Drugs and Behavior Class Notes from 1/14-1/28
Drugs and Behavior Class Notes from 1/14-1/28 PSY 245
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This 16 page Bundle was uploaded by Kristi Dorsey on Thursday February 4, 2016. The Bundle belongs to PSY 245 at University of North Carolina - Wilmington taught by Mark Galizio in Spring 2016. Since its upload, it has received 93 views. For similar materials see Drugs and Behavior in Psychlogy at University of North Carolina - Wilmington.
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Date Created: 02/04/16
History of Drug Use & Abuse No one is sure when it started; virtually every culture we’ve studied has engaged in psychoactive drug use; usually plants; fundamental cornerstones of religious beliefs; mostly date back to Pre-Columbian Era Early Alcohol Use Egyptians Old World; wine and beer Egyptian alphabet (cuneiform) deciphered; recipe discovered in one of the tombs (brewing beer); doesn’t taste good, highly alcoholic, produce intoxication Alcohol viewed as holy beverage Alcohol good candidate for first human drug Used opium to relieve pain Greeks/Romans Producing and consuming wine Bacchus/Dionysus (God of Wine) No chronicles of alcoholism Europe Fertile Crescent Greece, Egypt, and Italy Alcohol important food substance Beer used to preserve grain harvest Wine preserved fruit harvest Alcohol used for nutrition and survival Hallucinogenics The Incas in the low Andean slopes of modern day Ecuador, Peru, and Columbia discovered properties of coca plants and chewed coca leaf (1000 years ago) Cocaine; comes from the coca tree; Mama Coca (Inca Goddess) was the goddess of cocaine/important deity in Inca Pantheon Hallucinogenic drugs (vivid and dramatic visual hallucinations) native to Central and South America were discovered by Native peoples (mostly restricted to use by shaman) in the Pre-Columbian Era Mayan and Aztecs believed spirits (Gods) spoke to them Mostly restricted to use by Shaman Artifacts depicted Mushroom worship in Guatemala/Mayan peoples (3000 years ago); cultivated psilocybin (chemical in mushrooms)/used as entry to gods Marijuana China and India 10,000 years ago Not sure when psychoactive properties discovered Seen as sacred plant/part of religious ceremonies; Hinduism Only Culture w/out Psychoactive Drugs Arctic people (Eskimos) of Siberia and Alaska/Northern Canada No psychoactive plants/not much to discover Diet low in plants/vegetables When American Gold rush brought westerners to Alaska, white sellers exposed Eskimos to alcohol Alcoholism rate of Native Alaskans approaches 50% (10% in general population) 60% of residents in Nome, Alaska are alcoholics Reasons for Alcoholism among Modern-Day Alaskans Cultural void; most cultures were exposed to drug use/Eskimos weren’t; ill-prepared to handle alcohol use o In France and Italy, they consume a lot of alcohol (mostly wine); considered to be part of a meal; drink at early age; not something you drink to get high; low alcoholism rates o Ireland has high alcoholism rates; binge drink at Irish Wake o Cultural factors important in mediating those kinds of effects Genetics; may metabolize alcohol differently; may result in greater vulnerability to alcoholism; may be protective in other cultures Environmental; in Nome, grocery main streets typically have grocery stores or bars Social/Psychological; Athabaskan Indians and Nupiad Eskimos not prepared for western style living; adjustment issues; discrimination; difficulties in SES; education; lowest SES in Alaska; used to make living spearing seals and whales; without a permit there’s not many options for work Addiction direct result of SES; lower SES = higher substance use rate The Soldier’s Disease Morphine addiction; first description of drug addiction; 1860’s Civil War America/war-torn regions of Europe Morphine chemically derived from opium (from poppy plant); discovered to have pain relieving properties Hypodermic syringe developed in 1840’s; easier to consume morphine/inject it Pain dramatically reduced in injured soldiers for the first time After wounds healed, soldiers still demanded morphine; became sick without it/severe symptoms Came to be called Soldier’s Disease First time scientists recognized addiction as a phenomenon/epidemic Civil War America Drugs common; “dope fiend’s paradise” No drug laws Drug store to get morphine/syringe Beverage laudanum became popular among women in US and Europe (contained opium) Could order cocaine; readily available/inexpensive; could go to bar (chew coca leaf with beverage) Epidemic of cocaine abuse; 1890’s Recognition of Drug Epidemic Early 1900s; concern over drug addiction Discussion about how to fix the problem No government intervention State legislation ineffective 1906 Food and Drug Act First federal American drug law Did not make drugs illegal Companies had to label whether or not their products contained drugs Morphine, heroine, and cocaine use did not decline Questioned