Psychology Chapter 3 Notes.doc

Psychology Chapter 3 Notes: Nervous Tissue: Basic Hardware • Neurons: • cells that receive, integrate and transmit information • Soma or cell body contains nucleus and organelles • Dendrites extend from the cell and allow it to communicate with other cells • Axons are long thin fibre that communicate with other cells • Axons are covered in myelin sheath that conducts signals • MS is due to depletion of myelin sheaths • Axon ends in cluster of terminal buttons • Small knobs that secrete neurotransmitters • Neurons meet at the synapse Glia: • Cells that support and nourish the neurons Much smaller than a neuron • • Supportive, nutritive, insulate, protective (SNIP) Account for over 50% of brains volume • • Provide insulation around many axons • Myelin sheaths are derived from specialized glia cells • Orchestrate development of nervous system in the human embryo • May also send and receive signals • Play an important role in memory formation and experience of chronic pain • Impaired glial cells may contribute to schizophrenia and mood disorders The Neural Impulse: Using Energy to Send Information Work of Alan Hodgkin and Andrew Huxley (squid axons used) The Neuron at Rest: a Tiny Battery • Resting potential of a neuron is its stable, negative charge when the cell is inactive • -70 millivolts Action Potential • When neuron is stimulated, Na + ions rush into the cell Creates a positive action potential • • Channels that allows sodium ion in the cell then close and remain closed for a refrac- tory period • Makes sure the signal only travels one way • Relative refractory period occurs after this • Neuron can still be stimulated, just takes more intense stimulation to initiate an ac- tion potential The All or None Law • A neuron either fires or doesn’t • Signals travel at 100 m/s or 300 km/h The Synapse Sending Signals: Chemicals as Couriers • Neurons do not touch they are separated by synaptic cleft • Neurotransmitters are transferred through the cleft and to the post synaptic vesicle • Postsynaptic potential is a voltage change at the receptor site • Postsynaptic potentials are graded: they vary in size and increase or de- crease probability of a neural impulse in receiving cell • 2 types of messages can be sent from cell to cell: • Excitatory PSP Positive voltage change that increases likelihood that postsynaptic neuron • will fire action potentials Inhibitory PSP • • Negative voltage change that decreases the likelihood that the postsynaptic neuron will fire an action potential • Neurotransmitters are reabsorbed into the presynaptic neuron or are metabolized by enzymes on the post synaptic neuron Integrating Signals: Neural Networks • Thousands of signals are fired at a specific neuron at one time • If enough excitatory PSPs are fired, the threshold will be reached and an action poten- tial will be fired • Conversely, if enough inhibitory PSPs are fired, they can cancel the effects of the exci- tatory PSPs • The nervous system is constantly forming more synapses and eliminating less active synapses (synaptic pruning) • Donald Hebb: • Argued that understand the brain and its processes was key in understand- ing behaviour • Neurons work together in cell assemblies • “Hebbian Learning Rule” • Specifying how linkages might come about • One neuron stimulating another neuron repeatedly produces a change in synapse • Meaning: learning has taken place • Ideas are often referred to as “Hebb synapse” Neurotransmitters and Behaviour • There are 9 well established neurotransmitters • 40 additional neuropeptide chemicals that sometimes act as neurotransmitters • Neurotransmitters are specific to receptors Acetylcholine • Only transmitter between motor neurons and voluntary muscles • Contributes to attention, arousal, and memory • Inadequate amounts are associated with memory loss and even Alzheimer’s • Drug treatments available to amplify levels of acetylcholine to treat Alzheimer's • Agonist: chemical that mimics the action of a neurotransmitter (ex. Nicotine) • Antagonist: chemical that blocks the receptor but does not stimulate a PSP Monoamines • Parkinson’s disease: • Decline in synthesis of dopamine • Treated with “L-dopa” which is converted to dopamine in the brain (crosses blood-brain barrier) • Monoamines include 3 neurotransmitters: • Dopamine, norepinephrine, and serotonin • Dopamine: used by neurons that control voluntary movements • Serotonin releasing neurons also play an important role in: • regulation of eating behaviour, sleep and wakefulness as well as ag- gression and impulsiveness • Abnormal monoamine levels are related to psychological disorders • Depression is linked to lower levels of activation at norepinephrine and serotonin • Irregular serotonin circuits are also linked to eating disorders • The dopamine hypothesis • Abnormalities in activity at dopamine synapse play a crucial role in develop- ment of schizophrenia • Temporary alterations at monamine synapse •Due to drugs such as cocaine and amphetamines •These stimulants exert most of their effects by creating a storm of activity at dopamine and norepinephrine synapses •Disregulation in this dopamine pathway appears to be the chief factor underly- ing drug craving and addiction GABA and Glutamate • Amino acids can