Chapter 3 The Biological Bases of Behavior Outline Notes

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Rutgers University
Professor Stephen Killianski

Communicationin theNervous System Friday,December 07,2012 8:15PM • Nervous Tissue: The Basic Hardware ○ Neurons- individual cells in the nervous system that receive, integrate, and transmit information  Basic links that permit communication within the nervous system  Soma (cell body)- contains the cell nucleus and much of the chemical machinery common to most cells  Dendrites- parts of a neuron that are specialized to receive information  Axon- long, thin fiber that transmits signals away from the soma to other neurons or to muscles or glands □ Myelin sheath is the insulating material that encases some axons and that acts to speed up the transmission of signals that move along axons  Terminal Buttons- small knobs that secret chemicals called neurotransmitters □ Chemicals serve as messengers that may activate nearby neurons  Synapse- junction where information is transmitted from one neuron to another  Information is received at the dendrites, is passed through the soma and along the axon, and is transmitted to the dendritesof other cells at meeting points called synapses ○ Glia- cells found throughout the nervous system that provide various types of support for neurons  Tend to be much smaller than neurons, but outnumber neurons by about 10 to 1  Accountfor over 50% of the brain's volume  Has many functions: □ Supply nourishment to neurons □ Help remove neurons' waste products □ Provideinsulation around many axons □ Play a role in the development of the nervous system in the human embryo □ May also send and receive chemical signals  Can detect neural impulses and send signals to other glial cells • The Neural Impulse: Using Energy to Send Information ○ The Neuron at Rest: A Tiny Battery  Positively charged sodium and potassium ions and negatively charged chloride ions flow back and forth across the cell membrane, but they do not cross at the same rate □ Difference in flow rates leads to a slightly higher concentration of negatively charged ions inside the cell  RestingPotential- stable, negative charge when the cell is inactive □ Roughly about -70 millivolts ○ The Action Potential  ActionPotential- very brief shift in a neuron's electrical charge that travels along an axon □ Firing of an action potential is like a spark traveling along a trail of gunpowder, the voltage change races down the axon  Absolute RefractoryPeriod- minimum length of time after an action potential during which another action potential cannot begin □ Followed by a brief relative refractory period, during which the neuron can fire, but its threshold for firing is elevated, so more intense stimulation is required to start an action potential ○ The All-Or-NoneLaw  Can't half fire an impulse □ Either the neuron fires or it doesn't  Neuronscan convey information about the strength of a stimulus □ Do so by varying the rate at which they fire action potentials  Stronger stimulus will cause a cell to fire more rapid volley of neural impulses than a weaker stimulus will • The Synapse: Where Neurons Meet ○ Sending Signals: Chemicals as Messengers  Neuronsdon't actually touch □ Separated by synaptic cleft, a microscopic gap between the terminal button of one neuron and the cell membrane of another neuron  Signalshave to jump this gap to permit neurons to communicate ◊ The neuron that sends a signal across the gap is called the presynaptic neuron ◊ The neuron that receives the signal is called the postsynaptic neuron  Neurotransmitters- chemicals that transmit information from one neuron to another □ Most of these chemicals stores in small sacs, called synaptic vesicles □ Released when a vesicle fuses with the membrane of the presynaptic cell and its contents spill into the synaptic cleft  Neurotransmitters then spread across the synaptic cleft to the membrane of the receiving cell ◊ There they may bind with special molecules in the postsynaptic cell membrane at various receptor sites ► These sites are specifically "tuned" to recognize and respond to some neurotransmitters but not to others ○ Receiving Signals: Postsynaptic Potentials  PostsynapticPotential (PSP)- a voltage change at a receptor site on a postsynaptic cell membrane □ Do not follow the all-or-nonelaw □ Vary in size and may increase or decrease the probability of a neural impulse in the receiving cell in proportion to the amount of voltage change  Two types of messages can be sent from cell to cell □ Excitatory is a positive voltage shift that increases the likelihood that the postsynaptic neuron will fire action potentials □ Inhibitoryis a negative voltage shift