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Chapter 3

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PSYC 100
Samuel Reed

PSYC 100 Chap. 2 - Traditional method: Observing electrical activity of the brain through EEG recordings > Dalhousie’s John Connolly used EEG on patient experiencing locked-in syndrome (alert patient in an unresponsive body) >> EEG is devised to stimulate certain stimuli A) COMMUNICATION IN THE NERVOUS SYSTEM (PG 86) - behavior depends on rapid information processing; information travels instantaneously A)1) NERVOUS TISSUE Cells in the nervous system falls into 2 categories: http://www.youtube.com/watch?v=FR4S1BqdFG4 http://www.youtube.com/watch?v=jOkp68kUQvc&feature=related Neurons Glia (literally glue) - individual cells (video shows that neurons - provides various type of support for neurons aren’t connected to each other) - smaller than neurons - receive, integrate, transmit information - outnumber by 10:1; 50% of brain’s volume consisting glial cells - function: > supply nourishment to neurons > remove neuron’s waste product > provide insulation around many axons - orchestrate the development of the nervous system in the human embryo - may also send and receive chemical signals -may be implicated in diseases such as amyotrophic lateral sclerosis (ALS) and Parkinson - important role in memory formation - gradual deterioration: Alzheimer’s disease - play a role in the experience of chronic pain, schizophrenia, mood disorders b a d c a) Soma [cell body] - contains cell nucleus and much of the chemical machinery common to most cells b) Dendritic Trees (Branch: Dendrites) - receive information from many other cells c) Axon - long thin fibre (can be a metre long) - transmits information away from soma to other neurons, muscles or glands d) Myelin sheath - white, fatty substance - insulate material, derived from glial cells that encases some axons - the sheath speeds up the transmission of signals that move along axons - if deteriorates, signals may not be transmitted effectively > degeneration of myelin sheaths: causes loss of muscle control and seen with the disease multiple sclerosis So, what happened if the derived glial cells encases some axons? e) Terminal buttons - small knobs - secrete chemicals called neurotransmitters - may activate neighbouring neurons - points where neurons interconnect are called synapses - synapses: junction where information is transmitted from one neuron to another Information Path 1) Receive information through dendrites > Pass through soma > Move away through axon > Back to another the dendrites of other neurons at synapses (the meeting point) A)2) THE NEURAL IMPULSE: USING ENERGY TO SEND INFORMATION Experimenters: Alan Hodgkin and Andrew Huxley “dissect” axon from squid because it’s bigger Neutron at Rest: A Tiny Battery - Inside and outside neurons : Fluids containing electrically charged atoms and molecules called ion - Cell membrane: semipermeable < this permits movement of some ions - Sodium and potassium ions (+vely charged) and Chloride ions (-vely charged) flow back and forth - Difference in flow rates leads to slightly higher concentration of negatively charged ions inside the cell - Therefore at rest, neuron is a tiny battery - The resting potential of a neuron is its stable, negative charge when the cell is inactive; 70millivolts The Action Potential (page 88- re-read) - cell is quiet as long as the voltage of neuron remains constant and no messages are being sent - when neuron is stimulated, channels in its cell membrane open, allowing positively charged sodium ions to rush in - action potential: very brief shift in a neuron’s electrical charge (positive to negative or vice- versa) that travels along an axon (like a spark) - after the firing of an action potential, the cell membrane close up - some time is needed to open again and until that time, the neuron cannot fire - the absolute refractory period: a time period where the neuron has to wait for the cell membrane to reopen before being able to fire up again - the downtime period : 1 – 2 milliseconds The All-or-None Law - either neurons fires or they don’t - Action potentials are all the same size; weaker stimuli do not produce smaller action potentials - strength of a stimulus: determined by the varying rate of firing action potentials > the stronger the stimulus, the more rapid the volley of the neural impulses will be >> thicker axons transmit neural impulses more rapidly than thinner ones do A)3) The Synapse: Where Neurons Meet (pg 89) Sending Signals: Chemicals as Couriers Synaptical cleft: a microscopical gap between the terminal button of a neuron with the cell membrane of another neuron > for communication between neurons to occur, the signal has to cross this gap >> neuron that send: presynaptic neuron >>> neuron that receives: postsynaptic neuron Message Path 1) action potential arrives at axon’s terminal button and triggers the release of neurotransmitters (chemical that transmits information from one neuron to another) > neurot. Are stored in small sacs known as synaptic vesicles 2) neurotransmitters are released when the vesicle fuses with the membrane of the presynaptic neuron and its content spill into synaptic cleft 3) neurotransmitters will then diffuse to the postsynaptic cell (the membrane of the receiving cell) > neurot. may bind with special molecules at the receptor sites >> the sites: specifically tuned to recognize and respond to some neurotransmitters but not to others >>> so, what happen if the “sites” don’t recognize the neurot? In general, Axon (action potential) > neurotransmitters (synaptic vesicles) > fuses with