PRESENCE AND STRUCTURE OF INNERVATED MYOTENDINOUS CYLINDERS IN SHEEP EXTRAOCULAR-MUSCLE

Innervated myotendinous cylinders (IMCs) were for the first time descr ibed in a sheep extraocular muscle (EOMs). They were found at the dist al myotendinous junction of a medial rectus and were investigated by l ight and transmission electron microscopy. The IMCs are enveloped by a multi-layered capsule of fibrocytes and each contains the terminal po rtion of one multiply-innervated muscle fibre and its corresponding te ndon. The tendinous compartment of the IMC is entered by a single nerv e fibre which, inside, spreads into several terminal branches. Numerou s terminal branches were found among the collagen fibrils but few on t he muscle fibre tips. Nerve terminals contain mitochondria and are ful l of clear vesicles. Within the nerve terminals, vesicles are often co ncentrated in an area where the axolemma exhibits dense patches. Inner vated myotendinous cylinders of sheep EOMs exhibit the same ultrastruc tural features as those earlier described as palisade endings or myote ndinous cylinders in cat, monkey and man. (C) 1998 Elsevier Science Ir eland Ltd.