Today’s LessonToday’s Lesson

Nervous System and Nervous System and Drug AddictionDrug Addiction

Overview of Lesson

• Nervous system

• Synapses and neurohormones

• Drug addiction

Neuron

Based on: Raven et al., Biology, McGraw-Hill

•Sensory neuronsSensory neurons - carry impulses to the - carry impulses to the interneurons of the braininterneurons of the brain•Interneurons of the brainInterneurons of the brain - interpret impulses - interpret impulses•Motor neuronsMotor neurons - carry impulses to the muscles - carry impulses to the muscles

Types of Neurons

Based on: Mader, S., Inquiry Into Life, McGraw-Hill

Nerve ImpulseNerve Impulse•Stimulation of neuron, opens channels soStimulation of neuron, opens channels so that sodium (Nathat sodium (Na++) goes in, depolarizing the) goes in, depolarizing the membranemembrane

•The adjacent section of membrane allows The adjacent section of membrane allows Na+ to go in, depolarizing itNa+ to go in, depolarizing it

•This wave of depolarization continues at aThis wave of depolarization continues at a rapid rate down the neuron, resulting in arapid rate down the neuron, resulting in a nerve impulse traveling to the brain innerve impulse traveling to the brain in millisecondsmilliseconds

Neuron at Rest: Polarized MembraneNeuron at Rest: Polarized Membrane

Outside of Outside of neuron is neuron is positively positively charged due to charged due to positive sodium positive sodium ionsions

Inside of neuron Inside of neuron is negatively is negatively charged due to charged due to negative ionsnegative ions

+ + + + + + + + +

- - - - - - - - - - -

Inside of Neuron

+ + + + + + + +- - - - - - - - - -

+ + + + + + + +

- - - - - - - - - -

+ + + + +

- - - - - -0 0 0 0

Neuron

Neuron

Neuron

Polarized membrane Polarized membrane of resting neuronof resting neuron

Sodium (Na) moves Sodium (Na) moves inside to depolarizeinside to depolarize

Nerve impulse is wave Nerve impulse is wave of depolarization of depolarization moving down neuronmoving down neuronNerve

impulse

Nerve ImpulseNerve Impulse

Depolarization and Repolarization

Based on: Starr, C., Biology: Concepts and Connections, Brooks/Cole

•Operates when neuron is at rest or Operates when neuron is at rest or not transmitting nerve impulsenot transmitting nerve impulse

•Pump is a membrane proteinPump is a membrane protein

•The protein actively transports Na out The protein actively transports Na out of the axon to re-establish polarity of of the axon to re-establish polarity of membranemembrane

Sodium PumpSodium Pump

Overview of Lesson

• Nervous system

• Synapses and neurohormones

• Drug addiction

There are gaps or junctions There are gaps or junctions between neurons called synapses between neurons called synapses

Based on: Mader, S., Inquiry Into Life, McGraw-Hill

Synapses

Neurotransmitter being released into synapse and attaching to receptors on dendriteBased 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 Human behavior is controlled by natural chemical reward systems in the bodychemical reward systems in the body

For example, we like to eat fatty foods For example, we like to eat fatty foods because it make us feel goodbecause it make us feel good

It is the release of dopamine that is the It is the release of dopamine that is the chemical reward system responsible for the chemical reward system responsible for the good feelinggood feeling

Dopamine “reinforces behaviors essential to Dopamine “reinforces behaviors essential to our survival.”our survival.”

