Cricothyroid Muscle Research Articles

Scanning Electron Microscopic Study of the Neuromuscular Junctions of the Cricothyroid and Thyroarytenoid Muscles in Rats

Neuromuscular junctions were observed in the cricothyroid (CT) and thyroarytenoid (TA) muscles of adult rats by scanning electron microscopy after removing the intramuscular connective tissue components using the HCl hydrolysis method. Morphologically, the junctions were classified into three types in the CT muscle and two types in the TA muscle, based on the structural characteristics of the subneural apparatuses, including junctional folds. In the CT muscle, type 1 junctions (32%) consisted of more than 15 cup-like depressions with slit-like junctional folds. Type 2 junctions (20%) were characterized by approximately 10 cup-like depressions with a small number of pit- or slit-like junctional folds. Type 3 junctions (48%) had irregular labyrinthine gutters with slit-like junctional folds. In the TA muscle, type 1 (82%) and 2 (18%) junctions had similar structures to type 1 and 2 junctions in the CT muscle, respectively. Histochemical studies using myosin adenosine triphosphatase staining showed that both CT and TA muscles predominantly consisted of type II muscle fibers (78% and 82%, respectively), and that the diameter of type II fibers was larger than that of type I fibers. These findings suggest that the type 2 junction belongs to type I muscle fibers, while both type 1 and type 3 junctions belong to type II fibers, and that the type 3 junction is a structural variation of the type 1 junction. The significance of the structural differences of the subneural apparatuses in the intrinsic laryngeal muscles is discussed briefly.

ラット内喉頭筋神経下装置の年齢変化

The intrinsic laryngeal muscles have particular characteristics functionally, histochemically and ultrastructurally compared with common skeletal muscles. In the present study, age-related morphological changes of the subneural apparatus (SNA) is assessed of the cricothyroid (CT), thyroarytenoid (TA) and posterior cricoarytenoid (PCA) muscles in rats using scanning electron microscopy.The SNAs of these muscles were immature at 1 week postnatally showing single oval primary synaptic cleft and a small number of secondary synaptic clefts. At 4 weeks postnatally, structures of the SNAs of the CT and TA muscle became mature, while, those of the PCA muscle were delayed in maturation. In aged rats, the CT and TA muscles showed little age-related morphological change. However, the PCA muscle presented some changes including an increased number of depression-type primary synaptic clefts, multiple SNAs on muscle fiber, and thin muscle fiber containing immature SNA. The structure of the SNA was quantitatively analyzed by use of the following parameters, areas of primary and secondary synaptic clefts (APC and ASC, respectively) and length /width (L/W) ratio of the secondary synaptic clefts. APC was roughly constant througthout the tissue life. ASC and L/W ratio increased during the early postnatal period, while, it remained stable with aging. These findings suggest that age-related changes of the CT and TA muscles rarely occur, thereby contributing to their functional maintenance. However, in the PCA muscle, muscle fiber remodeling seems to occur more frequently than in the CT and TA muscles with aging.

Anastomosis between the external branch of the superior laryngeal nerve and the recurrent laryngeal nerve.

An incidental finding in the anatomy lab showed up a plexus of the external branch of the right superior laryngeal nerve (SLN), including an anastomosis with the recurrent laryngeal nerve (RLN). The external branch of the SLN divided in two extensions: The ventral extension reached the mesopharynx laterally and by supplying the latter, ended at the cricothyroid muscle. The dorsal extension formed a plexus a finger's breadth beneath the inferior margin of the pharynx, on the lateral aspect of the esophagus. The anastomosis ran from the lower part of the plexus to the RLN along the esophagus, laterally.

Superior laryngeal neurons directly excite cardiac vagal neurons within the nucleus ambiguus

The aim of this study was to test whether superior laryngeal neurons have axon collaterals that synapse upon cardiac vagal neurons. Superior laryngeal neurons were tested as likely mediators of cardio-respiratory interaction because these neurons are active in post-inspiration, co-localized with cardiac vagal neurons, and have many axon collaterals within the nucleus ambiguus. Nontoxic fluorescent tracers were utilized to identify, in vitro, both superior laryngeal neurons that innervated the crico-thyroid muscle, and cardiac vagal neurons that projected to cardiac ganglia. Co-localization of these two populations of neurons demonstrated that cardiac vagal and superior laryngeal neurons are both co-localized in the nucleus ambiguus. Simultaneous dual patch clamp recordings were used to either inject depolarizing current and evoke an action potential (current clamp configuration) or control the voltage and depolarize an identified single superior laryngeal neuron (voltage clamp configuration) while simultaneously recording from a cardiac vagal neuron. Depolarization of some, but not all, individual superior laryngeal neurons elicited post-synaptic excitatory currents in cardiac vagal neurons, indicating that at least some superior laryngeal neurons monosynaptically synapse upon cardiac vagal neurons within the nucleus ambiguus.

