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Chapter 3

Chapter 3 - The Biological Bases of Behaviour.docx

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Dax Urbszat

Chapter 3 - The Biological Bases of Behaviour The Biological Bases of Behaviour  Brain is assumed to be the basis of most of what differentiates us from other mammals— language, reasoning, consciousness, the self, and many other human qualities  Athletes who sustained head injuries 20 years ago, simply told to “walk off”  Neuropsychology: study of the brain  Sandra Witelson: well known for research for having one most extensive collections of preserved human brain, got opportunity to study brain of Albert Einstein  One of enduring mysteries in study of the brain related to localization of function— discovering which parts of the brain are associated with specific behaviours and functions Communication in the Nervous System  Nervous system is a complex communication network in which significant signals are constantly being transmitted, received, and integrated  Nervous system handles information, just as circulatory system handles blood  Nervous Tissue: The Basic Hardware o Neuron - cell in NS that receive, integrate, & transmit info  Soma or cell body - contains cell nucleus and much of chemical machinery common to most cells (soma is Greek word for body)  Dendrites - part of neuron that are specialized to receive information (feeler-like structures)  Axon - long, thin fibre that transmits signals away from the soma to other neurons or to muscles or glands (sometimes over meter long); may branch off to communicate with a number of other cells  Myelin sheath - insulating material, derived from glia cells, that encases some axons (deterioration of myelin sheath: multiple sclerosis)  Terminal buttons - small knobs that secrete chemicals called neurotransmitters  Synapse - a junction where info is transmitted from one neuron to another o Information is received at the dendrites, passed through the soma and along the axon, and is transmitted to the dendrites of other cells at meeting points called synapses o Glia - cells found throughout NS that provide various types of support for neurons; outnumber neurons by about 10 to 1; account for over 50% of brain’s volume; implicated in diseases such as amyotrophic lateral sclerosis and Parkinson’s disease; play important role in memory information and deterioration of glia tissue might contribute to emergence of Alzheimer’s disease; play role in experience of chronic pain and impaired neural-glia communication might contribute to psychological disorders such as schizophrenia and mood disorders  The Neural Impulse: Using Energy to Send Information o Resting potential - a neuron's stable, negative charge when the cell is inactive (like a tiny battery) o Action potential - very brief shift in neurons electrical charge that travels along an axon  The Absolute Refractory Period: the minimum length of time after an action potential during which another action potential cannot begin  Followed by relative refractory period: the neuron can fire, more intense stimulation is required to initiate an action potential o All-or-none law  Neural impulse: is an all-or-none proposition, like firing a gun -can’t half fire, either fire or doesn’t -action potentials all same size -weaker stimuli do not produce smaller action potentials  Neurons can convey information about strength of stimulus -do so by varying rate at which they fire action potentials  Stronger stimulus will cause cell to fire more rapid volley of neural impulses than weaker stimulus  Transmit neural impulses at different speeds  Thicker axons transmit neural impulses more rapidly than thinner ones do  Complicated process of neural transmission takes only few thousandths of second  The Synapse: Where Neurons Meet o Transmission takes place at special junctions called: synapses, which depend on chemical messengers Sending Signals: Chemicals as Couriers  Synaptic Clef: microscopic gap between the terminal button of one neuron and the cell membrane of another neuron -neuron that sends signal across gap from presynaptic neuron to postsynaptic neuron  How messages travel across the gaps between neurons: -the arrival of an action potential at axon’s terminal buttons triggers the release of neurotransmitters  Neurotransmitters: chemicals that transmit information from one neuron to another  Most of these chemicals are stored in small sacs called: synaptic vesicles  Neurotransmitters released when vesicle fuses with membrane of presynaptic cell and contents spill into synaptic cleft  Neurotransmitters diffuse across the synaptic cleft to membrane of receiving cell  Bind with special molecules in postsynaptic cell membrane at various receptor sites Sites tuned to recognize and respond to some transmitters but not to others  Receiving Signals: Postsynaptic Potentials  Postsynaptic potential (PSP): voltage change at receptor site on a postsynaptic cell membrane -do not follow the all-or-none law as action potentials do -are graded: vary in size and increase or decrease the probability of neural impulse in receiving cell in proportion to amount of voltage change  Two types of messages can be sent from cell to cell: excitatory and inhibitory  An inhibitory PSP: a negative voltage shift that decreases the likelihood that postsynaptic neuron will fire action potentials -direction of voltage shirt and nature of PSP, depend on which receptor sites are activated in postsynaptic neuron  The excitatory or inhibitory effects produced at synapse last only fraction of a second  Neurotransmitters drift away from receptor sites or are inactivated by enzymes that metabolize (convert) them into inactive forms  Reuptake: process in which neurotransmitters are sponged up from the synaptic cleft by presynaptic membrane -allows synapses to recycle their materials Integrating Signals: Neural Networks  Neuron may receive symphony of signals from thousands of other neurons  Same neuron may pass messages along to thousands of neurons as well  Neuron must do great deal more than simply relay messages it receives  Must integrate signals at many synapses before it decides whether to fire neural impulse  If enough excitatory PSPs occur in neuron, electrical