Unlike many cells in the body, which are relatively short-lived, neurons have evolved to live a long time-more than 100 years in humans. The brain has one of the richest blood supplies of any organ and consumes up to 20 percent of the energy used by the human body-more than any other organ. To perform this function, cells require energy in the form of oxygen and glucose, which are supplied by blood circulating through the brain. Metabolism-the breaking down of chemicals and nutrients within a cell-is critical to healthy cell function and survival. In fact, scientists estimate that in the brain’s communications network, one neuron may have as many as 7,000 synaptic connections with other neurons. Communication often occurs across networks of brain cells.
This process triggers chemical or electrical signals that either stimulate or inhibit activity in the neuron receiving the signal. Like a key fitting into a lock, each neurotransmitter molecule then binds to specific receptor sites on a dendrite of a nearby neuron. When a neuron receives signals from other neurons, it generates an electrical charge that travels down the length of its axon and releases neurotransmitter chemicals across a tiny gap, called a synapse. Neurons are constantly in touch with neighboring brain cells. The function and survival of neurons depend on several key biological processes:
The healthy human brain contains tens of billions of neurons-specialized cells that process and transmit information via electrical and chemical signals.
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