On the mechanism of lowering the voice fundamental frequency in the production of tones of Standard Chinese

While it is well known that the cricothyroid (CT) muscle is mainly responsible for lowering the voice fundamental frequency (F0) in many languages, the mechanism for F0 lowering in languages such as Standard Chinese (SC) has not been elucidated. Although several studies have shown that the sternohyoid (SH) muscle activity is strongly correlated with F0 lowering in SC, the mechanism itself is not clear since SH is not directly attached to the thyroid cartilage, whose movement is essential in changing the length and tension of the vocal chord. On the basis of an earlier finding on the production of Thai tones [D. Erickson, Annual Bulletin No. 27, RILP, Univ. Tokyo, pp. 135–149 (1993)], the present author has suggested the active role of the thyrohyoid (TH) muscle in F0 lowering in languages such as SC and Swedish [H. Fujisaki, Proc. XXIII World Congress of the International Association of Logopedics and Phoniatrics, pp. 156–159 (1995)]. The present study shows the detailed mechanism for F0 lowering involving both TH and SH in the production of the second, third, and fourth tones of SC based on new electromyographic observations.

Myosin heavy chain composition in human laryngeal muscles.

Myosin heavy chain (MHC) composition of human thyroarytenoid (TA), lateral cricoarytenoid (LCA), interarytenoid (IA), vocalis, posterior cricoarytenoid (PCA), and cricothyroid muscles were examined using sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and Western bolt techniques. The presence of superfast MHC was also assessed using antibodies directed against the extraocular MHC. MHC protein was analyzed using fresh human laryngeal muscles. Laryngeal muscles excised from cadavers were processed for SDS-PAGE. The composition of MHC isoforms was determined by densitometry. Western blot was carried out to identify specific bands. MHC types IIA and IIB are the predominant MHC components in human laryngeal muscles. The adductor muscles--TA, LCA, and IA--have a higher percentage of type IIB MHC and a lower percentage of type I when compared with the abductor--PCA. The rank file order for type IIB MHC composition (TA > LCA > or = IA > PCA) is the same in all specimens. A band migrating between type IIA and type I was observed in several specimens. Although similar to type IIL in rats, this atypical band did not react with anti-extraocular MHC antibody on Western blot. Characterization of laryngeal muscles determined by the composition of MHC is correlated with function and neural input. Human laryngeal muscle is characterized by a predominance of fast-type MHCs in laryngeal closing muscle and mixed fast-slow type MHCs in respiratory and phonatory muscle groups. Although an atypical myosin band similar to type IIL (superfast) MHC in rat was identified, it did not react with anti-extraocular MHC antibody.

Differential effects of clonidine on upper airway abductor and adductor muscle activity in awake goats.

The purpose of this study was to determine the extent to which alpha(2)-adrenoceptor (alpha(2)-AR) pathways affect the central motor output to upper airway muscles that regulate airflow. Electromyogram (EMG) measurements were made from posterior cricoarytenoid (PCA), cricothyroid (CT), thyroarytenoid (TA), and middle (MPC) and inferior (IPC) pharyngeal constrictor muscles in awake standing goats. Systemic administration of the alpha(2)-AR agonist clonidine induced a highly dysrhythmic pattern of ventilation in all animals that was characterized by alternating episodes of tachypnea and slow irregular breathing patterns, including prolonged and variable expiratory time intervals. Periods of apnea were commonly observed. Dysrhythmic ventilatory patterns induced by clonidine were associated with differential recruitment of upper airway muscles. alpha(2)-AR stimulation preferentially decreased the activity of the PCA, CT, and IPC muscles while increasing TA and MPC EMG activities. Clonidine-induced apneas were associated with continuous tonic activation of laryngeal (TA) and pharyngeal (MPC) adductors, leading to airway closure and arterial oxygen desaturation. Tonic activation of the TA and MPC muscles was interrupted only during the first inspiratory efforts after central apnea. Laryngeal abductor, diaphragm, and transversus abdominis EMG activities were completely silenced during apneic events. Ventilatory and EMG effects were reversed by selective alpha(2)-AR blockade with SKF-86466. The results demonstrate that alpha(2)-AR pathways are important modulators of central respiratory motor outputs to the upper airway muscles.

