Mastication in the rabbit: a description of movement and muscle activity

Abstract

1. Mastication was studied in awake rabbits that had previously been prepared for chronic recording of jaw movement and jaw muscle electromyography (EMG) under general anesthesia. Data were stored on tape and replayed for computer-assisted analysis. Most data was taken from the mastication of rabbit chow, but the basic features described in the paper also apply to eating of other foods. The series of movements was divided into cycles, and the phases that compose them, using peaks in the vertical movement, velocity, and acceleration. 2. The whole series of movements from ingestion to swallowing was termed the masticatory sequence. We found, as have others, that the sequence can be divided into three consecutive periods, based on the form of the movements. These were named the preparatory, reduction, and preswallowing series of cycles. 3. The results of earlier studies suggest that the food is transported back to the molar teeth during the preparatory series, ground up during the reduction series, and that the bolus is formed for swallowing during the preswallowing series. 4. The typical cycle of the preparatory series was called type I; it had two phases: opening (O) and fast closing (FC). The jaw-opening muscles were very active during O, but EMG bursts from the closer muscles were small or undefinable during FC. There was not much movement away from the midline in either phase, and the cycles were the shortest in the sequence. 5. The reduction series was predominantly composed of type II cycles. These were of intermediate duration and had three phases [O, a short FC, and a slow closing phase (SC)], during which the pellets were crushed between the molar teeth. The jaw moved toward the working side during FC. At or soon after the start of SC, the closer muscles became very active and continued to contract as the teeth were drawn toward the midline and slightly backwards. 6. The preswallowing series was made up of five-phase cycles that we called type III. These were the longest of the sequence. Jaw opening now occurred in three stages: O1 was the fall from tooth contact to approximately the postural position, O2 was a pause, and O3 was defined as the final movement to maximum opening. The digastric burst occurred during O3. There were again two closing phases, FC and SC, but closer bursts were smaller than in type II, and SC was shorter.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult human mylohyoid muscle fibers express slow‐tonic, α‐cardiac, and developmental myosin heavy‐chain isoforms

“…Contraction of the suprahyoid muscles depresses the mandible when the hyoid bone is fixed or elevates the hyoid bone when the mandible is fixed. Depression of the mandible is associated with jaw opening that occurs during lapping, licking, chewing, and phonation (FaaborgAndersen and Venard, 1964;Moller, 1966;Crompton et al, 1975;Schwartz et al, 1989;Yamada et al, 1993). Displacement of the hyoid bone occurs during swallowing (Logemann, 1983) and breathing (Lowe and Sessle, 1973;Van de Graaff et al, 1984).…”

Mammalian Oral Rhythms and Motor Control

“…By contrast, the durations of the closing phases did not correlate with T C . However, further work in rabbits demonstrated that correlations between phase durations and T C depended on cycle type, viz., Type I (preparatory series), II (reduction series), and III (pre-swallow series) (Schwartz et al, 1989). These investigators found positive correlations between opening phases and T C during Type I and III chews, but not during Type II chews.…”

“…Over the course of a chewing sequence, the functional nature of chewing shifts from ingestion and initial food handling in the front or anterior part of the mouth (preparatory series) to grinding and reducing the food in the molar region (reduction series) to introducing the food into the pharynx in preparation for swallowing (pre-swallow series). Chewing cycles tend to have the shortest durations during the preparatory series and the longest durations during the preswallow series as detailed in (Schwartz et al, 1989).…”

“…Orthodontic brackets or custom clutches with small footprints are often attached to teeth for holding jaw tracking markers (Flavel et al, 2002;Gerstner & Fehrman, 1999;Gerstner & Kinra, 1999;Gerstner & Parekh, 1997;Hiiemae et al, 1996;Plesh et al, 1993;Wintergerst et al, 2004). More invasive tracking methods such as anchored bone markers or cineradiography are easily used in non-human mammals (Byrd, 1981;Gerstner & Goldberg, 1991;Hylander et al, 1987;Kobayashi et al, 2002a;Schwartz et al, 1989;Yamada et al, 1988). The development of X-ray reconstruction of moving morphology (XROMM) has been used to study oral movements and promises to revolutionize comparative biomechanical studies of oral function (Brainerd et al, 2010).…”

“…Those involved with working the food into a bolus are the reduction series, Stage IIa chewing (Masuda et al, 1997;Morimoto et al, 1985), rhythmic chewing period Ootaki et al, 2004;Yamamura et al, 2002), or Type II chews (Schwartz et al, 1989). Those involved with preparing the food for swallowing by introducing the food into the pharynx are the preswallow series, Stage IIb chews (Masuda et al, 1997;Morimoto et al, 1985), the preswallow period Ootaki et al, 2004;Yamamura et al, 2002), or Type III chews (Schwartz et al, 1989).…”