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Chapter 3

PSY100 Chapter 3 Summary

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Dax Urbszat

Chapter 3 - Behaviour depends on rapid information processing - Nervous system is a complex communication network in which signals are constantly being transmitted, received and integrated - Glia: cells found throughout the nervous system that provide structural support, nourishment, and insulation for neurons, help to promote more efficient signalling - Neurons: individual cells in the nervous system that receive, integrate, and transmit information - 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 (usually extensive dendritic trees) - Axon: long, thin fiber that transmits signals away from the soma to other neurons or to muscles or glands - Myelin sheath: insulating material, derived from glial cells, that encases some axons, speed up the transmission of signals - Terminal buttons: small knobs that secrete chemical called neurotransmitters which act as messengers that may activate neighbouring neurons - Synapse: junction where information is transmitted from one neuron to another - Information is passed through the soma and along the axon, and is transmitted to the dendrites of other cells at meeting points called synapses Neural Impulse: - Alan Hodgkin and Andrew Huxley tried to define the neural impulse with axons removed from squid, which are about a hundred times larger than human axons but still small; they inserted fine wires called microelectrodes into them to record the electrical activity - Neural impulse is a complex electrochemical reaction of ions as positively charged sodium and potassium ions and negatively charged chloride ions flow back and forth across the membrane but not at the same rate, which leads to a higher concentration of negative ions on the inside of the membrane - Resting Potential of a neuron: its stable, negative charge when the cell is inactive - When the neuron is stimulated, channels in its cell membrane open, briefly allowing positively charged sodium ions to rush in so for an instant, the neuron’s charge is less negative or even positive, creating an action potential - Action potential: very brief shift in a neuron’s electrical charge that travels along an axon; the voltage change races down the axon - Absolute refractory period: minimum length of time after an action potential during which another action potential cannot begin; followed by a relative refractory period where intense stimulation is required to fire a neuron - Weaker stimuli do not produce smaller action potentials - Firing neurons is an all or nothing event but the rate of firing the action potential is relative to the strength of the impulse - Thicker axons transmit neural impulses more rapidly than thinner ones - Synaptic cleft: microscopic gap between the terminal button of one neuron and the cell membrane of another neuron; signals have to jump this gap to send the neural impulse - Presynaptic neuron is the one that sends a signal across the gap - Postsynaptic neuron is the one that receives the signal - Neurotransmitters: chemicals that transmit information from one neuron to another; these are stored in small sacs called synaptic vesicles o They bind with special molecules in the postsynaptic cell membrane at various receptor sites specifically tuned to recognize and respond with some neurotransmitters - Postsynaptic potential (PSP): a voltage change at a receptor site on a postsynaptic cell membrane, which are graded rather than all-or-nothing law so they vary in size and increase or decrease the probability of a neural impulse; excitatory or inhibitory depend on which receptor sites are activated - Excitatory PSP: a positive voltage shift that increases the likelihood that the postsynaptic neuron will fire action potentials - Inhibitory PSP: negative voltage shift that decreases the likelihood that the postsynaptic neuron will fire action potentials - The excitatory or inhibitory effects at the synapse last less than a second then neurotransmitters drift away from receptor sites or are inactivated by enzymes or undergo reuptake - Reuptake: process in which neurotransmitters are sponged up from the synaptic cleft by the presynaptic membrane - One neuron receives thousands of messages but must integrate the signals before it decides whether to fire an neural impulse - Our perceptions, thoughts, and actions depend on patterns of neural activity in elaborate neural networks - Synaptic pruning: key process in the formation of the neural networks that are crucial to communication Neurotransmitters: - Agonist: chemical that mimics the action of a neurotransmitter - Antagonist: chemical that opposes the action of a neurotransmitter - Acetylcholine: only transmitter between motor neurons and voluntary muscles, also contributes to attention, arousal, and perhaps memory o Nicotine can stimulate Ach synapses sometimes o Curare is also an agonist so paralyzes animals - Monoamines: dopamine, norepinephrine, and serotonin o Serotonin: regulation of sleep, wakefulness, eating behaviour, aggressive behaviour in animals o Lowered levels of activation at norepinephrine and serotonin synapses related to depression o Abnormalities in activity at dopamine synapses involved with schizophrenia o Some widely abused drugs like amphetamines and cocaine seem to cause an increase at dopamine and norepinephrine synapses - GABA: made of amino acids, gamma-aminobutyric acid and glycine seem to produce only inhibitory postsynaptic potentials, responsible for much of the inhibition in the central nervous system, regulation of anxiety in humans and involved in seizures - Endorphins: internally produced chemicals that resemble opiates in structure and effects, contribute to the modulation of pain o Candice Pert and Solomon Snyder discovered that morphine exerts its effect by binding to specialized receptors in the brain - 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 - Somatic Nervous System: made up of nerves that connect to voluntary skeletal muscles and to sensory receptors, carry info from receptors in skin, muscles and joints to the central nervous system and opposite o Afferent nerve fibres:
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