currents can add up, causing cell’s voltage to reach threshold at which action potential will be fired  Neuron weighted balance between excitatory and inhibitory influences  Rita Carter: “The firing of a single neuron is not enough to create the twitch of an eyelid in sleep, let alone a conscious impression… Millions of neurons must fire in unison to produce the most trifling thought”  Most neurons are interlinked in complex chains, pathways, circuits and networks  Networks consist of interconnected neurons that frequently fire together or perform certain functions  Links in networks are fluid  The elimination of old synapses appear to play larger role in sculpting of neural networks than creation of new synapses  Linkage of neurons to form networks was focus of work of McGill University’s Donald Hebb, said: “when an axon of cell A is near enough to excite a cell B and repeatedly or persistently takes part in firing it, some growth process or metabolic change takes place in one or both cells such that A’s efficiency, as one of the cells firing B, is increased”  One neuron stimulating another produces changes in the synapse (learning’s shadowing by Hebb)  Hebb’s ideas often referred to as the Hebb Synapse and continue to influence work today  Hebbs 1949 text set stage for focus on neurophysiology and been listed as number four of the 100 most influential publication in cognitive science -important resource in neuroscience  Neurotransmitters and Behaviour  Nervous system relies on chemical couriers to communicate information between neurons  Neurotransmitters are fundamental behaviour, playing key role in everything from muscle movements to moods and mental health  There are nine well-established transmitters, not only two, at least 40 additional neuropeptide chemicals that function, at least part-time  Specific neurotransmitters work at specific kinds of synapses  Transmitters deliver messages by binding to receptor sites on postsynaptic membrane  Transmitter can’t bind to just one site  Binding process operates like a lock and key- a transmitter has to fit into a receptor site for binding to occur  Specialization reduces cross talk between densely packed neurons, making nervous system’s communication more precise Acetylcholine  Discovery that cells communicate by releasing chemicals, was first made connection with transmitter acetylcholine (ACh)  Has been found throughout nervous system  It is the only transmitter between motor neurons and voluntary muscles  Every move you make depends on Ach released to muscles by motor neurons  Appears to contribute to attention, arousal, and memory  Ach in certain areas in brain associated with memory losses seen in Alzheimer’s disease - the drug treatments currently available, slow down progress of the disease  Activity of Ach influenced by other chemicals in the brain  Synaptic receptor sites are sensible to specific transmitters -sometimes they try to be fooled by other chemical substances  Agonist: chemical that mimics the action of a neurotransmitter  Not all chemicals that fool synaptic receptors are agonists  Some chemicals bond to receptors but fall to produce PSP - temporarily block action of natural transmitter by occupying its receptor sites - act as antagonist  Antagonist: chemical that opposes the action of a neurotransmitter Monoamines  Include three neurotransmitters: dopamine, norepinephrine (NE), and serotonin a. Dopamine (DA): used by neurons that control voluntary movements -degeneration of neurons causes Parkinsonism (a disease marked by tremors, muscular rigidity, and reduced control over voluntary movements)  Drug used to treat Parkinsonism: converted to dopamine in brain to compensate for diminished dopamine activity b. Serotonin releasing neurons appear to play prominent role in regulation of sleep and wakefulness and eating behaviour  Neural circuits using serotonin modulate aggressive behaviour in animals and evidence relates serotonin activity to aggression in humans  Abnormal levels of monoamines in brain been related to development of certain psychological disorders  Abnormalities in serotonin circuits has been factor in eating disorders and in obsessive compulsive disorders  Lower NE and serotonin synapses in depressed people  The dopamine hypothesis asserts: abnormalities in activity at dopamine synapses play crucial role in development of schizophrenia  Serve mental illness marked by irrational thought, hallucinations, poor contact with reality, and deterioration of routine adaptive behaviour  Schizophrenia requires hospitalization more often than other psychological disorders  The over activity in dopamine circuits constitutes neurochemical basis for schizophrenia because the therapeutic drugs that tame schizophrenic symptoms are known to be DA antagonists that reduce neurotransmitter’s activity  Alternations at monoamine synapses appear to account for powerful effects of amphetamines and cocaine  Theorists believe that rewarding effects of most abused drugs depend on increased activity in particular dopamine pathway -dysregulation in dopamine pathway appears to be chei factor underlying drug craving and addiction GABA and Glutamate  transmitters consists of amino acids  two of these, gamma-aminobutyric acid (GABA) and glycine produce only inhibitory postsynaptic potentials  some transmitters like Ach and NE are versatile  appear to have inhibitory effects at virtually all synapses where either is present  receptors are widely distributed in brain and present 40% of all synapses  GABA: responsible for much of inhibition in central nervous system  GABA is involved in regulation of anxiety in humans and that disturbances in GABA circuits may contribute to some types of anxiety disorders  Glutamate another amino acid neurotransmitter widely distributed in brain -always has excitatory effects -best known for contribution to learning and memory Endorphins  Occurs to Pert and others that the nervous system must have its own internally produced, morphine like substances  Endorphins: internally produced chemicals that resemble opiates in structure and effects  A number of opiate-substances were identified  Endorphins and receptors widely distributed in body, contribute to modulation of pain  Endogenous opioids contribute to