created a law that criminalized drug use; not sure if that’s constitutional 1914 Harrison Act Most important drug legislation in U.S. history First federal legislation to make non-medical drug use illegal/controlled by federal law Medical use of drugs legal; up to physician to decide medical/non-medical Created prescription drug use When government specified acceptable medical use of drugs, many physicians were jailed Tax act; tremendous concern about federal government right to regulate what you put into your body; could regulate taxes; any sales of drugs taxable so buying or selling illegal Often called Harrison Narcotics Act; regulated opiate drugs (opium and morphine/heroin); snuck cocaine in there Original use of Narcotic; narcosis = sleep/become depressed or sedated; cocaine didn’t do this Modern definition of narcotics refers to any illegal drug; no longer description of physical effects of the drug, but rather legal status Introduced illegal drug use/smuggling; making drugs illegal did not make the demand go away; use/smuggling not on a large scale Seen as a success; Use of opiate drug use declined in the US; use of cocaine declined; not a lot of data but use definitely decreased Prohibition Movement to ban alcohol in U.S.; first women’s rights movement Women’s Christian Temperance Union; found Cary Nation; women started taking hatchet to barrels of rum in saloons (50 or 60 men present); became a demonstration and social/political movement to ban alcohol; sought constitutional amendment to ban alcohol Women not allowed in saloons; men went to drink ; movement focused on saloon Alcoholism high during this period; idea that alcohol was harmful became popular WWI in Europe/at war with Germany (1915-1919); most big breweries founded by American immigrants from Germany; Brought beer brewing techniques; anti-German sentiment favored Prohibition Beer widely used; not wine/liquor; 3/4 of state have to vote to pass an amendment; 36 state ratified amendment; implemented in 1920; alcohol third illegal drug in U.S. Penalties with alcohol same as heroin or cocaine Effects of Prohibition Roaring 20’s; emergence of gangs; Mafia; AL Capone (king pen in Chicago) Created black market for alcohol; demand for alcohol remained strong Moonshine popular in NC Alcohol legal in Canada/smuggle from Canada to U.S. Mafiosa won control over traffic/organization of alcohol smuggling; small-time; not centralized prior to 1920; Prohibition fueled revenue for Mafiosa Speak Easy; illegal bar; talked quietly; password to get in; thousands/millions of people attended Alcohol consumption rose because women began drinking as well (previously not allowed in saloons) Legal to use for holy communion (used in Christian and Jewish religious ceremonies); alcohol consumption prohibited by Islam Could legally make apple cider/hard cider became popular Was Prohibition Effective? 1918; 18th Amendment (Prohibition) passed 1920; Prohibition lasts 10 years Could legally smoke pot Enormous growth in organized crime Smuggling alcohol from Canada Task forces/agencies developed to regulate alcohol; brought Al Capone to justice (tax evasion, not drugs) Speak Easy popular; women now drinking Millions of Americans became criminals Beer consumption dropped Change in consumption of distilled liquor (whiskey, vodka, tequila, rum) 1890-1920s; consumption pretty flat/40% mostly beer/hard liquor low 1920: 90% of alcohol consumed hard liquor (smugglers made more money per truckload for hard liquor compared to beer) Individuals sold industrial liquor which produced neuropathies; wood alcohol/rubbing alcohol toxins but used in alcohol; many people crippled/killed by consumption 1930s; beer takes front again; people originally for Prohibition originally wanted to repeal it; 3/4 of states wanted to repeal it Decrease in cirrhosis of the liver; primarily caused by heavy drinking of hard liquor; decrease in hospital admissions; hard to collect good data Failure of government to control alcohol December 5th, 1993; Probhition repealed NC never ratified the 21st amendment; remained a dry state until 1935; New Hanover was one of the first counties to ratify/Brunswick held out until 1989 Brown Bagging Laws; could not drink alcohol in public; put a brown paper bag over alcohol contained/bring your own alcohol into a restaurant War on Drugs Richard Nixon 1960s Purpose is to reduce availability of drugs; they will cause more harm if more available 1937 Marijuana Tax Act Result of increase marijuana use in Prohibition Illegal during mass marijuana campaign; said to cause insanity, addiction, and violent behavior 3rd class of drug to be illegal in the US 1940s and 50s; marijuana use at low level Cocaine/opiates at low level during this period 1965 Drug Abuse Control Amendment Federal Law; banned “any substance having potential for abuse because of stimulant, depressant, or hallucinogenic effects 1950s pharmacology began developing synthetic drugs 1920s and 30s; 1st