Importance of DopamineImportance of Dopamine

After neurotransmitter stimulates the After neurotransmitter stimulates the postsynaptic membrane, it is removed postsynaptic membrane, it is removed by an enzyme or transported out of by an enzyme or transported out of synapsesynapse

For example, acetylcholine is removed For example, acetylcholine is removed from synapses by an enzyme called from synapses by an enzyme called acetylcholinesteraseacetylcholinesterase

Synapses must be cleaned upSynapses must be cleaned up

Overview of Lesson

• Nervous system

• Synapses and neurohormones

• Drug addiction

•Cigarettes contribute to death rates from Cigarettes contribute to death rates from cancer and heart diseasecancer and heart disease

•Alcohol is the leading cause of violenceAlcohol is the leading cause of violence

•Needles are spreading AIDSNeedles are spreading AIDS

•Addiction to drugs, cigarettes and alcohol Addiction to drugs, cigarettes and alcohol account for a third of all hospital admissions, account for a third of all hospital admissions, and a majority of all crimesand a majority of all crimes

•Drug use costing us excess of 240 billion Drug use costing us excess of 240 billion dollars annuallydollars annually

Price of Drug Addiction in U.S.Price of Drug Addiction in U.S.

According to scientists, what is According to scientists, what is the master molecule of addiction the master molecule of addiction and where is it produced?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

1.1. After being released into the synapse (the gap After being released into the synapse (the gap between nerve endings and receiver cells), between nerve endings and receiver cells), dopamine binds to receptors on the next neurondopamine binds to receptors on the next neuron

2.2. The dopamine is either quickly reabsorbed or The dopamine is either quickly reabsorbed or broken down by the enzyme monoamine oxidase broken down by the enzyme monoamine oxidase (MAO)(MAO)

Dopamine’s Normal Action

Based on Time, May 5, 1997

Cocaine blocks the normal absorption of dopamine. As a result, dopamine accumulates in the synapse, where is 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 LevelsBased on Time, May 5, 1997

Physiology of AddictionPhysiology of Addiction• Drug enhances amount of dopamine in the Drug enhances amount of dopamine in the

synapsessynapses• Increased dopamine results in increased Increased dopamine results in increased

feelings of pleasurefeelings of pleasure• Nervous system responds by reducing the Nervous system responds by reducing the

number of dopamine receptor sitesnumber of dopamine receptor sites• Addict must take more drug to produce the Addict must take more drug to produce the

same “high”same “high”• ““So while addicts begin by taking drugs to feel So while addicts begin by taking drugs to feel

high, they end up taking them in order not to high, they end up taking them in order not to feel low.”feel low.”

WithdrawalWithdrawal• Physiological response to lack of drug Physiological response to lack of drug

effects, especially the drug’s substitution effects, especially the drug’s substitution for naturally produced neurotransmitterfor naturally produced neurotransmitter

• Withdrawal effects can be intense at first, Withdrawal effects can be intense at first, especially if the drug addict quits abruptlyespecially if the drug addict quits abruptly

• Eventually the body’s physiology returns Eventually the body’s physiology returns to normal, and the person will stop craving to normal, and the person will stop craving the drugthe drug

Treatment for Heroin AddictsTreatment for Heroin Addicts

• Heroin addicts are put on methadone to wean them off Heroin addicts are put on methadone to wean them off of heroin of heroin

• Methadone replaces the heroin without giving the Methadone replaces the heroin without giving the

“rush”“rush”

• If the addict tries to take heroin, the methadone blocks If the addict tries to take heroin, the methadone blocks the euphoric effects of itthe euphoric effects of it

• Eventually the addict’s neurotransmitter production Eventually the addict’s neurotransmitter production returns to normal if they can avoid taking heroinreturns to normal if they can avoid taking heroin

So how has the scientific view of So how has the scientific view of the cause of drug addiction and the cause of drug addiction and treatment changed?treatment changed?

Changing View of Drug AddictionChanging View of Drug Addiction

• Drug addiction has been viewed as a failure of Drug addiction has been viewed as a failure of character and combated with criminal laws and character and combated with criminal laws and imprisonmentimprisonment

• Now some scientists feel drug addiction may be a Now some scientists feel drug addiction may be a disorder of the brain no different from other forms disorder of the brain no different from other forms of mental illnessof mental illness– May be caused by deficiency in neurotransmittersMay be caused by deficiency in neurotransmitters– May be genetically basedMay be genetically based

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