This 6-week old baby presented with hypotonia at birth.
What are the structures indicated by arrows in Figures #1 and #2?
A. Angulated fibers
C. Motor end plates
D. Necrotic myofibers
Low magnification image showing skeletal muscle in longitudinal orientation with bands of small dark staining areas (intense esterase activity).
The correct answer is C. Motor End Plates
Neuromuscular junctions (NMJ) are most concentrated at the midbelly of muscles. This is nicely demonstrated in Figure #1 which highlights the band of NMJs in this longitudinally oriented frozen section of skeletal muscle.
Esterase enzyme histochemical stain demonstrates acetylcholinesterase activity concentrated within the neuromuscular junction.
Reference(s) / additional reading:
- Dubowitz V, Sewry C, Oldfors A. Muscle biopsy: A practical approach. St. Louis, MO: Elsevier Saunders; 2013.
- Blotnick-Rubin E, Anglister L. Fine Localization of Acetylcholinesterase in the Synaptic Cleft of the Vertebrate Neuromuscular Junction. Front Mol Neurosci. 2018 Apr 19;11:123. doi: 10.3389/fnmol.2018.00123. PMID: 29725289; PMCID: PMC5917012.
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