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Chapter 3

Ch. 3 - The Biological Bases of Behaviour.docx

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PSYC 1010
Jennifer Steeves

The Biological Bases of Behaviour Communication in the Nervous System - Behaviour depends on rapid information processing Nervous Tissue: The Basic Hardware - Neurons are individual cells in the nervous system that receive, integrate and transmit information - The soma, or cell body, contains the cell nucleus and much of the chemical machinery common to most cell o Rest of neurons devoted to handling information - Dendrites are the parts of a neuron that are specialized to receive information - The axon is a long, thin fibre that transmits signals away from the soma to other neurons or to muscles or glands. - The myelin sheath is insulating material, derived from glial cells, that encases some axons o Speeds up transmission of signals - End of axon = terminal buttons, which are small knobs that secrete chemicals called neurotransmitters - The points at which neurons interconnect are called synapses. A synapse is a junction where information is transmitted from one neuron to another Glia - Glia are cells found throughout the nervous system that provide various types of support for neurons o Much smaller, but outnumber 10:1 o 50% of brains volume o Supplies nourishment to neurons, help remove waste products, provide insulation, development of the nervous system o Send and receive chemical signals The Neural Impulse: Using Energy to Send Information The Neuron at Rest: A Tiny Battery - Neurons contain electrically charged atoms and molecules called ions - Semipermeable membrane - The resting potential of a neuron is its stable, negative charge when the cell is inactive The Action Potential - An action potential is a very brief shift in a neuron’s electrical charge that travels along an axon - The absolute refractory period is the minimum length of time after an action potential during which another action potential cannot begin o One or Two milliseconds The All-or-None Law - Neurons can convey info about the strength of a stimulus o Varying the rate which they fire action potentials  Stronger stimulus cause cell to fire a more rapid volley of neural impulses  Thicker axons transmit impulses more rapidly than thinner The Synapse: Where Neurons Meet - Transmission happens at synapse – depends on chemical messengers Sending Signals: Chemicals as Couriers - Neurons are separated by a synaptic cleft, a microscopic gap between the terminal button of one neuron and the cell membrane of another neuron - Sending signal = Presynaptic Neuron - Receive signal = Postsynaptic Neuron - Arrival of action potential at axon’s terminal buttons triggers release of neurotransmitters – chemicals that transmit information from one neuron to another - Neurotransmitters may bind with special molecules in the postsynaptic cell membrane at various receptor sites Receiving Signals: Postsynaptic Potentials - Neurotransmitter and a receptor molecule combine, cause a postsynaptic potential, a voltage change at a receptor site on a postsynaptic cell membrane o Vary in size – increase/decrease probability of neural impulse o Two types of messages sent:  Excitatory – Positive voltage shift that increases the likelihood that the postsynaptic neuron will fire action potentials  Inhibitory – Negative voltage shift that decreases the likelihood that the postsynaptic neuron will fire action potentials o Most neurotransmitters are reabsorbed (instead of drifting away) into the presynaptic neuron through reuptake, a process in which neurotransmitters are sponged up from the synaptic cleft by the presynaptic membrane Integrating Signals: Neural Networks - ‘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’ - Elimination of old synapses plays large role in sculpting of neural networks than the creation of new synapses - Neurons do not act alone – linked in complex networks (cell assemblies) o ‘When 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 is increased’ o Hebb Synapse Neurotransmitters and Behaviour - A transmitter has to fit into a receptor site for binding to occur (Key and lock) - Many neurotransmitters to reduce cross talk, nervous system’s communication more precise Acetylcholine - Activates motor neurons controlling skeletal muscles - Contributes to the regulation of attention, arousal, and memory - Some Ach receptors stimulated by nicotine o An agonist is a chemical that mimics the action of a neurotransmitter o An antagonist is a chemical that opposes the action of a neurotransmitter Dopamine - Contributes to control of voluntary movement, pleasurable emotions - Decreased levels associated with Parkinson’s disease - Over activity at DA synapses associated with Schizophrenia - Cocaine and amphetamines elevate activity at DA synapses Norepinephrine - Contributes to modulation of mood and arousal - Cocaine and amphetamines elevate activity at NE synapses Serotonin - Involved in regulation of sleep and wakefulness, eating, aggression - Abnormal levels may contribute to depression and obsessive-compulsive disorder - Prozac and similar antidepressant drugs affect serotonin circuits GABA - Serves as widely distributed inhibitory transmitter - Valium and similar antianxiety drugs work at GABA synapses - Resemble opiate drugs in structure and effects - Contribute to pain relief and perhaps to some pleasurable emotions - Endorphins – Internally produced chemicals that resemble opiates in structure and effects Organization of the Nervous System Peripheral Nervous System - The peripheral nervous system is made up of all those nerves that lie outside the brain and spinal cord. Nerves are bundles of neuron fibres (axons) that are routed together in the peripheral nervous system. - Subdivided into o Somatic Nervous System  The somatic nervous system is made up of nerves that connect to voluntary skeletal muscles and to sensory receptors  Carry info in the skin, muscles and joints to the central nervous system  Afferent nerve fibres are axons that carry information inward to the central nervous system from the periphery of the body. Efferent nerve fibres are axons that carry information outward from the central nervous system to the periphery of the body o Autonomic Nervous System  The autonomic nervous system is made up of nerves that connect the heart, blood vessels, smooth muscles, and glands  Fight or Flight response  Can backfire if stress leaves a person in a chronic state of autonomic arousal o Prolonged arousal can lead to physical diseases  Subdivided into two branches  The sympathetic division is the branch of the autonomic nervous system that