Schmidt-Lanterman clefts: a morphometric study in human sural nerve

Area of Science:

• Neuroscience
• Cell Biology
• Histology

Background:

• Schmidt-Lanterman (SL) clefts are specialized regions within the myelin sheath of nerve fibers.
• Understanding the structural characteristics of SL clefts is crucial for comprehending nerve fiber physiology and pathology.

Purpose of the Study:

• To quantify the incidence, extent, and morphological impact of SL clefts in large and small myelinated fibers of the human sural nerve.
• To investigate the relationship between SL clefts and myelin thickness.

Main Methods:

• Morphometric analysis of myelinated fibers in the human sural nerve.
• Quantification of Schmidt-Lanterman clefts per unit length.
• Measurement of SL cleft extent and its relation to internodal length.
• Analysis of fiber and axon diameter changes within SL and nodal regions.

Main Results:

• Large myelinated fibers exhibited 35 SL clefts/mm, while small fibers had 8 SL clefts/mm.
• SL cleft incidence correlated linearly with myelin thickness.
• SL clefts occupied ~50% of internodal length in large fibers and 6% in small fibers.
• Axon diameter was reduced by 17% (large) and 28% (small) fibers within SL regions.
• Axon diameter reduction of 40-50% was observed in the nodal region.

Conclusions:

• The density and extent of SL clefts are significantly different between large and small myelinated fibers.
• SL clefts represent substantial regions that influence axon caliber, particularly in smaller fibers.
• Nodal regions also show significant axon diameter reduction, highlighting regional specializations within nerve fibers.