[Ultrastructure of the muscle spindles in the extraocular muscles of pigs].
To define the morphological properties of muscle spindles relative to the accurate control of eyeball movement, muscle spindles were investigated in 6 extraocular muscles of three white pigs by an electron microscope. The muscle spindles were composed mainly of a thin outer capsule, nuclear bag and chain fibers. The bag fibers seem to be slow fibers and the chain fibers to be fast fibers in the external fashion, in so far as the former has a greater myofibril density than the latter. The intrafusal muscle fibers were innervated by three categories of nerve terminals; annulospiral and flower spray sensory terminals and gamma motor terminals. The annulospiral terminal was coiled sparsely on the bag fiber and densely on the chain fiber. The cross terminals were found in the pairing muscle fibers. We frequently observed that the satellite cells were controlled by the sensory terminals. It was also frequently observed that the muscle spindles were composed of only one intrafusal bag muscle fiber. It was suggested that the extraocular muscle spindles of the pig remained a primordial profile in the structure.
Kubota
M
M
Department of Ophthalmology, Faculty of Medicine, Tokyo Medical and Dental University, Japan.
D000818:Animals; D008854:Microscopy, Electron; D009470:Muscle Spindles / Q000648:ultrastructure*; D009210:Myofibrils / Q000648:ultrastructure; D009801:Oculomotor Muscles / Q000648:ultrastructure*; D013552:Swine