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Nervous System Overview • 2 ways body communicates to send signals. • 1st - endocrine system - hormones. • 2nd - nervous system - no chemical signaling – impulses - travel through network of cells to get to destination. Quic kTime™ and a dec ompres sor are needed to see this picture. http://www.drstandley.com/images/nervous5.bmp • Impulses allow organisms to receive and respond to stimuli in environment. • Controls all functions of life ability to move, think, breathe, etc. Quic kTime™ and a dec ompres sor are needed to see this pic ture. http://www.medicalook.com/systems_images/Autonomic_Nervous_System.jpg Functional unit Quic kTime™ and a dec ompres sor are needed to see this pic ture. • Functional unit of nervous system neurons. • Specialized cell designed to transmit electrochemical signals called action potentials (nerve impulses). • Signals formed by altering of voltage across plasma membrane. • Basic part of neuron’s structure cell body, dendrites, axon. • Cell body contains nucleus, most organelles - site of protein synthesis. • Dendrites project from body and receive chemical information from other neurons; carry this information to cell body. Quic kTime™ and a dec ompres sor are needed to see this pic ture. http://www.nida.nih.gov/JSP/MOD3/images/NEURON2.gif • Axon - projection of neuron that transmits information to cell body to target cells. • Has to be long enough to carry action potential from central nervous system to extremities. Quic k Ti me™ and a dec ompres s or are needed to s ee t his pic t ure. Fig. 48.2 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Resting potential QuickTime™ and a d eco mpres sor are nee ded to s ee this picture. • Action potential requires that voltage manipulated across membrane. • Altered by moving ions back and forth across membrane (ions charged). • Cells have voltage across plasma membrane generated through actions of protein called Na+/K+ ATPase. http://openwetware.org/images/thumb/a/a6/Action-potential.jpg/300px-Action-potential.jpg.png QuickTime™ and a d eco mpres sor are nee ded to s ee this picture. • Hydrolysis of ATP for energy protein pumps sodium ions out of cell and potassium into cell. • Activity essential in maintaining osmotic balance of cells. • Some potassium leaks back out of cell through potassium channel. http://scienceblogs.com/clock/upload/2006/08/Potassium-Channel-2-2004.JPG • Potassium channel is ion channel that selectively allows potassium ions to flow down K+ gradient established by ATPase. • Resting potential about -70mVolts most positive ions on outside of cell. 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Action potential QuickTime™ and a d eco mpres sor are nee ded to s ee this picture. • Most cells maintain membrane potential at resting potential. • Membrane excited - potential changed - allows information to be carried via action potential. • Neurons, muscle cells have ion channel proteins in plasma membrane that open to allow ions through. http://www.unm.edu/~lkravitz/MEDIA2/Action%20Potential.jpg QuickTime™ and a decompressor are needed to see this picture. • Happens in response to decrease in membrane potential. • Protein that does this in neurons voltage-gated sodium channel. • When membrane potential more negative than resting potential, (from -70mVolts to -90mVolts), membrane hyperpolarized. http://courses.washington.edu/conj/membrane/chan.gif • When membrane potential less negative than usual, (-70mVolts to 50mVolts or 0mVolts) membrane depolarized. • Voltage-gated sodium channels closed at resting potential - do not let ions through membrane. • Change in membrane potential causes voltage-gated sodium channels to open to allow sodium through. QuickTime™ and a decompressor are needed to see this picture. • If membrane voltage becomes less negative than resting potential (70mVolts to -50mVolts) voltagegated sodium channels in membrane will open. • Voltage at which voltage-gated channels open - threshold potential. QuickTime™ and a d eco mpres sor are nee ded to s ee this picture . http://openwetware.org/images/thumb/a/a6/Action-potential.jpg/300px-Action-potential.jpg.png • When channels open, sodium diffuses freely