that decreases the likelihood that the postsynaptic neuron will fire action potentials  Depends on which receptor sites are activated in the postsynaptic neuron  Reuptake- process in which neurotransmitters are sponged up from the synaptic cleft by the presynaptic membrane □ Allowssynapses to recycle their materials ○ Integrating Signals: Neural Networks  A neuron may receive signals from thousands of other neurons □ That same neuron may pass its messages along to thousands of neurons as well □ It must integrate signals arriving at many synapses before it "decides" whether to fire a neural impulse  If enough excitatory PSPs occur in a neuron, the electrical currents can add up, causing the cell's voltage to reach the threshold at which an action potential will be fired  The 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 ones □ Elimination of old or less-active synapses is called synaptic pruning, and it is a key process in the formation of the neural networks that are crucial to communication in the nervous system that are crucial to communication in the nervous system • Neurotransmitters and Behavior ○ Acetylcholine(ACh)  Only transmitter between motor neurons and voluntary muscles  Also contributes to attention, arousal, and memory  Inadequate supply in certain areas of the brain is associated with the memory losses seen in Alzheimer'sdisease ○ Receptor sites can sometimes be "fooled" by other chemical substance  Have the same shape as the receptor sites and will bind, causing postsynaptic potentials □ Agonist- chemical that mimics the action of a neurotransmitter  Somechemicals bind to receptors but fail to produce postsynaptic potentials □ Antagonist- chemical that opposes the action of a neurotransmitter ○ Monoamines  Dopamine □ Used by neurons that control voluntary movements □ Degeneration of such neurons in a specific area of the brain causes Parkinson's disease  Marked by tremors, muscular rigidity, and reduced control over voluntary movements □ Dopaminehypothesis asserts that abnormal activity at dopamine synapses plays a crucial role in the development of schizophrenia  Serotonin □ Plays a prominent role in the regulation of sleep and wakefulness and of eating behavior □ Modulates aggressive behavior in animals, and some preliminary evidence relates serotonin activity to aggression in humans  Norepinephrine □ Contributes to modulation of mood and arousal □ Related to depressive disorders  Temporary alterations at monoamine synapses also appear to account for the powerful effects of amphetamines and cocaine □ Stimulants seem to exert most of their effect by creating a storm of increased activity at dopamine and norepinephrine synapses ○ GABA and Glutamate  Consists of amino acids  Gamma-aminobutyricAcid(GABA) □ Produces only inhibitory postsynaptic potentials □ Appearsto have inhibitory effects at virtually all synapses where it is present □ Responsible for much of the inhibition in the central nervous system □ May be involved in the regulation on anxiety in humans  May be linked with some types of anxiety disorders  Glutamate □ Alwayshas excitatory effects □ Best know for its contribution to learning and memory □ Implicated as factors that might contribute to certain features of schizophrenic disorders ○ Endorphins  Actslike morphine: exerts its effects by binding to specialized receptors in the brain  Internally produced chemicals that resemble opiates in structure and effects  Contributeto the modulation of pain, the regulation of eating behavior, and the body's response to stress  Opiate drugs such as morphine and heroin produce highly pleasurable feelings of euphoria □ Suggests that the body's natural endorphins may also be capable of producing feelings of pleasure Organizationof the Nervous System Friday,December 07,2012 10:21PM • The Peripheral Nervous System ○ Peripheral Nervous System (PNS)- 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 the peripheral nervous system  Part that extends outside the central nervous system  Composed of two primary systems □ SomaticNervous 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 commandsfrom the central nervous system to the muscles  These function require two kinds of nerve fibers ◊ Afferent nerve fibers- axons that carry information inward to the central nervous system from the periphery of the body ◊ Efferent nerve fibers- axons that carry information outward from the central nervous system to the periphery of the body ► Each body nerve contains many axons of each type ► Somatic nerves are "two-way streets" with incoming (afferent) and outgoing (efferent) lanes □ AutonomicNervous System- made up of nerves that connect to the heart, blood vessels, smooth muscles, and