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Table 8. Electron Microscopic
Classification of Human Extraocular Muscle Neuromuscular Junctions and
Corresponding Fiber Morphology
| |
Neuromuscular Junction Type |
| Classification |
1 |
2 |
3 |
3a |
4 |
5 |
| Number observed |
2 |
10 |
3 |
2 |
3 |
1 |
| Schwann cell investment |
+ |
+ |
+ or - |
- |
+ |
+ |
| Terminal axon |
Thick |
Thin |
Thin |
7 |
7 |
7 |
| Diameter |
3 μm |
1 μm |
|
|
|
|
| Terminal varicosity |
? |
± |
+ |
+ |
9 |
9 |
| Neurofilaments |
+ |
- |
- |
- |
- |
|
| Synaptic vescicles |
|
|
|
|
|
|
| Clear |
+ |
+ |
+ |
+ |
+ |
+ |
| Granulated |
+ |
+ |
|
+ |
+ |
|
| Ellipsoidal |
|
+ |
|
+ |
|
|
| Muscle cell at neuromuscular junction |
|
|
|
|
|
|
| Junctional folds |
+ |
+ |
- |
- |
± |
± |
| Soleplate specializations* |
- |
- |
+ |
- |
+ |
± |
| Depression of cell surface |
+ |
- |
- |
- |
- |
± |
| Incidence of laminated structures |
2/2 |
2/10 |
0/3 |
0/2 |
2/3 |
1/2 |
| Muscle cell morphology |
|
|
|
|
|
|
| T systems and triads |
+ to + + |
+ |
± |
+ |
+ + to + + + |
+ + |
| Sarcoplasmic reticulum |
+ to + + |
+ |
± |
± to + |
+ + to + + + |
+ |
| Glycogen granules |
+ to + + |
+ |
± |
+ to + + |
+ to + + |
± to + |
| Mitochondria |
+ to + + |
+ to + + |
± |
+ to + + |
+ to + + |
+ |
| Z line |
Straight, slender |
Irregular |
Inconspicuous |
Irregular, thicker |
Straight, slender |
Straight, thick |
| Myofibrils |
Moderately defined at T band level |
Irregular |
Irregular |
Slightly regular |
Well-defined at I band level |
Irregular |
*Hill-like elevations or bridgelike process.
Mukuno K: Fine structure of the human extraocular muscles: III. Neuromuscular
junctions in the normal human extraocular muscles. Acta Soc Ophthalmol
Jpn 72:104, 1968.
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