A Micro View Of The Brain - How The Brain Works: Stroke

Content provided by the Faculty of the Harvard Medical School

A micro view of the brain

The brain consists of about 100 billion neurons, specialized nerve cells that communicate with one another using chemical and electrical signals. Each neuron has a body that contains a nucleus, a long fiber called an axon, and many shorter branching fibers called dendrites. Neurons talk with one another across microscopic gaps called synapses. When a cell body or dendrite receives a message from a neighboring neuron, an electrical impulse is generated. This signal travels the length of the neuron to the end of the axon, where it prompts the cell to release a chemical messenger called a neurotransmitter into the synapse. Certain neurotransmitters pass on messages by creating an electrical impulse in the receiving cell, and the process of electrical-to-chemical signaling is repeated. Other neurotransmitters suppress the transmission of signals to neighboring neurons (see Figure 2).

Figure 2: How brain cells communicate Brain cells (neurons) communicate with each other by generating an electrical impulse that travels down an arm called an axon. Chemicals called neurotransmitters (see inset) cross the space (synapse) between neurons to deliver messages by activating receptors on a neighboring neuron.

The connections between neurons are where the brain's work is done. This is where thinking and feeling take place and all the basic processes of human life, including movement and breathing, are controlled. In the early stages of development, the brain is highly flexible: Damage to a specific area can often be repaired because existing neurons can form new connections with other nerve cells. By the end of childhood, however, the brain loses much of this reparative power. While the adult brain can rewire itself to some degree, most of the neurons that die cannot be replaced. Unlike the heart, which can still support a marathon runner after losing 10% of its tissue, a 10% loss in the adult brain can result in devastating disability.

Last updated:	September 05, 2008