Neuron, Nerve Cell, Neural Cell, Synapse, Neuraxis Tract, Nerve Fasciculus, Neuraxis Peduncle, Neuraxis Lemniscus, Neural Nucleus, Dendrite, Neuron Cell Body, Neuron Soma, Perikaryon, Axon, Myelin Sheath, Action Potential, Nerve Impulse, Membrane Potential, Membrane Depolarization, Nerve Conduction

  • Definitions
  1. Neuron
    1. Conducting cell of the neurologic system which receives, conducts and transmits small electrical signals
  2. Synapse
    1. Connections between Neurons in which they communicate via chemical signals (neurotransmitters)
  3. Neurologic Pathway
    1. Chain of communicating Neurons
  4. Neuraxis Tract (or fasciculus, peduncle or lemniscus)
    1. Bundle of axons in a pathway within the Central Nervous System (CNS)
  5. Nerve
    1. Bundle of axons in a pathway within the peripheral nervous system
  6. Neural Nucleus
    1. Group of Neuron cell bodies (soma) with attached group of axons (nerve tracts)
    2. Includes brain nucleii, Cranial Nerve nucleii, cerebellar nucleii and spinal cord nucleii
    3. Ganglia are the peripheral nerve versions of the CNS neural neuclei
  • Anatomy
  1. Images
    1. neuron.png
    2. nerveActionPotential.png
  2. Dendrites
    1. Tree-like structures that receive signals from other Neurons
  3. Cell Body (Soma)
    1. Nucleus
    2. Cytoplasm (Perikaryon)
  4. Axon
    1. Transmits signal from cell body to axon terminals
    2. Myelin Sheath
      1. Most axons are insulated with a thin layer of cells to conserve and speed electrical transmission
      2. Myelinated axons appear as white matter (while Neuron cell bodies appear as gray matter)
  5. Neurotransmitters
    1. Released from axon terminals to transmit a signal into Synapse (inter-Neuron space)
  6. Neuron types
    1. Sensory Neurons
    2. Motor Neurons
    3. Interneurons (interconnections between Neurons forming a pathway)
  7. Group of Neurons
    1. Peripheral nervous system
      1. Nerves
    2. Central Nervous System (interchangeable names)
      1. Nerve Tract
      2. Fasciculus
      3. Lemniscus
      4. Peduncle
  • Physiology
  • Nerve Impulse (Action Potential)
  1. Neurons are specialized cells capable of tranmsitting an electrical signal
  2. Neuron resting Membrane Potential is more positive on outside of cell than on inside (e.g. -60 mv difference)
    1. sodiumPotassiumATPase.jpg
    2. Maintained by Sodium-Potassium ATP Pump (exchanges 3 Na+ moved extracellular for 2+ intracellular)
    3. Potassium leaks out of the cell more than Sodium leaks back in
  3. Depolarization
    1. Voltage gated electrical channels specific for Potassium and Sodium allow for electrical signal transmission
    2. Voltage channels are activated when there is a neutralization of resting Membrane Potential
      1. Membrane Potential decreases below a threshold (e.g. 15-35 millivolts or mv)
    3. Voltage-Gated Sodium channels suddenly open
      1. Sodium rushes into Neuron, resulting in neutralization of resting potential and depolarization
      2. Inside and outside of Neuron may have minimal difference of charge at depolarization
    4. Voltage-Gated Calcium channels may also be involved
      1. Most common in cardiac muscle (esp. Purkinje Fibers) and smooth muscle (uncommon in axons)
      2. As with Sodium, Calcium concentrations outside the cell are higher
      3. When Calcium channels open, Calcium rushes into the muscle cell
      4. However Calcium channels are slower than Sodium channels
        1. Results in an Action Potential plateau and a delayed repolarization/recovery
        2. Allows for a sustained, prolonged contraction of muscles
    5. Signal spreads along the axon via contiguous regions, each depolarizing in turn
  4. Repolarization
    1. Voltage-Gated Sodium channels close in response to neutralized Membrane Potential
    2. Voltage-Gated Potassium channels open
      1. Potassium flows rapidly out of cell
    3. Resting Membrane Potential is Restored
      1. Neuron refractory period is related to the time required to Restore the resting Membrane Potential
  • Images
  1. NeuroCellGrayBB629.gif Lewis (1918) Gray's Anatomy 20th ed (in public domain at Yahoo or BartleBy)
  2. NeuroCellGrayBB626.gif Lewis (1918) Gray's Anatomy 20th ed (in public domain at Yahoo or BartleBy)
  3. NeuroCellGrayBB625.gif Lewis (1918) Gray's Anatomy 20th ed (in public domain at Yahoo or BartleBy)
  • References
  1. Goldberg (2014) Clinical Physiology, MedMaster, p. 36-7