Role of proprioceptors in the mylohyoid muscle

Variations in the posterior division branches of the mandibular nerve in human cadavers

INTRODUCTION

The lingual, inferior alveolar and auriculotemporal nerves, being branches of the posterior division of the mandibular nerve, mainly innervate the mandibular teeth and all the major salivary glands. Anomalous communications among these branches are widely reported due to their significance to various treatment procedures undertaken in the region. This study was performed as detailed exploration of the functional perspectives of such communicating branches would further enhance the scope of these procedures.

METHODS

A total of 36 specimens were dissected to examine the infratemporal region. The branches from the posterior division of the mandibular nerve--namely the lingual, inferior alveolar and auriculotemporal nerves--were carefully dissected, and their branches were studied and analysed for abnormal course.

RESULTS

Communication between branches of the posterior division of the mandibular nerve was observed in four specimens. In two of the four specimens, communication between the mylohyoid and lingual nerves was observed. A rare and seldom reported type of communication between the auriculotemporal and inferior alveolar nerves is described in this study. This communicating nerve split into two to form a buttonhole for the passage of the mylohyoid nerve.

CONCLUSION

Such communicating branches between nerves found in this study are developmental in origin and thought to maintain functional integrity through an alternative route.

Impact of swallowing and ventilation on oropharyngeal cortical representation

Our aim was to determine whether ventilation and swallowing tasks can modify oropharyngeal cortical motor organisation. Mylohyoid motor-evoked potentials (MEP) induced by non-focal (NF) and focal (F) magnetic stimulations were recorded in nine healthy volunteers four times, with 1 week between each recording. Baseline values were evaluated and their reproducibility was assessed 1 week later. Thereafter, the subjects were asked to perform swallowing and ventilation tasks in random order 15 min per day for 1 week. The NF MEP amplitudes after the swallowing and ventilation tasks increased after effortful swallows (p<0.001) and ventilation efforts (p<0.001). The F MEP amplitudes obtained after focal cortical stimulations increased after effortful swallows (p<0.01) and ventilation efforts (p<0.05). The cortical magnitude of the oropharyngeal muscle representation increased after swallowing practice (p<0.01). In conclusion, swallowing and ventilation tasks modified the motor cortex of oropharyngeal muscles and should be evaluated for use in rehabilitation strategies.

Role of suprahyoid musculature on mandibular morphology and growth orientation in rats

This study was undertaken in rats to study the influence of the suprahyoid muscles on mandibular growth, morphology, and orientation. The aim was to investigate the effect of bilateral suprahyoid muscle myectomy on the skeletal growth and orientation of the mandible and on its orientation in rats. Forty-eight 4-week-old rats were divided into 2 experimental and 2 control groups as follows: A, 12 animals in which bilateral excision of the anterior digastric muscle was performed; B, 12 animals in which bilateral excision of the anterior digastric, transverse mandibular, and mylohyoid muscles was performed; C, 12 animals that were sham-operated bilaterally without any muscular excision; D, 12 control animals not subjected to any operation. The experimental period was 30 days. Lateral and dorsoventral radiographs were taken on days 1 and 30, after muscular excision. Cephalometric analysis was performed for each animal according to a method and procedure established in our laboratory and described earlier. The findings support the occurrence of decreased mandibular growth in the group in which bilateral digastric, transverse mandibular, and mylohyoid excision was performed as compared with controls. In addition, the mandible in the bilateral digastric excision group exhibited a more upward orientation. It was thus proven that the absence of the suprahyoid musculature does affect both skeletal growth and orientation of the mandible.

Serratus posterior muscles: anatomy, clinical relevance, and function

The serratus posterior superior and inferior muscles are generally considered clinically insignificant muscles that, based on attachments, probably function in respiration. Interestingly, however, there is no evidence supporting a respiratory role for these muscles. In fact, some electromyographic data refute a respiratory function for these muscles. We suggest that the serratus posterior muscles function primarily in proprioception. Further, these muscles, especially the superior, have been implicated in myofascial pain syndromes and therefore may have greater clinical relevance than commonly attributed to them.

Short-latency changes in voice F0 and neck surface EMG induced by mechanical perturbations of the larynx during sustained vowel phonation

Nineteen healthy young adult males with normal voice and speech attempted to sustain the vowel /u/ at a constant pitch (target: 180 Hz) and a constant and comfortable loudness level while receiving a sudden mechanical perturbation to the larynx (thyroid prominence) via a servo-controlled probe. The probe moved toward or away from the larynx in a ramp-and-hold fashion (3.3-mm displacement, 0.7 N force, 20-ms rise time, 250-ms duration) as the subjects attempted to maintain a constant probe-larynx pressure. Eighty stimuli were applied in each direction, one stimulus per phonation. Pairs of surface electromyography (EMG) electrodes were attached to the skin of the anterior neck over laryngeal, infralaryngeal, and supralaryngeal areas. The rectified EMG signals, the voltage analog of the voice fundamental frequency (VAF0), and the voltage analog of the probe displacement were digitized and signal-averaged relative to the onset of the stimulus. Sudden perturbation of the larynx induced an instantaneous decrease or increase in VAF0, depending on the direction of the probe's movement, and a short-latency increase in the EMG (30-35 ms) and VAF0 (55-65 ms). We argue that the instantaneous VAF0 change was related to a mechanical effect, and the short-latency VAF0 and EMG changes to reflexogenic effects-the latter most likely associated with both intrinsic and extrinsic laryngeal sensorimotor mechanisms. Further physiological studies are needed to elucidate the sources of the VAF0 and EMG responses. Once elucidated, the present method may provide a powerful noninvasive tool for studying laryngeal neurophysiology. The theoretical and clinical implications of the present findings are addressed.

The distribution of afferent neurons in the trigeminal mesencephalic nucleus and the central projection of afferent fibers of the mylohyoid nerve in the rat

Horseradish peroxidase conjugated to wheatgerm agglutinin (HRP:WGA) was injected into the proximal cut ends of three branches of the mylohyoid nerve in rats: the branch to the mylohyoid muscle (BrMh), the branch to the anterior belly of the digastricus muscle (BrDg), and the cutaneous branch (BrCu). HRP-labeled cells were detected in the ipsilateral caudal portion of the trigeminal mesencephalic nucleus (Vmes) and the ipsilateral ventromedial division of the trigeminal motor nucleus, except when HRP:WGA was applied to the BrCu. Morphologically, all labeled Vmes cells were of the pseudounipolar type. Projections of the primary afferents of the BrMh were observed in the ipsilateral trigeminal nucleus caudalis, the upper cervical dorsal horns of laminae I-III, and the dorsolateral recticular formation (Rf), whereas the primary afferents of the BrDg terminated in the ipsilateral trigeminal nucleus principalis and Rf. These observations suggest that the role of the afferent inputs of the mylohyoid muscle differs from that of those of the anterior belly of the digastricus muscle in terms of several functions associated with jaw-closing and infrahyoid muscles.