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Exam 3 Review Sheet11: Fundamentals of the Nervous System and Nervous TissueObjectivesFunctions and Divisions of the Nervous System1.List the basic functions of the nervous system.2.Explain the structural and functional divisions of the nervous system. Histology of Nervous Tissue3.List the types of neuroglia and cite their functions.4.Define neuron, describe its important structural components, and relate each to a functional role. 5.Differentiate between a nerve and a tract, and between a nucleus and a ganglion. 6.Explain the importance of the myelin sheath and describe how it is formed in the central and peripheral nervous systems. 7.Classify neurons structurally and functionally.Membrane Potentials8.Define resting membrane potential and describe its electrochemical basis. pare and contrast graded potentials and action potentials.10.Explain how action potentials are generated and propagated along neurons. 11.Define absolute and relative refractory periods. 12.Define saltatory conduction and contrast it to conduction along unmyelinated fibers. The Synapse13.Define synapse. Distinguish between electrical and chemical synapses by structure and by the way they transmit information.14.Distinguish between excitatory and inhibitory postsynaptic potentials.15.Describe how synaptic events are integrated and modified.Neurotransmitters and Their Receptors16.Define neurotransmitter and name several classes of neurotransmitters.Developmental Aspects of Neurons17.Describe how neurons develop and form synapses.Lecture OutlineI.Functions and Divisions of the Nervous System (pp. 386–387; Figs. 11.1–11.2)A.The central nervous system consists of the brain and spinal cord, and is the integrating and command center of the nervous system (p. 386; Figs. 11.1–11.2).B.The peripheral nervous system is outside the central nervous system (pp. 386–387; Fig. 11.2).1.The sensory, or afferent, division of the peripheral nervous system carries impulses toward the central nervous system from sensory receptors located throughout the body.2.The motor, or efferent, division of the peripheral nervous system carries impulses from the central nervous system to effector organs, which are muscles and glands.a.The somatic nervous system consists of somatic nerve fibers that conduct impulses from the CNS to skeletal muscles, and allow conscious control of motor activities.b.The autonomic nervous system is an involuntary system consisting of visceral motor nerve fibers that regulate the activity of smooth muscle, cardiac muscle, and glands.II.Histology of Nervous Tissue (pp. 388–395; Figs. 11.3–11.5; Table 11.1)A.Neuroglia, or glial cells, are closely associated with neurons, providing a protective and supportive network (pp. 388–389; Fig. 11.3).1.Astrocytes are glial cells of the CNS that regulate the chemical environment around neurons and exchange between neurons and capillaries.2.Microglia are glial cells of the CNS that monitor health and perform defense functions for neurons.3.Ependymal cells are glial cells of the CNS that line the central cavities of the brain and spinal cord and help circulate cerebrospinal fluid.4.Oligodendrocytes are glial cells of the CNS that wrap around neuron fibers, forming myelin sheaths.5.Satellite cells are glial cells of the PNS whose function is largely unknown. They are found surrounding neuron cell bodies within ganglia.6.Schwann cells, or neurolemmocytes, are glial cells of the PNS that surround nerve fibers, forming the myelin sheath.B.Neurons are specialized cells that conduct messages in the form of electrical impulses throughout the body (pp. 389–395; Figs. 11.4–11.5; Table 11.1).1.Neurons function optimally for a lifetime, are mostly amitotic, and have an exceptionally high metabolic rate requiring oxygen and glucose.a.The neuron cell body, also called the perikaryon or soma, is the major biosynthetic center containing the usual organelles except for centrioles.b.Dendrites are cell processes that are the receptive regions of the cell.c.Each neuron has a single axon that generates and conducts nerve impulses away from the cell body to the axon terminals.d.The myelin sheath is a whitish, fatty, segmented covering that protects, insulates, and increases conduction velocity of axons.2.There are three structural classes of neurons.a.Multipolar neurons have three or more processes.b.Bipolar neurons have a single axon and dendrite. c.Unipolar neurons have a single process extending from the cell body that is associated with receptors at the distal end.3.There are three functional classes of neurons.a.Sensory, or afferent, neurons conduct impulses toward the CNS from receptors.b.Motor, or efferent, neurons conduct impulses from the CNS to effectors.c.Interneurons, or association neurons, conduct impulses between sensory and motor neurons, or in CNS integration pathways.III.Membrane Potentials (pp. 395–406; Figs. 11.6–11.15)A.Basic Principles of Electricity (p. 395)1.Voltage is a measure of the amount of difference in electrical charge between two points, called the potential difference.2.The flow of electrical