Chapter 2: Neurons

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  1. Neurons vary in size and complexity
    • Cell bodies: genetic center
    • Dendrites: receptive surface area to receive info via synapses
    • Axons: conduct impulses away from cell body (one-way conduction)
    • Synapses: allow communication between neurons
    • Chemical neurotransmitters released (chemical synapses) or electrical signals pass directly from cell to cell (electrical synapses)
  2. Neuron Groupings and Types
    • Nuclei are compact groups of nerve cell bodiesĀ 
    • In the peripheral system, groups are called ganglia
    • Projection neurons carry impulses to other parts of the CNS
    • Interneurons are short relay neurons
    • Axon bundles = tracts or fasciculiĀ 
    • In the spinal cord, collections of tracts = columns or funiculi
  3. Neuroglia
    • Support cells that do not transmit signals
    • Important for myelin and neuron production
    • Maintenance of K+ levels and reuptake of neurotransmitters after neural transmission at synapses
  4. Resting Membrane Potential
    • Positive on outside
    • Negative on inside (about 70mV)
  5. Action Potential
    • Increased permeability of Na+
    • Influx into cell with outflux of K+
    • Results in polarity changes (inside to about +35 mV) and depolarization
    • Generation of an action potential = all or none
  6. Conduction Velocity
    • Proportional to axon diameter
    • Largest myelinated fibers = conduct the fastest
  7. Repolarization
    Results from activation of K+ channels
  8. Myelinated Axons
    • Many axons are covered with myelin with small gaps (nodes of Ranvier) where myelin is absent
    • Action potential jumps from one node to next (saltatory conduction)
    • Myelin functions to increase speed of conduction and conserve energy
  9. Nerve Fiber Types: A Fibers
    • Large, myelinated, fast-conduction
    • Alpha: proprioception, somatic motor
    • Beta: touch, pressure
    • Gamma: motor to muscle spindles
    • Delta: pain, temperature, touch
  10. Nerve Fiber Types: B Fibers
    • Small, myelinated
    • Conduct less rapidly
    • Preganglionic autonomic
  11. Nerve Fiber Types: C Fibers
    • Smallest, unmyelinated, slowest conducting
    • Dorsal root: pain, reflex responses
    • Sympathetic: postganglionic sympathetics
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Chapter 2: Neurons
2015-03-07 04:32:43
NPTE: Chapter 2
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