amphetamines synthesized; prescribed for medical use in 1950s Synthetically produced stimulants available Tranquilizers developed for medical purpose; legal; not regulated; quite intoxicating Synthetic hallucinogen; LSD became popular; initially legal Explosion of marijuana use in the 1960s Recognized that new drugs were being developed daily 1970s Controlled Substances Act Developed from 1965 Act Established legal scheduled system for drug use today Drugs classified according to two criteria (medical use/abuse potential) Schedule Medical Abuse Potential Example Miscellaneous information Highest and harshest penalties; possession is a felony; pharmaceutical firms can’t create drugs without permit; I No High Heroin/LSD hospitals can’t keep Schedule I drugs except for researchers; protocol has to be reviewed by the DEA; only viable for research purposes Can be produced by pharmacy, can be held in hospital, a physician can prescribe; although schedule II drugs II Yes High Morphine, are highly controlled, there are allowances put into cocaine, PCP (phencyclidine) place that make it possible for people who need these drugs medically to have access to them III Yes Some Barbiturates, Penalties for possession/sales are not felonies; ketamine prescriptions, refills, more availability Prescription phoned in/multiple refills; tranquilizers, sleeping pills, Ambien are all controversial; college IV Yes Low Valium, Xanax students have problems with drug dependence on these drugs Cough medicines No prescription, show ID, precursors for making meth (small amount of V Yes Very low opiates) In the late 1970s in NC, thousands of young people were being charged with felonies for possession of marijuana; in NC, a decriminalization act was passed VI N/A N/A Marijuana (true in many other states, but not all); In NC, if you look at our state drug Schedule, the 6th schedule is marijuana only; state law that allows NC to treat marijuana possession as a misdemeanor, rather than a felony, in contradiction to federal law Medical use for cocaine is restrictive; causes pronounced vaso-constriction; capillaries clamp down/stretch/restrict bleeding; nose bleeds/nose surgery; first local anesthetic discovered; inject into tissue/nerve region; delicate tissues around your eye or face blocks conduction of nerves/don’t feel pain in that region; surgery in these regions is likely to cause a lot of bleeding; Novocaine/Zylecane used by dentist has similar properties to cocaine w/out abuse problem Controversy; heroin should be a schedule II drug; terminal cancer patients in Europe get medical heroin once morphine stops working; in U.S. you would get IV morphine once opiate pain killers lose effectiveness Drugs can change schedules; many have gone up; less have gone down Restrictions/permission in each state Marijuana is currently a Schedule I drug in the U.S.; tension between states that have legalized it (California, Washington, and Oregon) and federal government Bush, prior to Obama stepping in, had the FBI shut down a number of California medical clinics because the federal government absolutely can enforce the marijuana laws – in principle, if the next President decides to enforce marijuana laws, you could be busted with a joint and charged with a Class I felony, because that is what marijuana is classed as in the medical system PCP & Ketamine Scheduled where they are because they have valid use in veterinary medicine PCP (schedule II); Ketamine (schedule III); valid use in veterinary medicine Criteria to Determine a Drug’s Schedule Value drugs bring to society; medical use approved by AMA? Abuse potential; how do you decide which drugs do/don’t have a high abuse potential? No consensus; large continuum of definition of drug abuse Christian scientists believe that drug use for any reason is abuse/religious beliefs dictate that if God wants you to get well you will be healed/taking a drug is morally wrong Some people don’t believe that drug abuse exists Most people fall in the middle of the continuum Partial Consensus on what Constitutes Substance Abuse Physical harm to oneself and others (frequent cause for physical abuse/partner violence) Psychological harm to oneself and others The question becomes “what is harm?” Depending on the drug, different patterns of use make it hard to determine if the person is harming themselves or not Drug Addiction Is drug addiction abuse? Does it always cause harm? When a person becomes addicted, they’re said to be enslaved by the drug Comparison of Insulin and Heroin Insulin; addiction helpful/necessary for well-being (if you don’t take insulin you’ll die); not considered drug abuse Diabetic (type I); pancreas fails to produce sufficient insulin/compensation for pancreas failure Chemical in human brain that resembles heroin; is it possible that some people don’t produce enough of that chemical, which makes them vulnerable to heroin addiction? Most people assume that the heroin addict chose to