be neurotransmitters too • GABA (gamma-aminobutyric acid) and glycine • Only produce inhibitory action potentials • GABA is present in 40% of all synapses and is responsible for inhibition in the central nervous system •Also contributes to regulation of anxiety in humans •Plays a central role in expression of seizures • Glutamate always has excitatory effects • Best known for learning and memory • Subset of glutamate circuits play a key role in “long term potentiation” • Involves durable increases in excitability at synapses • One of the basic building blocks of memory formation Endorphins • Candace Pert: •Horse riding accident, he received morphine •Morphine exerts its effects by binding to specialized receptors in the brain •Why would the brain have morphine receptors? • Nervous system produces its own morphine like substances •Endorphins • Resemble opiates in structure and effects • Contribute to modulation of pain Heredity and Behaviour: Is it all in the Genes? • Behavioural genetics: field that studies the influence of genetic factors in behaviour Basic Principles of Genetics Chromosomes and Genes • Chromosomes carry genetic information • Every cell contains 46 chromosomes, except haploid cells (23 chromosomes) • Most human characteristics are polygenic • Influenced by more than one pair of genes Investigating Hereditary Influence: Research Methods • Family Studies: hereditary influences are assessed by examining blood relatives to see how much they resemble each other on a specific trait • Ex. Schizophrenia relatives show 9 times increased risk of attaining it themselves • Twin Studies: identical and fraternal twins are assessed about a trait • Identical twins have the same genotype, while fraternal twins do not • Adoption Studies: examine resemblance between adopted children and both biologi- cal and adoptive parents • Nature vs. Nurture Genetic Mapping Process of determining location and chemical sequence of specific genes • • Will lead to advances in diagnosis and treatment of diseases • Most behavioural traits are polygenic therefore, it will be extremely difficult to deter- mine what groups of genes affect certain behaviors Interplay of Heredity and Environment • Robert Plomin • Heredity and experience influence most behaviour The Nervous System Organization of the Nervous System Peripheral Nervous System: • Composed of nerves that lie outside the brain and spinal cord • Somatic Nervous System • Composed of nerves that connect to voluntary skeletal muscles and sen- sory receptors • Require two kinds of nerve fibres • Afferent nerve fibres: axons that carry info inward to CNS • Efferent nerve fibres: axons that carry info. Outward to body • Autonomic Nervous System • Made up of nerves that connect to heart, blood vessels, smooth muscles and glands • Separate but ultimately governed by CNS • Responsible for arousal associated with emotion Composed of sympathetic and Parasympathetic • • Walter Cannon: First to study fight or flight response • • Organisms respond to threat by preparing physiologically for attack or fleet- ing from the enemy • Prolonged arousal can contribute to physical disease • Sympathetic: mobilizes body’s resources for emergencies • Creates fight or flight response • Activation slows digestive processes and drains blood from periphery (lessening bleeding in case of injury) • Sends signals to adrenal glands (release hormones) • Parasympathetic: • Conserves bodily resources • Allows body to store energy • Slows heart rate, reduces blood pressure • Promotes digestion Central Nervous System: • Protected by enclosing sheaths called “meninges” • Meningitis-when sheaths become inflamed • CNS is bathed in cerebrospinal fluid • Nourished brain & provides protective cushion • Found in hollow brain cavities “ventricles” • Brain: 1.5 kg in mass, contains billions of cells • Spinal Cord: Connects brain to PNS, runs from base of brain to below waist • •Enclosed by meninges & bathed in CSF Houses bundles of axons • •Many forms of paralysis result from cord damage Key role: transmitting signals from brain to motor neurons • Neurological Research Methods: Electrical Recordings • Hodgkin & Huxley: recorded electrical activity of neurons • Hans Berger: • German psychiatrist • Invented a machine to record brain electrical activity • “electroencephalograph” (EEG) Monitors activity of brain over time by recording electrodes attached to scalp • •Sums and amplifies electric potentials occurring in many thousands of brain cells •Recordings are translated into “brain waves” •Different wave patterns associated with different behaviour and mental activities •Used to diagnose neurological disorders Lesioning: • Observations of behavioural changes in brain damage case studies (H.M. Studied by MILNER) • Suffered from epilepsy as a child • Had portions of his brain removed (medial temporal lobe, hippocampus & amyg- dala) • Surgery reduced effects but also had cons • He then suffered from amnesia (anterograde-could not form new longterm memo- ry) • Had normal short term memory • Case studies have limitations: subjects not plentiful, hard to determine severity of brain damage, variations in subject history • Lesioning involves destroying a piece of the brain to determine its role • By inserting a high frequency el