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York University
PSYC 1010

Chapter 3: The Biological Bases of Behaviour - Albert Einstein died in April 1955 - his brain was removed by Tom Harvey - Tom Harvey injected it with formalin to preserve it and took it - Harvey read about the scientific work of Sandra Witelson and offered her the brain to examine - She compared the results of her examination of Einsteinʼs brain with other “control” brains - Hi brain was similar to most other brains with the exception of a wider parietal region and distinct sylvian fissure. --> visuospatial cognition mathematical thought, and imagery of movement are strongly dependent on this region KEY POINTS IN THIS CHAPTER (pages 78-86) - Behaviour depends on complex information processing in the nervous system. Cells in the nervous system receive integrate, and transmit information - Neurons are the basic communication links. They normally transmit a neural impulse along an axon to a synapse with another neuron. The neural impulse is a brief change in a neuronʼs electrical charge that move along an axon. An action potential is an all- or-none event. Neurons convey information about the strength of a stimulus by variations in their rate of firing. - Action potentials trigger the release of chemicals called neurotransmitters that diffuse across a synapse to communicate with other neurons. Transmitters bind with receptors in the postsynaptic cell membrane, causing excitatory or inhibitory PSPs. - Whether the postsynaptic neuron fires a neural impulse depends on the balance of excitatory and inhibitory PSPs. Our thoughts and actions depend on patterns of activity in neural circuits and networks. - The transmitter ACh plays a key role in muscular movement. Serotonin may contribute to the regulation of sleep, eating, and aggression. Depression is associated with reduced activation at norepinephrine and serotonin synapses. - Schizophrenia has been linked to overactivity at dopamine synapses. Cocaine and amphetamines appear to exert their main effects by altering activity at DA and NE synapses. GABA is an important inhibitory transmitter. Endorphins, which resemble opiates, contribute to pain relief. Communication in the Nervous System - The nervous system handles information Nervous Tissue: The Basic Hardware - Nervous system is living tissue composed of cells - Two major categories of cells: (1) Glia (2) Neurons - (1) Glia are cells found throughout the nervous system that provide structural support, nourishment, and insulation for neurons - also involved in the removal of waste - help maintain the chemical environment of the neurons, which promotes more efficient signaling in the nervous system Chapter 3: The Biological Bases of Behaviour - (2) Neurons are individual cells in the nervous system that receive, integrate and transmit information - links that permit communication within the NS (nervous system) - majority of them communicate only with other neurons - small minority receive signals from outside the nervous system (from sensory organs) or carry messages from the NS to the muscles that move the body - neurons come in a variety of types an shapes - - - - - - - - - - - - Soma / cell body - contains the cell nucleus and much of the chemical machinery common to most cells - Rest of neuron is devoted exclusively to handling information - The neuron has a number of branches, feeler-like structures called dendritic trees - Dendrites - the parts of a neuron that are specialized to receive information - from the many dendrites, information flows into the cell body ad then travels away from the soma along the axon - Axon - a long, thin fibre that transmits signals away from the soma to other neurons or to muscles or glands - Axons may be quite long (sometimes > 1 metre) and may branch off to communicate with a numerous cells - In humans, many axons are wrapped in cells with a high concentration of a white, fatty substance call myelin - Myelin Sheath - insulting material, derived from glial cells, that encases some axons - It speeds up the transmission of signals that move along axons - degeneration of myelin sheaths - signals may not be transmitted effectively - as seen by the loss of muscle control with multiple sclerosis - The axon ends in a cluster of terminal buttons - Terminal buttons - small knobs that secrete chemicals called neurotransmitters - These chemicals serve as messengers that may activate neighbouring neurons, - Synapse - a junction where information is transmitted from one neuron to another (points at which neurons interconnect) - SUMMARY - information received at the dendrites which is passed through the soma and along the axon and is transmitted to the dendrites of other cells at meeting points called synapses Chapter 3: The Biological Bases of Behaviour - Exceptions: - some neurons have no axons whereas some have multiple - typically synapse on the dendrites of other cells but may also synapse on a soma or an axon The Neural Impulse: Using Energy to Send Information - Alan Hodgkin and Andrew Huxley - unravelled the mystery of the neural impulse with squid axons THE NEURON AT REST: A Tiny Battery - neural impulse is a complex electrochemical reaction - Inside and outside the neuron are fluids containing electrically charged atoms