All brain cells are not alike. There are as many as 10,000 specific types of neurons in the brain.
The core component of the nervous system in general, and the brain in particular, is the neuron or nerve cell, the "brain cells" of popular language. A neuron is an electrically excitable cell that processes and transmits information by electrochemical signaling. Unlike other cells, neurons never divide, and neither do they die off to be replaced by new ones. By the same token, they usually cannot be replaced after being lost, although there are a few exceptions.
The average human brain has about 86 billion neurons (or nerve cells) and many more neuroglia (or glial cells) which serve to support and protect the neurons (although see the end of this page for more information on glial cells). Each neuron may be connected to up to 10,000 other neurons, passing signals to each other via as many as 1,000 trillion synaptic connections, equivalent by some estimates to a computer with a 1 trillion bit per second processor. Estimates of the human brain's memory capacity vary wildly from 1 to 1,000 terabytes (for comparison, the 19 million volumes in the US Library of Congress represents about 10 terabytes of data).