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Nervous Tissue

Nervous Tissue. Chapter 12. Nervous Tissue. Overview of the nervous system Nerve cells (neurons) Supportive cells (neuroglia) Electrophysiology of neurons Synapses Neural integration. Overview of Nervous System. Master Control of the Body

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Nervous Tissue

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  1. Nervous Tissue Chapter 12

  2. Nervous Tissue • Overview of the nervous system • Nerve cells (neurons) • Supportive cells (neuroglia) • Electrophysiology of neurons • Synapses • Neural integration

  3. Overview of Nervous System • Master Control of the Body • Endocrine and nervous system maintain internal coordination • endocrine = _____________________________ • nervous • _______________________ receive information • brain and spinal cord determine responses • brain and spinal cord __________________________ _____________________________________________

  4. Subdivisions of Nervous System Two major subdivisions • _________________________ • brain and spinal cord enclosed in bony coverings • _________________________ • nerve = _________________ _______________________ • _____________ = swelling of ____________ in a nerve

  5. Functional Divisions of PNS • Sensory (____________) divisions (receptors to CNS) • visceral sensory and somatic sensory division • Motor (_______________) division (CNS to effectors) • visceral motor division (ANS) effectors: cardiac, smooth muscle, glands • sympathetic division (action) • parasympathetic division (digestion) • somatic motor division effectors: skeletal muscle

  6. Fundamental Types of Neurons • Sensory (afferent) neurons • __________________________________________________ • Transmit info to brain/spinal cord • ___________________________ • In between sensory and motor pathways in CNS • 90% of neurons are interneurons • _________________________ _________________________ • ___________________________ • send signals to muscles and glands • organs respond called effectors

  7. Properties of Neurons • ____________________________ • ability to respond to changes (stimuli) in/out of body • Conductivity • _______________________________ • ____________________________ • ____________________________________

  8. Structure of a Neuron • _________________________ _________________________ • single, central nucleus • cytoskeleton • microtubules and neurofibrils (bundles of actin filaments) • RER  Nissl bodies • _________________________ • ______________________ • Singe axon (nerve fiber) arising from axon hillock for rapid conduction • _______________________ _______________________

  9. Variation in Neural Structure • ____________________ • most common • many dendrites/one axon • Bipolar neuron • ______________________ • ______________________ • ____________________ • sensory from skin and organs to spinal cord • Anaxonic neuron • many dendrites/no axon • help in visual processes

  10. Types of Neuroglial Cells • ___________________________________________ • wraps around nerve fibers • ___________________________________________ • ___________________________________________ • in areas of infection, trauma or stroke

  11. Types of Neuroglial Cells • ________________________________ • _________________________________________________ • regulate composition of brain tissue fluid • convert glucose to lactate to feed neurons • secrete nerve growth factor promoting synapse formation • electrical influence on synaptic signaling • sclerosis – damaged neurons replace by hardened mass of astrocytes • ________________________________________

  12. Myelin • ________________________________________ • formed from wrappings of plasma membrane • 20% protein and 80 % lipid (looks white) • all myelination completed by late adolescence • In PNS, hundreds of layers wrap axon • ____________________________________________ • covered by basal lamina and endoneurium • Gaps between myelin segments = _________________

  13. Speed of Nerve Signal • Diameter of fiber and presence of myelin • ______________________________________________ • Speeds • small, unmyelinated fibers = 0.5 - 2.0 m/sec • small, myelinated fibers = 3 - 15.0 m/sec • large, myelinated fibers = up to 120 m/sec • Functions • slow signals supply the stomach and dilate pupil • fast signals supply skeletal muscles and transport sensory signals for vision and balance

  14. Regeneration of Peripheral Nerves • Soma and neurilemmal tube intact • Stranded end of axon and myelin sheath degenerate • cell soma swells, ER breaks up and some cells die • Axon stump puts out several sprouts • _____________________________ _____________________________ • schwann cells produce nerve growth factors

  15. Local Potentials • Local disturbances in membrane potential • ___________________ ___________________ • depolarization (opens gated Na+ channels) decreases potential across cell membrane • Na+ rushes in • Na+ diffuses for short distance inside membrane producing a change in voltage called a local potential

  16. Local Potentials 2 • ___________________________ • vary in magnitude with stimulus strength • get weaker the farther they spread • are reversible as K+ diffuses out of cell • ________________________________________________________________________

  17. Action Potentials • __________________________________________ __________________________________________ • If threshold potential (-55mV) is reached voltage-gated Na+ channels open (Na+ enters causing depolarization) • Slow K+ gates fully open • K+ exits repolarizing the cell • __________________________________________ • excessive exiting of K+

  18. The Refractory Period • Resists stimulation • ________________________ • as long as Na+ gates are open • _________________________ • ________________________ • as long as K+ gates are open • __________________________ __________________________ • Refractory period occurs to a small patch of membrane at one time (quickly recovers)

  19. Impulse Conduction - Unmyelinated Fibers

  20. _______________________________ • Voltage-gated channels needed for APs • fewer than 25 per m2 in myelin-covered regions • up to 12,000 per m2 in nodes of Ranvier • Fast Na+ diffusion occurs between nodes

  21. Saltatory Conduction • Notice how the action potentials jump from node of Ranvier to node of Ranvier.

  22. Chemical Synapse Structure • ______________________ have synaptic vesicles with neurotransmitter and ____________________ have receptors

  23. Types of Neurotransmitters • _______________________________ • formed from acetic acid and choline • Amino acid neurotransmitters • _______________________________ • replace –COOH in amino acids with another functional group • ______________________ (epi, NE and dopamine) • indolamines (serotonin and histamine) • ________________

  24. Synaptic Transmission 3 kinds of synapses with different actions • _______________________________ = ACh • Inhibitory GABA-ergic synapse = GABA • ________________________________ = NE Synaptic delay (.5 msec) • time from arrival of nerve signal at synapse to start of AP in postsynaptic cell

  25. Neural Integration • More synapses a neuron has the greater its information-processing capability • cerebral cortex  40,000 synapses • estimated to contain 100 trillion synapses • Chemical synapses are decision-making components • ______________________________________

  26. Postsynaptic Potentials- EPSP • __________________________________ _____________________ • a positive voltage change causing postsynaptic cell _____________________ • result from Na+ flowing into the cell • glutamate and aspartate are excitatory neurotransmitters • ACh and norepinephrine may excite or inhibit depending on cell

  27. Postsynaptic Potentials- IPSP • ___________________________________ postsynaptic cell to be less likely to fire (hyperpolarize) • result of Cl- flowing into the cell or K+ leaving the cell • glycine and GABA are inhibitory neurotransmitters • ACh and norepinephrine may excite or inhibit depending upon cell

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