Jr. Lukas et al., NUMBER AND DISTRIBUTION OF NEUROMUSCULAR SPINDLES IN HUMAN EXTRAOCULAR-MUSCLES, Investigative ophthalmology & visual science, 35(13), 1994, pp. 4317-4327
Purpose. To examine the number and distribution of muscle spindles in
all extraocular muscles (EOMs) in humans. Methods. Thirty-six EOMs wer
e obtained after death from three persons 67, 72, and 83 years of age.
Serial sections were made throughout the length of these muscles. Con
secutive sections were stained with different methods. To discriminate
true spindles from false spindles, light microscopic criteria were de
fined and were subject to ultrastructural investigation. A distal port
ion of a single EOM was gained from a multiorgan donor 17 years of age
, processed for electron microscopy, and analyzed. Results. Spindles w
ere observed in all muscles studied,with the medial rectus exhibiting
a mean of 18.83 spindles (standard deviation), the lateral rectus 19.3
1.9, the superior rectus 15.82.5, the inferior rectus 34.04.4, the sup
erior oblique 27.38.2, and the inferior oblique 4.31.8 per muscle. For
each different human EOM, a typical distribution of spindles was obse
rved in the persons examined. The ultrastructural investigation reveal
ed sensory endings in structures primarily identified as spindles. Con
clusions. By comparing 1 g of tissue, spindles are found to be at leas
t as frequent in human EOM as in skeletal muscles known to have a high
density of spindles. This fact and the peculiar distribution of spind
les in human EOMs suggest that spindles are functionally important pro
prioceptors in EOM.