charge from point to point is called current, and is dependent on voltage and resistance (hindrance to current flow).3.In the body, electrical currents are due to the movement of ions across cellular membranes.B.The Role of Membrane Ion Channels (p. 395; Fig. 11.6)1.The cell has many gated ion channels.a.Chemically gated (ligand-gated) channels open when the appropriate chemical binds.b.Voltage-gated channels open in response to a change in membrane potential.c.Mechanically gated channels open when a membrane receptor is physically deformed.2.When ion channels are open, ions diffuse across the membrane, creating electrical currents.C.The Resting Membrane Potential (pp. 396–398; Figs. 11.7–11.8) 1.The neuron cell membrane is polarized, being more negatively charged inside than outside. The degree of this difference in electrical charge is the resting membrane potential.2.The resting membrane potential is generated by differences in ionic makeup of intracellular and extracellular fluids, and differential membrane permeability to solutes.D.Membrane Potentials That Act as Signals (pp. 398–404; Figs. 11.9–11.14) 1.Neurons use changes in membrane potential as communication signals. These can be brought on by changes in membrane permeability to any ion, or alteration of ion concentrations on the two sides of the membrane.2.Changes in membrane potential relative to resting membrane potential can either be depolarizations, in which the interior of the cell becomes less negative, or hyperpolarizations, in which the interior of the cell becomes more negatively charged.3.Graded potentials are short-lived, local changes in membrane potentials. They can either be depolarizations or hyperpolarizations, and are critical to the generation of action potentials.4.Action potentials, or nerve impulses, occur on axons and are the principle way neurons communicate.a.Generation of an action potential involves a transient increase in Na+ permeability, followed by restoration of Na+ impermeability, and then a short-lived increase in K+ permeability.b.Propagation, or transmission, of an action potential occurs as the local currents of an area undergoing depolarization cause depolarization of the forward adjacent area.c.Repolarization, which restores resting membrane potential, follows depolarization along the membrane.5.A critical minimum, or threshold, depolarization is defined by the amount of influx of Na+ that at least equals the amount of efflux of K+.6.Action potentials are all-or-none phenomena: they either happen completely, in the case of a threshold stimulus, or not at all, in the event of a subthreshold stimulus.7.Stimulus intensity is coded in the frequency of action potentials.8.The refractory period of an axon is related to the period of time required so that a neuron can generate another action potential.E.Conduction Velocity (pp. 404–406; Fig. 11.15)1.Axons with larger diameters conduct impulses faster than axons with smaller diameters.2.Unmyelinated axons conduct impulses relatively slowly, while myelinated axons have a high conduction velocity.IV.The Synapse (pp. 406–413; Figs. 11.16–11.19; Table 11.2) A.A synapse is a junction that mediates information transfer between neurons or between a neuron and an effector cell (p. 406; Fig. 11.16).B.Neurons conducting impulses toward the synapse are presynaptic cells, and neurons carrying impulses away from the synapse are postsynaptic cells (p. 406).C.Electrical synapses have neurons that are electrically coupled via protein channels and allow direct exchange of ions from cell to cell (p. 406). D.Chemical synapses are specialized for release and reception of chemical neurotransmitters (pp. 407–408; Fig. 11.17).E.Neurotransmitter effects are terminated in three ways: degradation by enzymes from the postsynaptic cell or within the synaptic cleft; reuptake by astrocytes or the presynaptic cell; or diffusion away from the synapse (p. 408).F.Synaptic delay is related to the period of time required for release and binding of neurotransmitters (p. 408).G.Postsynaptic Potentials and Synaptic Integration (pp. 408–413; Figs. 11.18–11.19; Table 11.2)1.Neurotransmitters mediate graded potentials on the postsynaptic cell that may be excitatory or inhibitory.2.Summation by the postsynaptic neuron is accomplished in two ways: temporal summation, which occurs in response to several successive releases of neurotransmitter, and spatial summation, which occurs when the postsynaptic cell is stimulated at the same time by multiple terminals.3.Synaptic potentiation results when a presynaptic cell is stimulated repeatedly or continuously, resulting in an enhanced release of neurotransmitter.4.Presynaptic inhibition results when another neuron inhibits the release of excitatory neurotransmitter from a presynaptic cell. 5.Neuromodulation occurs when a neurotransmitter acts via slow changes in target cell metabolism, or when chemicals other than neurotransmitter modify neuronal activity.V.Neurotransmitters and Their Receptors (pp. 413–421; Fig. 11.20; Table 11.3)A.Neurotransmitters are one of the ways neurons communicate, and they have