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Chapter 48 Nervous System

Chapter 48 Nervous System. http://youtube.com/watch?v=NqVeH26i7Kg&feature=related. Nervous systems. Effector cells~ muscle or gland cells Nerves~ bundles of neurons wrapped in connective tissue Central nervous system (CNS)~ brain and spinal cord

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Chapter 48 Nervous System

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  1. Chapter 48 Nervous System http://youtube.com/watch?v=NqVeH26i7Kg&feature=related

  2. Nervous systems • Effector cells~ muscle or gland cells • Nerves~ bundles of neurons wrapped in connective tissue • Central nervous system (CNS)~ brain and spinal cord • Peripheral nervous system (PNS)~ sensory and motor neurons

  3. Structural Unit of Nervous System • Neuron~ structural and functional unit • Cell body~ nucelus and organelles • Dendrites~ impulses from tips to neuron • Axons~ impulses toward tips

  4. Structural Unit of Nervous System • Myelin sheath~ supporting, insulating layer • Schwann cells~PNS support cells • Synaptic terminals~ neurotransmitter releaser • Synapse~ neuron junction

  5. Simple Nerve Circuit • Sensory neuron: convey information to spinal cord • Interneurons: information integration • Motor neurons: convey signals to effector cell (muscle or gland) • Reflex: simple response; sensory to motor neurons • Ganglion (ganglia): cluster of nerve cell bodies in the PNS • Supporting cells/glia: nonconductiong cell that provides support, insulation, and protection

  6. The Resting Potential • http://bcs.whfreeman.com/thelifewire/content/chp44/4402001.html • http://youtube.com/watch?v=iA-Gdkje6pg&feature=related

  7. Resting potential • Membrane potential (voltage differences across the plasma membrane) • Intracellular/extracellular ionic concentration difference • K+ diffuses out (Na+ in); large anions cannot follow….selective permeability of the plasma membrane • Net negative charge of about -70mV

  8. The Action Potential • http://youtube.com/watch?v=SCasruJT-DU&feature=related • http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120107/bio_d.swf::Action Potential Propagation in an Unmyelinated Axon • http://bcs.whfreeman.com/thelifewire/content/chp44/4402s.swf

  9. Neural signaling - 1 • Excitable cells~ cells that can change membrane potentials (neurons, muscle) • Resting potential~ the unexcited state of excitable cells • Gated ion channels (open/close response to stimuli): photoreceptors; vibrations in air (sound receptors); chemical (neurotransmitters) & voltage (membrane potential changes)

  10. Neural signaling - 2 • Graded Potentials (depend on strength of stimulus): • 1- Hyperpolarization (outflow of K+); increase in electrical gradient; cell becomes more negative • 2- Depolarization (inflow of Na+); reduction in electrical gradient; cell becomes less negative

  11. Neural signaling - 3

  12. Neural signaling - 3 • Threshold potential: if stimulus reaches a certain voltage (-50 to -55 mV)…. • The action potential is triggered…. • Voltage-gated ion channels (Na+; K+) • 1-Resting state •both channels closed • 2-Threshold •a stimulus opens some Na+ channels • 3-Depolarization•action potential generated •Na+ channels open; cell becomes positive (K+ channels closed) • 4-Repolarization•Na+ channels close, K+ channels open; K+ leaves •cell becomes negative • 5-Undershoot•both gates close, but K+ channel is slow; resting state restored • Refractory period~ insensitive to depolarization due to closing of Na+ gates

  13. Neural signaling - 4 • “Travel” of the action potential is self-propagating • Regeneration of “new” action potentials only after refractory period • Forward direction only • Action potential speed: • 1. Axon diameter (larger = faster; 100m/sec) • 2. Nodes of Ranvier (concentration of ion channels); saltatory conduction; 150m/sec

  14. Synaptic communication • Presynaptic cell: transmitting cell • Postsynaptic cell: receiving cell • Synaptic cleft: separation gap • Synaptic vesicles: neurotransmitter releasers • Ca+ influx: caused by action potential; vesicles fuse with presynaptic membrane and release…. • Neurotransmitter

  15. Signal transmission • http://youtube.com/watch?v=90cj4NX87Yk&feature=related • http://youtube.com/watch?v=HXx9qlJetSU&feature=related • http://youtube.com/watch?v=CiZLnbKVIhM&feature=related

  16. Neurotransmitters • Acetylcholine (most common) •skeletal muscle • Biogenic amines(derived from amino acids) •norepinephrine •dopamine •serotonin • Amino acids • Neuropeptides(short chains of amino acids) •endorphin

  17. Vertebrate PNS • Cranial nerves (brain origin) • Spinal nerves (spine origin) • Sensory division • Motor division •somatic system voluntary, conscious control •autonomic system parasympathetic conservation of energy sympathetic increase energy consumption

  18. The Vertebrate Brain • Forebrain•cerebrum~memory, learning, emotion •cerebral cortex~sensory and motor nerve cell bodies •corpus callosum~connects left and right hemispheres•thalamus; hypothalamus • Midbrain •inferior (auditory) and superior (visual) colliculi • Hindbrain•cerebellum~coordination of movement•medulla oblongata/ pons~autonomic, homeostatic functions

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