The afferent innervation of two infrahyoid muscles of the cat

Use of suction electrodes for measurement of intrinsic tongue muscular endurance during lingual pressure generation

BACKGROUND

Lingual pressure (LP) generation is cooperatively controlled not only by the intrinsic tongue (I-ton) muscles but also by hyoid muscle activation. However, the measurement of endurance and fatigue properties of I-ton muscles is difficult due to the instability of electrodes.

OBJECTIVE

The purpose of this study was to apply suction electrodes to measure electromyograms (EMGs) of I-ton muscle and to evaluate integrated EMG amplitude (iEMG) and mean power frequency (MPF) of EMG in the I-ton and hyoid muscles performing continuous LP.

METHODS

Twenty healthy adult volunteers (10 males, 10 females, mean age 28.8 years) were instructed to perform 10-s LP generation tasks at 25%, 50%, 75% and 100% of maximum LP in randomised order with visual feedback. During each task, EMGs of the I-ton, suprahyoid (S-hyo), infrahyoid (I-hyo) and masseter (Mass) muscles were simultaneously recorded. The iEMG and MPF of EMG burst during 10-s LP tasks were compared. The recording period was divided into three substages to analyse temporal changes with the Friedman test.

RESULTS

During the 10-s task, the iEMG significantly increased as the LP strength increased (p < .001). There was no time-dependent change in the I-ton iEMG; however, the MPF of the I-ton EMG burst decreased in all tasks (p < .05). The S-hyo and I-hyo iEMGs gradually increased, especially with strong LP (p < .01).

CONCLUSION

While I-ton muscles may easily fatigue during 10-s LP generation, S-hyo and I-hyo muscles may help compensate for the weakened I-ton muscle activity by increasing their activity to maintain LP.

Endurance measurement of hyoid muscle activity and hyoid-laryngeal position during tongue lift movement

BACKGROUND

Tongue lift movement (TLM) is used as a therapy to improve tongue pressure against the hard palate for dysphagic patients.

OBJECTIVE

The present study aimed to characterize the time-dependent endurance changes in hyoid muscle activity and hyoid-laryngeal displacement during TLM in different ways.

METHODS

Sixteen young healthy volunteers were instructed to perform TLM at maximum effort (100%) against the anterior and posterior parts of the hard palate using a balloon-type tongue pressure instrument, followed by a 10-second recording during anterior 80% TLM, anterior 100% TLM, posterior 80% TLM and posterior 100% TLM with visual feedback. Electromyography (EMG) of suprahyoid (S-Hyo) and infrahyoid (I-Hyo) muscles and videofluorography were simultaneously recorded. To evaluate temporal changes, the recording period was divided into three substages: early, middle and late. Tongue pressure, integrated EMG (iEMG), power frequency of EMG burst and hyoid-laryngeal position were compared among the conditions (80% vs 100%, anterior vs posterior and early vs middle vs late).

RESULTS

Tongue pressure was stably maintained for 10 seconds in all conditions. S-Hyo iEMG and I-Hyo iEMG were significantly greater at 100% than at 80%, while no significant difference was observed between positions. S-Hyo iEMG and I-Hyo iEMG significantly increased at the late stage, while power frequency of EMG burst gradually decreased. Significant temporal changes in laryngeal elevation were observed only in posterior 100% TLM.

CONCLUSION

The current results suggested that isometric posterior TLM may be more useful compared with anterior TLM in clinical situations for dysphagic patients to elevate the hyolaryngeal complex.

Muscle receptors: content of some of the extrinsic and intrinsic muscles of the larynx in the bonnet monkey (Macaca radiata)

The number of muscle receptors and in particular the muscle spindle content of some of the intrinsic and extrinsic laryngeal muscles was evaluated, using bonnet monkeys (Macaca radiata). The technique of Barker and Ip [J. Physiol. (Lond) 169:73-74, 1963] was used to stain the muscle receptors. The results indicate that the intrinsic laryngeal muscles were devoid of muscle spindles. The extrinsic laryngeal muscles that were examined contain muscle spindles, though their density is less than that reported in the spindle-rich muscles like the rotators of the head and some of the intrinsic muscles of the hand (Cooper in: Structure and Function of Muscle, Vol. I, G.H. Bourne, ed, Academic Press, New York and London, 1960).