glands  Controlsautomatic, involuntary, visceral functions that people don't normallythink about  Controlsmust of the physiological arousal that occurs when people experience emotions  Fight-or-lightresponse: organisms generally respond to threat by preparing physiologicallyfor attacking (fight) or fleeing (flight) from the enemy  Can be subdivided into two branches ◊ SympatheticDivision- branch of the autonomic nervous system that mobilizesthe body's resources for emergencies ► Creates the fight-or-flightresponse ► Inhibitsdigestive processes and drains blood from the periphery, lessening bleeding in the case of injury ► Key sympathetic nerves send signals to the adrenal glands, triggering the release of hormones that ready the body for exertion ◊ ParasympatheticDivision- branch of the autonomic nervous system that generally conserves bodily resources ► Activates processes that allows the body to save and store energy • The Central Nervous System ○ Central Nervous System (CNS)- consists of the brain and the spinal cord  Protected by the skull and by enclosing sheaths called meninges  Contained in its own special fluid, the cerebrospinal fluid (CSF) □ Nourishesthe brain and provides a protectie cushion for it □ Ventricles are filled with CSF ○ The Spinal cord  Extension of the brain  Connects the brain to the rest of the body through the peripheral nervous system  Houses bundles of axons that carry the brain's commands to peripheral nerves and that relay sensations from the periphery of the body to the brain ○ The Brain  Contains billionsof interacting cells □ These cells integrate information from inside and outside the body, coordinate the body's actions, and enable human beings to talk, think, remember, plan, create, and dream LookingInside theBrain: Research Methods Friday,December 07,2012 10:47PM • Electrical Recordings ○ Electroencephalograph (EEG)- device that monitorsthe electrical activity of the brain over time by means of recording electrodes attached to the surface of the scalp  EEG electrode sums and amplifies electric potentials occurring in many thousands of brain cells  Results are translated into line tracings, commonly called brain waves • Lesioning ○ Lesioning- destroying a piece of the brain  Used to study more precisely the relations between brain and behavior □ Scientists sometimes observe what happens when specific brain structures in animals are purposely disabled  Typically 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  Use a stereotaxis instrument, a device used to implant electrodes at precise brain locations  Has proven invaluable in neuroscientists' research on brain functioning • Electrical Stimulation of the Brain ○ Electrical Stimulationof the Brain (ESB)- involves sending a weak electric current into a brain structure to stimulate (activate) it  Current delivered through an electrode, but the current is different from that used in lesioning  Doesn't exactly duplicate normal signals in the brain, however, it is usually a close enough approximation to activate the brain structures in which the electrodes are lodged  May be used on humans during brain surgery in order to map his or her brain so that they don't slice through critical areas • Transcranial Magnetic Stimulation ○ Transcranial MagneticStimulation (TMS)- a new technique that permits scientists to temporarily enhance or depress activity in a specific area of the brain  A magnetic coil mounted on a small paddle is held over a specific area of a subject's head □ Coil creates a magnetic field that penetrates to a depth of 2 centimeters  By varying the timing and duration of the magnetic pulses, a researcher can either increase or decrease the excitability of neurons in the targeted tissue  Allowsscientists to create "virtual lesions" in human subjects for short periods of time, using a painless, noninvasive method □ Avoidsthe numerous uncontrolled variables that plague the study of natural lesions in humans with brain damage  Cannot be used to study areas deep within the brain • Brain-Imaging Procedures ○ Computerized TopographyScan (CT)- computer-enhanced X-ray of brain structure  Multiple X-rays are shot from many angles, and the computer combines the readings to create a vivid image of horizontal slice of the brain  Entire brain can be visualized by assembling a series of images representing successive slices  Least expensive and most widely used ○ Positron Emission Tomography(PET) Scan- examines the brain function by mapping actual activity in the brain over time  Radioactively tagged chemicals are introduced into the brain that serve as markers of blood flow or metabolic activity in the b
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