Natural Pathways in the Brain
In the brain, networks of neurons form, each with an axon, dendrites, soma, myelin sheath, nodes of ranvier, synaptic cleft, and an axon hillock. They send chemical and electrical signals to control sensory feelings and motor functions. For example, the reward pathway uses signals from sensory neurons so you are rewarded for advantageous behavior like eating, drinking, and reproduction. It creates this feeling so you are more likely to complete this action again.
These neurons communicate through the synapse. The small area between the sending neuron and the receiving neuron is known as the synaptic cleft. At the end of the sending neuron are vesicles, small packets that hold together neurotransmitters. In the reward pathway, the neurotransmitter of choice is dopamine. Once an axon reaches its action potential, it lets in Ca++ ions, which triggers the vesicles to release. They spill into the synaptic gap, and make their way into the dopamine receptors at the end of the receiving neuron. The dopamine receptors trigger a second messenger to be created, which then triggers a nerve impulse that releases any neurotransmitter of the axon of the receiving cell. The receiving cell then becomes the sending cell and the process repeats.
However, glial cells also function to assist the neurons. There are three main types of glial cells: oligodendrocytes, microglia, and astrocytes. Oligodendrocytes form the myelin sheath, speeding up chemical impulses during action potential while protecting the axon, too. They are made of lipids, or fats. Microglia defend the neurons, chomping up any invading bacteria. Astrocytes are the arguably the most important and mysterious of all glia, that keep the structural integrity of the neuron, while feeding it nutrients and eating any unneeded neurons. Also, they regulate blood flow with "end feet" on blood vessels. But above all, they can create and modify transmission. These are known as "gliotransmitters". Scientists are confused on the process, but the astrocytes are extremely involved with Alzheimer's, ALS, and AIDS.
Drugs Alter the Brain's Reward Pathway
How drugs work
All drugs either inhibit or excite the release of neurotransmitters and their associated processes. These include alcohol, anabolic steroids, cocaine, dissociative drugs, GHB, Rohypnol, hallucinogens, heroin, inhalants, marijuana, MDMA, methamphetamine, and nicotine. Drugs emphatically change the way the brain works quickly. For example, methamphetamine triggers the quick release of dopamine into the synapse throughout the reward system, causing addiction due to the reward of having something that chemically makes you happy. Also, the quicker the drug causes a high, the more addictive it is.
What drugs do to you
Drugs truly rewire the brain. Even a one-time abuser will have decreased brain activity due to the extreme releases of dopamine. Because of this, the brain tries to compensate for large release, so the brain needs even more the next time to get high. All of the brain is affected by drugs, even the decision making, judgement, memory and movement parts. Another consequence of this rewiring is the subconscious seeking for drugs.
Also, immense health effects are incurred. Heroin and alcohol both cause constriction of the airways, which can easily lead to death, especially when combined. Heroin constricts the airways by increasing levels of the inhibitory GABA, while alcohol decreases the excitatory glutamate to constrict the airways. Alcohol can also cause unconsciousness and vomiting. All stimulants can cause heart attacks, overheating, and brain damage due to popped blood vessels. All smoking can cause lung cancer, throat cancer, esophageal cancer, and strokes.