several chemical classes (pp. 413–419; Table 11.3).B.Functional classifications of neurotransmitters consider whether the effects are excitatory or inhibitory, and whether the effects are direct or indirect (pp. 419–420).C.There are two main types of neurotransmitter receptors: channel-linked receptors mediate direct transmitter action and result in brief, localized changes; and G protein–linked receptors mediate indirect transmitter action resulting in slow, persistent, and often diffuse changes (pp. 420–421; Fig. 11.20).VI.Developmental Aspects of Neurons (pp. 423–424; Fig. 11.24) A.The nervous system originates from a dorsal neural tube and neural crest, which begin as a layer of neuroepithelial cells that ultimately become the CNS (p. 423).B.Differentiation of neuroepithelial cells occurs largely in the second month of development (p. 423).C.Growth of an axon toward its target appears to be guided by older “pathfinding” neurons and glial cells, nerve growth factor and cholesterol from astrocytes, and tropic chemicals from target cells (pp. 423–424).D.The growth cone is a growing tip of an axon. It takes up chemicals from the environment that are used by the cell to evaluate the pathway taken for further growth and synapse formation (p. 424; Fig. 11.24).E.Unsuccessful synapse formation results in cell death, and a certain amount of apoptosis occurs before the final population of neurons is complete (p. 424).9: Muscles and Muscles TissueObjectivesOverview of Muscle pare and contrast the basic types of muscle tissue.2.List four important functions of muscle tissue.Skeletal Muscle3.Describe the gross structure of a skeletal muscle.4.Describe the microscopic structure and functional roles of the myofibrils, sarcoplasmic reticulum, and T tubule(s) of skeletal mucle fibers.5.Describe the sliding filament model of muscle contractions.6.Explain how muscle fibers are stimulated to contract by describing events that occur at the neuromuscular junction.7.Describe how an action potential is generated.8.Follow the events of excitation-contraction coupling that lead to cross bridge activity.9.Define motor unit and muscle twitch and describe the events occurring during the three phases of a muscle twitch.10.Explain how smooth, graded contractions of a skeletal muscle are produced.11.Differentiate between isometric and isotonic contractions.12.Describe three ways in which ATP is regenerated during skeletal muscle contraction.13.Define oxygen deficit and muscle fatigue. List possible causes of muscle fatigue.14.Describe factors that influence the force, velocity, and duration of skeletal muscle contraction.15.Describe three types of skeletal muscle fibers and explain the relative value of each type.pare and contrast the effects of aerobic and resistance exercise on skeletal muscles and on other body systems.Lecture OutlineI.Overview of Muscle Tissues (pp. 276–277; Table 9.3)A.Types of Muscle Tissue (p. 276; Table 9.3)1.Skeletal muscle is associated with the bony skeleton, and consists of large cells that bear striations and are controlled voluntarily.2.Cardiac muscle occurs only in the heart, and consists of small cells that are striated and under involuntary control.3.Smooth muscle is found in the walls of hollow organs, and consists of small elongated cells that are not striated and are under involuntary control.B.Special Characteristics of Muscle Tissue (p. 276)1.Excitability, or irritability, is the ability to receive and respond to a stimulus.2.Contractility is the ability to contract forcibly when stimulated.3.Extensibility is the ability to be stretched.4.Elasticity is the ability to resume the cells’ original length once stretched.C.Muscle Functions (pp. 276–277; Table 9.3)1.Muscles produce movement by acting on the bones of the skeleton, pumping blood, or propelling substances throughout hollow organ systems.2.Muscles aid in maintaining posture by adjusting the position of the body with respect to gravity.3.Muscles stabilize joints by exerting tension around the joint. 4.Muscles generate heat as a function of their cellular metabolic processes.II.Skeletal Muscle (pp. 277–305; Figs. 9.1–9.25; Tables 9.1–9.3)A.Gross Anatomy of Skeletal Muscle (pp. 277–278; Fig. 9.2; Tables 9.1, 9.3)1.Each muscle has a nerve and blood supply that allows neural control and ensures adequate nutrient delivery and waste removal.2.Connective tissue sheaths are found at various structural levels of each muscle: endomysium surrounds each muscle fiber, perimysium surrounds groups of muscle fibers, and epimysium surrounds whole muscles.3.Attachments span joints and cause movement to occur from the movable bone (the muscle’s insertion) toward the less movable bone (the muscle’s origin).4.Muscle attachments may be direct or indirect.B.Microscopic Anatomy of a Skeletal Muscle Fiber (pp. 278–284; Figs. 9.2–9.6; Tables 9.1, 9.3)1.Skeletal muscle fibers are long cylindrical cells with multiple nuclei beneath the sarcolemma.2.Myofibrils account for roughly 80% of cellular volume, and contain the contractile elements of the muscle cell.3.Striations are due to a repeating series of dark A bands and