be a heroin addict, whereas the diabetic did not choose to be diabetic; most people don’t choose to be a drug addict (even though they choose to take the drug) Arguably, a person with Type II Diabetes “chose” to get the disease because they didn’t take care of their body (as a comparison to how we view Heroin/drug addiction) Psychologists view voluntary behavior as a “disorder of choice”; decision making determined by the drug; today we think of addiction as a disorder of choice where the person’s decision making becomes damaged by the drug Physical vs. Psychological Addiction Believed that the reason people fail to quit is because of withdrawal Some drugs don’t produce withdrawal symptoms Physical dependence no longer considered a useful diagnosis because of cocaine; consider cocaine an addictive drug because of psychological symptoms produced (not physical) Easier to treat physical symptoms than psychological symptoms Within 6 weeks of detox (treatment for physical addiction) 80-90% of heroin addicts will still be addicted (psychological addiction) Psychological dependence historically viewed as a lesser problem WHO Definition of Drug Dependence With most drugs we’ll talk about, there is a characteristic set of symptoms that define withdrawal Drug dependence specified by the occurrence of withdrawal symptoms (abstinence syndrome) of any form (physical/psychological) Syndrome; cluster of symptoms that tend to go together In withdrawal, most drugs produce a cluster of specific symptoms (abstinence syndrome/withdrawal syndrome) In absence of drug, person experiences a characteristic symptoms/set of symptoms and that presence defines addiction According to WHO, you can’t know if someone’s addicted unless withdrawal symptoms are present with the absence of the drug Rebound Effect Most withdrawal syndromes are associated with a rebound effect Whatever the drug does when you take it, you experience the opposite effect during withdrawal Once you learn the effects of a drug, physical and psychological, you can often predict withdrawal symptoms if you know physical symptoms (EX: heroin causes constipation/rebounds as diarrhea; EX: cocaine causes euphoria, intense pleasure, and good mood/rebounds as depression) Patient has elbow surgery; given opiate every 4 hours to relieve pain; if elbow still hurts after withdrawal of medication it isn’t seen as addiction because those symptoms were there prior to drug use Antidepressants; when people stop taking them their depression will reoccur; not sure if it’s withdrawal symptoms or because original depression is no longer being treated DSM-IV (4) Substance dependence and substance abuse disorder separately Most research today comes from DSM-IV because DSM-V is new The first seven symptoms in the DSM-V are pretty much the same as “substance dependence” as defined in the DSM-IV More symptoms were added to the DSM-V (beyond the 7 original criterion for substance dependence) DSM-V (5) DSM-5 no longer differentiates dependence from abuse because it’s hard to separate someone who’s abusing the substance but not dependent from someone who is dependent Substance Use Disorder; problematic pattern of substance use leading to a clinically significant impairment or distress as manifested by at least 2 of the following symptoms in a 12-month period 1. Tolerance; After regular use, a larger dose is required to produce a given effect; a given dose of the drug has less effect upon repetition 2. Withdrawal; person shows psychological or physical symptoms when they stop taking the drug If a patient shows tolerance and withdrawal, they would meet criterion for substance use disorder 3. Taking more than intended; has person intended to cut down use of the drug and failed? 4. Unable to cut down or control; EX: person realizes they drink too much alcohol, try to cut down the amount they drink, and fail to do so 5. Excessive time spent revolved around the drug; drug becomes an obsession debate over what’s meant by “excessive” 6. Important activities given up relating to the drug; EX: person quits running track in college because they would rather smoke 7. Continuing use despite persistent social/interpersonal problems DSM-V (5) vs. DSM-IV (4) Continued DSM-V = substance use disorder; tolerance, withdrawal, taking more than intended, unable to cut down or control, excessive time spent on the drug, important activities given up, continuing use despite persistent social or interpersonal problems; 2/11 criteria have to be met; additional criteria to DSM-IV Failure to fulfill major role obligations at work, school or home Recurrent use in physically dangerous situations Persistent social/psychological problems Cravings (strong desire to use substance/difficult to control); Rinaldi’s psychological dependence DSM-V Substance Use Disorder Continuum Criteria Mild; 2-3 symptoms Moderate; 4-5 symptoms Severe; 6+ symptoms; becoming more common DSM-IV; substance dependence distinct from substance abuse; substance dependence disorder consider of the 7 items; had to meet 3 of the 7 criteria; captured tolerance, withdrawal, AND drug had to interfere with daily functioning/interpersonal problems Tolerance What is changing in the user that produces tolerance? 