Innervation of the three bellies of the human cricothyroid muscle

Innervation of the three bellies of the human cricothyroid muscle

The role of the two bellies of cricothyroid muscle during running speech

The role of the two bellies of cricothyroid muscle during running speech

The posterior thyroplasty window: anatomical considerations.

Explain surgical technique of performing a posterior thyroplasty window. Describe the internal laryngeal anatomy and structures available through the posterior window approach. Describe posterior window approach. Review of lateral laryngeal anatomy and retrospective review of 125 cases involving a posterior thyroplasty window approach. Review mechanics of stress and stress concentration inherent with partial removal of rigid substance. Describe anatomical considerations and surgical complications. Charts were reviewed and tabulated for surgical complications, efficacy and safety of surgical approach, specific anatomical variations, and variety of surgery available through the posterior window. Performance of 125 posterior thyroplasty windows revealed no evidence of entry into the piriform sinus. Three thyroid ala fractures ensued, two of the body and one of the inferior cornu. Operations available included arytenoid adduction, arytenoid fixation, lysis of joint adhesions, and access to the posterior cricoarytenoid muscle for botulinum toxin injections. The posterior thyroplasty window affords easy, direct access to the internal, posterolateral larynx while preserving the cricothyroid joint, the action of the cricothyroid muscle, and the internal division of the recurrent laryngeal nerve.

A detailed description of the pars media of the cricothyroid muscle

A detailed description of the pars media of the cricothyroid muscle

Cricothyroid muscle reinnervation by muscle-nerve-muscle neurotization

Cricothyroid muscle reinnervation by muscle-nerve-muscle neurotization

Synaptology and ultrastructural characteristics of laryngeal cricothyroid and posterior cricoarytenoid motoneurons in the nucleus ambiguus of the rat.

The laryngeal motoneurons innervating the cricothyroid muscle (CT) are located in the semicompact formation just ventral to the rostral part of the compact formation of the nucleus ambiguus. The motoneurons innervating the posterior cricoarytenoid muscle (PCA) are located in the loose formation. We retrogradely labeled the CT and the PCA motoneurons using cholera toxin subunit B-conjugated horseradish peroxidase, and determined the ultrastructure and synaptic organization of these neurons. The CT and the PCA motoneurons had the appearance of alpha-motoneurons, i.e., large, oval or polygonal cells containing well-developed organelles and a prominent spherical nucleus. Two kinds of neurons were recognized among the PCA motoneurons. The one (PCA-A) was significantly smaller than the other (PCA-B). The average number of axosomatic terminals in a section was significantly largest in the PCA-B (56.6), smaller in the PCA-A (36.0), and smallest in the CT (32.3) neurons. Most of the axosomatic terminals (64.7%) contained pleomorphic vesicles and made symmetric synaptic contacts (Gray's type II) with the PCA-A neurons, while more than 60% contained round vesicles with asymmetric synaptic contacts (Gray's type I) in the CT (69.5%) and the PCA-B (60.6%) neurons. A few terminals associated with subsurface cisterns were present on all laryngeal motoneurons. These results indicated that the CT motoneurons may receive mostly excitatory terminals, whereas the PCA muscle may be regulated by neurons having many inhibitory terminals, and neurons having many excitatory terminals.

Cricoid cartilage masquerading as a tumour on thyroid ultrasound.

On ultrasound scanning of the thyroid gland in a sagittal plane, the cricoid cartilage can falsely create the impression of a mass in the gland if the transducer is angled slightly medially. The illusion of a mass is fortified on transverse view if the cricothyroid and inferior pharyngeal constrictor muscles, which lie between the upper pole of the thyroid gland and the cricoid cartilage, are misinterpreted as a solid lesion. The purpose of this study was to describe the ultrasound features of the cricoid cartilage and to determine the frequency in which a pseudolesion is created. In 15 of 26 volunteers the cartilage was seen as a hypoechoic structure surrounded by an anechoic halo and containing foci of calcification, closely resembling a thyroid nodule. In 11 of the subjects, with a mean age of 55 years, the cartilage was heavily calcified, poorly visualized and did not simulate a thyroid lesion. Awareness of the cause and appearance of this pseudolesion should help radiologists avoid a potential pitfall and prevent unnecessary invasive procedures.

An anatomical study of anastomoses between the laryngeal nerves.

