Neuron and Nerves

Neurons vs. Nerves

  • Nerves are not interchangeable with neurons.
  • A nerve is a bundle of axons, which are parts of neurons.
  • These bundles are covered in layers of connective tissue.
  • Nerves are present in the peripheral nervous system.
  • Sensory (afferent) nerves bring information to the central nervous system.
  • Motor (efferent) nerves carry information from the central nervous system to the rest of the body.
  • Organs are innervated, meaning they have nerves communicating with them.

Nerve Structure

  • A nerve is composed of axons bundled together.

Layers of Connective Tissue

  1. Endoneurium

    • A thin, delicate layer of connective tissue.
    • Wraps around an individual nerve fiber (axon).
    • Innermost layer: endo- meaning "inner."

  2. Fascicles

    • Axons wrapped in endoneurium are bundled into fascicles.
    • A fascicle is a bundle or cluster (not exclusive to the nervous system).

  3. Perineurium

    • A layer of connective tissue that surrounds fascicles.
    • Separates fascicles from each other.
    • Peri- meaning "besides" or "next to."

  4. Epineurium

    • The outermost layer of connective tissue.
    • Wraps around multiple fascicles to form a complete nerve.
    • Epi- meaning "on the outside."
  • Analogy: Axon covered in endoneurium, then bundled into a fascicle covered by perineurium, several fascicles bundled together covered by epineurium to form a nerve.

Blood Vessels

  • Blood vessels are present within the connective tissue layers between fascicles.
  • They ensure the nerves are nourished and healthy.

Communication

  • Nerves facilitate communication between the peripheral and central nervous systems.
  • Sensory nerves transmit information in.
  • Motor nerves transmit information out to the body.