3 Mechanisms of Tolerance 1. Dispositional/Metabolic Tolerance Tolerance of the Liver; liver has enzymes (“deadly poisons”) that break down toxins; most drugs broken down here; functional dose of drug left reaches the brain (psychoactive); it’s not how much you take, but how much reaches your brain; if drugs weren’t broken down by enzymes the toxin would persist in the body/effects would be permanent If you take certain drugs regularly/frequently, your liver changes/gets better at producing these enzymes, but then if you stop taking the drug/abstain, gradually that tolerance will be lost and you’ll return to baseline (normal) levels Some drugs produce tolerance rapidly; others less so; as a rule, you lose the tolerance at a rate that is similar to the rate that you acquired it; developing rapidly, tends to dissipate rapidly, develops gradually, will tend to dissipate slowly/gradually; only a small fraction of the tolerance that you see, even with alcohol Oral; absorbed in gut/small intestine; absorbed slowly into bloodstream; first pass through liver IV/intravenously; more efficient; directly/immediately to bloodstream; large % reaches brain w/out passing through liver; what’s left goes through liver; effects more intense than any other method; rapid onset of large quantities of drug to brain responsible for intense rush/flash users experience after injecting drug Inhalation/smoke; similar to IV; lungs have large volume/good at absorption/drugs stored rapidly in lungs; delivered to heart; delivered to brain without first pass through liver; small quantities broken down by liver before entering brain Inhalation + IV = produce extremely intense effects/most liable for drug dependence Patch; slowly absorbed through skin; passes through liver; dose calculated to produce desired effect given metabolism Snorting/insufflation; absorbed through mucosa/mucus membranes; absorbed slowly compared to IV/smoke; no first pass through liver; bloodstream; capillaries in mucosa capable of absorbing only small amount of drug/depends on drug; a lot of drug absorbed in stomach rather than mucosa In dispositional/metabolic, you’re taking the same amount of the drug but the liver’s breaking it down faster; taking the same amount of the drug but not getting as much to your brain 2. Functional Tolerance; most of the psychoactive drugs operate through functional tolerance Tolerance of the brain; most important mechanism of tolerance that we see with psychoactive drug use Drug isn’t changing; brain has changed in such a way that the drug is no longer producing the same magnitude of effect it initially did; biological basis for drug addiction; also reversible 3. Behavioral/Learned Tolerance Not well understood; drugs goes to brain/brain reacts to drug; because of environment/past experiences drug doesn’t affect you as much EX: alcohol affects balance/first time you got drunk you had terrible balance/several times later you’re adjust your body so that you don’t seem as impaired 4. Environmental/Learned Tolerance In one environmental circumstance (person driving after having smoked marijuana) the person is behaving intoxicated and when environment changes (police pulls them over) intoxication is decreased; anxiety it produces seems to reverse the drug effect If you take a drug in a particular environment, the tolerance to that drug seems to be linked to that environment; if you take it in the presence of different environmental cues, the effect can be stronger 5. Acute/Protracted Tolerance Tolerance develops gradually/some drugs faster than others; with certain drugs there seems to be tolerance after/during a single use of the drug EX: Cocaine; very short acting drug; after a matter of minutes the person doesn’t feel the intense flash/rush; still have cocaine in system/craving drug; take it again to re-experience flash/rush Person uses crack and 15 minutes later they smoke the same dose, they won’t get the same intense flash; feel some effect but not at the intensity of the first use; develops rapidly/dissipates rapidly; if they abstain from cocaine for 1-2 days, they will have the original/intense effect; if they take a couple of times w/in a short time frame, they will not experience same intense feelings EX: alcohol; binge drinking; blood alcohol level rises (.08); continue drinking/high blood alcohol level; BAC beings to drop; gets back to .08 a couple of hours later; as the blood alcohol level is rising, person feels intoxicated; on the way down, person feels sick, even though they have the same BAC; same blood alcohol concentration that produced positive effects on the way up (ascending limb) of blood alcohol level curve, produces very different effects