Neurilemma and Myelin Sheath

All axons in the PNS (myelinated and unmyelinated) are surrounded by a continuous, living sheath of Schwann cells, known as the neurilemma, or sheath of Schwann. The axons of the CNS, by contrast, lack a neurilemma (Schwann cells are only found in the PNS). This is significant in terms of regeneration of damaged axons, as will be described shortly.

Some axons in the PNS and CNS are surrounded by a myelin sheath. In the PNS, this insulating covering is formed by successive wrappings of the cell membrane of Schwann cells; in the CNS, it is formed by oligodendrocytes. Those axons smaller than 2 micrometers (2 |im) in diameter are usually unmyelinated (have no myelin sheath), whereas those that are

Fox: Human Physiology, I 7. The Nervous System: I Text I I © The McGraw-Hill

Eighth Edition Neurons and Synapses Companies, 2003

The Nervous System: Neurons and Synapses 157

Schwann cell cytoplasm

Schwann cell cytoplasm

Neurilemma

Unmyelinated

Schwann cell cytoplasm

Oligodendrocyte

Unmyelinated

Schwann cell cytoplasm

■ Figure 7.7 An electron micrograph of unmyelinated and myelinated axons. Notice that myelinated axons have Schwann cell cytoplasm to the outside of their myelin sheath, and that Schwann cell cytoplasm also surrounds unmyelinated axons.

larger are likely to be myelinated. Myelinated axons conduct impulses more rapidly than those that are unmyelinated.

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Responses

  • Omar
    Are neurilemma found in the pns and cns?
    8 years ago
  • Natsnet Kiros
    Why do schwann cells have a neuralemma annolegodendracytes do not?
    8 years ago
  • Sauli Hakola
    Where do we find myelinated and unmyelinated axons in our body?
    8 years ago
  • meghan
    Where are axons surrounded by neurilemma?
    8 years ago
  • monica haanp
    Do unmyelinatednaxons have a neurolemma?
    8 years ago
  • conrad
    Why do myelin sheaths in the CNS lack a neurilemma?
    7 years ago
  • SCOTT
    Why CNS lack neurolemma?
    7 years ago
  • Maisie
    Why is the neurolemma important?
    6 years ago
  • Vincenzo
    Do unmyelinated axons have a neurilemma?
    6 years ago
  • J
    Do unmyelinated axons have a neurolemma?
    6 years ago
  • barbara
    Is the neurolemma outside of the myelin?
    5 years ago
  • ghenet
    Do unmyelinated axons have neurolimma?
    4 years ago
  • Tom Furst
    Is neurolemma continuous in axon?
    4 years ago
  • miikka
    What is neurolemma sheath?
    4 years ago
  • CLOTILDE
    Is axonemma found under neurilemma?
    4 years ago
  • Berylla
    Is neurilemma continuous?
    4 years ago
  • Sinit
    What is neurilemma and what is its importance?
    4 years ago
  • kyran hamilton
    Is neurilemma found outer to axon?
    3 years ago
  • mateusz
    Do myelinated nerves have a neurolemma sheath..?
    3 years ago
  • robin
    Do unmyelinated fibers have a neurilemma?
    3 years ago
  • amanda
    What happens to neurilemma in the nervous system?
    3 years ago
  • veli-matti tuikka
    What is neurilemma and why is it important?
    2 years ago
  • EDUARDO
    Where is neurilema found?
    2 years ago
  • terhi
    Which neurons have present myelin sheeth in human body?
    2 years ago
  • asmait
    Are neurilemma xontinuous?
    2 years ago
  • rosamunda
    What is the advantage to having a neurilemma?
    11 months ago
  • caramella
    What liquid does the neurilemma contain?
    3 months ago
  • nelma
    What cells myelinate axons in the pns and cns?
    20 days ago

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