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PSYCH 485 (23)


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University of Waterloo
Jiahua Chen

Chapter 4: Biology of Behaviour ● human brain = 1.5 kg ● contains 10 billion – 100 billion nerve cells and about as many helper cells  nerve cells differ in shape, size, and chemicals they produce  nerve cells organized into modules (clusters of nerve cells that communicate with each other) that are connected through neural circuits to other modules that communicate with each other ● Peirre Flourens – suggested different parts of nervous system were responsible for different functions but conflicting evidence now – some functions more spread out ● Donald Hebb (50 years ago) – provided better understanding by showing that nerve cells are organized into larger units – functioning could be understood by individual cells and larger networks they comprised Structure of Nervous System: ● brain – controls behaviour, processes and retains information we receive from environment, and regulates body's physiological processes  receives information from body's sensory receptors and is connected with muscles and glands of body ● nervous system consists of two divisions:  central nervous system – brain and spinal cord ■ spinal cord – long, thin collection of nerve cells attached to base of brain and running length of spinal collumn ● contains circuits of nerve cells that control some simple reflexes (pulling away from hot) ■ communicates with rest of body through nerves ● nerves – bundle of nerve fibers that transmit information netween CNS and body's sense organs, muscles, and glands  attached to spinal cord and base of brain  peripheral nervous system – cranial and spinal nerves; that part of the nervouse system peripheral to brain and spinal cord ■ consists of nerves that connect central nervous system with sense organs, muscles and glands ● human brain has 3 major parts: brain stem, cerebellum, cerbral hemisphere  lower part of cerebellum and brain stem projects beneath left cerebral hemisphere – upper part is normally hidden (see fig. 4.3) ● Brain stem – most primitive regions of brain, and its functions are basic ones – control of physiological functioning and automatic behaviour (amphibeans have brain stem and simple cerebellum) ● cerebral hemispheres – constitue large portion of brain  contains parts of brain that evolved most recently: involved in behaviours of particular interest to psychology ● cerebellum – attached to bain of brain, looks like miniature version of cerebral hemispheres  functions are control and coordination of posture and movement, especially rapid ones ● brain is encased in skull and spinal cord runs through middle of hollow bones (vertebra: vertebral column) ● both brain and spinal cord are enclosed in 3 layered set of membrane called meninges ● float in clear liquid called cerebrospianl fluid (CSF)  fills between 2 meninges, providing cushioning ● cerebral cortex – outer layer of cerebral hemisphere of brain, approxiamtely 3 mm thick  often referred to as grey matter – contains billions of nerve cells (abundant in nerve cell bodies rather than axons)  where perceptions take place,memories are stored, plans are formulated and executed  nerve cells in cerebral cortex are connected to other parts of brain by layer of nerve fibres called white matter ■ shiny white appearance of substance that coats and insulates axons that travel trough area (axons' myelin sheath)  very wrinkled appearance – full of bulges seperated by grooves ■ bulges – gyri ■ grooves – fissures ● they expand amount of surface are of cortex and greatly increase number of nerve cells – more complex the brain, larger cortex ● Peripheral nervous system – consists of nerves that connect central nervous system with sense organs, muscles and glands  nerves carry incoming and outgoing information  sense organs detect changes in environment and send signals throughnerves to central nervous system  brain sends signals trhough nerves to muscles (causing behaviour) and glands (producing adjustments in internal physiological processes) ● nerves – bundles of many thousands of individual fibres all wrapped in tough, protective membrane (look like table clothes)  nerve fibres transmit message through nerve, from sense organ to brain or from brain to muscle/gland  these make up white matter and other axon tracts  some attached to spinal cord and others to brain ■ spinal nerves – bundle of nerve fibres attached to spinal cord; conveys sensory information from body and carries mesages to muscles and glands ■ cranial nerves – 12 pairs, attached to base of brain; conveys sensory information from face and head and carries messages to muscles and glands Cells of Nervous System ● Neurons – nerve cell; consists of cell body with dentrites and an axon whose branches end in terminal bittons that synaps to muscle fibres, gland cells, or other neurons  elements of nervous system that bring sensory information to brain, store memories, reach decisions, control activity of muscles  assisted by glia ● Glial cells – cell of central nervous system that