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7.How do chemicals work in the brain?

The brain is a complex organ composed of gray matter and white matter. Gray matter consists of the cell bodies of neurons and other support cells, and the white matter consists of long tracts of axons that run between the neurons. Each area of the brain has a somewhat specific function.

For example, the motor cortex controls voluntary movements of the body, and the sensory cortex processes information to the senses. Different areas of the brain communicate with other areas nearby as well as more distantly. Information travels via the axons of the neurons within the white matter areas of the brain.

The brain contains billions of neurons, which interact with each other electrochemically. This means that when a nerve is stimulated, a series of chemical events occur that in turn create an electrical impulse. The resulting impulse propagates down the nerve length known as the axon and causes a release of chemicals called neurotransmitters into a space between the stimulated nerve and the nerve it wishes to communicate with, known as the synaptic cleft. The neurotransmitters interact with receptors on the second nerve, either stimulating them or inhibiting them.

The interaction between the neurotransmitters and receptors can be likened to a key interacting with a lock where the neurotransmitter or “key” engages the receptor or “lock,” causing it to “open.” This “opening” is really a series of chemical changes within the second nerve that either causes that nerve to “fire” or not “fire.” Thus brain activity is the result of an orchestrated series of nerves firing or not firing in binary fashion. In that sense it is much like a computer, where very complicated processes begin their lives as a series of 1s or 0s (on or off, fire or don’t fire).

After the nerve fires, releasing neurotransmitters into the synaptic cleft, the neurotransmitters must be removed from the area in order to turn the signal off. There are two ways these chemicals can be removed in order to turn the signal off. The first is by destroying the chemical through the use of another chemical known as an enzyme with that specific purpose in mind.

The second is by pumping the chemical back up into the nerve that released it by utilizing another special chemical known as a transporter or transport pump. The process of pumping chemicals back into the nerve is known as reuptake. It is important to understand these basic principles of neurophysiology because all psychoactive compounds, whether neurotransmitters, hormones, medications, or addictive drugs, involve one or more of these simple mechanisms.

Terms:

Gray matter - the part of the brain that contains the nerve cell bodies, including the cell nucleus and its metabolic machinery, as opposed to the axons, which are essentially the “transmission wires” of the nerve cell. The cerebral cortex contains gray matter.

White matter - tracts in the brain that consist of sheaths (called myelin) covering long nerve fibers.

Neuron - a nerve cell made up of a cell body with extensions called the dendrites and the axon. The dendrites carry messages from the synapse to the cell body, and the axon carries messages to the synapse to communicate with other nerve cells.

Axon - a single fiber of a nerve cell through which a message is sent via an electrical impulse to a receiving neuron. Each nerve cell has one axon.

Motor cortex - portion of the cerebral cortex that is directly related to voluntary movement. Also known as the motor strip, its anatomy correlates accurately with specific bodily movements, such as moving the left upper or lower extremities.

Electrochemically - the way in which signals are transmitted neurologically. Brain chemicals, or neurotransmitters, alter the electrical conductivity of nerve tissue, causing a signal to be transmitted.

Neurotransmitter - chemical in the brain that is released by nerve cells to send a message to other cells via the cell receptors.

Synaptic cleft - the junction between two neurons where neurotransmitters are released thereby continuing or changing communication

Receptor - a protein on a cell upon which specific chemicals from within the body or from the environment bind, in order to cause changes in the cell that result in an electrochemical message for a certain action to be taken by that cell.

Enzyme - a protein made in the body that breaks down or creates other molecules. Enzymes serve as catalysts to biochemical reactions in the body.

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