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DREXEL PSY 310 - Ch 4 The Nervous System

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HomeostasisComponents of the Nervous SystemNeuronsNeuron SchematicGliaNeurotransmissionThe Nervous System(s)Somatic Nervous SystemAutonomic Nervous SystemCentral Nervous SystemChemical Pathways in the BrainDopamineDopamine PathwaysNorepinephrineSerotoninAcetylcholineEndorphinsGABA (Gamma-amino butyric acid)GlutamateCommon NeurotransmittersMajor Brain StructuresLife Cycle of a NeurotransmitterSynthesisSchematic Representation of the Action of…Examples of Drug ActionsChemical Theories of BehaviorBrain Imaging TechniquesThe Nervous System Homeostasis- Humans maintain their internal environment within certain limits Examples: body temperature, water content, glucose concentrations, etc- Psychoactive drugs influence homeostasis Alcohol inhibits vasopressin release (antidiuretic hormone) Thus, after a drink more urine is produced Compared to light drinkers, heavy drinkers produce less urine after a drink During alcohol withdrawal, heavy drinkers exhibit increased vasopressin releaseComponents of the Nervous System- Two major types of cells in the nervous system Neurons (or nerve cells) Glia (or glial cells)Neurons- Major function: primary elements of the nervous system that analyze and transmit information- Four defined regions:Cell body Contains the nucleus and other sustaining substancesDendrites Contains receptors which respond to chemical signals  Psychoactive drugs activate or inhibit neuron based on type of receptorAxon Conducts the action potentialAxon terminals Contains synaptic vesicles which store neurotransmittersNeuron SchematicGlia- Major functions: Provide firmness and structure to the brain Get nutrients into the system Eliminate waste Form myelin Communicate with other glia & neurons- Glia also create the blood-brain barrier Protects the brain from toxic chemicals Psychoactive drug molecules must be able to pass the barrierNeurotransmission- Action potential: a brief electrical signal transmitted along the axon- Brief chain of events:1. Resting potential is caused by uneven distribution of ionso The neuron is hyperpolarized2. Ion channels open allowing electrically charged particles to move inside the cello As a result, the neuron may become depolarizedo “all-or-none” action potential occurso Note: Blocking ion channels prevents the action potential and disrupts neuronal communication3. Neurotransmitters are releasedThe Nervous System(s)Somatic nervous system - Sensory information into the CNS- Motor information back out- Voluntary actionsAutonomic nervous system (ANS) - Sympathetic branch- Parasympathetic branch- Involuntary functions of the bodyCentral nervous system (CNS) - Brain- Spinal cordSomatic Nervous System- Controls voluntary actions- Carries sensory information into the central nervous system- Carries motor (movement) information back out to the peripheral nerves- Acetylcholine is the neurotransmitter at neuromuscular junctionsAutonomic Nervous System- Monitors and controls the body’s internal environment and involuntary functions Examples: heart rate and blood pressure Many psychoactive drugs affect the brain and the autonomic nervous system - Two branches often act in oppositionSympathetic branch “Fight or Flight”Parasympathetic branchnorepinephrine is involved in  heart rate acetylcholine is involved in  heart rateCentral Nervous System- Consists of the brain and the spinal cord- Has many functions: Integration of information Learning and memory Coordination of activityChemical Pathways in the BrainDopamine- Mesolimbic dopamine pathway From the ventral tegmental area to the nucleus accumbens Proposed to mediate some psychotic behavior Possible component of the “rewarding” properties of drugs- Nigrostriatal dopamine pathway From the substantia nigra to the striatum Substantial cell loss leads to Parkinson’s DiseaseDopamine PathwaysNorepinephrine- Multiple pathways: Arising from the locus ceruleus in the brain stem and projecting to multiple brain areas Regulates level of arousal and attentiveness Plays a role in initiation of food intake (appetite)Serotonin- Multiple pathways: Arising from the brain stem raphe nuclei and projecting to multiple brain areas May have a role in impulsivity, aggression, depression, control of food and alcohol intake- Hallucinogenic drugs influence serotonin pathways Example: LSDAcetylcholine- Arising from nucleus basalis and projecting widely throughout the cerebral cortex- Involved in Alzheimer’s disease and learning and memoryEndorphins- Found throughout the brain- Naturally occurring opioid-like chemicals- Play a role in pain relief and other functionsGABA (Gamma-amino butyric acid)- Found in most regions of the brain- Inhibitory neurotransmitterGlutamate- Found in most regions of the brain- Excitatory neurotransmitterCommon NeurotransmittersNeurotransmitterType of effect CNS changes Drugs of abuseDopamine inhibitory-excitatoryeuphoriaagitationparanoiaamphetaminescocaineGABA inhibitory sedationrelaxationdrowsinessdepressionalcoholbarbituratesSerotonin excitatory-inhibitorysleeprelaxationsedationLSDAcetylcholine excitatory-inhibitorymild euphoriaexcitationinsomnianicotineEndorphins inhibitory mild euphoriablock painslow respirationopioidsMajor Brain StructuresLife Cycle of a Neurotransmitter1 Neurotransmitter precursors are found circulating in the blood supply2 Uptake Selected precursors are taken up by cells3 Synthesis Precursors are synthesized into neurotransmitters through the action of enzymes4 Storage Neurotransmitters are stored in small vesicles5 Release When the action potential arrives, neurotransmitters are released into the synapse6 Binding Released neurotransmitters bind with receptors on the membrane of the postsynaptic neuron-Neurotransmitters may have excitatory or inhibitory effects7 MetabolismOnce a signal has been sent, neurotransmitters are removed from the synapse; may return or be metabolizedSynthesis Schematic Representation of the Action of…synthetic enzyme metabolic enzymeExamples of Drug Actions- Alter neurotransmitter availability in the synapse Through actions on: synthesis, storage, release, uptake, metabolism Example: Many antidepressants block the reuptake of dopamine, serotonin and/or norepinephrine- Direct action on the receptorDrug as agonist Drug as antagonistMimic neurotransmitters by activating the Occupy neurotransmitter and prevent receptorreceptor


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DREXEL PSY 310 - Ch 4 The Nervous System

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