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Nervous Tissues 11/14

Nervous Tissues 11/14. How do the peripheral and central nervous systems differ? What is the difference between afferent and efferent neurons? What are the anatomical structures of a neuron? What are the functions and classes of neuron? How do myelinated and unmyelinated neurons differ?

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Nervous Tissues 11/14

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  1. Nervous Tissues 11/14 • How do the peripheral and central nervous systems differ? • What is the difference between afferent and efferent neurons? • What are the anatomical structures of a neuron? • What are the functions and classes of neuron? • How do myelinated and unmyelinated neurons differ? • What is the difference and significance of slow and fast axonal transport? • What are neurotransmitter subclasses? • How is target cell activity modified? • What are direct messengers and 2nd messengers? • How do we end a signal? • Why are post-synaptic effects seldom all-or-none?

  2. Structures associated with Neurons: Soma (perikaryon)- Nucleus/Nucleolus Endoplasmic reticulum/Golgi apparatus Cytoskeleton: Microtubules and Actin/Neurofibrils Alzheimer Disease and neural tangles Plasma Membrane composition- Polyunsaturated FA, FA length and cholesterol Membrane width and separation of charge Baby formula FA vs. Breast Milk FA? Dendrite- Axon- Synaptic Knob/Terminal Button/Synaptic Node Terminal Arborization Axon Collateral Neurons rarely (if ever) undergo mitosis (good and bad) Lipofuscin: indicator of aging, wear and tear (lysosomes)

  3. What are the universal properties of neurons? What are the functional classes of neurons? • Universal Properties of neurons: • Excitability/Irritability- • AP Conduction- • Neurotransmitter secretion- • Functional Classes of neurons: • Sensory (Afferent)- • Interneurons (Association)- • Motor (Efferent)- • Glial cells are not excitable (not neurons)

  4. What are the three primary types of neuron and what are their common characteristics? 1) Multipolar Neurons: most common in body Contain many dendrites! 2) Bipolar Neurons: associated with smell One main dendrite and one axon 3) Unipolar neurons: Dendrite + Axon! Soma is placed off to the side! Common Characteristics: • Established Membrane Potential: • More Na+ outside/K+ inside • Hyperpolarized (normal is about -90mVolts) • Excitability: Ability to create/send a wave of depolarization across the lipid bilayer of these cells (action potential)! • This wave of self-promoting depolarization is called an “Action Potential”

  5. Neuroglial cells far outnumber neurons (50:1) and are critical for the support of neuron function. CNS: • Astrocytes: 90% of brain tissue Support/Protect neurons Blood Brain Barrier • Ependymal cells: produce cerebral spinal fluid • Microglial cells: macrophages of CNS • Oligodendrites: wrap around neurons in CNS PNS: • Satellite cells near soma in a ganglion • Schwann Cells: wrap around neurons in PNS

  6. Neuoglial cells far outnumber neurons (50:1) and are critical for the support of neuron function. What are the types of supportive cell for improved AP conduction? • Oligodendrites form myelin sheath around axons in the brain/CNS Multiple sclerosis- • Schwann cells form form myelin sheath around axons in the PNS Nerve regeneration pathways- • Myelin sheath is very rich in polyunsaturated fats! Sensitive to toxic lipids • Myelin Sheath does not permit electrical conduction! • Ions cannot pass though! • The gaps of exposed axolemma are called “Nodes of Ranvier”! • Unmyelinated neurons also exist but have limits to their function! • Especially neuronal regeneration: they have no pathway to retrace!

  7. Myelin sheaths help protect neurons and helps to conduct Action Potentials at a high rate of speed! Neurons can be unmyelinated (slow action potential velocity)!

  8. A myelin sheath creates a “pathway” for damaged axons to follow/grow into/regenerate into following injury!Unmyelinated neurons are poor at regeneration!

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