mobilizes the body’s resources for emergencies  The parasympathetic division is the branch of the autonomic nervous system that generally conserves the body’s resources The Central Nervous System - The central nervous system consists of the brain and the spinal cord o Protected by meninges o The cerebrospinal fluid nourishes the brain and provides a protective cushion for it The Spinal Cord - Runs from base of brain to lower than waist - Transmit signals from brain to the motor neurons that move the body’s muscles The Brain - Central of nervous system - Coordinate body’s actions, enable human beings to talk, think, remember, plan, create and dream Review of Key Points - The nervous system divided into two main divisions – Central nervous system and peripheral nervous system o CNS consist of brain and spinal cord o PNS consist of nerves outside brain and spinal cord  Divided into somatic (connects muscles and sensory receptors) and autonomic (connects blood vessels, smooth muscles and glands) o Autonomic mediates large automatic arousal accompanying emotion and fight-or-flight response to stress  Divided into sympathetic – mobilizes bodily resources – and parasympathetic – conserves bodily resources Looking Inside the Brain: Research Methods Electrical Recordings - The electroencephalograph is a device that monitors the electrical activity of the brain over time by means of recording electrodes attached to the surface of the scalp o Sums + amplifies electric potentials o Translated into brain waves Lesioning - Lesioning involves destroying a piece of the brain o Inserting an electrode into a brain structure and passing a high-frequency electric current through it to burn the tissue and disable the structure o Involves inserting an electrode to a particular place buried deep in the brain  Done by stereotaxic instruments – Device used to implant electrodes at precise locations Electrical Stimulation of the Brain - Electrical stimulation if the brain involves sending a weak electric current into a brain structure so stimulate (activate) it. Transcranial Magnetic Stimulation - Transcranial magnetic stimulation is a new technique that permits scientists to temporarily enhance or depress activity in a specific area of the brain - Chief limitation of TMS – cannot study areas deep within the brain Brain-Imaging Procedures - CT scan – less expensive, most used, portray brain structure - Positron emission tomography – can examine brain function, mapping actual activity in the brain over time o Radioactively tagged chemicals introduced to brain, providing a colour-coded map indicating areas of brain becoming active when subjects clench a fist, sing, or contemplate etc. etc. - Magnetic Resonance Imaging scan o Uses magnetic fields, radio waves, and computerized enhancement to map out brain structure Review of Key Points - Neuroscientists use variety of methods to investigate brain-behaviour relationships o EEG record broad patterns of electrical activity o EEG brain waves associated with states of consciousness - Lesioning involves destroying piece of brain o Both techniques depend on use of stereotaxic instruments – permits researchers to implant electrodes at precise locations in animals; brains - CT scans, PET scans, MRI scans and fMRI scans used to image the brain o Not precise or unambiguous as they appear to be o Increased metabolic activity in areas do not prove crucial to a particular psychological function The Brain and Behaviour - Three major regions – Hindbrain, midbrain, forebrain The Hindbrain - The hindbrain includes the cerebellum and two structures found in the lower part of the brainstem: the medulla and the pons o Medulla – attaches to spinal cord – in charge of largely unconscious but vital functions including circulating blood, breathing, maintaining muscle tone, regulating reflexes such as sneezing, coughing, salivating o Pons – bridges of fibres connecting brainstem with cerebellum  Also contains clusters of cell bodies involved with sleep and arousal - Cerebellum (Little brain) o Large, folded structure, adjacent to back surface of brainstem o Critical to coordination of movement, sense of equilibrium (physical balance) o It allows you to hold your hand out to the side o Key role in organizing sensory information The Midbrain - The midbrain is the segment of the brainstem that lies between the hindbrain and the forebrain o Areas concerned with integrating sensory processes, such as vision and hearing o Running through hindbrain and midbrain is the reticular formation  Central core of brainstem, reticular formation contributes to the modulation of muscle reflexes, breathing, and pain perception  Regulation of sleep and arousal The Forebrain - The forebrain is the largest and most complex region of the brain, encompassing a variety of structures, including the thalamus, hypothalamus, limbic system, and cerebrum o Thalamus, hypothalamus, and limbic system form core of forebrain, located near top of brainstem o Above is cerebrum – seat of complex thought o Wrinkled surface on cerebrum is cerebral cortex The Thalamus: A Way Station - The thalamus is a structure in the forebrain through which all sensory information (except smell) must pass to get to the cerebral cortex o Plays active role in integrating information from various senses The Hypothalamus: A Regulator of Biological Needs - The hypothalamus is a structure found near the base of the forebrain that is involved in regulation of basic biological needs o Lies below thalamus o Functions – Control autonomic nervous system, vital link between brain and endocrine system (A network of hormone-producing glands discussed later in this chapter) o Major role in regulation of biological drives (Fighting, Fleeing, Feeding, and Mating) The Limbic System: The Seat of Emotion - The limbic system is a loosely connected network of structures located roughly along the border between the cerebral cortex and deeper subcortical areas o Parts of thalamus and hypothalamus, the hippocampus, the amygdala and other structures o Involved in regulation of emotion, memory, and motivation o Hippocampus play a role in memory o Limbic system links to experience of emotion o Amygdala plays central role in learning of fear responses o Heaviest concentration – Medial Forebrain Bundle (Bundle of axons) passes through the hypothalamus  Rich in dopamine-releasing neurons The Cerebrum: The Seat of Complex Thought - The cerebral cortex is the convoluted outer layer of cerebrum o Two halves  Cerebral Hemispheres are the right and left halves of the cerebrum  The Corpus Callosum is the structure that connects the two cerebral hemispheres
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