To systematize the anatomy of the connecting branches between laryngeal nerves. Microdissection of 90 larynges obtained from necropsies (57 men and 33 women; age range, 41-95 y). Anastomoses between the internal and recurrent nerves appeared in four different patterns: 1) Galen's anastomosis, as the connection between the dorsal branches of both nerves (100%); 2) arytenoid plexus, as the connection between the arytenoid branches of both nerves, in relation with the arytenoid muscle, and divided in a deep part (100%) and a superficial part (86%); 3) cricoid anastomosis, previously only described in cows, located in the front of the cricoid lamina (6/10 cases); and 4) thyroarytenoid anastomosis, as the connection of a descending branch of the internal laryngeal nerve and an ascending branch of the recurrent nerve (14%). Anastomosis between the internal laryngeal and the external laryngeal nerves appeared as a connecting branch throughout the foramen thyroideum (21%). Anastomosis between the external laryngeal and recurrent nerves appeared as a connecting branch throughout the cricothyroid muscle (68%). At least two anastomoses (Galen's anastomosis and arytenoid plexus) appeared in 21% of hemilarynges, and 79% of cases had three or more anastomoses between the laryngeal nerves. The different prevalence of this complex anastomotic pattern suggests functional differences in the sensory and motor innervation of individual subjects.

Postnatal Development of Myosin Heavy Chain Isoforms in Rat Laryngeal Muscles

The developmental transitions of myosin heavy chain (MHC) isoforms of rat posterior cricoarytenoid (PCA), thyroarytenoid (TA), cricothyroid (CT), and lateral cricoarytenoid (LCA) muscles were examined by means of sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blot techniques. The muscles were microscopically dissected from animals on postnatal days 0, 3, 7, 10, 14, 21, 28, 35, 45, and 55 and from adult animals. Silver-stained SDS-PAGE gels of each muscle were analyzed densitometrically to measure the composition of MHC isoforms, and Western blot was carried out to identify specific bands. Characterizations of the internal laryngeal muscles determined by the composition of MHCs were correlated with their function in the adult. Temporally, differentiation reflects onset of function. Differentiation of isoforms and transition to adult forms occur first in the TA muscle, followed by the PCA, LCA, and CT muscles. Expression of type IIL was observed only in muscles innervated by the recurrent laryngeal nerve. Postnatally observed developmental differences of myosin phenotypes suggest that regulation of MHC expression is influenced by neural activity or other environmental factors.

Cricothyroid activity in high and low vowels: exploring the automaticity of intrinsic F0

Although vowels can be produced with any F0 in a speaker's range, the high vowels tend to be produced with a higher F0 than low vowels. This “intrinsic F0” (IF0) has been found for every language that has been examined for it (Whalen & Levitt, 1995) and has also been found in the babbling of prelinguistic infants (Whalen, Levitt, Hsiao & Smorodinsky, 1995), suggesting that it is an automatic consequence of articulation. Nonetheless, some researchers have suggested that IF0 is a deliberate enhancement of the perception of vowel height (Diehl & Kluender, 1989; Kingston, 1992; Fahey & Diehl, 1996). The only positive evidence in favor of this view is that EMG activity for the cricothyroid (CT) muscle has been reported to be higher for high vowels than for low, suggesting active control of F0. The present experiment examines CT activity in four English-speaking subjects saying isolated vowels. In one condition, target tones that differed by the same amount as the IF0 magnitude itself were presented for the subjects to match; in the other condition, there were no targets. CT activity for the condition with targets was higher for the high vowels for only one of the four subjects; the patterns for the other three were negative, neutral or mixed. Since only two subjects from the previous literature are comparable to the present work, the basic assumption of higher CT activity for high vowels must be called into question. Further, when F0 was shifted by an amount equivalent to that seen in IF0, it was found that the high vowels needed more CT activity to effect a change than the low vowels did. This indicates that it is impossible to compare absolute values of CT activity as indications of direct F0 control. In the condition without targets, CT activity for three subjects followed the pattern of the target condition, being neutral, negative or mixed. Thus, the EMG evidence cited in favor of IF0 being deliberate is contradicted, leaving a preponderance of evidence that IF0 is an automatic consequence of successful vowel articulation.

Active and passive characteristics of the canine cricothyroid muscles.