light I bands.4.Myofilaments make up the myofibrils, and consist of thick and thin filaments.5.Ultrastructure and Molecular Composition of the Myofilamentsa.There are two types of myofilaments in muscle cells: thick filaments composed of bundles of myosin, and thin filaments composed of strands of actin.b.Tropomyosin and troponin are regulatory proteins present in thin filaments.6.The sarcoplasmic reticulum is a smooth endoplasmic reticulum surrounding each myofibril.7.T tubules are infoldings of the sarcolemma that conduct electrical impulses from the surface of the cell to the terminal cisternae. C.The sliding filament model of muscle contraction states that during contraction, the thin filaments slide past the thick filaments. Overlap between the myofilaments increases and the sarcomere shortens (p. 284; Fig. 9.6).D.Physiology of a Skeletal Muscle Fiber (pp. 284–289; Figs. 9.6–9.12; Table 9.3)1.The neuromuscular junction is a connection between an axon terminal and a muscle fiber that is the route of electrical stimulation of the muscle cell.2.A nerve impulse causes the release of acetylcholine to the synaptic cleft, which binds to receptors on the motor end plate, triggering a series of electrical events on the sarcolemma.3.Generation of an action potential across the sarcolemma occurs in response to acetylcholine binding with receptors on the motor end plate. It involves the influx of sodium ions, which makes the membrane potential slightly less negative.4.Excitation-contraction coupling is the sequence of events by which an action potential on the sarcolemma results in the sliding of the myofilaments.5.Ionic calcium in muscle contraction is kept at almost undetectable levels within the cell through the regulatory action of intracellular proteins. 6.Muscle fiber contraction follows exposure of the myosin binding sites, and follows a series of events. E.Contraction of a Skeletal Muscle (pp. 289–296; Figs. 9.13–9.18)1.A motor unit consists of a motor neuron and all the muscle fibers it innervates. It is smaller in muscles that exhibit fine control.2.The muscle twitch is the response of a muscle to a single action potential on its motor neuron.3.There are three kinds of graded muscle responses: wave summation, multiple motor unit summation (recruitment), and treppe.4.Muscle tone is the phenomenon of muscles exhibiting slight contraction, even when at rest, which keeps muscles firm, healthy, and ready to respond.5.Isotonic contractions result in movement occurring at the joint and shortening of muscles. 6.Isometric contractions result in increases in muscle tension, but no lengthening or shortening of the muscle occurs. F.Muscle Metabolism (pp. 296–300; Figs. 9.19–9.20)1.Muscles contain very little stored ATP, and consumed ATP is replenished rapidly through phosphorylation by creatine phosphate, glycolysis and anaerobic respiration, and aerobic respiration.2.Muscles will function aerobically as long as there is adequate oxygen, but when exercise demands exceed the ability of muscle metabolism to keep up with ATP demand, metabolism converts to anaerobic glycolysis.3.Muscle fatigue is a problem in excitation-contraction coupling or within the muscle cells themselves.4.Oxygen deficit is the extra oxygen needed to replenish oxygen reserves, glycogen stores, ATP and creatine phosphate reserves, as well as conversion of lactic acid to pyruvic acid glucose after vigorous muscle activity.5.Heat production during muscle activity is considerable. It requires release of excess heat through homeostatic mechanisms such as sweating and radiation from the skin.G.Force of Muscle Contraction (pp. 300–302; Figs. 9.21–9.22)1.As the number of muscle fibers stimulated increases, force of contraction increases.2.Large muscle fibers generate more force than smaller muscle fibers.3.As the rate of stimulation increases, contractions sum up, ultimately producing tetanus and generating more force.4.There is an optimal length-tension relationship when the muscle is slightly stretched and there is slight overlap between the myofibrils.H.Velocity and Duration of Muscle Contraction (pp. 302–303; Figs. 9.23–9.25; Tables 9.2–9.3)1.There are three muscle fiber types: slow oxidative fibers, fast oxidative fibers, and fast glycolytic fibers.2.Muscle fiber type is a genetically determined trait, with varying percentages of each fiber type in every muscle, determined by specific function of a given muscle.3.As load increases, the slower the velocity and shorter the duration of contraction. 4.Recruitment of additional motor units increases velocity and duration of contraction.I.Effect of Exercise on Muscles (pp. 304–305)1.Aerobic, or endurance, exercise promotes an increase in capillary penetration, the number of mitochondria, and increased synthesis of myoglobin, leading to more efficient metabolism, but no hypertrophy.2.Resistance exercise, such as weight lifting or isometric exercise, promotes an increase in the number of mitochondria, myofilaments and myofibrils, and glycogen storage, leading to hypertrophied cells. ................
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