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Biology of Behaviour

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PSYC 2520
Hernan Humana

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
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