through channel to cross membrane from outside of cell into cytoplasm. • Opening of channels in one region of membrane, entry of sodium through channels causes membrane depolarization (membrane less polarized, moving toward 0) QuickTime™ and a d eco mpres sor are nee ded to s ee this picture . QuickTime™ and a decompressor are needed to see this picture. • After voltage-gated sodium channels opened and depolarization complete, channels close rapidly again, allowing membrane voltage to normal potential (millisecond). • Return of voltage to normal negative state - repolarization. • Section of membrane depolarizes, triggers threshold for voltagegated channels in next section of membrane to depolarize. Quic kTime™ and a dec ompres sor are needed to see this pic ture. http://www.cidpusa.org/nervous_repolarization.gif QuickTime™ and a decompressor are needed to see this picture. • Action potential moves along length of axon in wavelike manner until it reaches end of neuron at synapse. • Some vertebrate – neurons have myelin - surrounds axon, allows action potentials to travel more quickly. Quic kTime™ and a dec ompres sor are needed to see this pic ture. QuickTime™ and a decompressor are needed to see this picture. • Myelin formed by glial cells - wrap plasma membrane around axons, insulating it. • Small spaces between myelin nodes of Ranvier. • Myelinated neurons - action potential jumps from 1 node to another node bypassing insulated myelin regions where no ions cross membrane. QuickTime™ and a d eco mpres sor are nee ded to s ee this picture. http://butler.cc.tut.fi/~malmivuo/bem/bembook/02/fi/0201.gif QuickTime™ and a decompressor are needed to see this picture. • Allows action potential to travel much quicker - can jump forward instead of traveling whole length of axon - saltatory conduction. • Larger neurons carry action potentials more quickly. QuickTi me™ and a decompressor are needed to see thi s pi ctur e. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Size and frequency of action potentials • Every action potential in neuron same size. • Once membrane reaches threshold for depolarization - fully depolarize - all-or-nothing response. • Either neuron fires an action potential or it doesn’t. QuickTime™ and a decompressor are needed to see this pict ure. http://education.vetmed.vt.edu/Curriculum/VM8054/Labs/Lab10/IMAGES/MOTOR%20END%20PLATES%20SMALL%201.jpg QuickTime™ and a decompressor are needed to see this picture. • Strength of stimulus does not change size of action potential depolarization or duration of depolarization. • Strength of stimulus determines intensity of action potential. • Light touch will trigger less frequent response. QuickTime™ and a decompressor are needed to see this picture. http://www.unmc.edu/physiology/Mann/pix_3/f3-17.gif QuickTime™ and a decompressor are needed to see this picture. • Action potential same in strength but frequency of action potentials change with intensity of stimulus. • When action potential passes through section of membrane cannot carry action potential again immediately. • Must first finish depolarizing, then repolarize. QuickTime™ and a d eco mpres sor are nee ded to s ee this picture. QuickTime™ and a decompressor are needed to see this picture. http://www.gregalo.com/action_potential.jpg • Limit to frequency of action potential firing in neuron refractory period. • Places upper limit on number of action potentials that can pass through neuron in unit of time. • Action potentials carried in one direction, from cell body to end of axon. QuickTi me™ and a decompressor are needed to see thi s pi ctur e. QuickTime™ and a decompressor are needed to see this picture. The synapse • When action potential reaches end of neuron - neurotransmitters released to communicate with next cell across small gap between cells synapse. • 2 types of synapses, chemical and electrical. Quic kTime™ and a dec ompres sor are needed to see this pic ture. http://universe-review.ca/I10-40-synapse.jpg QuickTime™ and a decompressor are needed to see this picture. • At chemical synapse - action potential reaches end of axon, comes in contact with rounded terminal filled with vesicles - have neurotransmitters in them. • Include