and molecules called ions - cell membrane is semi-permeable which permits the movement of some ions - (+) Na and K ions and (-) chloride ions flow back and forth across but at different rates - this difference in rate leads to a slightly higher concentration of (-) ions inside the cell. - Therefore the neuron at rest is a store of potential energy - resting potential of a neuron is its stable, negative charge when the cell is inactive THE ACTION POTENTIAL - when stimulated, channels in the neuronʼs cell membrane open, briefly allowing (+) Na ions to rush in - neuronʼs charge is less (-) or even (+) creating an action potential - action potential - a very brief shift in a neuronʼs electrical charge that travels along an axon - firing of an action potential is reflected in the voltage spike - the voltage change races down the axon - channels in the cell membrane that opened, close up. Time is needed before they can open again - absolute refractory period - the minimum length of time after an action potential during which another action potential cannot begin. - not very long (1-2 milliseconds) - followed by brief relative refractory period when the neuron can fire but its threshold for firing is elevated, so more intense stimulation is required to initiate an action potential THE ALL-OR-NONE LAW - either the neuron fires or it doesnʼt and action potentials are all the same size - Neurons can however, convey information about the strength of a stimulus by varying the rate at which they fire action potentials - various neurons transmit neural impulses at different speeds (ex: thicker axons more rapidly than thinner) The Synapse: Where Neurons Meet SENDING SIGNALS: Chemicals as Couriers - Two neurons are separated by the synaptic cleft Chapter 3: The Biological Bases of Behaviour - Synaptic Cleft - microscopic gap between the terminal button of one neuron and the cell membrane of another neuron - signals must cross gap to permit neurons to communicate - presynaptic neuron - neuron that sends a signal across the gap - postsynaptic neuron - neuron that receives the signal - Arrival of an action potential at an axonʼs terminal buttons triggers the release of neurotransmitters - chemicals that transmit information from one neuron to another - within buttons, chemicals are stored in small sacs called synaptic vesicles - neurotransmitters released when a vesicle fuses with the membrane of the presynaptic cell and its contents spill into the synaptic cleft - After release, neurotransmitters diffuse across the synaptic cleft to the membrane of the receiving cell. There they bind with special molecules in the postsynaptic cell membrane at various receptor sites - receptor sites recognize and respond to some neurotransmitters but not to others RECEIVING SIGNALS: Postsynaptic Potentials - neurotransmitter and a receptor molecule combine--> reactions in the cell membrane case a postsynaptic potential (PSP) - a voltage change at a receptor site on a postsynaptic cell membrane - postsynaptic potentials are graded - they vary in size and they increase or decrease the probability of a neutral impulse in the receiving cell in proportion to the amount of voltage change - Two types of messages can be sent cell to cell: (1) excitatory PSP - a positive voltage shift that increases the likelihood that the postsynapyic neuron will fire action potentials (2) inhibitory PSP - a negative voltage shift that decreases the likelihood that the post synaptic neuron will fire action potentials - depends on which receptor sites are activated in the postsynaptic neuron - excitatory or inhibitory effects produced at a synapse last only a fraction of a second. Then neurotransmitters drift away from receptor sites or are inactivated by enzymes that convert them into inactive forms - most are reabsorbed 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 - neuron must do more than simply relay messages it receives --> must integrate signals arriving at many synapses before it “decides” whether to fire a neural impulse - State of the neuron is weighted balance between excitatory and inhibitory influences (many excitatory PSP - electrical currents build up and an action potential will be fired however if man inhibitory PSPs also occur - tend to cancel the effects of excitatory PSPs) - Most neurons are interlinked in complex pathways, chains, circuits and networks - our perceptions, thoughts and actions depend on patterns of neural activity in elaborate neural networks consisting of interconnected neurons that frequently fire together or sequentially to perform certain functions Chapter 3: The Biological Bases of Behaviour - elimination of old synapses appears to play a larger role in the sculpting of neural networks than the creation of new synapses - nervous system normally forms more synapses than needed and then gradually eliminates the less active synapses. - synaptic pruning is a key process in the formation of the neural networks that are crucial to communication in the nervous system - Donald Hebb realized that neurons are linked in complex networks or cell assemblies - Hebbian LEarning Rule - these linkages might operate and come about. Neurotransmitters and Behaviour - Nine well established, small molecule transmitters, about 40 additional neuropeptide chemicals