on the way down 6. Cross-Tolerance Tolerance to one drug crosses over to other drugs; EX: person takes Heroin/develops tolerance; injured/physician prescribes them another opiate (OxyContin); will be tolerant of that opiate, even if they’ve never taken it; tolerance to heroin has crossed over to other closely related drugs Drugs used to produce surgical anesthesia show cross tolerance with alcohol Why is there cross tolerance? Drugs that show cross tolerance act through a common brain pathway 7. Cross-Dependence If you’re in Heroin withdrawal you can make symptoms go away by administering closely related rugs (OxyContin/Methadone); closely related drugs can suppress withdrawal symptoms of one another Can’t give heroin to alleviate withdrawal symptoms in a heroin addict because it’s a schedule I drug In alcohol withdrawal we would give them another sedative/depressant drug to relieve potentially fatal withdrawal symptoms Detoxification: giving the person a drug that shows cross-dependence with the drug that they’re withdrawing from; drugs to treat withdrawal can produce dependence but goal is to get person through crisis/withdrawal The Brain Brain locus of action of psychoactive drugs; the one thing that all psychoactive drugs have in common is they all act on the brain Looking at human brain doesn’t give us a lot of information; cannot differentiate gender, intelligence, substance abuse, etc.; only exception is alcohol use (heavy use of alcohol in long-term binge drinkers exhibits loss of brain mass); would have to internally measure loss of brain volume; Einstein; statistically unusual brain pathways Nervous System Central Nervous System; brain/spinal cord; central/right down midline or organism’s body; most important drug effects occurring at CNS (drugs that affect the brain) Peripheral Nervous System; nerve cells outside of CNS/midline; includes nerves that send info to brain from your skin sense, eyes, auditory nerves from ear; sensory/afferent nerves send information to the brain; motor nerves output/nerves that send info from brain to activate muscles/allow you to behavior (drugs generally don’t affect these because they are far away from the brain) o Autonomic Nervous System; neural pathways in body outside of CNS that regulate organ systems/functions; keeps your heart beating, diaphragm moving, kidneys working, etc. without your awareness; 2 branches; sympathetic/parasympathetic Sympathetic; activated when in a state of emotional arousal (angry, excited, fearful, happy, sexual, etc.); Fight or Flight (Walter Cannon); more blood goes to big muscle groups/brain; blood shuns away from digestion/other processes/slow down substantially; pupils dilate; some psychoactive drugs mimic sympathetic arousal (produce physical symptoms of emotional arousal); duplicate psychological symptoms of arousal Parasympathetic; brings body back to resting state; not much drug action Neuron What we know about how drugs affect the brain/biological actions relevant to drug abuse occur at microscopic level of brain (individual cell/neuron) 1. Cell body 2. Nucleus 3. Dendrites 4. Myelin 5. Axon 6. Axon 7. Axon Terminals Neuron; most crucial for understanding drug action; specialized to communicate with one another; what’s unique are branches/most neurons look like this one (# of small branches extending out in 3 dimensions); billions are interacting in pathways with one another; vary enormously in structure, shape, size/how bushy they are; neurons in the spinal cord have extremely long axons that can conduct an electrical signal Soma; cell body; branch like processes that extend out (most interesting); nucleus (genetic material contained)/other organelles responsible for energy metabolism/other things needed to keep cell alive Branches called dendrites; all neurons have hundreds/thousands extending from cell body (like branches on a tree); designed to receive input from other neurons Axon; branches not as long or dense as dendrites; tip of each branch has button structure (originally called terminal button/now axon terminals); extended structure; larger/longer than dendrites Could think of cell as specialized to conduct electrical current/transmitted from soma to axon terminal; diode th (conducts only in a single direction); how neurons communicate with each other; discovered in 19 century o Current initiates when dendrite is stimulated; triggers passage (we have equipment that allows us to measure voltage in the action potential as current is transmitted along the axon in terms of mV/thousandths of a volt); action potential = 70 mV o Electroencephalogram; electrodes around scalp; measure current/amplify electrodes; measures activity of hundreds of thousands of neurons in order to measure a single neural action; neuron has to be isolated from brain and measured with specialized microscopic equipment Up until the middle of the last century, scientists believed that the brain was an electrical system in which a