An electron microscopic study of the muscle spindle in the arytenoid muscle of the human larynx

Summary We used transmission electron microscopy to examine a muscle spindle found in serial sections of the arytenoid muscle of the human larynx. Eight intrafusal fibers were observed at the equatorial region and contained two types of muscle fibers, nuclear bag fibers and nuclear chain fibers. The sensory nerve endings found on the nuclear bag fibers were annular or varicose in shape and contained numerous mitochondria. Another small sensory ending was composed of many vesicles and some dense granules. The fusimotor nerve endings found on the nuclear chain fibers had three types of endings with different sizes and complexities.     

An electron microscopic study of the muscle spindle in the arytenoid muscle of the human larynx

We used transmission electron microscopy to examine a muscle spindle found in serial sections of the arytenoid muscle of the human larynx. Eight intrafusal fibers were observed at the equatorial region and contained two types of muscle fibers, nuclear bag fibers and nuclear chain fibers. The sensory nerve endings found on the nuclear bag fibers were annular or varicose in shape and contained numerous mitochondria. Another small sensory ending was composed of many vesicles and some dense granules. The fusimotor nerve endings found on the nuclear chain fibers had three types of endings with different sizes and complexities.     

Motor end-plate distribution in the human interarytenoid muscle

Histochemical and computer graphic techniques were used to determine the distribution of neuromuscular junctions in the human interarytenoid (IA) muscle. The motor end-plates of four IA specimens obtained from normal postmortem larynges were visualized using an acetylcholinesterase stain. The three-dimensional distribution of motor end-plates was later reconstructed using computer graphics. The motor end-plates in the IA were found to be distributed in an inverted "Y" configuration. A broad band of end-plates was found at the midpoint of the muscle fibers in the superior and middle aspect of the muscle. This band divided obliquely in a lateral direction toward the inferior border of the muscle. This pattern of motor end-plate distribution is possibly consistent with the bilateral innervation of the IA by the recurrent laryngeal nerves.     

Anatomy and fiber type composition of human interarytenoid muscle

Intrinsic laryngeal muscle investigations, especially those of the interarytenoid (IA) muscle, have been primarily teleologically based. We determined IA muscle anatomy and histochemical and immunohistochemical classification of extrafusal and intrafusal (muscle spindle) fibers in 5 patients. Extrafusal fibers were oxidative type I and glycolytic types IIA and IIX. Intrafusal fibers of muscle spindles were identified by the presence of tonic and neonatal myosin. The results demonstrate that the IA muscle has a phenotype similar to that of limb skeletal muscle. Myosin coexpression, the absence of intrafusal fibers, and fiber type grouping were unusual features found previously in the thyroarytenoid and posterior cricoarytenoid muscles, but they were not present in the IA muscle. These findings lead to the conclusion that the IA muscle has functional significance beyond its assumed importance in maintaining vocal fold position during phonation. The presence of spindles demonstrates differences in motor control as compared to the thyroarytenoid and posterior cricoarytenoid muscles. Further, extrafusal fiber characteristics implicate IA muscle involvement in muscle tension dysphonia and adductor spasmodic dysphonia. Given the unique physiologic characteristics of the human IA muscle, further research into the role of the IA muscle in voice disorders is warranted.     

Electron microscopic study on the esophageal mucosa in human fetuses

Morphogenetic studies of the esophageal mucosa in human fetuses have been few and there is only one report at the ultrastructural level. We thus studied the esophageal mucosa in human fetuses (at the gestational ages from the 7th to 21st week) by scanning (SEM) as well as transmission electron microscopy (TEM). Our results and the review of the literature lead to the following conclusions: 1) Primary cilia were seen in the 7th and 8th week of gestation. 2) Ciliated cells appeared around the 8th week of gestation. They increased in number according to the fetal ages, but gradually decreased after the 14th week of gestation. Their degenerative process at the ultrastructural level was similar to that reported previously. 3) The stratified squamous epithelia appeared at the 14th week of gestation, but the squamous cells remained immature even at the 21st week. 4) Glycogen granules in non-ciliated cells decreased as the differentiation of the cells proceeded, suggesting that they provide an energy source necessary for the cell differentiation.     

Electron microscopic study on the epiglottic mucosa in human fetuses

The differentiation of the epiglottic mucosa in human fetuses has so far been studied only by light microscopy. So, we studied the epiglottic mucosa in human fetuses (at gestational ages from the 7th to 21st week) by scanning (SEM) and transmission electron microscopies (TEM), and could disclose more detailed features of cellular differentiation of this mucosa. These results and the review of the literatures lead to the following conclusions: 1. Primary cilia appeared in the epiglottic mucosa around the 7th week of gestation. 2. Ciliated cells and the stratified squamous epithelium of the lingual surface appeared at the similar period as reported by others, but our study revealed that the squamous cells are immature even at the 21st week. 3. Glycogen granules in non-ciliated cells decreased paralleling the differentiation of the cells, suggesting that they provide a source of energy necessary for the cell differentiation.     