that function, at least part-time, as neurotransmitters, and a handful of recently recognized “novel” neurotransmitters - Specific neurotransmitters work at specific kinds of synapses - transmitter must fit into receptor site for binding to occur - variety and specificity reduces cross-talk between densely packed neurons, making the NSʼs communication more precise ACETYLCHOLINE - ACh - Activates motor neurons controlling skeletal muscles - Contributes to the regulation of attention, arousal, and memory - Some ACh receptors stimulated by nicotine - nicotine is an ACh agonist - a chemical that mimics the action of a neurotransmitter - other chemicals are not agonists - bind to receptors, block them but do not produce a PSP - they act as antagonist(s) - a chemical that opposes the action of a neurotransmitter MONOAMINES - Abnormal levels of monoamines in the brain have been related to the development of certain psychological disorders - include dopamine, norepinephrine and serotonin - Dopamine (DA) - Contributes to control of voluntary movement, pleasurable emotions - Decreases levels associated with Parkinsonʼs disease - Overactivity at DA synapses associated with schizophrenia - Cocaine and amphetamines elevate activity at DA synapses - Norepinephrine (NE) - Contributes to modulation of mood an 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 Chapter 3: The Biological Bases of Behaviour GABA - consists of amino acids - “gamma-aminobutyric acid” and “glycine” seem to produce only inhibitory postsynaptic potentials - Serves as widely distributed inhibitory transmitter - GABA appears to be responsible for much of the inhibition in the central NS - Valium and similar antianxiety drugs work at GABA synapses ENDORPHINS - Resemble opiate drugs in structure and effects - Contribute to pain relief and perhaps to some pleasurable emotions KEY POINTS IN THIS CHAPTER (pages 87-89) - The nervous system can be divided into two main subdivisions, the central nervous system and the peripheral nervous system. The central nervous system consists of the brain and spinal cord - The peripheral nervous system consists of the nerves that lie outside the brain and spinal cord. It can be subdivided into the somatic nervous system, which connects to muscles and sensory receptors, and the autonomic nervous system, which connects to blood vessels, smooth muscles, and glands - The autonomic nervous system mediates the largely automatic arousal that companies emotion and the fight-or- flight response to stress. The ANS is divided into the sympathetic division, which mobilizes bodily resource and the parasympathetic division, which conserves bodily resources Organization of the Nervous System The Peripheral Nervous System - most important division is the division that separates the central nervous system (the brain and spinal cord) from the peripheral nervous system - peripheral nervous system - made up of all those nerves that lie outside the brain and spinal cord - Nerves - bundles of neuron fibres (axons) that are routed together in the peripheral nervous system - Subdivided into the somatic nervous system and the autonomic nervous system THE SOMATIC NERVOUS SYSTEM - made up of nerves that connect to voluntary skeletal muscles and to sensory receptors - cables that carry information from receptors in the skin, muscles, and joints to the central nervous system and that carry commands from the CNS to the muscles - Require two kinds of nerve fibres: (1) Afferent nerve fibres - axons that carry information inward to the CNS from the periphery of the body (2) Efferent nerve fibres - axons that carry information outward from the CNS to the periphery of the body - somatic nerves contain many axons of each type - incoming and outgoing Chapter 3: The Biological Bases of Behaviour THE AUTONOMIC NERVOUS SYSTEM - made up of nerves that connect to the heart, blood vessels, smooth muscles, and glands - separate system although it is ultimately governed by the CNS - controls automatic, involuntary, visceral functions that people donʼt normally think about - heart rate, digestion and perspiration, etc - mediates much of the physiological arousal that occurs when people experience emotions - Walter Cannon - fight-or-flight response - Can be subdivided into two branches (1) sympathetic division - the branch of the autonomic nervous system that mobilizes the bodyʼs resources for emergencies - creates the fight-or-flight response - activation of sympathetic division slows digestive processes and drains blood from the periphery, lessening bleeding in the case of an injury - Key sympathetic nerves send signals to the adrenal glands, triggering the release of hormones that ready the body for exertion (2) parasympathetic division - the branch of the autonomic nervous system that generally conserves bodily resources - activates processes that allow the body to save and store energy - slows heart rate, reduce blood pressure and promote digestion The Central Nervous System - portion of the NS that lies within the skull and spinal column - consists of the brain and the spinal cord - protected by enclosing sheaths call the meninges - bathed in cerebrospinal fluid - nourishes the brain and provides a protective cushion for it SPINAL CORD - connects the brain to the rest of the