1、Todays LessonNervous System and Drug Addiction,Overview of Lesson,Nervous system Synapses and neurohormones Drug addiction,Neuron,Based on: Raven et al., Biology, McGraw-Hill,Sensory neurons - carry impulses to the interneurons of the brain Interneurons of the brain - interpret impulses Motor neuron

2、s - carry impulses to the muscles,Types of Neurons,Based on: Mader, S., Inquiry Into Life, McGraw-Hill,Nerve Impulse,Stimulation of neuron, opens channels so that sodium (Na+) goes in, depolarizing the membrane The adjacent section of membrane allows Na+ to go in, depolarizing it This wave of depola

3、rization continues at a rapid rate down the neuron, resulting in a nerve impulse traveling to the brain in milliseconds,Neuron at Rest: Polarized Membrane,Outside of neuron is positively charged due to positive sodium ions Inside of neuron is negatively charged due to negative ions,+ + + + + + + + +

4、,- - - - - - - - - - -,Inside of Neuron,+ + + + + + + +,- - - - - - - - - -,+ + + + + + + +,- - - - - - - - - -,+ + + + +,- - - - - -,0 0 0 0,Neuron,Neuron,Neuron,Polarized membrane of resting neuron,Sodium (Na) moves inside to depolarize,Nerve impulse is wave of depolarization moving down neuron,Ne

5、rve impulse,Nerve Impulse,Depolarization and Repolarization,Based on: Starr, C., Biology: Concepts and Connections, Brooks/Cole,Operates when neuron is at rest or not transmitting nerve impulse Pump is a membrane protein The protein actively transports Na out of the axon to re-establish polarity of

6、membrane,Sodium Pump,Overview of Lesson,Nervous system Synapses and neurohormones Drug addiction,There are gaps or junctions between neurons called synapses,Based on: Mader, S., Inquiry Into Life, McGraw-Hill,Synapses,Neurotransmitter being released into synapse and attaching to receptors on dendrit

7、e,Based on Harvard Medical School Family Health Guide,50 Known Neurotransmitters,Examples include: Acetylcholine Dopamine Serotonin,Why do we need a neurotransmitter like dopamine?,Human behavior is controlled by natural chemical reward systems in the body For example, we like to eat fatty foods bec

8、ause it make us feel good It is the release of dopamine that is the chemical reward system responsible for the good feeling Dopamine “reinforces behaviors essential to our survival.”,Importance of Dopamine,After neurotransmitter stimulates the postsynaptic membrane, it is removed by an enzyme or tra

9、nsported out of synapse For example, acetylcholine is removed from synapses by an enzyme called acetylcholinesterase,Synapses must be cleaned up,Overview of Lesson,Nervous system Synapses and neurohormones Drug addiction,Cigarettes contribute to death rates from cancer and heart disease Alcohol is t

10、he leading cause of violence Needles are spreading AIDS Addiction to drugs, cigarettes and alcohol account for a third of all hospital admissions, and a majority of all crimes Drug use costing us excess of 240 billion dollars annually,Price of Drug Addiction in U.S.,According to scientists, what is

11、the master molecule of addiction and where is it produced?,Dopamine is thought to be the master molecule of addiction It is made in the brain and affects primitive parts of the brain,Based on Time, May 5, 1997,After being released into the synapse (the gap between nerve endings and receiver cells),

12、dopamine binds to receptors on the next neuron The dopamine is either quickly reabsorbed or broken down by the enzyme monoamine oxidase (MAO),Dopamines Normal Action,Based on Time, May 5, 1997,Cocaine blocks the normal absorption of dopamine. As a result, dopamine accumulates in the synapse, where i

13、s stimulates the receiver cell.,Amphetamines stimulate excess release of dopamine, overwhelming the processes of reuptake and enzyme breakdown.,Nicotine stimulates the release of dopamine, while another substance in cigarette smoke blocks the action of MAO.,How Drug Affect Dopamine Levels,Based on T

14、ime, May 5, 1997,Physiology of Addiction,Drug enhances amount of dopamine in the synapses Increased dopamine results in increased feelings of pleasure Nervous system responds by reducing the number of dopamine receptor sites Addict must take more drug to produce the same “high” “So while addicts beg

15、in by taking drugs to feel high, they end up taking them in order not to feel low.”,Withdrawal,Physiological response to lack of drug effects, especially the drugs substitution for naturally produced neurotransmitter Withdrawal effects can be intense at first, especially if the drug addict quits abr

16、uptly Eventually the bodys physiology returns to normal, and the person will stop craving the drug,Treatment for Heroin Addicts,Heroin addicts are put on methadone to wean them off of heroin Methadone replaces the heroin without giving the “rush” If the addict tries to take heroin, the methadone blo

17、cks the euphoric effects of it Eventually the addicts neurotransmitter production returns to normal if they can avoid taking heroin,So how has the scientific view of the cause of drug addiction and treatment changed?,Changing View of Drug Addiction,Drug addiction has been viewed as a failure of character and combated with criminal laws and imprisonment Now some scientists feel drug addiction may be a disorder of the brain no different from other forms of mental illness May be cause