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Chapter 2

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McGill University
PSYC 211
Yogita Chudasama

PSYC211 Chapter 2 Notes Definitions: Sensory Neuron: A neuron that detects changes in the external or internal environment and sends information about these changes to the CNS Motor Neuron: A neuron located within the CNS that controls the contraction of a muscle or the secretion of a gland Interneuron: A neuron located entirely within the CNS Central Nervous System (CNS): The brain and spinal cord Peripheral Nervous System (PNS): The part of the nervous system outside the brain and spinal cord, including the nerves attached to the brain and spinal cord Soma: The cell body of a neuron, which contains the nucleus Dendrite: A branched, treelike structure attached to the soma of a neuron; receives information from the terminal button of an axon and the membrane of another neuron Synapse: A junction between the terminal button of an axon and the membrane of another neuron Axon: The long, thin, cylindrical structure that conveys information fro the soma of a neuron to its terminal buttons Multipolar Neuron: A neuron with one axon and may dendrites attached to its soma Bipolar Neuron: A neuron with one axon and one dendrite attached to its soma Unipolar Neuron: A neuron with one axon attached to its soma; the axon divides, with one branch receiving sensory information and the other sending the information into the CNS Terminal Button: The bud at the end of a branch of an axon; forms synapses with another neuron; sends information to that neuron Neurotransmitter: A chemical that is released by a terminal button; has an excitatory or inhibitory effect on another neuron Membrane: A structure consisting principally of lipid molecules that defines the outer boundaries of a cell and also constitutes many of the cell organelles, such as the Golgi apparatus Nucleus: A structure in the central region of a cell, containing the nucleolus and chromosomes Nucleolus: A structure within the nucleus of a cell that produces the ribosomes Ribosomes: A cytoplasmic structure, made of protein, that serves as the site of production of proteins translated from the mRNA Chromosome: A strand of DNA, with associated proteins, found in the nucleus; carries genetic information DNA: A long, complex macromolecule consisting of two interconnected helical strands; along with associated proteins, strands of DNA constitute the chromosomes Gene: The functional unit of the chromosome, which directs synthesis of one or more proteins mRNA: A macromolecule that delivers genetic information concerning the synthesis of a protein from a portion of a chromosome to a ribosome Enzyme: A molecule that controls a chemical reaction, combining two substances or breaking a substance into two parts Non-coding RNA (ncRNA): A form of RNA that does not encode for protein but has functions of its own Cytoplasm: The viscous, semiliquid substance contained in the interior of a cell Mitochondrion: An organelle that is responsible for extracting energy from nutrients Adenosine Triphosphate (ATP): A molecule of prime importance to cellular energy metabolism; its breakdown liberates energy Endoplasmic Reticulum: Parallel layers of membrane found within the cytoplasm of a cell. Rough endoplasmic reticulum contains ribosomes and is involved with production of proteins that are secreted by the cell. Smooth endoplasmic reticulum is the site of synthesis of lipids and provides channels for the segregation of molecules involved in carious cellular process Golgi Apparatus: A complex of parallel membranes in the cytoplasm that wraps the products of a secretory cell Exocytosis: The secretion of a substance by a cell through means of vesicles; the process by which neurotransmitters are secreted Lysosome:An organelle surrounded by membrane; contains enzymes that break down waste products Cytoskeleton: Formed of microtubules and other protein fibers, linked to each other and forming a cohesive mass that gives a cell its shape Microtubule: A long strand of bundles of protein filaments arranged around a hollow core; part of the cytoskeleton and involved in transporting substances from place to place within the cell Axoplasmic Transport: An active process by which substances are propelled along microtubules that run the length of the axon Anterograde: In a direction along an axon from the cell body toward the terminal buttons Retrograde: In a direction along an axon from the terminal buttons toward the cell body Glia: The supporting cells of the CNS Astrocyte: A glial cell that provides support for neurons of the CNS, provides nutrients and other substances, and regulates the chemical composition of the extracellular fluid Phagocytosis: The process by which cells engulf and digest other cells or debris caused by cellular degeneration Oligodendrocyte: A type of glial cell in the CNS that forms myelin sheaths Myelin Sheath: A sheath that surrounds axons and insulates them, preventing messages from spreading between adjacent axons Node of Ranvier: A naked potion of a