hart13 ppt ch04

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Chapter 4Chapter 4

The Nervous System

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HomeostasisHomeostasis

Humans must maintain their internal environment within certain limits Temperature Acidity Water content Sodium content Glucose concentrations Other physical and chemical factors

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Components of the Nervous Components of the Nervous SystemSystem

Nerve cells (neurons) Analyze and transmit information Over 100 billion neurons in system Four defined regions

Cell body Dendrites Axon Presynaptic terminals

Stimulation of receptors by psychoactive drugs can activate or inhibit a neuron

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NeuronNeuron

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Components of the Nervous Components of the Nervous SystemSystem

Glial cells (Glia) Provide firmness and structure to the brain Get nutrients into the system Eliminate waste Form myelin Create the blood-brain barrier Communicate with other glia & neurons

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NeurotransmissionNeurotransmission

Action potential = a brief electrical signal transmitted along the axon Neurotransmitters are the “messengers” Resting action potential is caused by uneven

distribution of ions Action potential occurs when sodium ions move

across channels Blocking channels prevents the action potential

and disrupts communication between neurons

Action PotentialAction Potential

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© 2011 McGraw-Hill Higher Education. All rights reserved.

The Nervous SystemsThe Nervous Systems

Somatic nervous system Sensory information Voluntary actions

Autonomic nervous system (ANS) Sympathetic branch Parasympathetic branch

Central nervous system (CNS) Brain Spinal cord

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Somatic Nervous SystemSomatic Nervous System

Carries sensory information into the central nervous system

Carries motor (movement) information back out to the peripheral nerves

Controls voluntary actions Acetylcholine is the neurotransmitter at

neuromuscular junctions

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Autonomic Nervous SystemAutonomic Nervous System

Monitors and controls the body’s internal environment and involuntary functions

Many psychoactive drugs affect the brain and the autonomic nervous system

Two branches often act in opposition Sympathetic branch

“Fight or flight”

Parasympathetic branch

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Central Nervous SystemCentral Nervous System

Consists of the brain and the spinal cord

Has many functions Integration of information Learning and memory Coordination of activity

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Chemical PathwaysChemical Pathways

1. Dopamine Found in basal ganglia and other regions Nigrostriatal dopamine pathway

Related to muscle rigidity

Mesolimbic dopamine pathway Related to psychotic behavior Possible component of the “reward” properties of

drugs

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Chemical PathwaysChemical Pathways

2. Acetylcholine Found in the cerebral cortex & basal ganglia Involved in Alzheimer’s disease, learning,

memory storage

3. Norepinephrine Regulates level of arousal and attentiveness May play a role in initiation of food intake

(appetite)

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Chemical PathwaysChemical Pathways

4. Serotonin Found in the brain stem raphe nuclei May have a role in impulsivity, aggression,

depression, control of food, and alcohol intake Hallucinogenic drugs influence serotonin

pathways5. GABA (Gamma-amino butyric acid) Found in most regions of the brain Inhibitory neurotransmitter

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Chemical PathwaysChemical Pathways

6. Glutamate Found in most regions of the brain Excitatory neurotransmitter

7. Endorphins Opioid-like chemical occurring naturally

in the brain Play a role in pain relief, other functions

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Common NeurotransmittersCommon NeurotransmittersNeurotransmitter Type of effect CNS changes Drugs of abuse

dopamine

GABA

serotonin

acetylcholine

endorphins

inhibitory-excitatory

inhibitory

excitatory-inhibitory

excitatory-inhibitory

inhibitory

euphoria agitation paranoiasedation relaxation drowsiness depressionsleep relaxation sedationmild euphoria excitation insomniamild euphoria block pain slow respiration

amphetamines, cocaine

alcohol, Valium-type barbiturates

LSD

tobacco, nicotine

opioid

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The Brain: Major StructuresThe Brain: Major Structures

Cerebral cortex Basal ganglia Hypothalamus Limbic system Midbrain, pons, and medulla Brain stem

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Cross-section of the brain: Major structures

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Life Cycle of a Life Cycle of a NeurotransmitterNeurotransmitter

1. Neurotransmitter precursors are found circulating in the blood supply

2. Uptake: Selected precursors are taken up by cells, a process requiring energy

3. Synthesis: Precursors are changed (synthesized) into neurotransmitters through the action of enzymes

4. Storage: Neurotransmitters are stored in small vesicles

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Life Cycle of a Life Cycle of a NeurotransmitterNeurotransmitter

5. When the action potential arrives, neurotransmitters are released into the synapse

6. Released neurotransmitters bind with receptors on the membrane of the next neuron

7. Neurotransmitters may have excitatory or inhibitory effects

8. Once a signal has been sent, neurotransmitters are removed from the synapse; may return or be metabolized

Neurons use enzymes to synthesize neurotransmitters

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Schematic representation of the action of a synthetic enzyme. A precursor molecule and another chemical fragment both bind to the enzyme. The fragment has a tendency to connect with the precursor, but the connection is made much more likely because of the way the enzyme lines up to the two parts. After the connection is made, the new transmitter molecule separates from the enzyme.

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Schematic representation of the release of neurotransmitter molecules from synaptic vesicles in the axon terminal of one neuron and the passage of those molecules across the synapse to receptors in the membrane of another neuron.

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Schematic representation of the action of a metabolic enzyme. The transmitter molecule binds to the enzyme is such a way that the transmitter molecule is distorted and “pulled apart.” The fragments then separate from the enzyme.

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© 2011 McGraw-Hill Higher Education. All rights reserved.

Examples of Drug ActionsExamples of Drug Actions

Alter neurotransmitter availability Agonists

Mimic neurotransmitters

Antagonists Occupy neurotransmitter and prevent its

activation

Interference with reuptake

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Chemical Theories of Chemical Theories of BehaviorBehavior

Attempts to explain normal variations in behavior in terms of changes in brain chemistry Greek physician Hippocrates and the four

humors Chinese philosophy—yin and yang

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Chemical Theories of Chemical Theories of BehaviorBehavior

No single biochemical theory of drug dependence has achieved sufficient experimental support

Monoamine theory of mood—too little activity in monoamine systems can cause depression, too much can cause mania

Brain Imaging Techniques: Brain Imaging Techniques: PET ScanPET Scan

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Brain Imaging Techniques: Brain Imaging Techniques: MRI ScanMRI Scan

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© 2011 McGraw-Hill Higher Education. All rights reserved.

Chapter 4Chapter 4

The Nervous System