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The ultrastructural study of human cochlear nerve at different ages
Punit Kumar1, Saroj Sharma2, Charanjeet Kaur3
1Department of Anatomy, All India Institute of Medical Sciences, New Delhi, India.
Hearing Research
|January 25, 2022
Summary
Aging degrades the human cochlear nerve (CN) myelin, with significant reductions in axon diameter and myelin thickness observed in older adults. These ultrastructural changes in the cochlear nerve likely contribute to age-related hearing loss.
Area of Science:
- Neuroscience
- Otolaryngology
- Aging Research
Background:
- Age-related hearing loss is linked to cochlear nerve (CN) myelin changes.
- Previous studies primarily used animal models or limited human samples.
Purpose of the Study:
- To investigate the ultrastructural changes in human cochlear nerve myelin across different age groups.
- To correlate these changes with age-related hearing acuity decline.
Main Methods:
- Human CN samples from young, middle, and old age groups were analyzed using transmission electron microscopy (TEM).
- Morphometric analysis included axon diameter, myelin thickness, and G-ratio calculation.
- K-Means cluster analysis identified distinct myelinated nerve fiber populations.
Main Results:
- Middle and old age CN samples exhibited axon degeneration, myelin sheath splitting, and myelin balloons.
- Significant decreases in axon diameter, inner nerve fiber area, myelin thickness, nerve fiber diameter, and G-ratio were found between middle and old age groups.
- Large myelinated nerve fibers present in younger individuals were absent in older individuals.
Conclusions:
- Morphological deterioration of human cochlear nerve fibers occurs with aging.
- These visible changes may reflect underlying molecular degeneration contributing to decreased hearing acuity.
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