Role of extraocular muscles in the rabbit (Oryctolagus cuniculus) nictitating membrane response

The contributions of the extraocular and retractor bulbi muscles to the nictitating membrane response (NMR) were assessed using transections of the abducens nerve or the extraocular muscles. Transection of the six extraocular muscles or the muscle that attaches to the nictitating membrane had no effect on the NMR in otherwise intact animals. Transections of the abducens nerve reduced the NMR by 50%, and transections of the abducens nerve and the extraocular muscles abolished the NMR. These results indicate that the NMR can be effected by the six extraocular muscles, but that these six muscles may play a role that is redundant in the intact animal. The anatomical location of the motoneurons innervating the retractor bulbi is discussed.