Temporal muscle

Abstract: The possibility that the temporal muscles may affect the form of the brain case has been recognized for many years. The matter was already being debated by Fick and Virchow in 1859 and is discussed by Hooton in 1946. The reason that such an old problem is still unsettled is that description alone cannot untangle the various factors, all of which may play some part in shaping the developing skull. To HrdliEka ( '24) the importance of the muscles in moulding the brain case was self-evident. Yet T'eidenreich ( '41), after a comprehensive review of the evolution of the skull, concludes that it is the size of the brain which determines cranial form. Such disagreement should occasion 110 surprise, f o r even the simple relation of the temporal muscle to the form of the coronoid process of the mandible cannot be elucidated by comparative means. In nature, a functioning bone-muscle complex is always present, so that the relative roles of intrinsic factors in the bone and of function in shaping the process can be evaluated only by experiment. In spite of the interest which has centered on the comparative anatomy and anthropology of the head, the experimental analysis of the mammalian skull has never attracted many investigators. The result is that studies based on few animals of various kinds are inconclusive. Fickl believed that the

Abstract: 1. Mastication was produced by stimulation of the right motor-sensory cortex of urethan-anesthetized rabbits with 15-s trains of shocks (1-ms duration) at 50 Hz. Movements of the lower jaw and jaw muscle electromyograms (EMGs) were recorded on magnetic tape for later computer analysis. 2. The stimulus site was chosen, and stimulus intensity adjusted, so that stereotyped movements were produced that included a wide swing of the mandible to the left side during jaw closure. 3. Control trials were alternated with trials in which a steel ball (2 mm diam) was thrust between the anterior molar teeth on the left side and left in place for several seconds. 4. When the obstruction was first introduced, a jaw opening reflex was sometimes evoked if the ball struck the buccal surface of the advancing mandibular molar teeth. Thereafter, when the ball was crushed between the occlusal surfaces of the teeth, no jaw opening reflex was seen. 5. Instead, the amplitude and duration of all the jaw closing EMGs increased, beginning at least 12 ms after contact with the ball. This caused a prolongation of the slow closing (SC) phase of the cycle that, coupled with a delay in the start of activity in the digastric muscle (jaw opener), prolonged the cycle by more than 60 ms. 6. During the SC phase of the obstructed trials, the medially directed grinding stroke was exaggerated because of an increase in the contraction of the contralateral zygomaticomandibular and anterior temporal muscles. 7. After collecting data, the sensory nerves to the maxillary and mandibular anterior molar teeth were cut to eliminate feedback from the periodontal pressoreceptors. Control and obstructed trials were repeated. 8. Following denervation, the obstructed cycles were of shorter duration. The mandible still moved to the right during SC in some animals, but the increase in closer muscle EMG activity was much reduced. 9. We conclude that periodontal receptors provide positive feedback to the jaw closing muscles during mastication. This is supplemented by input from other receptors, probably muscle spindles. In addition, an increase in periodontal feedback prolongs the SC phase and the early phases of the opening stroke.

Abstract: An operation to place the temporal muscles on the brain surface, namely EncephaloMyo Synangiosis, was carried out on 10 patients with “Moyamoya” disease lacking the middle cerebral artery on the brain surface for anastomosis. Postoperative superselective deep temporal angiogram proved the development of rich vascular supply from the temporal muscle to the brain surface. Satisfactory clinical improvements were seen in nine patients. The remaining one child with transient ischemic attacks (TIA) and major neurological deficits showed slight improvement in spite of being unable to take care of himself. The other nine patients also showed improved electroencephalographic findings. Significant blood supply through the external carotid system to the operated area of the brain was shown in some cases by appearance of diffuse slow activity when the common carotid artery on the same side was compressed.

Abstract: The activity patterns of the masseter and the anterior temporal muscles were studied in twenty-one healthy male subjects while clenching at 10, 20, 30, 40 and 50% of the maximum clenching level. At low clenching levels the temporal muscle activity tended to dominate, at high levels the masseter muscle activity was stronger (P less than 0.001). The asymmetry in muscle activity also depended upon the clenching level (P less than 0.001), while at each level the masseter muscle asymmetry was greater than the temporal muscle asymmetry (P less than 0.05-P less than 0.025). By comparing the electromyographic activities of the left and right side within each subject it was found that the masseter muscle with the higher electromyographic activity tended to have the larger cross-sectional area (P less than 0.01) and at the 50% clenching level it tended to be on the side with the greater number of post-canine tooth contacts (P less than 0.001).