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Nervous Tissues 11/5 and 11/7

Nervous Tissues 11/5 and 11/7. 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?

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Nervous Tissues 11/5 and 11/7

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  1. Nervous Tissues 11/5 and 11/7 • 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? No Supplemental Instruction Tuesday Evening Nov 7th: Election Day (MN State Law), so you will need to arrange your own make-up time. Peer-reviewed Literature Writing Assignment: 20 points Due NEXT Wednesday November 14th

  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. Dendrites carry the AP towards the cell body and axons carry the AP away from cell body to the next cell! If the stimulus occurs artificially in the middle of an axon, the AP can travel both ways!

  6. 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

  7. 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!

  8. 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)!

  9. Once a local depolarization that exceeds threshold is created the AP spreads in either direction from the origin. Normally this is from the cell body towards the synapse!

  10. What happens to the AP-velocity if we wrap layers of electrical insulation (sphingomyelin) in a sheath between pockets of VGC?Extremely Rapid Saltatory Conduction Results! • Unmyelinated Velocity is about 0.5 meters/sec • Myelination increases velocity to up to 70-100 meters/sec Blue Whale: How long will it take to go from brain to tail? 30 Meters: With Myelination:__ Without Myelinationation:__ How tall are you head to tail? Why does sphingomyelin help? What is a Node of Ranvier? Why no VGC between nodes? Why does Saltatory Conduction use less Glucose/ATP?

  11. The myelin sheath is created by cells to GREATLY increases Action Potential velocity! Oligodendrites in the central nervous systemSchwann Cells in the peripheral nervous systemGaps between cells are called Nodes of Ranvier

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

  13. Lets consider the transport of materials inside of and along the length of a neuron. How fast and how efficient is the process of molecular/organelle transport? Soma is the source of mRNA and most biosynthesis. Axoplasmic or Axonal transport describes how things get to the synaptic ending or back to soma (FAST OR SLOW). Fast axonal transport (20-400 mm/day) • Daily use materials: organelles, vesicles, proteins, mitochondria • Pathogens: Anterograde- towards end of axon Retrograde- axon toward soma • Herpes Simplex Virus (Nerve soma to skin escape from body/coldsore • Rabies Virus: Dendrite to soma and protection from antibodies within CNS • If you know where the pathogen entered a neuron, you can time the appearance of symptoms in the CNS to the rate of transport! Slow axonal transport (0.5 to 10mm/day) provides materials for axonal growth/repair/regeneration If a nerve was cut at shoulder, how long to regenerate “finger tip innervation” if distance was 30 cm? 300mm X 0.5mm/day=600days

  14. How do neurotransmitters modify target cell activity? • Post Synaptic Membrane Potential? • Direct Ionotrophic Effects: Ions such as Na+ or K+ enter/leave cell • Indirect effects: Second Messenger Systems • Neuromodulation: • Partial Hyperpolarization- • Partial Depolarization- • IPSPs and K+ vs EPSPs and Na+ • Modified vesicle release • Potential for positive or negative feedback!

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