provides support for neruons and supplies them with essential chemicals  during development of brain, some types of glial cells form long fibres that guide develping neurons from place of birth to final resting place  manufacture chemicals that neurons need to perform tasks and absorb chemicals that might impair neuron's functioning  form protective insulating sheaths around nerve fibres  serve as brain's immune system, protecting it from micro-organisms ● Three basic parts of neruron:  soma – cell body; largest part of neuron ■ containts mechanisms that control metabolism and maintenance of cell ■ receives messages from other neurons  dentrites – treelike part of neuron on which other neurons form synapses ■ transmit information they receive down trunks to soma  axon – long,thin part of neuron attached to soma; divides into a few or many branches, ending in a terminal button ■ carries message away from soma toward cell with which neuron communicates – action potential (brief changes in electrical charge) also referred to as firing of an axon ● Two complex structures seen in neurons:  dentritic spines – small protuberance on surface of dentrite; appear on neurons in brain ■ synapse can occur on smooth dentrite or on dentritic spine  terminal button – round swelling at end of axon; releases transmitter substance ■ connect to dentrites, dentritic spine, soma, and axon on other neuron ■ secrete transmitter substance/neurotransmitter (chemical that causes postsynaptic neuron to be excited or inhibited) whenever AP travels down axon ● many axons insulated with myelin sheath  myelin – part protein, part fat ■ produced by glial cells that individually wrap themselves around segments of axon  insultates axons from each other and prevents scrambling of messages  increases speed of AP ■ multiple sclerosis – immune system attack protein in myelin and so suffer from various sensory and motor impairments The Action Potential ● travels less than 100 m/second ● membrane of axon is electrically charged – at rest is -70 milivolts with respect to outside ● action potential – brief electrochemical event that is carried by an axon from soma of neuron to its terminal button; causes release of transmitter signal  unequal distribution of + or - charge occurs inside axon and in fluid that surrounds it  axon membrane contains ion channels – special protein molecule located on membrane of cell which controls entry or exit of particular ion  ion transporters – special protein moelcule located in membran of cell taht actively transports ions into or out of cell ■ use energy resource from cell to acituvely pump ● outside of membrane is + charged and inside is – charged ● when axon is resting, ion channels are closed ● AP is caused by opening of some ion channels in membrane at end of axon near soma – opening permits + charged sodium ions to enter, which reverses membrane potential at that location causing nearby ion channels to open, producing reversal at that point too – prossess continues all way down to terminal button ● as soon as charge reverses, ion channels close and another set opens letting + charged potassium ions out of axon – restores normal charge ● ion transporters pump sodium back out of cell and potassium back in Synapses ● synapse – junction between terminal button of one neuron and membrane of muscle fibre, gland, or other neuron ● terminal button belongs to presynaptic neuron and sends out message (neurotransmitter) to postsynaptic neuron ● motor neuron – neuron whose terminal button forms synapse with muscle fibres; when AP travels down its axon, associated muscle fibres with twitch ● Two types of synapses:  excitatory – transmitter signal excites postsynaptic neuron increasing chances it will fire too  inhibitory – transmitter signal inhbits postsynaptic neuron decreasing chances it will fire ● when AP reaches terminal button, it causes terminal button to release small amount of transmitter substance into synaptic cleft (fluid-filled gap between pre- and postsynaptic neuron) ● reactions are triggered by special submicroscopic protein molecules embedded in postsynaptic membrane called receptor molecules (receptors that respond to opiates are sometimes found elsewhere on surface of neuron) ● once activated, receptor molecules produce excitatory or inhibitory effects of postsynaptic neuron – open ion channels  excitatory – sodium channels open and Na+ moves in  inhibitory – potasssium channels open and K+ moves in ● reuptake – process by which terminal buttom retrieves molecules of transmitter substance that it has just released; terminates effect of transmitter substance on receptors of postsynaptic neuron Simple Neural Circuit ● simple withdrawal reflex (triggered by noxious stimulus) requires 3 types of neurons:  sensory neuron – neuron that detects changes in external or internal environment and sends information about these changes to central nervous system ■ detects noxious stimulus and conveys information to spinal cord  interneuron – located entirely within central nervous system (brain or spinal cord) and receives sensory information and in turn stimulates motor