current was transmitted along an axon; when electron microscopy came in you could look at the neurons; axon terminal of one cell did not quite touch dendrite of the other cell; came close by separated by a synaptic gap; question became – how do neurons communicate/how do they bridge that gap? Understanding Neurotransmission Neurotransmission historically understood as electrical phenomenon; anatomy of neuron consistent with this before development of electron microscopy You would see neurons connecting to each other at the level of the dendrite(s) Telephone metaphor for understanding neurotransmission; junction b/ween neurons (where one neurons meets another) is like a telephone pole; one set of wires communicate with another set of wires; axon would be the extended wire Electrical model ran into problems with electron microscopy allowed us to see the connection b/ween neurons; most neurons don’t directly make contact w/one another Synapse; place where one neuron junctions with another; began to realize that the axon terminal of a neuron (2) came close to but did not quote make contact with the dendrite receptor of another neuron (1); if it’s an electrical system this will not work/well known by the 30s and 40s; became well known in 50’s; debate sparked between Spark and Soup theorists Spark vs. Soup Theorists Spark Theorists; when the nerve impulse reaches the axon terminal, there must be a specialized mechanism that shoots a spark across the synaptic cleft/gap; this makes the neuron fire; commonly used metaphor but incorrect Soup Theorists; axon terminals contain chemicals and when that electrical signal reaches the axon terminal that causes it to open up and release those chemicals into the synaptic cleft; presynaptic neuron sends signal; postsynaptic neuron receives signal; chemicals are being stored in the axon terminals; vesicles (sacs that hold neurotransmitters/chemicals) located in axon terminal; as the electrical signal approaches the presynaptic neuron (axon terminal) the vesicles come to the surface/open up spilling their contacts; chemicals inside vesicles are released into the synapse When the electrical signal is transmitted along the axon we say the neuron fires; synapse is wet/not ideal medium for conducting current (0.09 saline); another reason soup theory makes sense Soup Theory revolutionized our understanding of psychoactive drugs; tells us that drugs are chemicals; neural transmission is electrical along the axon, but when it reaches the synapse it’s a chemical process (electrochemical); psychoactive drugs produce their effect at the synapse These chemicals that are released into the synapse are called neurotransmitters; chemicals released at the synapse that deliver the signal from one neuron to another Feeling Pain? Disembodied Finger Scenario If I smash your finger with a hammer I will break blood vessels, damage tissue, etc.; but you don’t feel pain yet; squishing a number of specialized cells that send an electrical signal through neurons (only when intense pressure is received); pressure results in electrical signal Transduction; force of the hammer is converted into electrical signal/transmitted along neurons The neurons will go from finger to wrist; axon would branch and those branches would come close to but not make contact with the dendrites of other neurons located in nerves (run along your wrist) At the synapse those axon terminals release neurotransmitters/hammer blow has turned into a release of chemicals; the release cell firing in post synaptic neurons; electrical process; when they go to the synapse in your elbow or shoulder they’re releasing chemicals and those chemicals are firing in a postsynaptic neuron That electrical signal is going to reach the spinal cord (highway of the nervous system); neurons there are long/conduct rapidly; triggering electrical activity in axons in the spinal cord that are sending messages to brain; electrical signals ascending along the spinal cord into the brain In the brain, axon terminals might synapse with as many as 100,000 neurons; dense/packed with dendrites; single electrical signal might trigger activity in other neurons once those chemicals are released at the axon terminal; you still don’t feel pain yet Afferent/sensory neurons sending sensory information to the brain; when they reach the spinal cord, there’s an automatic trigger of the efferent/motor neurons; reflex/pulling finger back occurs before the signal reaches the brain You can measure reaction time if I hammer your toe vs. your finger; slower to react if I hammer your toe; longer to travel, more synapses/takes a fraction of a second longer for those signals to reach the brain; direct function of the number of synapses/electrochemical events that have to take place for it to register in the brain Because signal transmission takes time, you pull your finger back before those signals register in the brain
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