Burst characteristics of daily jaw muscle activity in juvenile rabbits

T Van Wessel,G E J Langenbach,P Brugman,T M G J Van Eijden,E Tanaka,N Kawai

doi:10.1242/jeb.01677

Abstract

Muscle activation varies with different behaviors and can be quantified by the level and duration of activity bursts. Jaw muscles undergo large anatomical changes during maturation, which are presumably associated with changes in daily muscle function. Our aim was to examine the daily burst number, burst length distribution and duty time (fraction of the day during which a muscle was active) of the jaw muscles of juvenile male rabbits (Oryctolagus cuniculus). A radio-telemetric device was implanted to record muscle activity continuously from the digastric, superficial and deep masseter, medial pterygoid and temporalis during maturation week 9-14. Daily burst characteristics and duty times were determined for activations, including both powerful and non-powerful motor behavior. All muscles showed constant burst numbers, mean burst lengths and duty times during the recording period. Including all behavior, the temporalis showed significantly larger daily burst numbers (205,000) and duty times (18.2%) than the superficial and deep masseter (90,000; 7.5%). Burst numbers and duty times were similar for the digastric (120,000; 11.1%) and medial pterygoid (115,000; 10.4%). The temporalis and deep masseter showed many short low activity bursts (0.05 s), the digastric showed many long bursts (0.09 s). For activations during powerful behaviors the superficial masseter and medial pterygoid had the largest burst numbers and duty times. Both muscles showed similar burst characteristics for all activation levels. It was concluded that activation of the jaw muscles is differently controlled during powerful and non-powerful motor behaviors and the functional organization of motor control patterns does not vary from 9 to 14 weeks of age.

Highlights

Most muscles can be used to perform different types of motor behavior that range between short powerful contractions for the generation of rapid movements and prolonged low level contractions for the maintenance of posture
The total duration of muscle activity during the day, which is defined by the duty time (Hensbergen and Kernell, 1997; Langenbach et al, 2004), is associated with both the number of bursts and their lengths generated during the different motor tasks
All animals continued to grow throughout the recording period, resulting in a doubling of the weight of each animal

Summary

Introduction

Most muscles can be used to perform different types of motor behavior that range between short powerful contractions for the generation of rapid movements and prolonged low level contractions for the maintenance of posture. These different types of motor behavior are reflected in the muscle’s electromyogram (EMG) and can be quantified in terms of the level and duration of EMG bursts. Muscles largely involved in postural activities generally show high duty times and contain a large percentage of slow type fibers. More phasically active muscles show relatively low duty times and generally contain a small percentage of slow type fibers

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