DREXEL PSY 310 - Ch 4 The Nervous System (6 pages)

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Ch 4 The Nervous System



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Ch 4 The Nervous System

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Pages:
6
School:
Drexel University
Course:
Psy 310 - Drugs & Human Behavior
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The 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 release Components 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 substances Dendrites Contains receptors which respond to chemical signals Psychoactive drugs activate or inhibit neuron based on type of receptor Axon Conducts the action potential Axon terminals Contains synaptic vesicles which store neurotransmitters Neuron Schematic Glia 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 barrier Neurotransmission Action potential a brief electrical signal transmitted along the axon Brief chain of events 1 Resting potential is caused by uneven distribution of ions o The neuron is hyperpolarized 2 Ion channels open allowing electrically charged particles to move inside the cell o As a result the neuron may become depolarized o all or none action potential occurs o Note Blocking ion channels prevents the action potential and disrupts neuronal communication 3 Neurotransmitters are released The Nervous System s Somatic nervous system Autonomic nervous system ANS Central nervous system CNS Sensory information into the CNS Motor information back out Voluntary actions Sympathetic branch Parasympathetic branch Involuntary functions of the body Brain Spinal cord Somatic 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 junctions Autonomic 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 opposition Sympathetic branch Fight or Flight norepinephrine is involved in heart rate Central Nervous System Consists of the brain and the spinal cord Has many functions Integration of information Learning and memory Coordination of activity Chemical Pathways in the Brain Dopamine Parasympathetic branch acetylcholine is involved in heart rate 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 Disease Dopamine Pathways Norepinephrine 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 LSD Acetylcholine Arising from nucleus basalis and projecting widely throughout the cerebral cortex Involved in Alzheimer s disease and learning and memory Endorphins Found throughout the brain Naturally occurring opioid like chemicals Play a role in pain relief and other functions GABA Gamma amino butyric acid Found in most regions of the brain Inhibitory neurotransmitter Glutamate Found in most regions of the brain Excitatory neurotransmitter Common Neurotransmitters Neurotransmitte r Dopamine Type of effect CNS changes Drugs of abuse inhibitoryexcitatory amphetamines cocaine GABA inhibitory Serotonin excitatoryinhibitory Acetylcholine excitatoryinhibitory Endorphins inhibitory euphoria agitation paranoia sedation relaxation drowsiness depression sleep relaxation sedation mild euphoria excitation insomnia mild euphoria block pain slow respiration alcohol barbiturates LSD nicotine opioids Major Brain Structures Life Cycle of a Neurotransmitter 1 2 3 4 5 Neurotransmitter precursors are found circulating in the blood supply Uptake Selected precursors are taken up by cells Synthesis Precursors are synthesized into neurotransmitters through the action of enzymes Storage Neurotransmitters are stored in small vesicles Release When the action potential arrives neurotransmitters are released into the synapse 6 Binding Released neurotransmitters bind with receptors on the membrane of the postsynaptic neuron Neurotransmitters may have excitatory or inhibitory effects 7 Metabolis m Once a signal has been sent neurotransmitters are removed from the synapse may return or be metabolized Synthesis Schematic Representation of the Action of synthetic enzyme metabolic enzyme Examples 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 receptor Drug as agonist Drug as antagonist Mimic neurotransmitters by activating the Occupy neurotransmitter and prevent receptor receptor activation Chemical Theories of Behavior Many attempts to explain normal variations in behavior in terms of changes in brain chemistry Historical precedents Greek physician Hippocrates and the four humors Chinese philosophy yin and yang Monoamine theory of mood Dopamine serotonin noreprinephrine Too little activity in monoamine systems can cause depression Too much can cause mania No single biochemical theory of mood or drug dependence has achieved sufficient experimental support Brain Imaging Techniques Benefits Positron Emission Tomography PET Direct measure of brain activity Limitation s Injection of radioactive materials No information about brain structure Functional Magnetic


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