body through the peripheral nervous system - spinal cord is an extension of the brain - runs from the base of the brain to just below the level of the waist - houses bundles of axons that carry the brainʼs commands to peripheral nerves and that relay sensations from the periphery of the body to the brain THE BRAIN - part of the CNS that fills the upper portion of the skull - wighs only about 1.5 kilograms, contains billions of interacting cells that integrate information from inside and outside the body, coordinate to bodyʼs actions, and enable human beings to talk, think, remember, plan, create and dream Chapter 3: The Biological Bases of Behaviour KEY POINTS IN THIS CHAPTER (pages 90-95) - Neuroscientists use a variety of methods to investigate brain-behaviour relations. The EEG can record broad patterns of electrical activity in the brain. Different EEG brain waves are associated with different states of consciousness - Lesioning involves destroying a piece of the brain. Another technique is electrical stimulation of area in the brain in order to activate them. Both techniques depend on the use of stereotaxic instruments that permit researchers to implant electrodes at precise locations in the animalsʼ brains - In recent years, new brain-imaging procedures have been developed, including CT scans, PET scans, MRI scans, and fMRI scans. These techniques have enormous potential for exploring brain-behaviour relations, as we saw in the Featured Study Looking Inside the Brain: Research Methods Electrical Recordings - Electrical activity in the brain can be recorded - Hans Berger invented a machine that could record broad patterns of brain electrical activity - Electroencephalograph (EEG) 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 - sums and amplifies electric potentials occurring in many thousands of brain cells - EEG recordings are translated into line tracings commonly called brain waves that provide an overview of electrical activity in brain - often used for clinical diagnosis of brain damage and neurological disorders Lesioning - Many major insights about brain-behaviour relations have resulted from observations of behavioural changes in people who have suffered damage in specific brain areas - case study method - Brenda Milner - conducted one of the most famous case studies of this kind - her work with patients was pivotal in establishing the role of the medial structures of the temporal lobes in memory and the existence of multiple memory systems - has limitations - subjects are not plentiful, and neuroscientists canʼt control the location or severity of their subjectsʼ brain damage. Variations in the participantsʼ histories create many extraneous variables that make it difficult to isolate cause-and effect relationships between brain damage and behaviour. - Sometimes observe what happens when purposefully remove parts of the brain in animals - Lesioning - involves destroying a piece of the brain. - Done by inserting electrode into a brain structure and burning the tissue to disable the structure with high-frequency electric current - electrodes implanted with a stereotaxic instrument Electrical Stimulation of the Brain - Electrical stimulation of the brain (ESB) involves sending a weak electric current into a brain structure to stimulate (activate) it Chapter 3: The Biological Bases of Behaviour - current through electrode - close enough approximation to normal signals in the brain to activate the brain structures in which the electrodes are lodged - Most ESB research conducted with animals but occasionally on humans in the context of brain surgery required for medical purposes - Wilder Penfield founded the world-famous Montreal Neurological Institute - systematically mapped out man of the functions of the brain Brain-Imaging Procedures - CT (computerized tomography) scan is a computer-enhanced X-ray of brain structure - the entire brain can be visualized by assembling a series of images representing successive slices of the brain by multiple x-rays - least expensive of all the brain-imaging techniques - PET (positron emission tomography) scannign is proving especially valuable in research on how brain and behaviuor are related - can examine brain function, mapping actual activity i nteh brain over time - radioactively tagged chemicals are introduced int othe brain and serve as markers of blood flow or metabolic activity in the brain which can be monitered with X-rays - MRI (magnetic resonance imaging) scan uses magnetic fields, radio aves, and computerized enhancement to map out brain structure - provide better images of brain structure than CT scans producing 3-D pictures of the brain that have remarkably high resolution - fMRI (functional magnetic resonance imaging) consists of several new variations on MRI tech that monitor blood and oxygen flow in the brain to identify areas of high activity - can provide both functional and structural information in same image KEY POINTS IN THIS CHAPTER (pages 95-101) - The brain has three major regions: the hindbrain, the midbrain, and forebrain. Structures in the hindbrain include the medulla, pons, and cerebellum. These structures handle essential functions such as breathing, circulation, coordination of movement, and
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