seratonin, dopamine, acetylcholine, and glutamate. Quic kTime™ and a dec ompres sor are needed to see this picture. QuickTime™ and a decompressor are needed to see this picture. • When action potential signals it, voltage-gates calcium channels open and allow calcium into cell. • Calcium causes some vesicles to fuse with plasma membrane and release contents into synapse. • Synapse and target cell together synaptic cleft. QuickTime™ and a d eco mpres sor are nee ded to s ee this picture. http://findlaw.doereport.com/imagescooked/2728W.jpg QuickTime™ and a decompressor are needed to see this picture. • Neurotransmitter diffuses across synaptic cleft and binds to receptors on target cell plasma membrane. • When bound, receptors will open ion channels - allows specific ions through membrane in response to neurotransmitter. • Ions cause response in postsynaptic cell (cell after synapse) Quic kTime™ and a dec ompres sor are needed to see this pic ture. Fig. 48.12 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • Each neurotransmitter has specific receptors that it interacts with at synapse; each receptor opens channel that allows specific ion through. • Excitatory neurotransmitter binds to receptor that depolarizes membrane of postsynaptic cell. Quic kTime™ and a dec ompres sor are needed to see this pic ture. http://www.chemistryexplained.com/images/chfa_03_img0602.jpg QuickTime™ and a decompressor are needed to see this picture. • Acetylcholine used with skeletal muscle, diffuses across synaptic cleft - binds to receptors for it. • Receptors - ligand-gated ion channels that bind Ach - open to allow sodium ions to diffuse into cell. • When sodium enters - depolarizes plasma membrane of target muscle cell. QuickTime™ and a d eco mpres sor are nee ded to s ee this picture . http://thebrain.mcgill.ca/flash/d/d_06/d_06_m/d_06_m_mou/d_06_m_mou_2a.jpg QuickTime™ and a decompressor are needed to see this picture. • If depolarization of target reaches threshold - action potential will be initiated in muscle cell membrane by voltage-gated channels, and will be sent throughout muscle cell membrane, which triggers muscle cell to contract. QuickTime™ and a decompressor are needed to see this pict ure. QuickTime™ and a decompressor are needed to see this picture. http://www.blackwellpublishing.com/korfgenetics/jpg/300_96dpi/Fig16-2.jpg • More action potentials that reach muscle and more muscle cells involved, stronger muscle contraction. • Neurotransmitter can bind to receptor -opens to allow chloride to enter postsynaptic membrane causing hyperpolarization. • Membrane potential moves away from threshold for triggering an action potential. Quic kTime™ and a dec ompres sor are needed to see this pic ture. http://www.gregalo.com/action_potential.jpg QuickTime™ and a decompressor are needed to see this picture. QuickTime™ and a d eco mpres sor are nee ded to s ee this picture. • If neurotransmitter inhibits - more difficult for action potential to start in target cell. • Most common - GABA. • Neuron can form synapses with many neurons; release neurotransmitter to alter membrane potential of target cell. QuickTime™ and a decompressor are needed to see this picture. http://huguenard-lab.stanford.edu/beta3/gaba.jpg • Information from all synapses neuron interacts with combined in cell body of neuron in summation single neuron processes information from all of its stimulating neurons. • Then decides whether or not to initiate an action potential itself. QuickTime™ and a decompressor are needed to see this picture. http://www.biologymad.com/NervousSystem/summation.jpg QuickTime™ and a decompressor are needed to see this picture. • If changes in potential of neuron cause it to reach threshold depolarization to open voltagegated channels, it will fire an action potential. • If not, neuron will not fire an action potential. QuickTime™ and a decompressor are needed to see this pict ure. QuickTime™ and a decompressor are needed to see this picture. http://www.unm.edu/~lkravitz/MEDIA2/Action%20Potential.jpg • To turn off signal • Once neurotransmitter released into synaptic cleft, continues to bind to postsynaptic receptors unless removed from synapse. • One way - neurotransmitter to diffuse into surrounding