presynaptical neuron (neurot. are released) > synaptical cleft > postsynaptical neuron (may bind with special molecules at receptor sites). http://www.youtube.com/watch?v=ifD1YG07fB8&feature=related Receiving Signals: Postsynaptic Potentials http://www.youtube.com/watch?v=LT3VKAr4roo http://www.youtube.com/watch?v=Gt5g4bfrtxs / http://www.youtube.com/watch? v=YP_P6bYvEjE Postsynaptic Potential (PSP) : occurred when neurot. and receptor molecule combine > which is a voltage change at receptor site on postsynaptical cell membrane PSP: do not follow all-or-none law; but it is graded. They vary in size, increase or decrease the probability of a neural impulse in the receiving cell proportion to the amount of voltage change Two types of message can be sent from cell to cell: Excitatory or inhibitory > Excitatory PSP: +ve voltage shift that increases the likelihood of PSP to fire action potentials >> Inhibitory PSP: -ve voltage shift that decreases the likelihood of PSP to fire action potentials Excitatory and Inhibitory PSP: only last for a fraction of seconds, then neurotransmitters drift away from receptor sites or deactivated by enzymes that convert them in an inactive form > Neurot. become inactive But, most are reabsorbed by presynaptical potential through the reuptake process > Reuptake: neurot. are sponged (absorbed) up from the synaptic cleft by the presynaptic membrane >> reuptake: allows neurot. to be recycled Integrating Signals: Neural Networks - neuron has to integrate signals arriving at many synapses before deciding whether or not to fire neural impulse - enough excitatory PSPs = electrical currents can add up and fire action potentials - enough inhibitory PSPs = electrical currents tend to cancel the effect of excitatory PSPs In general, The state of neuron is balanced by excitatory and inhibitory influences. - Neurons are interlinked in complex chains, pathways, circuits and networks - Perceptions, thoughts and actions depend on patterns of neural activity in elaborate neural networks - The networks contain interconnected neurons that fire together or sequentially to perform certain functions - Links in the networks are fluid- here new synapses will replace old synapses - Ironically, elimination of old synapses play a larger role in scalpting the neural networks compared to the creation of new synapses - Reason: nervous system always create new synapses more than needed, thus gradually replace the old synapses - Synaptic pruning: the process of eliminating less active/old synapses > key process in the neural networks formation which is important to communication in the nervous system Donald Hebb: focused his work on the linkage of neurons to form networks > understanding the brain and its processes was fundamental to understanding behavior >> neurons are linked in complex neural networks or cell assemblies (they don’t work alone) >> Hebbian Learning Rule >>>> Neurophysiological postulate: one neuron stimulating another neuron repeatedly produce changes in the synapse; learning has taken place. * The change failed to be described by Hebb Neurotransmitters and Behavior - 9 well-established, classic (small molecule) transmitters - 40 neuroceptide chemicals that function, at least part-time as neurotransmitters - a handful recently recognized “novel” neurot. - specific neurot. work at specific kinda synapses > the binding process work like a matching lock and key >> specific transmitters can only delivers signals only at certain locations on cell membranes >>> this specialization reduces cross talk between densely packed neurons – nervous system’s communication becomes more precise Types of Neurotransmitters and Behavior Neurotransmitters Functions and Characteristics Acethylcoline - transmitter between motor neurons and voluntary muscles (Ach) - contribute to your attention, arousal and memory - associated with certain memory lossess such as Alzheimer – treatment of Ach through drug treatment can slow down Alzheimer > by amplifying Ach activity BUT, Ach (and other neurot.) maybe influenced by other chemicals in the brain - Synaptic receptor sites are sensitive to specific neurot. but can be fooled (e.g: nicotine “distinguish” and act as Ach) - Agonist: chemical that mimics the action of a nuerot. > produce PSPs - Antagonist: chemical that opposes the action of a neurot. > do not produce PSPs **Not all chemical other than neurot. can successfully become agonist. The failed ones will block the action of “natural transmitter” by occupying the receptor sites causing the muscle to become jammed/paralyzed—caused by an antagonist. Monoamines - Consist: Dopamine (DA), serotonin and norepinephrine (NE) (includes dopamine norepinepherine, - DA and NE can produce excitatory or inhibitory PSPs depend on the synapses serotonin) - regulate many aspects of everyday behavior - temporary alteration at monoamine synapses account more powerful effect of cocaine and amphetamines. > Those stimulants create a storm of increased activity at DA and NE synapses >> accountable for drug craving and addiction Dopamine(DA) - control voluntary movement - abnormal level could develop certain psychological disorder - degeneration causes Parkinsonism (reduced control over voluntary mvmnt) - Treatment: by using L-dopa which is converted into Dopamine to compensate the diminished dopamine activity in the brain - Also, abnormalities (overactivity) at dopamine synapses develops schizophrenia > irrational thought, hallucination, poor contact with reality, deterioration of routine adaptive behavior >> therapeutic drugs that attempt to tame schizo. are also Dopamine antagonists Serotonin - has a role in wakefulness