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  • Addiction is a neurological disorder that affects the reward system in the brain. In

  • a healthy person, the reward system reinforces important behaviors that are essential for

  • survival such as eating, drinking, sex, and social interaction. For example, the reward

  • system ensures that you reach for food when you are hungry, because you know that after

  • eating you will feel good. In other words, it makes the activity of eating pleasurable

  • and memorable, so you would want to do it again and again whenever you feel hungry.

  • Drugs of abuse hijack this system, turning the person’s natural needs into drug needs.

  • The brain consists of billions of neurons, or nerve cells, which communicate via chemical

  • messages, or neurotransmitters. When a neuron is sufficiently stimulated, an electrical

  • impulse called an action potential is generated and travels down the axon to the nerve terminal.

  • Here, it triggers the release of a neurotransmitter into the synaptic cleft - a space between

  • neurons. The neurotransmitter then binds to a receptor on a neighboring neuron, generating

  • a signal in it, thereby transmitting the information to that neuron.

  • The major reward pathways involve transmission of the neurotransmitter dopamine from the

  • ventral tegmental areathe VTA - of the midbrain to the limbic system and the frontal

  • cortex. Engaging in enjoyable activities generates action potentials in dopamine-producing neurons

  • of the VTA. This causes dopamine release from the neurons into the synaptic space. Dopamine

  • then binds to and stimulates dopamine-receptor on the receiving neuron. This stimulation

  • by dopamine is believed to produce the pleasurable feelings or rewarding effect. Dopamine molecules

  • are then removed from the synaptic space and transported back in to the transmitting neuron

  • by a special protein called dopamine-transporter. Most drugs of abuse increase the level of

  • dopamine in the reward pathway. Some drugs such as alcohol, heroin, and nicotine indirectly

  • excite the dopamine-producing neurons in the VTA so that they generate more action potentials.

  • Cocaine acts at the nerve terminal. It binds to dopamine-transporter and blocks the re-uptake

  • of dopamine. Methamphetamine – a psychostimulantacts similarly to cocaine in blocking

  • dopamine removal. In addition, it can enter the neuron, into the dopamine-containing vesicles

  • where it triggers dopamine release even in the absence of action potentials.

  • Different drugs act different way but the common outcome is that dopamine builds-up

  • in the synapse to a much greater amount than normal. This causes a continuous stimulation,

  • maybe over-stimulation of receiving neurons and is responsible for prolonged and intense

  • euphoria experienced by drug users. Repeated exposure to dopamine surges caused by drugs

  • eventually de-sensitizes the reward system. The system is no longer responsive to everyday

  • stimuli; the only thing that is rewarding is the drug. That is how drugs change the

  • person’s life priority. After some time, even the drug loses its ability to reward

  • and higher doses are required to achieve the rewarding effect. This ultimately leads to

  • drug overdose.

Addiction is a neurological disorder that affects the reward system in the brain. In

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大腦中的藥物成癮機制,動畫。 (Mechanism of Drug Addiction in the Brain, Animation.)

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    Caurora 發佈於 2021 年 01 月 14 日
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