myelinated axon between adjacent oligodendroglia or Schwann cells Microglia: The smallest of glial cells; act as phagocytes and protect the brain from invading microorganisms Schwann Cell: A cell in the peripheral nervous system that is wrapped around a myelinated axon, providing one segment of its myelin sheath Blood-Brain Barrier: A semipermeable barrier between the blood and the brain produced by the cells in the walls of the brain’s capillaries Area Postrema: A region of the medulla where the blood-brain barrier is weak; poisons can be detected there and can initiate vomiting Electrode: A conductive medium that can be used to apply electrical stimulation or to record electrical potentials Microelectrode: A very fine electrode, generally used to record activity of individual neurons Membrane Potential: The electrical charge across a cell membrane; the difference in electrical potential inside and outside the cell Oscilloscope: A laboratory instrument that is capable of displaying a graph of voltage as a function of time on the face of a cathode ray tube Resting Potential: The membrane potential of a neuron when it is not being altered by excitatory or inhibitory postsynaptic potentials; approximately -70mV in the giant squid axon Depolarization: Reduction (toward zero) of the membrane potential of a cell from its normal resting potential Hyperpolarization: An increase in the membrane potential of a cell, relative to the normal resting potential Action Potential: The brief electrical impulse that provides the basis for conduction of information along an axis Threshold of Excitation: The value of the membrane potential that must be reached to produce an action potential Diffusion: Movement of molecules from regions of high concentration to regions of low concentration Electrolyte: An aqueous solution of a material that ionizes - namely, a soluble acid, base, or salt Ion: A charged molecule. Cations are positively charged, and anions are negatively charged Electrostatic Pressure: The attractive force between atomic particles charged with opposite signs or the repulsive force between atomic particles charged with the same sign Intracellular Fluid: The fluid contained within cells Extracellular Fluid: The body fluids located outside the cells Sodium-Potassium Transporter: A protein found in the membrane of all cells that extrudes sodium ions from and transports potassium ions into the cell Ion Channel: A specialized protein molecule that permits specific ions to enter or leave the cells Voltage-Dependent Ion Channel: An ion channel that opens or closes according to the value of the membrane potential All-or-None Law: The principle that once an action potential is triggered in an axon, it is propagated, without decrement, to the end of the fiber Rate Law: The principle that variations in the intensity of a stimulus or other information being transmitted in an axon are represented by variations in the rate at which that axon fires Cable Properties: The passive conduction of electrical current, in a decremental fashion, down the length of an axon Saltatory Conduction: Conduction of action potentials by myelinated axons. The action potential appears to jump from one node of Ranvier to the next Postsynaptic Potential: Alterations in the membrane potential of a postsynaptic neuron, produced by liberation of neurotransmitter at the synapse Binding Site: The location on a receptor protein to which a ligand binds Ligand: A chemical that binds with the binding site of a receptor Dendritic Spine: A small bud on the surface of a dendrite, with which a terminal button of another neuron forms a synapse Presynaptic Membrane: The membrane of a terminal button that lies adjacent to the postsynaptic membrane and through which the neurotransmitter is released Postsynaptic Membrane: The cell membrane opposite the terminal button in a synapse; the membrane of the cell that receives the message Synaptic Cleft: The space between the presynaptic membrane and the postsynaptic membrane Synaptic Vesicle: A small, hollow, beadlike structure found in terminal buttons; contains molecules of a neurotransmitter Release Zone: A region of the interior of the presynaptic membrane of a synapse to which synaptic vesicles attach and release their neurotransmitter into the synaptic cleft Postsynaptic Receptor: A receptor molecule in the postsynaptic membrane of a synapse that contains a binding site for a neurotransmitter Neurotransmitter-Dependent Ion Channel: An ion channel that opens when a molecule of a neurotransmitter binds with a postsynaptic receptor Ionotropic Receptor: A receptor that contains a binding site for a neurotransmitter and an ion channel that opens when a molecule of the neurotransmitter attaches to the binding site Metabotropic Receptor: A receptor that contains a binding site for a neurotransmitter; activates an enzyme that begins a series of events that opens an ion channel elsewhere in the membrane of the cell when a molecule of the neurotransmitter attaches the binding site G Protein: A protein coupled to a metabotropic receptor; conveys messages to other