Understanding How Psychoactive Drugs Impact Brain Function

Introduction - Psychoactive drugs alter brain activity - The brain is the basis of our emotions and behavior - Drugs can change the structure of the brain - Must first understand how the normal brain functions to understand how drugs affect The brain Neuron - Neuron - Basic type of cell found in the brain - Receives and transmits electrochemical information Parts of the Neuron - Cell body - Command center of the cell - Contains nucleus of the cell - Nucleus houses genetic material - Dendrites - Branch-like structures - Contain receptor sites that receive information from other neurons - Axon - Rope-like extension coming out of cell body - Helps send a message on to the next neuron - Can be thousands of times longer than the diameter of the cell body - Myelin - Layer of fatty tissue that covers axons - Insulates the axon to protect the electrical current - Allows electrical message to travel more rapidly Gray Matter vs. White Matter - White matter – contains myelinated axons - Gray matter – no myelinated axons Neurotransmission - Two types of signals - Electrical signals occur within a neuron - The distribution of ions inside and outside of the cell determines whether the cell fires Or not - Resting potential - Action potential - Chemical signals occur between neurons to allow neurons to communicate with one Another - Neurotransmitters Synapse - Synapse - The space between two neurons - Neurons do not actually touch each other - Neurons communicate chemically via neurotransmitters at the synapse Neurotransmission: Chemical - In the presynaptic neuron - Action potential reaches axon terminal - Vesicles triggered to move toward synapse - Neurotransmitters released into synapse and travel via diffusion to the postsynaptic Neuron - In the postsynaptic neuron - Neurotransmitters attach to specific receptors contained on dendrites and cell body of The postsynaptic neuron - Activity in postsynaptic neuron triggered - Receptor binding - Neurotransmitters fit into receptors like a key fit into a lock - Only certain neurotransmitters fit into certain receptors - Depending on receptor binding the postsynaptic neuron will - Fire - Or not fire - Postsynaptic receptor types - Excitatory - Action potential likely to happen - Inhibitory - Action potential not likely to happen - After receptor binding - Re-uptake - Neurotransmitter taken back by the presynaptic neuron to be used again - Enzyme breakdown - Enzymes deactivates the neurotransmitter Neurotransmitters - 50 neurotransmitters - A neurotransmitter can have multiple subtypes - Dopamine - Regulation of movement, emotion, cognition, motivation, and feelings of pleasure - Drugs used for pleasure target the brain reward pathway via dopamine - Drugs cause twice or ten times more dopamine release than natural rewards - Plays role in many brains’ functions - Norepinephrine - Emotional arousal and the regulation of hunger and alertness - “Flight or fight” response - Insufficient levels of norepinephrine - Attention deficit/hyperactivity disorder and major depression - Serotonin - Regulation of sleep, mood, appetite, sex, and body temperature - Major depression and other psychiatric disorders are associated with deficient Levels of serotonin - Antidepressants increase serotonin - Hallucinogens like LSD stimulate serotonin activity - Acetylcholine - First neurotransmitter discovered - Found in brain and skeletal muscles - Acetylcholine binding causes muscle contractions in skeletal muscles - In the brain, it important for memory, attention, and sensory processing - Nicotine stimulates acetylcholine activity - Endorphins - Large molecule called peptides - Brain’s natural killer - Release blocks pain and feels good - Gamma amino-butyric acid - Abundant neurotransmitter - Most important inhibitory neurotransmitter - Causes feelings of relaxation and sedation - Anti-anxiety drugs act on GABA - Glutamate - Abundant excitatory neurotransmitter - Important in learning and memory - NDMA is one type of glutamate receptor - Important role in synaptic plasticity - Adenosine - Inhibitory neurotransmitter found in the central and peripheral nervous system - Levels naturally rise over the course of the day and are believed to promote sleep - Caffeine blocks adenosine receptors and increases wakefulness - Anandamide - Discovered in 1992 - May play an important role in appetite, sleep, and pain - Binds to cannabinoid receptors - The THC in marijuana binds to the same receptors Drugs Affect Neurotransmission - Neurotransmitters are influenced by drug use - Agonists - Bind to receptors, mimic neurotransmitter - Activate neuron - Antagonists - Bind to receptors, block neurotransmitters from binding - Prevent neuron from firing - In addition to receptor binding drugs can affect how neurotransmitters are synthesized, Transported, stored, released, and broken down. The Brain - Complex organ with billions of neurons - Weighs about 3 pounds - Three major sections - Hindbrain - Midbrain - Forebrain