Single fiber electromyography in cat extraocular muscles.

Single fiber electromyography (SFEMG) was carried out in the extraocular muscles (EOMs) of 40 adult cats, and the recordings were analyzed. The small fluctuations of the interpotential interval (IPI), so-called "jitter phenomenon", were represented quantitatively as a mean consecutive difference (MCD). The MCD and the IPI recorded from the orbital layer of the rectus muscles were similar among the 4 rectus muscles: the MCD and the mean IPI measured in 58 motor units from the 4 rectus muscles averaged 25.82 microseconds and 0.94 ms, respectively. These values were similar to those recorded from the oblique muscles. The MCD and IPI were 34.12 microseconds and 1.70 ms, respectively, in the retractor bulbi muscles and 45.54 microseconds and 1.23 ms, respectively, in the triceps muscles. The MCDs of the rectus and inferior oblique muscles were considerably smaller than those in the retractor bulbi and the skeletal muscles.