pathways.
The process of information transfer between neurons, which occurs at the synapse, is both electrical and chemical. A small electrical charge travels the length of the transmitting neuron until it arrives at the synaptic space. A neurotransmitter, a messenger chemical, is released, travels across the synaptic space, and activates or turns on a receiving neuron. This begins another electrical charge that becomes a chemical charge and the process continues, electrical to chemical, until the signal reaches its destination.
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In addition, the development of the brain allows room for shaping by the environment. The two forces, genetic and environmental (nature and nurture), include everything from nutrition and the family setting to incidence of disease. This makes each of our brains both unique and similar at the same time.
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