fluid. QuickTime™ and a dec ompres sor are needed to s ee this pic ture. QuickTime™ and a decompressor are needed to see this picture. http://www.elmhurst.edu/~chm/vchembook/images2/661synapse.gif • Another way - enzyme that degrades neurotransmitter. • Acetylocholinesterase acts on acetylcholine to inactivate it. • Pesticides, nerve gas inactivate this enzyme. • 3rd way - take neurotransmitter back up into cells at synapse. • Happens with norepinephrine,seratonin. QuickTime™ and a dec ompres sor are needed to s ee this pic ture. QuickTime™ and a decompressor are needed to see this picture. Organization of nervous system • As complexity of organism increases, complexity of nervous system also increases. • Simple organisms can respond to simple stimuli, more complex organisms can discern stimuli (i.e.shades of color) Quic kTime™ and a dec ompres sor are needed to see this pic ture. QuickTime™ and a decompressor are needed to see this picture. Invertebrate nervous systems • Protozoa - single celled, no nervous system. • Receptors that respond to stimuli (heat, light, chemicals). • Sponges - multicellular - have almost no response to environment, no nerves. • Cnidarians - network of cells nerve net, located between inner and outer layers of cells of bodies. Quic kTime™ and a dec ompres sor are needed to see this pic ture. • Annelids - primitive nervous system consisting of ventral nerve cord and anterior brain of fused ganglia. • Arthropods - better developed nervous system - specialized sense organs, including sight and hearing organs. Quic kTime™ and a dec ompres sor are needed to see this pic ture. Human nervous system • Central nervous system - brain, spinal cord. • Brain contains all functions beyond simple reflexes - consists of outer portion containing neuronal cell bodies (gray matter), inner portion containing axons (white matter). • CNS processes information, sends response out to body through neurons. Quic kTime™ and a dec ompres sor are needed to see this pic ture. http://www.medem.com/MEDEM/images/ama/ama_brain_stroke_lev20_thebraineffectsstroke_01.gif QuickTime™ and a decompressor are needed to see this picture. Human brain • 1Cerebral cortex – all voluntary motor activity - initiates responses of motor neurons present within spinal cord. • Controls higher functions (memory, creative thought). • Cortex divided into hemispheres (left and right), with some specialization of function between them. Quic kTime™ and a dec ompres sor are needed to see this pic ture. http://www.morphonix.com/software/education/science/brain/game/specimens/images/cerebral_cortex.gif QuickTime™and andaa QuickTime™ decompressor decompressor areneeded neededto tosee seethis thispicture. picture. are • 2Olfactory lobe – center of reception and integration of olfactory input. • 3Thalamus – nervous impulses and sensory information relayed and integrated in this section as impulse travels to and from cerebral cortex. • 4Hypothalamus – hunger, thirst, pain, temperature regulation, water balance controlled here. Qui ckTime™ and a decompressor are needed to see thi s pi cture. QuickTime™ and a decompressor are needed to see this picture. • 5Cerebellum – muscle activity coordinated, modulated. • 6Pons –relay center for cortical fibers on their way to cerebellum. • 7Medulla oblongata –controls vital physiological functions - breathing, heart rate, gastrointestinal activity - has receptors for CO2 levels. QuickTime™ and a decompressor are needed to see this picture. Fig. 48.20 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • Spinal cord is part of central nervous system. • Route axons to travel out of brain. • Serves as center for reflex actions - do not involve brain. • Dorsal horn of spinal cord is entrance point for sensory nerve fibers whose cell bodies are contained within dorsal root ganglion. Quic kTime™ and a dec ompres sor are needed to see this pic ture. http://www.futuremedicalsupply.com/scipages/_images/content/spine/spine%252Bnerves.jpg QuickTime™ and a decompressor are needed to see this picture. • Ventral horn contains cell bodies of motor neurons - initiate muscular contractions. • Lower sections of brain perform more primitive functions (spinal cord, medulla, cerebellum); forebrain