molecules when a ligand binds with an activates the receptor Second Messenger: A chemical produced when a G protein activates an enzyme; carries a signal that results in the opening of the ion channel or causes other events to occur in the cell Excitatory Postsynaptic Potential (EPSP): An excitatory depolarization of the postsynaptic membrane of the a synapse caused by the liberation of a neurotransmitter by the terminal button Inhibitory Postsynaptic Potential (IPSP): An inhibitory hyperpolarization of the postsynaptic membrane of a synapse caused by the liberation of a neurotransmitter by the terminal button Reuptake: The reentry of a neurotransmitter just liberated by a terminal button back through its membrane, thus terminating the postsynaptic potential Enzymatic Deactivation: The destruction of a neurotransmitter by an enzyme after its release - for example, the destruction of acetylcholine by acetylcholinesterase Acetylcholine (ACh): A neurotransmitter found in the brain, spinal cord, and parts of the peripheral nervous system; responsible for muscular contraction Acetylcholinesterase (AChE): The enzyme that destroys ACh soon after it is liberated by the the terminal buttons, thus terminating the postsynaptic potential Neural Integration: The process by which inhibitory and excitatory postsynaptic potentials summate and control the rate of firing of a neuron Autoreceptor: A receptor molecule located on a neuron that responds to the neurotransmitter released by that neuron Presynaptic Inhibition: The action of a presynaptic terminal button in an axoaxonic synapse; reduces the amount of neurotransmitters released by the postsynaptic terminal button Presynaptic Facilitation: The action of a presynaptic terminal button in an axoaxonic synapse; increases the amount of neurotransmitter released by the postsynaptic terminal button Gap Junction: A special junction between cells that permits direct communication by means of electrical coupling Neuromodulator: A naturally secreted substance that acts like a neurotransmitter except that it is not restricted to the synaptic cleft but diffuses through the extracellular fluid Peptide: A chain of amino acids joined together by peptide bonds. Most neuromodulators, and some hormones, consist of peptide molecules Hormone: A chemical substance that is released by an endocrine gland that has effects on target cells in other organs Endocrine Gland: A gland that liberates its secretions into the extracellular fluid around capillaries and hence into the blood stream Target Cell: The type of cell that is directly affected by a hormone or other chemical signal Steroid: A chemical of low molecular weight, derived from cholesterol. Steroid hormones affect their target cells by attaching to receptors found within the nucleus Introduction: • Behaviour is the primary function of the nervous system • Information, in the form of light, sound waves, odors, tastes, or contact with objects, is gathered from the environment by specialized cells called sensory neurons • Movements are controlled by motor neurons which contract the muscles • Interneurons lie entirely within the CNS between the motor and sensory neurons • Local interneurons form circuits with nearby neurons and analyze small pieces of information Relay interneurons connect circuits of local interneurons in one region of the brain with those in • other regions • There are 100 billion neurons in the human nervous system • The CNS consists of the parts that are encased by the bones of the skull and spinal column: brain and spinal cord • The PNS is found outside these bones and consists of the nerves and most of the sensory organs Cells of the Nervous System: • The neuron (nerve cell) is the information-processing and information-transmitting element of the nervous system Structure Description Function Soma (cell body) Shape varies in different kinds of Contains the nucleus and much of neurons. the machinery that helps the life processes of the cell. Dendrites Treelike structure attached to the Important for receiving messages cell body. from the terminal buttons of the sending neurons across the synapse (a junction between the terminal buttons of the sending neuron and the membrane of the somatic membrane of the receiving one). Axon A long, slender tube covered by a Carries information from the cell myelin sheath. body to the terminal buttons. Terminal buttons (bouton or Little knobs found at the end of Produces neurotransmitters when terminals) axons. an action potential reaches them and excites or inhibits the receiving cell determining whether an action potential will occur there. • Multipolar neurons are most common type found in the CNS. The somatic membrane gives rise to one axon but to the trunks of many dendritic trees • Bipolar neurons give rise to one axon and one dendritic tree at opposite ends of the soma. It is typically sensory neurons that detect events occurring the environment • Unipolar neurons has only one stalk, which leaves the soma and divides into two branches a short distance away. They transmit sensory information from the environment