and sleep and eating behavior - neural circuits containing serotonin modulates aggressive behavior in human and animal - abnormalities in this area cause eating disorders and obsessive- compulsive disorders Norepinephrine (NE) - low levels of NE and Serotonin activation cause depressive disorders - both are identified as the major cause for depression as most antidepressant drugs exert main effect at these synapses GABA and - consists of amino acids Glutamate Gamma-aminobutyric acid (GABA) and Glycine (-ve team) - produce only inhibitory PSPs - GABA is widely distributed in the brain and may present at 40% of all synapses - GABA is mostly responsible for the inhibition in the central nervous system > also, responsible for anxiety in humans >> disturbances may cause anxiety disorders Glutamate (+ve team) - always has excitatory effects - contribution in learning and memory - disturbances in glutamate circuits may contribute to schizophrenic disorders Endorphins - internally produced chemicals that resembles opiates in structures and effects - endorphins and receptors are widely distributed in the human body - contribute to the modulation of pain - body’s natural endorphins may be able to create similar pleasurable feeling created by opiate drugs like marijuana and heroin > such that while running, the pain may be neutralized by the feeling of exhilaration (runner’s high) - endogenous opioids contribute to the modulation of eating behavior and body’s response to stress - opiate drugs: like morphine and heroin produce highly pleasurable feeling of euphoria A)4) ORGANIZATION OF THE NERVOUS SYSTEM - communication in the nervous system is fundamental to behavior - organization of the nervous system as a whole http://www.youtube.com/watch?v=dOYOdJG0E0s&feature=g-high-c The Peripheral Nervous System - the part that extend outside the central nervous system (parts other than brain and spinal cord) - made up of nerves (bundles of neuron fibres (axons) that are routed together in the peripheral nervous system) - can be divided into 2 systems: somatic nervous system (SNS) and autonomic nervous system (ANS) 1) The Somatic Nervous System [SNS] - lets you feel the world and move around it - made up of nerves that connect to voluntary skeletal muscles and to sensory receptors [HOW INFORMATION FLOW] Receptors (in the skin, muscles and joints) >> CNS >> command from CNS >> muscles Afferent Nerve Efferent Nerve - to allow this, need 2 kind of nerve fibres: > afferent nerve fibres (axons that carry information inwards from PNS to CNS) >> efferent nerve fibres (axons that carry information outwards from CNS to PNS) * Somatic nerves are two-ways streets 2) The Autonomic Nervous System [ANS] Divided into 2 branches: a) Sympathetic division - mobilizes (use) the body’s resources for emergencies - activates fight-or-flight response - slows digestive processes - e.g: drains blood from the periphery; lessening bleeding during an injury b) Parasympathetic division - conserves bodily resources - activates processes that allow body to save and store energy - e.g: promote digestion, slow heart rate, reduce blood pressure Also, - connect to heart, blood vessels, glands and smooth muscles - completely governed by CNS but it is a separate (autonomous) system - controls: automatic, involuntary, visceral (emotional) functions that people don’t normally think about >> heart rate, digestion, perspiration - mediates physiological arousal that occurs when people experience emotions > getting goosebumps when watching horror movies >> difficult-to-control reactions are aspects of autonomic arousal - Legend: Walter Cannon introduces flight-or-fight theory > organisms respond to threat by preparing physiologically for fighting or fleeing - Hans Selye (McGill) – prolonged autonomic arousal could lead to the development of physical disease The Central Nervous System (CNS) - consists of brain and spinal cord - protected by enclosing sheath (meninges); meningitis (inflamed meninges) - CNS is immersed/soaked in fluid known as cerebrospinal fluid (CSF) > cerebrospinal fluid: nourishes and protect brain >> ventricle: hollow cavity (space) that contains cerebrospinal fluid a) The Spinal Cord - connects the brain to the rest of the body through the peripheral nervous system - also enclosed by meninges and soaked with CSF - runs from the base of the right until right below level waist - houses bundles of axons that carry brain’s commands to peripheral nerves and relay sensations from the periphery of the body to the brain >> that’s why damaging spinal cord will cause one to paralyze because it transmits signals from the brain to the motor neurons that move the body’s muscles b) The Brain - occupy the upper part of the skull - weighs 1.5kg and can be held in one hand - contains billions of interacting cells that integrate information from inside and outside the body - coordinate body’s action - enable human being to: talk, think, remember, plan, create and dream B) LOOKING INSIDE THE BRAIN: RESEARCH METHOD - mapping the brain is easy : achieved by dissecting donor’s brain - mapping the brain function is hard: need a still-functioning brain - Neuroscientist: investigators who conduct research on the brain or other part of nervous system > brain research often involves neuroscientist from different disciplines; anatomy, phyisio, bio, pharma - Usual method: electrical recordings, lesioning, electrical stimulation and brain-imaging (observe brain structure and function) 1) Electrical Recordings - Hodgkin and Huxley can record electrical activity of a single neuron but not simultaneous ac
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