Contraction Properties of Cat Facial Muscles

The contraction properties of some facial muscles of the cat have been investigated. The contraction time of a maximal isometric twitch is 8.5 ms for the orbicularis oculi. 24 ins for the depressor conchae and 33 ms for the orbicularis oris. It is suggested that a slower decay of the active state may be one factor explaining the longer contraction time of the orbicularis oris as compared to the orbicularis oculi. The duration of a maximal compound action potential is also longer for the orbicularis oris than for the orbicularis oculi (8.5 and 2.8 ms respectively). Muscle length is more critical for the twitch amplitude of the orbicularis oculi than for the orbicularis oris. Summation of individual twitches occurs at a stimulus frequency of minimum 20–22 Hz for the orbicularis oculi and at 10–12 Hz for the orbicularis oris. Apparent fusion occurs at 100 Hz for the orbicularis oculi and at 60 Hz for the orbicularis oris. The rate of tension development increases for both muscles with stimulus frequencies up to 200 Hz. Average tetanus/twitch ratios are 4.5 for the orbicularis oris and 7.0 for the orbicularis oculi.