Morphological and Functional Questions on the Growth and Plasticity of Mammalian and Avian Jaw Muscles

SYNOPSIS: Growth studies of mammalian jaw muscles and studiesdetermining the degree of plasticity of these muscles are few.There are questions concerning the degrees and types of morphologicaland physiological change occurring in these muscles during normalgrowth and the ability of external forces to modify this growthprocess. There are also questions on the effects of sensoryloss on muscle growth and on changes in the motor system asthese muscles change. In this report, questions are proposedand hypotheses presented that deal with these areas relativeto the jaw muscles. It is suggested that (1) changes in themorphology and function of jaw muscles during growth vary regionallyand are related to the action of the muscle and the loadingforces imposed; (2) the degree of muscle plasticity varies regionallyand varies depending on the type of loading forces and age ofthe animal; (3) loss of sensory input during the growth of thejaw muscles would produce marked changes in the histochemicalprofile, the distribution of motor neurons, and the activitypattern of these muscles; and (4) organization of the trigeminalmotor nucleus changes as the jaw muscles grow and may also changein response to sensory loss or application of different typesof loading forces. In addition, possible approaches to thesequestions are discussed.