The BrainMarijuana, Cocaine, And The Opiates Part 1Brain Regions And Neuronal PathwaysCertain parts of the brain govern specific functions. Nerve cells or neurons travel from one area to another via pathways to send and integrate information. The reward pathway gets activated when a person receives positive reinforcement for certain behaviors (rewards). This happens when a person takes an addictive drug. Neuronal StructurePathways are made up of neurons. A neuron is real - as viewed through a microscope. The normal direction of impulse flow, is when dendrites and soma receive chemical information from neighboring neuronal axons. This chemical information is converted to electrical currents which travel toward and converge on the soma. A major impulse is produced (the action potential) and travels down the axon toward the terminal.
 A Picture Of The Brains Neuronal Structure The Synapse And Synaptic NeurotransmissionVesicles containing a neurotransmitter, such as dopamine, move toward the presynaptic membrane as an electrical impulse arrives at the terminal. The process of dopamine release (vesicles fuse with the presynaptic membrane), happens as follows. Once inside the synaptic cleft, the dopamine can bind to specific proteins called dopamine receptors (in blue) on the membrane of a neighboring neuron. Occupation of receptors by neurotransmitters causes various actions in the cell; activation or inhibition of enzymes, entry or exit of certain ions.
 A Picture Of The Synapse And Synaptic Neurotransmission Dopamine NeurotransmissionDopamine is synthesized in the nerve terminal and packaged in vesicles. The vesicle fuses with the membrane and releases dopamine. The dopamine molecules can then bind to a dopamine receptor. After the dopamine binds, it comes off the receptor and is removed from the synaptic cleft by uptake pumps (also proteins) that reside on the terminal. This process is important so that not too much dopamine is left in the synaptic cleft at any one time. There is a neighboring neuron, which releases another compound called a neuromodulator. In this case it is an endorphin. Endorphins bind to opiate receptors which reside on the post-synaptic cell or in some cases on the terminals of other neurons. The endorphins are destroyed by enzymes rather than removed by uptake pumps.
 A Picture Of Dopamine Neurotransmission Dopamine And The Production Of Cyclic AMPWhen dopamine binds to its receptor, another protein called a G-protein moves up close to the dopamine receptor. The G-protein signals an enzyme to produce cyclic adenosine monophosphate (cAMP) molecules inside the cell. Sometimes the signal can decrease production of cAMP, depending on the kind of dopamine receptor and G-protein present. The dopamine receptor-G-protein/adenylate cyclase complex is generated when dopamine binds to its receptor. cAMP controls many important functions in the cell including the ability of the cell to generate electrical impulses. Books Buzzed: |