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Neurons • Vary in size and shape • Share certain features – Dendrites- receive signal – Cell body- contains nucleus – Axon- transmits signal to another neuron Neuron structure • Dendrites – Receive incoming signals – Transfer to cell body of neuron • Cell body – Typical cell structures – cytoskeleton Neuron structure • Axon – Transmits signal to synapse Neuron structure- synapse • Region where axon meets target cell • Space across which neurotransmitter diffuses Myelination of axons • Myelin- lipids and proteins that wrap around an axon • White matter – Contains myelinated neurons • Gray matter – Contains unmyelinated neurons Dendrite Unmyelinated region of axon Myelinated region of axon Node of Ranvier Axon Neuron cell body Neuron nucleus • http://www.youtube.com/watch?v=x4PPZCLn VkA&list=PL3EED4C1D684D3ADF&index=26 Types of Neuroglial Cells •Abundant (50 X more glial cells than neurons) •Nourish neurons •May send and receive messages •Provide supportive framework Types of Neuroglial Cells in the PNS Schwann Cells •produce myelin found on peripheral myelinated neurons speed neurotransmission Satellite Cells •support clusters of neuron cell bodies (ganglia) Types of Neuroglial Cells in the CNS Astrocytes • CNS, scar tissue • mop up excess ions, etc • induce synapse formation • connect neurons to blood vessels Microglia CNS phagocytic cell Oligodendrocytes • CNS • myelinating cell Ependyma •CNS ciliated • line central canal of spinal cord • line ventricles of brain Neurons • Cell body • Axon conducts impulses away from the cell body Nodes of Ranvier Myelin sheath • Dendrites transmit impulses into the cell body Neuron Structure 10-7 Resting Membrane Potential • inside is negative relative to the outside • polarized membrane due to distribution of ions by the Na+/K+ pump 10-14 •at rest membrane is polarized •threshold stimulus reached • sodium channels • open and membrane depolarizes • potassium leaves cytoplasm and membrane repolarizes Potential Changes Action Potentials 10-18 Action potential • All or none response • Movement of Na+ and K+ ions – Calcium ions are required to close sodium channels – Low Ca+2 may cause tentany • Changes in membrane permeability can change the impulse conduction – High K+ excitable convulsions – Low K+ paralysis – Some anesthetic medications can change membrane permeability to sodium and prevent impulses (eg procaine) 20 Saltatory Conduction 10-20 10.3 Clinical Application Factors Affecting Impulse Conduction 22 Videos • http://www.youtube.com/watch?v=dSkxlpNs3tU • http://www.youtube.com/watch?v=9euDb4TN3b0 • http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter 14/animation__transmission_across_a_synapse.ht ml The Synapse Nerve impulses pass from neuron to neuron at synapses 10-21 Synapse Greek to clasp or join • typical neuron has 1,000-10,000 terminals • mechanism by which the action potential passes from one neuron to another is NOT the same as the way the action potential is conducted along the neuron. • transmission across the synapse is dependent on chemical neurotransmitters • the neurotransmitter diffuses across the synapse and alters the membrane potential of the next neuron Synaptic Transmission 10-22 Synaptic Potentials Excitatory postsynaptic potential (EPSP) • Graded • Depolarizes membrane of postsynaptic neuron •Action potential of postsynaptic neuron becomes more likely Inhibitory postsynaptic potential (IPSP) • •Graded • Hyperpolarizes membrane of postsynaptic neuron • Action potential of postsynaptic neuron becomes less likely Summation of EPSPs and IPSPs Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. • EPSPs and IPSPs are added together in a process called summation • More EPSPs •Increased probability of an action potential Neuron cell body Nucleus Presynaptic knob Presynaptic axon • Summation usually occurs at the trigger zone 29 30 Neurotransmitters 31 Neuropeptides • Neurons in the brain or spinal cord synthesize neuropeptides. • Some act as neurotransmitters. • Others act as neuromodulators (substances which alter a neuron’s response to a neurotransmitter or block the release of a neurotransmitter) • Examples include: • Enkephalins • Beta endorphin • Substance P 32 10.4 Clinical Application Opiates in the Human Body 33 Regeneration of A Nerve Axon 10-13 Referred Pain