The ultrastructure of the perinuclear region of nuclear-bag fibres in the muscle spindles of lumbrical muscles of the hand in Macaca irus

Abstract

The ultrastructure of the perinuclear or equatorial region of nuclear-bag fibres in the muscle spindles of the lumbrical muscles of the hand in the Malaysian long-tailed monkey (Macaca irus) was studied since knowledge in this subject area is still vague. This area corresponds to the region of the all important primary or annulo-spiral sensory nerve ending. It was observed that this region of the nuclear-bag fibre displayed an abundance of mitochondria and various other organelles like a Golgi zone, rough and smooth endoplasmic reticulum, various vacuoles, and free and polyribosomes. The organelle-apparatus is one designed for a synthetic process - probably protein in nature. Since the nuclear-bag fibre is a stretch receptor, the abundance of mitochondria could be directed to providing energy for its proprioceptive function as well as its synthetic function. Unusual features noted were the presence of multivesicular bodies, electron-dense bodies, and multi-lamellated bodies. These could be end-products of a degenerative process.