The distribution of infrahyoid motoneurons in the cat: a retrograde horseradish peroxidase study

The distribution of cell bodies and the peripheral course of axons of infrahyoid motoneurons were examined in the cat by the retrograde horseradish peroxidase method after application of the enzyme to the peripheral nerve branches supplying the infrahyoid muscles. Infrahyoid motoneurons were observed to constitute a slender cell column, which extended from a level of the caudal part of the hypoglossal nucleus usually to the most caudal level of the C1 cord segment, or occasionally to the lower levels of the C2 cord segment. The cell column was located immediately lateral to that of motoneurons of the spinal accessory nerve. In the cell column, thyrohyoid motoneurons were distributed in the medulla oblongata; sternohyoid motoneurons were located somewhat more cranially than sternothyroid motoneurons in the medulla oblongata and cervical cord. However, the level of craniocaudal distribution of thyrohyoid, sternohyoid or sternothyroid motoneurons highly overlapped. The experiments involving severance of the hypoglossal and/or cervical nerves indicated that axons of thyrohyoid and sternohyoid motoneurons passed via the roots of both hypoglossal and C1 nerves, that axons of sternohyoid motoneurons passed via the C1 nerve roots, and that axons of infrahyoid motoneurons innervating the conjugated part of the sternohyoid and sternothyroid muscles passed usually via the C1 nerve roots, or occasionally via the roots of both C1 and C2 nerves.

Opto-electronic analyses of masticatory mandibular movements and velocities in the rat

High-speed, high-resolution data (frontal plane) were collected from 6 Sprague-Dawley rats by opto-electronic mandibular tracking (OMT), followed by microcomputer analysis of individual chew cycles. Mastication comprised rapidly alternating, unilateral cycles with variable degrees of lateral translation. There was no evidence of bilateral mastication (simultaneous chewing on both left and right sides). Analysis revealed significant (p less than or equal to 0.01) differences between whole-cycle, slow-open (SO) phase, fast-open (FO) phase, fast-close (FC) phase, and slow-close (SC) phase duration, height, width, and velocity during mastication of standardized foods (pellets and slurry). Regression analysis between millimetres of vertical/horizontal movement (Y) and vertical/horizontal velocity (X) revealed differences during these mastications. Whole-cycle and SO-phase regression equations had the greatest disparity between pellet and slurry chewing for both vertical and horizontal movements. Correlation coefficient analysis between movement and velocity data indicated that (1) vertical correlations were smaller than horizontal ones, (2) slurry correlations were greater than pellet ones except for whole cycles, (3) FO phase had the largest movement/velocity correlation during both pellet and slurry mastication, and, that (4) SC phase had the smallest movement/velocity correlation. Vertical and horizontal movements during pellet FC phase were significantly (p less than or equal to 0.01) greater than slurry ones; both vertical and horizontal movements during pellet SC phase were significantly (p less than or equal to 0.01) less than slurry ones. This phase-isostasy was also detected during vertical movements in SO and FO phases.(ABSTRACT TRUNCATED AT 250 WORDS)

An HRP study of the motoneurons supplying the rat hypobranchial muscles: central localization, peripheral axon course and soma size

The locations of motoneurons (MNs) supplying the rat hypobranchial muscles (lingual, geniohyoid, and infrahyoid) and the peripheral courses of axons of these MNs were investigated by using a method of HRP injection into the hypoglossal nerve or these muscles in combination with severing of the hypoglossal and/or cervical components of the plexus hypoglossocervicalis. Moreover, some sizes of the MNs were investigated in both transverse and horizontal sections. The hypobranchial MNs formed a sequence of cell columns extending caudally from the hypoglossal nucleus, via the supraspinal nucleus, to the medial and then the ventrolateral subnuclei of the ventral horn of C1 to C3. The lingual and geniohyoid MNs were located in the hypoglossal nucleus. The majority of their axons passed solely through the hypoglossal nerve, whereas a small number of axons, whose somata lay in the caudal hypoglossal nucleus, passed through the first cervical nerve and then through the ansa cervicalis to reach the hypoglossal nerve. The infrahyoid MNs were located in the supraspinal nucleus and the ventral horn, and their axons passed through the first to third cervical nerves. The hypobranchial MNs were divided into three groups according to their size: the lingual, the geniohyoid and thyrohyoid, and lastly the other infrahyoid MNs, in order of smaller to larger size. The sizes of lingual, geniohyoid, and thyrohyoid MNs displayed a unimodal distribution both in transverse and horizontal sections, whereas the other infrahyoid MNs showed a bimodal distribution.

Identification of stretch receptors in the frog geniohyoid muscle by sinusoidal stretching

This study revealed the absence of muscle spindles and the presence of leaf-like receptors in the frog's geniohyoid muscle. The response pattern was studied during sinusoidal stretching of the muscle. Results are compared with the response patterns of two kinds of stretch receptors in the sartorius muscle.