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Abstract
Abstract
Anatomy and Physiology of Extraocular Eye Muscles and their Innervation in Degeneration
Horn A., Büttner-Ennever J.
Anatomy Institute, Ludwig-Maximilians-Universität Munich
Purpose: The extraocular muscle consists of an orbital and a global layer and contains six different muscle fibre types, which can be divided into two main categories: singly-innervated twitch muscle fibres (TMF) and multiply innervated, non-twitch muscle fibres (non-TMF), also known as Fibrillenstruktur- and Felderstruktur-fibres, respectively. These fibres are differentially affected by central denervation or peripheral chemodenervation with botulinum toxin A: transsection of the oculomotor nerve in the monkey results in considerable ultrastructural changes in singly-innervated TMFs, whereas the non-TMFs are virtually unaffected. Botulinum toxin A injections into the extraocular muscle cause severe structural changes in the orbital singly-innervated TMFs, but not in the other muscle fibre types. Up to now it has not been possible to correlate function and dysfunction of extraocular muscle with muscle fibre types. One hypothesis suggests that the non-TMFs are part of a sophisticated proprioceptive apparatus together with the palisade endings at the myotendinous junction, which are exclusively associated with non-TMFs of the global layer. A lesion of this system could cause disturbances in gaze stabilisation, such as congenital nystagmus.
Method: In an attempt to discover more about this system we identified the non-TMF motoneurons in monkey with tract-tracing methods. With combined immunocytochemica