to the CNS typically from sensations relating to the skin of a human • Other unipolar neurons detect events in our joints, muscles, and internal organs • Neurotransmitters either excites or inhibits the receiving cell and thus helps to determine whether an action potential occurs in its axon • The membrane defines the boundary of the cell. It consists of a double layer of lipid molecules. Some proteins detect substances outside the cell (such as hormones) and pass information about • the presence of these substances to the interior of the cell. Other proteins control access to the interior of the cell, permitting some substances to enter but barring others • Proteins may act as transporters, actively carrying certain molecules into or out of the cell • The chromosomes and nucleolus resides in the nucleus • Nucleolus is responsible for the production of ribosomes, small structures that are involved in protein synthesis • Chromosomes consist of DNA which contain the organism’s genetic information • When they are active, portions of the chromosomes (genes) cause production of another complex molecule, mRNA which receives a copy of the information stored at that location. The mRNA leaves the nuclear membrane and attaches to ribosomes, where it causes the production of a particular protein • Proteins provide structure and serve as enzymes, which direct the chemical processes of a cell by controlling chemical reactions. Enzymes are special protein molecules that act as catalyst • A genome is the sequence of nucleotide bases on the chromosomes that provide the information needed to synthesize all the proteins that can be produced by a particular organism Genomes of most vertebrates contain junk DNA, which did not contain information needed to • produce proteins. Only 1.5% of human genome encodes for proteins • Further research showed that the amount of non-protein-coding DNA correlates with the complexity of an organism • Non-coding RNA (ncRNA) are constituents of spliceosomes and to attach and modify proteins that regulate gene expression • Cytoplasm is a jellylike semiliquid substance that fills the space inside the cell membrane. It holds organelles • Mitochondria have double membrane and helps produce ATP. Mitochondria also contain their own DNA and reproduce independently of the cells in which they reside • Endoplasmic reticulum serves as a storage reservoir and a channel for transporting chemicals through the cytoplasm. Rough ER transports new proteins out of membrane while smoother ER provides channels for the segregation of molecules involved in various cellular processes. Lipid molecules are produced here • Golgi apparatus is a special form of smoother ER and it serves as a wrapping or packaging agent and also produces lysosomes (small sacs that contain enzymes that break down substances no longer needed by the cell • When a cell secretes its products, it uses a process called exocytosis. The container migrates to the inside of the outer membrane of the cell, fuses with it, and bursts, spilling its contents into the fluid surrounding the cell • Cytoskeleton gives the neuron its shape and is made of three kinds of protein strands, linked to each other and forming a cohesive mass • Microtubules are bundles of thirteen protein filaments arranged around a hollow core and is the thickest of the strands • Axoplasmic transport is an active process by which substances are propelled along microtubules that run the length of the axon • Movement from the soma to the terminal buttons is called anterograde axoplasmic transport accomplished by molecules of the protein kinesin • Dynein carries substances from the terminal buttons to the soma, this process is known as retrograde axoplasmic transport • Retrograde axoplasmic transport is about half as fast as anterograde transport Supporting Cells: • Glia (neuroglia) glues the CNS together by buffering (both physical and chemical) neurons. They hold neurons in place, controlling their supply of nutrients and some of the chemicals they need to exchange messages with other neurons, insulate neurons from one another so that neural messages do not get scrambled; and they destroy and remove carcasses of neurons that are killed by disease or injury • Astrocyte is shaped like a star and provides physical support to neurons and clean up debris within the brain. It also produce some chemicals that neurons need to fulfill their functions and they help to control the chemical composition of the fluid surrounding neurons by actively taking up or releasing substances whose concentrations must be kept within critical levels. They also provide nourishments to neurons and are responsible for communication between neurons • Astrocytes bond to both capillaries and soma/dendrites. They take glucose from the capillaries and break it down to lactate, a chemical used by the mitochondria in the neuron for energy. It also stores glycogen for future use • Astrocyte typically holds neurons in place and helps limit the dispersion of neurotransmitters that are released by the terminal
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