modulation of eating behaviour and body’s response to stress  In addition to painkilling effects, opiate drugs (morphine and heroin) produce highly pleasurable feelings of euphoria  Euphoric effect explains why heroin is in widely abused  Pain caused by long run may trigger release of endorphins Organization of the Nervous System  The Peripheral Nervous System  First and most important division separates central nervous system from peripheral nervous system  Made up of all those nerves that lie outside the brain and spinal cord  Nerves: bundles of neuron fibers (axons) that are routed together in he peripheral nervous system  Part extends outside central nervous system  Can be subdivided into somatic nervous system and autonomic nervous system The Somatic Nervous System  Made up of nerves that connect to voluntary skeletal muscles and to sensory receptors  Nerves are cables to carry information from receptors in skin, muscles and joints to central nervous system and carry commands from CNS to muscles -functions require two kinds of nerve fibers  Afferent nerve fibers: axons that carry information inwards to the central nervous system from the periphery of the body  Efficient: axons that carry information outwards from central nervous system to the periphery of the body  Somatic nerves are “two-way streets”  Let’s you feel the world and move around in it The Autonomic Nervous System  Made up of nerves that connect to the heart, blood vessels, smooth muscles and glands  Is a separate system  Controls automatic, involuntary, visceral functions that people don’t normally think about (heart rate, digestion, and perspiration)  Mediates much of physiological arousal that occurs when people experience emotions  Walter Cannon: called it the fight-or-flight of preparing physiology for attacking or fleeing from the enemy  Subdivided into two branches  Sympathetic division: branch of the autonomic nervous system that mobilizes the body’s resources for emergencies -creates fight-or-flight response -slows down digestive process and drains blood from the periphery  Parasympathetic division: branch that generally conserves bodily resources -slow down heart rate, reduce blood pressure, and promote digestion  The Central Nervous System  Consists of the brain and spinal cord  Protected by enclosing sheaths called the meninges  Bathed in its own special nutritive soup, the cerebrospinal fluid  Cerebrospinal fluid: nourishes the brain and provides a protective cushion for it -the hallow cavities that are in the brain and filled with CSF are called ventricles The Spinal Cord o Connects the brain to the rest of the body through peripheral nervous system o Bathed in CSF o Is an extension of the brain o Runs from base of brain to the waist o Houses bundles of axons that carry brain’s commands to peripheral nerves and relay sensations form periphery of the body to brain o Many forms of paralysis result from spinal cord damage o Spinal cord transmits signals from brain to motor neurons that move the body’s muscles The Brain  The crowning glory of the central nervous system  Fills the upper portion of the skull  Weighs about 1.5 kilograms and could be held in one hand  Contains billions of interacting cells that integrate information from inside and outside the body Looking Inside the Brain: Research Methods  The brain can be mapped out relatively by examining and dissecting brains removed from animals or from deceased humans  Mapping of brain function requires working brain  People who conduct this research: neuroscientists  Anatomy, physiology, biology, pharmacology, neurology, neurosurgery, and psychology  Depended on electrical recordings, lesioning and electrical stimulation  Electrical Recordings  Hodgkin and Huxley recorded the electrical activity of individual neurons  Recordings of single cells in brain have been valuable, but need ways of recording simultaneous activity  Electric activity: 1875à no way of excessing neurons without opening skull  1929: Hans Bergerà invented machine that could record broad patterns of brain electrical activity from intact skulls  Electroencephalograph (EGG): device that monitors the electrical activity of the brain over time by means of recording electrodes attached to surface of the scalp  sums and amplifies electric potentials occurring in brain cells  translated into line tracings, called brain waves - provide useful overview of electrical activity  Different brain waves are determined by different mental states  EGG often used in clinical diagnosis of brain damage and neurological disorders  EGG can be used to identify patterns of brain activity that occur when participants engage in behaviors or experience emotions  Lesioning  Brenda Milner: studies the case of an individual suffering from specific brain damage -after his surgery suffered amnesia (anterograde amnesia) -her work was establishing the role of the medial structures of the temporal loves in memory and the existence of multiple memory systems  Scientists were able to generate and examine many ideas about the connection between brain structures (hippocampus and memory)  Doing research on patients who have brain damage have limitations  Lesioning: destroys a piece of the brain -done by inserting an electrode into a brain structure and passing a high-frequency electric current through it to burn the tissue and disable the structure -requires researchers to get to an electrode to particular place buried deep inside the brain -do it with a stereotaxic instrument: device used to implant electrodes at precise locations in brain  Electrical Stimulation of the Brain  Involves a weak electric current into a brain structure to stimulate (activate) it  Current delivered through an electrode  Does not exactly duplicate normal signals to brain  If areas in brain are stimulated, the electrodes are implanted with same stereotaxic techniques using in lesioning procedures  Most ESB research conducted on animals  Wilder Penfield: founding of world-famous Montreal Neurological Institute and Hospital  Transcranial Magnetic Stimulation  A new technique that permits scientists to temporarily enhance or depress activity in a specific area of the brain  Magnetic coil is mounted on sm
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