Myelin incisure

Diagram of longitudinal sections of medullated nerve fibers. (Incisure labeled at upper left.)

Details
System| Nervous system
Anatomical terms of microanatomy

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Myelin incisures (also known as Schmidt-Lanterman clefts, Schmidt-Lanterman incisures, clefts of Schmidt-Lanterman, segments of Lanterman, medullary segments) are small pockets of cytoplasm left behind during the Schwann cell myelination process.

They are histological evidence of the small amount of cytoplasm that remains in the inner layer of the myelin sheath created by Schwann cells wrapping tightly around an axon (nerve fiber).

## Development

In the peripheral nervous system (PNS) axons can be either myelinated or unmyelinated. Myelination refers to the insulation of an axon with concentric surrounding layers of lipid membrane (myelin) produced by Schwann cells. These layers are generally uniform and continuous, but due to imperfect nature of the process by which Schwann cells wrap the nerve axon, this wrapping process can sometimes leave behind small pockets of residual cytoplasm displaced to the periphery during the formation of the myelin sheath. These pockets, or "incisures", can subdivide the myelinated axon into irregular portions. These staggered clefts also provide communication channels between layers by connecting the outer collar of cytoplasm of the Schwann cell to the deepest layer of myelin sheath. Primary incisures appear ab initio in myelination and always extend across the whole radial thickness of the myelin sheath but initially around only part of its circumference. Secondary incisures appear later, in regions of a compact myelin sheath, initially traversing only part of its radial thickness but commonly occupying its whole circumference.[1]

## References

This article incorporates text in the public domain from the 20th edition of Gray's Anatomy (1918)

1. ↑ Small, J. R., Ghabriel, M. N., & Allt, G. (1987). The development of Schmidt-Lanterman incisures: an electron microscope study. Journal of Anatomy, 150, 277–286.

## External links

* Histology image: 22801loa – Histology Learning System at Boston University

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Nervous tissue

CNS|

| Tissue Types|

* Grey matter
* White matter
* Projection fibers
* Association fiber
* Commissural fiber
* Lemniscus
* Nerve tract
* Decussation
* Neuropil
* Meninges

|

Cell Types|

| Neuronal|

* Pyramidal
* Purkinje
* Granule
* Spindle
* Interneuron

|

Glial|

| insulating:|

* Myelination: Oligodendrocyte

|

other|

* Astrocyte
* Ependymal cells
* Tanycyte
* Microglia

PNS|

| General|

* Dorsal
* Root
* Ganglion
* Ramus
* Ventral
* Root
* Ramus
* Ramus communicans
* Gray
* White
* Autonomic ganglion (Preganglionic nerve fibers
* Postganglionic nerve fibers)
* Nerve fascicle
* Funiculus

|

Connective tissues|

* Epineurium
* Perineurium
* Endoneurium

Neuroglia|

* Myelination: Schwann cell
* Neurilemma
* Myelin incisure
* Node of Ranvier
* Internodal segment
* Satellite glial cell

Neurons/
nerve fibers|

| Parts|

| Soma|

* Axon hillock

|

Axon|

* Telodendron
* Axon terminals
* Axoplasm
* Axolemma
* Neurofibril/neurofilament

Dendrite|

*     * Nissl body
* Dendritic spine
* Apical dendrite/Basal dendrite

Types|

* Bipolar
* Unipolar
* Pseudounipolar
* Multipolar
* Interneuron
* Renshaw

Afferent nerve fiber/
Sensory neuron|

* GSA
* GVA
* SSA
* SVA
* fibers
* Ia or Aα
* Ib or Golgi or Aα
* II or Aβ and Aγ
* III or Aδ or fast pain
* IV or C or slow pain

Efferent nerve fiber/
Motor neuron|

* GSE
* GVE
* SVE
* Upper motor neuron
* Lower motor neuron
* α motorneuron
* β motorneuron
* γ motorneuron

Termination|

| Synapse|

* Electrical synapse/Gap junction
* Chemical synapse
* Synaptic vesicle
* Active zone
* Postsynaptic density
* Autapse
* Ribbon synapse
* Neuromuscular junction

|

Sensory receptors|

* Meissner's corpuscle
* Merkel nerve ending
* Pacinian corpuscle
* Ruffini ending
* Muscle spindle
* Free nerve ending
* Nociceptor
* Olfactory receptor neuron
* Photoreceptor cell
* Hair cell
* Taste bud

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