neurons that cause appropriate muscle to contract ■ sometimes neural circuit from brain forms synapse on inhibitory interneuron releasing inhibitory neurotransmitter, decreasing amount of firing on motor neuron Neuromodulators ● neuromodulators – substance secreted in brain that modulates activity of neurons that contain appropriate receptor molecules ● opioids (endorphins) – neuromodulator whose action is mimicked by synthetic heroin or opiate like morphin, heroin, or opium  behaviour effects include decreased sensitivity to pain and tendency to persist in ongoing behaviour  released during species specific behaviour like mating or fighting  discovered in mid-1970s when neurobiologists learned that natural opiote substances from poppy stimulated receptor molecules located on neurons in brain  similar situation exists with THC (delta9-tetrahydrocannabinol) ■ chemical activates cannabinoid receptors, which in some areas of brian are 12 times more numerous than opiod receptors ■ Giuffrida has recently discovered regions of the brain where neural activity releases endogenous cannabinoid called anandamine (ananda – sanskrit for bliss and tranquility)  evidence suggests that opiates and marijuana mimic effects of special neuromodulators that brain uses to refulate some species-typical behaviour ● neuromodulators – help organize body's response to stress, reduce anxiety, promote sleepiness, promote eating, help end meal Summary ● brain has three main functions:  control of behaviour  processing and storing information about environment  regulation of body's physiological processes ● central nervous system:  brain and spinal cord ■ brain - three major divisions: ● brain stem ● cerebellum ● cerebral hemisphere  cerebral cortex covers cerebral hemisphere – wrinkled by fisures and gyri ■ communicates with body through peripheral nervous system ● peripheral nervous system:  spinal nerves and cranial nerves ● basic element of nervous system is neuron: soma, detrite, and axon  neurons – assisted by glial cells ■ glials cells: ● provide structure ● provide protection (myelin sheath) ● protect for infection ● aid in development of neurons – form long fibres that guide neurons from birth to final resting place ● provide neurons with chemicals and remove unwanted chemicals ■ neurons: ● communicate with each other at synapses  synapse is junction of terminal button of presynaptic neuron with membrane of postsynaptic neuron ● synaptic communication is chemical – AP fires down axon causing release of transmitter substance out of terminal button  AP – brief change in electric charge (-70 to +) ■ ion channels allow sodium in, and potassium out ■ ion transporter pump sodium out and potassium in ● molecules of transmitter substance cause excitatory or inhibitory reaction – cause more firing or stop firing of postsynaptic neuron ● neuromodulators:  resemble transmitter substances but travel farther and are more widely dispersed  released by terminal buttoms and modulate activity of many neurons Study of the Brain ● last 15 years many new techniques in field of neuroscience  genetics, cell biology, medical physics Methods of Physiological Psychology: ● physiological knowledge has been important to psychology since time of Johannes Muller ● as biological organ:  brain changes in response to disease of accident  shows electrical and chemical responses  responds to intructions encoded in its genes ● earliest research method of physiopsych involved study of change ● using experimental ablation Paul Broca and Pierre Flourens came to insights about brain by correlating behavioural deficit with physical disruption of specific part of nervous system  brain lesion – damage to particular part of brain (experimental ablation) ● anaesthetizes animal, drills hole in skull and uses special device called stereotaxic apparatus (device used to insert an electrode into particular part of brain for purpose of recording electrical activity, stimulating brain electrically, or producing localized damage) to insert fine wire (electrode) or thin tube (cannula) into particular location of brain  stereotaxic – ability to manipulate object in 3-D space  eletric lesions – produced by passing electrical current through electrode, which produces heat that destroys small portion of brain around tip of electrode  excitotoxic lesions – established by injecting chemical through cannula that causes lethal overstimulation of neurons  reversible lesion – special anaesthetics that temporarily suppress action of region ● in addition to structural change, brain also ahows effects of AP and synaptic changes of myriad neurons ● detected using recording techniques and deliberately triggered using stimulation methods ● recording techniques for both electrical and chemical processes  electrical: ■ microelectrodes – thin electrode made of wire or glass tube filled with electrically conductive fluid that can measure electrical activity of single neuron ■ magnetoencephalography – method of brain study that measures changes in magnetic field accompanying AP in cerebral cortex by placing large electrodes outside skulls  chemical: ■ microdialysis – procedure that collects solutions surrounding brain's neurons for subsequent chemical analysis by using set of concentric tubes to circulate a carrier fluid into and out of brain; neurotransmitters and similar secretions are carried off through this current; sensitive enough to detect small amounts of neurotransmitters that escape from synaptic cleft  moderate currents delivered through electrode can mimic effects of AP and activate neurons located near tip of electrode ■ Olds and Milner – if tip of electrode is placed near certain parts of brain, rat will continually press lever (reward mechanism)  some procedures less invasive: ■ transcranial magnetic stimulation - direct stimulation of cerebral cortex induced by magnetic field generated on scalp; can be used on conscious humans  can also be detected through neurochemical methods and some mimic body's own machinery for detecting chemicals ■ immune system: ● when foreign protein enters body immune system produces antibodies that chemically attach themselves to protein ● antibodies serve as homing beacons for white blood cells that can destroy inavde ● synthetic antibodies that recognize proteins specific to neurons can be produced ● if antibodies are also attached to special chemical dye they will show up in microscope ● using this physiopsychs can detect presence of neurotransmitters or enzymes that create them ■ genes: ● can also manipulate genetic mechanisms that control nervous system ● this control allows them to perform neurochemical version of experimental ablation – genetic knockout  section of new genetic code for different species can be implanted into animal's genome to determine how gene regulates neural development or function Visualization Methods: ● brain exhibits plasticity – structural change resulting from experience:  new synapses form, old ones disappear, dentrites grow and shrink and oxons of neurons become myelinated ● physiopsychs can trace effects of physical maturation and plasticity by using techniques that mark or stain neruons chemically  can part percentage of neurons, making their dentrites prominent so that they an estimate the growth of dentrites and infer possible changes in number of synapses  other stains could highlight axonal growth, showing how axons grow to connect with specific areas of brain  also used to examine large portions of brain – when human patient dies from brain injury can use dye to locate injury ● until recently most useful technique of brain imaging was CT Scanner (compurized tomography)– device that uses special X-ray machine and computer to produce images of brain that appear as slices taken parallel to top of skull  scanner sends narrow beam of X-ray through patient's head and is then moved around head while computer calculates amount of radiation passing through it at various points along each angle  results in 2D slice of head parallel to skull ■ can determine approximate location of brain injury ● 2 other recent developments: ● positron emission tomography (PET) - relies on radioactive substance which is incorporated into brain tissue metabolically, where it emits an antimatter particle (positron)  positron travels 2 cm through brain before it collides with matter particle causing emmission of photon which can be measured and used to construct brain image ● magnetic reasonance imaging (MRI) – produced by plaing individual in strong magnetic field  causes molecules within its influence to become aligned with lines of magnetic force  radio signal is then generated around person which has effect of tilting these aligned atoms (just as you might nudge spinning top to wobble)  scanner measures time it takes molecule to stop wobbling and recover to aligned state  because different molecules take different times to recover an image can be constructed based on relative amounts of different materials within scanner ■ eg. myelinated axons recover at different time than unmyelinated producing contrast between white and grey matter  produce high resolution images of brain regions and are safe to use (no radiation)  Paus – used MRI to trace development of white matter as children matured into adolescents  one study found evidence of plasticity resulting from learning to drive taxicab in London Functional Measurement ● measure neural acitivty as brain performs some function – combines knowledge of brain's physiology and visualization technology  eg. functional MRI (fMRI) ■ measures different recovery times of blood hemoglobin ■ Hb reacts to magnetic field of MRI but its recovery time after radio signal is applied depends on whether it has released its complement of oxygen ■ contrast of oxygentated and deoxygenated Hb can be measured in MRI very quickly, allowing sequence of scans to be taking in short span ■ by synchronizing scans with psychological task fMRI scans show what parts of brain are metabolically active at time task is performed ● must assume that oxygen levels correlate with neural acitivity ● recent support for this found by comparing human fMRI scans to electrode recording data from monkeys in visual areas of brain  physics of