and cortex more advanced. • Cortex and forebrain important in evolution of vertebrates. QuickTime™ and a decompressor are needed to see this pict ure. QuickTime™ and a decompressor are needed to see this picture. http://www.cartage.org.lb/en/kids/science/Biology%20Cells/Nervous%20System/Explore%20the%20Nervous%20System/Spinal%20Cord/Segments%20Spinal%20Cord/vert3.gif Peripheral nervous system • Carries nerves from CNS to target tissues in body. • 12 cranial nerves (head and shoulders), 31 spinal nerves (rest of body). • Cranial nerves exit from brainstem, spinal nerves exit from spinal cord. • 2 divisions: somatic and autonomic. Quic kTime™ and a dec ompres sor are needed to see this pic ture. QuickTime™ and a decompressor are needed to see this picture. http://www.web-books.com/eLibrary/Medicine/Physiology/Nervous/cranial_nerves.jpg Somatic nervous system • Innervates skeletal muscle, responsible for voluntary movement. • Motor neurons release acetylcholine (neurotransmitter ACh) onto ACh receptors in skeletal muscle. • Causes depolarization of skeletal muscle leading to muscle contraction. QuickTi me™ and a decompressor are needed to see t his pict ure. QuickTime™ and a decompressor are needed to see this picture. http://thebrain.mcgill.ca/flash/d/d_06/d_06_m/d_06_m_mou/d_06_m_mou_2a.jpg • Somatic nervous system also important in reflexes. • 2 types of reflexes: monosynaptic (one synapse between sensory neuron and motor neuron) and polysynaptic (sensory neurons synapse with > 1 neuron) QuickTime™ and a decompres sor are needed to s ee this picture. http://nawrot.psych.ndsu.nodak.edu/Courses/Psych465.S.02/Movement/Fig.%208-2a.jpg QuickTime™ and a decompressor are needed to see this picture. • Example of monosynaptic - kneejerk response. • When patella hit, stretch receptors sense this - action potentials sent up sensory neuron into spinal cord. • Sensory neuron synapses with motor neuron in spinal cord stimulates leg muscles to contract, causing leg to move. Quic kTime™ and a dec ompres sor are needed to see this pic ture. QuickTime™ and a decompressor are needed to see this picture. http://www.public.iastate.edu/~zool.255/Pics/Q1.jpg • Example of polysynaptic is withdrawal reflex. • Person steps on nail - injured leg withdraws in pain, while other leg extends to retain balance. Quic kTime™ and a dec ompres sor are needed to see this pic ture. Autonomic nervous system • Regulates involuntary functions of body. • Innervates heart and blood vessels, GI tract, urinary system, respiratory system, muscles of eye. • Innervates glands and smooth muscle (not skeletal muscle). • Made up of sympathetic and parasympathetic nervous systems. QuickTime™ and a decompressor are needed to see this pict ure. QuickTime™ and a decompressor are needed to see this picture. http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/A/autonomic.gif Sympathetic nervous system • System uses epinephrine as its transmitter. • Activates body for emergency situations and actions (fight or flight response). • Strengthens heart contractions, increases heart rate, dilates pupils and bronchioles, constricts vessels feeding digestive tract. QuickTime™ and a d eco mpres sor are nee ded to s ee this picture . http://cache.eb.com/eb/image?id=72120&rendTypeId=35 QuickTime™ and a decompressor are needed to see this picture. • Adrenal gland regulated by this system. • Produces epinephrine in response to stimulation - produces many of same fight or flight responses. QuickTime™ and a decompressor are needed to see t his picture. http://www.beliefnet.com/healthandhealing/images/exh45027_ma.jpg QuickTime™ and a decompressor are needed to see this picture. Parasympathetic nervous system • Acetylcholine - primary neurotransmitter for this system. • System deactivates or slows down activities of muscles and glands. • Constricts pupils, slows down heart rate, constricts bronchioles, dilates vessels of digestive tract. • Principle nerve - vagus nerve. Quic kTime™ and a dec ompres sor are needed to see this pic ture. http://www.pharmainfo.net/files/images/stories/article_images/Sympathetic%20and%20parasympathetic%20neurons%20with%20ganglion.JPG QuickTime™ and a decompressor are needed to see this picture.