Active and passive characteristics of the canine cricothyroid muscle were investigated through a series of experiments conducted in vitro and compared with their counterparts in the thyroarytenoid muscle. Samples from separate portions of canine cricothyroid muscle, namely, the pars recta and pars obliqua, were dissected from dog larynges excised a few minutes before death and kept in Krebs-Ringer solution at a temperature of 37 degrees C +/- 1 degrees C and a pH of 7.4+/-0.05. Active tetanic stress was obtained in isometric and isotonic conditions by applying field stimulation to the muscle samples through a pair of parallel-plate platinum electrodes and using a train of square pulses of 0.1-ms duration and 85-V amplitude. Force and elongation of the samples were obtained electronically with a dual-servo system (ergometer). The results indicate that the dynamic response of the canine cricothyroid muscle is almost twice as slow as that of the thyroarytenoid muscle. The average 50% tetanic contraction times for pars recta and pars obliqua were 84 ms and 109 ms, respectively, in comparison to 50 ms for thyroarytenoid. The examination of force-velocity response of this muscle indicates a maximum shortening velocity of 2 to 3 times its length per second, which is about half of the thyroarytenoid shortening speed. The passive properties of the pars recta and pars obliqua portions are similar to those of thyroarytenoid muscle.

Expression of Myosin Heavy Chain mRNA in Rat Laryngeal Muscles

The composition of myosin heavy chain mRNA was analysed quantitatively in 5 intrinsic laryngeal muscles of rats, using a competitive polymerase chain reaction. Intrinsic laryngeal muscles with the fastest contraction times, e.g. ventricular thyroarytenoid muscle, lateral cricoarytenoid muscle, and vocalis muscle, contained 2 fast isoforms, comprising mainly type 2B myosin heavy chains (52.1, 44.6 and 8.2%, respectively) and type 2X myosin heavy chains (21.9, 37.6 and 80.8%, respectively). Conversely, muscles with slower contraction times, such as posterior cricoarytenoid muscle and cricothyroid muscle, contained more than 85% of 2 fast isoforms; mainly type 2X myosin heavy chains (52.4-72.1%, respectively) and type 2A myosin heavy chains (34.6-25.2%, respectively). The results show a strong correlation between the composition of fast myosin heavy chain isoforms and muscle contraction times. Type 2L myosin heavy chain transcripts specific for laryngeal muscles and extra-ocular muscles were expressed in the order of ventricular thyroarytenoid (9.5%)>lateral cricoarytenoid (4.8%)>vocalis (2.5%)>posterior cricoarytenoid muscle (0.9%), but were not expressed in cricothyroid muscle. Neonatal myosin heavy chain was also expressed in all laryngeal muscles, ranging from 0.04 to 3%, but embryonic myosin heavy chain was expressed in ventricular thyroarytenoid, posterior cricoarytenoid and cricothyroid muscle at very low levels. These results suggest that intrinsic laryngeal muscles have different expression patterns for myosin heavy chain isoforms and may have different regulatory roles related to their functional requirement.

頚部・縦隔気腫の増悪にて緊急挿管された喉頭外傷例

A 35-year-old man was involved in an automobile collision and was brought to the emergency room of our hospital by ambulance. He had cuts on his forehead and left knee, and complained of dyspnea and hoarseness. Since swelling and crepitation were palpable on his anterior neck without any other external injury, he was suspected of having sustained a laryngeal trauma caused by the seatbelt pressing on his neck. A CT scan indicated a slight disruption of the lower part of the laryngeal framework, which appeared to cause emphysema extending from the neck to the mediastinum. Examination with a flexible endoscope was tried, resulting in an unexpected exacerbation of the emphysema into a respiratory crisis possibly due to increased subglottic pressure. An immediate oral intubation relieved this crisis.After his general condition was observed for two days in the ICU, we studied his larynx and hypopharynx using endoscopes under general anesthesia by tracheostomal intubation and found a mucosal disruption in the subglottic area. Under sequential open reduction, we also found fractures of the antero-lateral cricoid arch and the lower thyroid cartilage with disruptions of the sternohyoid muscle and the crico-thyroid muscle and ligament. The injuries healed well under repairs by suturing and wiring. We observed no sign of subglottic stenosis without a stent for a period of 5 weeks, and then repaired the tracheostome. Presently, the patient's vocal cords are mobile, and the vibratory patterns observed with a stroboscope appear normal. However, he has continued to demonstrate limitations in high-pitched phonation for 2 months.We discuss in detail the effects of the laryngeal injuries in this case regarding postoperative phonatory function using 3D images reconstructed with a helical CT. In addition, we also discuss the usefulness of so-called endoscopic 3D-CT images in cases of laryngeal trauma with mucosal disruption as a non-invasive examination in place of endoscopy.