radioactive agents limit spatial resolution of method but are readily suited to measure biochemical processes in brain and can therefore trace neurotransmitter substances Understanding the Limitations of Brain Methods ● strength of conclusion depends on quality of control ● must be careful when we interpret functional role of particular brain region, regardless of technique being used  Vanderwolf and Cain – point out many possible confounds that can occur in system as complicated as brain: modules within brain are highly interconnected with many feedback loops between different regions ● problems of generalizaiton – research is highly specialized and tasks that are used are developed for specific purposes; more study is needed before many of these findings can be applied to real-world problems  Mozart for Babies Biology and Culture: environmental effects on brain development ● Maguire, using fMRI found that taxi cab drivers in london brains' were physically different than other people Evidence for Effects of Experience on Brain Development: ● Rosenzweig began research study 25 eyars ago to exmine question:  delivered litters of rats and placed them in different environments – enriched or impoverished  brains of rats in enriched environment had thicker cerebral cortex, better blood supply, more protein content, and more acetylcholine (transmitter substance that appears to play important role in learning) ● subsequent studies found changes at microscopic level:  Greenough and Volkmar – neurons of rats raised in enriched environment had larger and more complex dentritic trees  Turner and Greenough – found synapses in their cerebral cortexes were larger and more synapses were found on each neuron  Black, Shafron, and Greenough – rats placed in enriched environment between ages of 30-60 days, capillaries in their visual cortex grew more branches and their surface areas increased, presumably to accomodate growth that was stimulated by experience ● David Hubel – if one eye closed during critical period of brain development that occurs shortly after birth, normal synaptic connections are not established between that eye and visual cortex and becomes blind and neurons from other eye have taken over region of cortex that would normally have formed connections to covered eye ● Field, Whishaw and Pellis – pattern of “dodging” while rat eats depended on exposure to testosterone around time of birth and injecting female rat pups with testosterone after birth produced male-like dodging in adults; males that had gonadal tissue removed at birth showed female dodging patterns but if later removed no change in behaviour ● Moore – indicates effects of heredity on sexual behaviour are sometimes indirect  rat mothers lick baby's genitals, more so rats and found that it effects their behaviour as adults: ■ male sex hormone was responsible for odour of urine that was attractive to mothers and if mother cannot smell urine, will not give them attention ■ when this happened males showed decreased sexual behaviour as adults ■ if researchers stroke it then no effect on behaviour ■ research indicates that licking affects development of genitals and group of neurons in spinal cord and may also affect brain development How does experience affect brain development: ● brain's development is programmed by genome to respond to experiences that occur during llifetime ● Hebb – felt that brain plasticity reflected changes in strength, location, and number of synapses – true but not all beneficial ● Robinson, Gorny, Mitton, and Kolb – looked at structure of dentrites in several regions of brain after rats pressed lever a lot  examining region deep in brain that controls motivation, they found significant increase in branching of dentrites and in density of dentritic spines  in another region which controls decision making and planning, they found abnormally shaped bulbs on dentrites that presumably decreased thei effectiveness ■ cocaine use may increase incentive for drug while decreasing individual's judgement ● brain researchers have found many other examples where experience seems to alter functioning of synapses – ne research also indicates that brain can grow new neurons in response to experience ● adult brain has been found to contain stem cells (undifferentiated cells that are important in fetal development) – located in narrow layers within brain, stems cells migrate to other regions, where they can differentiate into neurons ● Van Praag, Kempermann, and Gage – foudn that giving mice chance to exercis voluntarily in running wheel produced new neurons from neurons precursors in hippocampus – new neurons appear to function as normal brain cells, showing Aps and synaptic-like activity  hippocampus - involved in learning and memory ● genetic functions that cause brain's stem cells to differentiate into functioning neurons is unknown, although surround extracellular environment must be involved ● Plasticity in brain occurs because DNA code for presence of stem cells in brain – genetic code is expressed within environment that partially determines
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