The superior laryngeal nerve and the interarytenoid muscle in humans: an anatomical study

The course and distribution of the rami perforantes of the superior laryngeal nerve was studied in 12 human larynges. Dissections utilized a Zeiss operating microscope. All branches were found to perforate the muscle; none terminated in the muscle. This eliminates anatomically any possibility of motor supply to the mterarytenoid muscle from the superior laryngeal nerve. The rami perforantes also contribute to mucosal innervation on the posterior surface of the larynx. Histologic studies of whole fetal larynges corroborated the findings from the dissections. No evidence of innervation across the midline was found. No extra-laryngeal division of the recurrent laryngeal nerve into abductor and adductor branches was found. A ganglion around the superior laryngeal nerve was described.     

Embryonic development of the human organ of Corti: Electron microscopic study

A morphological approach by the electron microscope was used to obtain findings suggestive of the onset of auditory function in the fetal human cochlea. The organs of Corti at three different embryonic ages: 20 weeks 3 days, 22 weeks, and 24 weeks, were studied from the following standpoints: auditory hairs; hair cell bodies; the interrelationship between sensory cells and supporting cells; fluid spaces in the organ of Corti; and nerve endings to the sensory cells. Assessment of these findings implies that the peripheral auditory organ is ready for sending afferent impulses at around 24 weeks of embryonic age.     

Treatment of the interarytenoid muscle with botulinum toxin for laryngeal dystonia

The treatment of laryngeal dystonia with botulinum toxin has provided various degrees of relief to the majority of patients with adductor dysphonia; however, a significant number of patients have limited or no improvement with this type of therapy. It remains unclear why some patients respond to the routine administration of toxin to the thyroarytenoid muscles whereas others do not. Injections into the lateral cricoarytenoid muscles have provided an improved voice in some patients who were unresponsive to injections into the thyroarytenoid muscles. Fine-wire electromyography can demonstrate the particular dystonic activity of these muscles to help determine which muscle is predominantly involved. It can also demonstrate dramatic dystonic activity in the interarytenoid (IA) muscle in many patients. We present the results of 23 patients treated with injections to the IA muscle after demonstration of dystonic IA activity. Ten have benefited from IA therapy. Five of these 10 patients did not have a good result from botulinum toxin until IA injections were added to the treatment plan. In 8 patients, IA therapy provided no improvement, and 5 patients were lost to adequate follow-up. According to fine-wire electromyography and clinical response, the IA muscle is an active dystonic muscle in some patients with laryngeal dystonia and should be treated with botulinum toxin in selected patients.     

Electron microscopic and functional aspects of the human vomeronasal organ

The vomeronasal organ or Jacobson's organ is essential for pheromone detection and reproductive behavior in most mammals. The purpose of this article is to describe the fine structure of the adult human vomeronasal organ in 14 specimens and to discuss functional aspects. Our studies show a duct-like invagination of the epithelium, surrounded by numerous exocrine glands with short ducts; their fine structure suggests serous secretion. In the depth of the invagination, pseudostratified columnar epithelial cells are seen, with plump processes, kinocilia, and microvilli at the apical cell membrane. There are several cell types that differ regarding their organelles and electron density; the light sensory cells exhibit neurofilaments. Underneath the typical basement membrane, in the very vascular lamina propria, numerous myelinated and unmyelinated axons are present. These morphologic findings, which are unique in the human body, suggest that a chemosensory epithelium corresponding to a vomeronasal organ may exist. Its central connections and the possible functional significance for pheromone detection are unknown. Preservation of the vomeronasal organ in endonasal surgery could become important both clinically and medicolegally, should function be demonstrated in humans.     

Electron microscopic observation of acoustic neurinoma

The ultrastructural pattern of the acoustic neurinoma was studied with 10 excised tumors as well as one from the temporal bone. Under transmission electron microscope, the ultrastructural characteristics of the tumor were as follows: (1) The cytoplasm formed bundles of very thin, long processes in intimate contact with each other and/or with similar processes from neighboring cells. (2) All of these cells and their processes were surrounded by a basement membrane. (3) In the dense areas, the extracellular spaces were occupied by banded fusiform fibers (Luse bodies). (4) In some tumors, the extracellular space of the loose areas contained a moderate amount of collagen. (5) The extracellular space in many tumors appeared either "empty" or filled with fine granular material and small bundles of fine filaments. Fully and partially myelinated nerve fibers were found in some tumors. Pathological classification based on the ultrastructure of the acoustic neurinoma had been discussed.