Influence of lung volume on activities of branches of the recurrent laryngeal nerve

To investigate the influence of inspiratory lung inflation on the respiratory activities of laryngeal motor nerves, vagally intact decerebrate paralyzed cats were ventilated by a servorespirator in accordance with their own phrenic nerve activity. Records were made of the activities of the phrenic nerve, the superior laryngeal nerve (SLN), the recurrent laryngeal nerve (RLN), and the intralaryngeal branches of the RLN serving the thyroarytenoid (TA) and posterior cricoarytenoid (PCA) muscles. Neural activities were assessed in the steady state at different end-tidal O2 and CO2 concentrations. Transient responses to withholding inspiratory lung inflation and to preventing expiratory lung emptying were also studied. Hypercapnia and hypoxia increased the inspiratory activities of the phrenic nerve, SLN, RLN, and its PCA branch. TA inspiratory activity was not changed. Expiratory activities of RLN, PCA, and TA were all increased in hypoxia. When lung inflation was withheld, neural inspiratory duration and the inspiratory activities of all nerves increased. The subsequent period of neural expiration was marked by an exaggerated burst of activity by the TA branch of the RLN. TA expiratory activity was also sharply increased after inspiratory efforts that were reflexly delayed by the prevention of lung emptying. TA activity in expiration was enhanced after vagotomy and was usually more prominent than when lung inflation was withheld before vagal section. The results demonstrate the importance and complexity of the influence of vagal afferents on laryngeal motor activity.     

Characterization of the postnatal development of superior laryngeal nerve fibers in the postnatal kitten

A combined electron microscopic and electrophysiological study of the superior laryngeal nerve (SLN) was undertaken in postnatal kittens ranging in age from 1–63 days. The superior laryngeal nerve is predominantly a sensory nerve innervating the upper respiratory tract, and could play a potential role in the modulation of respiration, particularly in the infant animal. Distribution of fibers in the developing SLN indicates that within the first postnatal month, 75% of the fibers are unmyelinated, and by 42 days, the myelinated fibers increase in number to approximately 50%. Of the myelinated fibers present in the one day old kitten, 3–4% of those exceeded 4 μm in total diameter, which is the minimum diameter for normal conduction velocity of action potentials. The distribution of the diameter sizes of the myelinated fibers is bell-shaped within the first 45 days after which the curve becomes skewed to the right (43–61 days; mean 2.6 μm, range 0.5–8.0 μm) to resemble the adult distribution of myelinated fibers (mean 4.2 μm, range 1.6–13.0 μm). Two variable plots of myelin width to axon diameter suggest a steeper slope for developing fibers as compared to that of the adult fibers. Electrical stimulation of the sectioned SLN indicates that evoked potentials could be recorded from the recurrent laryngeal nerve innervating the laryngeal intrinsic muscles and from the hypoglossal nerve to the tongue musculature in the youngest kittens tested (i.e., age 9 days). Stimulation at selected frequencies of 3 and 30/sec readily evoked apnea in the youngest kitten studied (i.e., age 5 days), while swallowing was more readily evoked at 28–30 days when using electrical stimulation.     

Upper airway muscle paralysis reduces reflex upper airway motor response to negative transmural pressure in rat.

The reflex upper airway (UA) motor response to UA negative pressure (UANP) is attenuated by neuromuscular blockade. We hypothesized that this is due to a reduction in the sensitivity of laryngeal mechanoreceptors to changes in UA pressure. We examined the effect of neuromuscular blockade on hypoglossal motor responses to UANP and to asphyxia in 15 anesthetized, thoracotomized, artificially ventilated rats. The activity of laryngeal mechanoreceptors is influenced by contractions of laryngeal and tongue muscles, so we studied the effect of selective denervation of these muscle groups on the UA motor response to UANP and to asphyxia, recording from the pharyngeal branch of the glossopharyngeal nerve (n = 11). We also examined the effect of tongue and laryngeal muscle denervation on superior laryngeal nerve (SLN) afferent activity at different airway transmural pressures (n = 6). Neuromuscular blockade and denervation of laryngeal and tongue muscles significantly reduced baseline UA motor nerve activity (P < 0.05), caused a small but significant attenuation of the motor response to asphyxia, and markedly attenuated the response to UANP. Motor denervation of tongue and laryngeal muscles significantly decreased SLN afferent activity and altered the response to UANP. We conclude that skeletal muscle relaxation reduces the reflex UA motor response to UANP, and this may be due to a reduction in the excitability of UA motor systems as well as a decrease of the response of SLN afferents to UANP.     

Fibre size in the left and right recurrent laryngeal nerves (RLNs) in the man

Some morphological data of the right and left human RLNs were evaluated with the aim of verifying possible differences in the fibre composition of the two nerves. The following parameters were evaluated in the right and left RLNs of five human cases: 1) the maximum diameter of the fibres; 2) the axon diameter and area; 3) the myelin sheath area obtained substracting the axon area from the total area of each fibre. The obtained data were plotted on histograms for each case: moreover, histograms of all fibres of both left and right nerves of all five cases were made. The results show that the values of the maximum diameter of the fibres and of the myelin sheath area are always greater in a statistically significant way in the left RLNs than in the right RLNs. On the other hand the axon diameter is nearly the same in the nerves of both sides. These data suggest that the greater calibre of the myelin sheath in the fibres of the left inferior laryngeal nerve can be responsible of the faster conduction speed in this nerve. This fact might explain the simultaneous arrival of the impulses to the laryngeal muscles of the two sides in spite to the different length of the two nerves.     

Significance of the pattern of motor innervation of the intrinsic laryngeal muscles of cat.

Simple and compound forms of motor endings, showing a particular distribution, were found in the intrinsic laryngeal muscles of the cat. The muscles carrying compound and multiple endings were stained densely black with Sudan black B; while the muscles with simple and single endings showed black and pale fibres. A probable relationship is suggested between the contraction properties and the pattern of motor innervation of intrinsic laryngeal muscles of the cat.     

The anatomy and physiology of the stomatogastric nervous system ofSquilla

Summary The stomatogastric nervous system of a mantis shrimp,Squilla oratoria, is described. The motor nerves of the stomatogastric ganglion (STG) and their innervation of muscles of the posterior cardiac plate (pcp) and pyloric systems are detailed.The STG contains more than 25 neurons. It sends out one pair of major output nerves. The pcp-pyloric cycle recorded from the motor axons in this nerve consists of rhythmic bursts of several units which fire with a characteristic phase relationship to each other. The rhythm is intrinsic to the STG itself, but it is modifiable.Recordings from the peripheral nerves reveal that identifiable cardiac plate, pyloric dilator and pyloric neurons control sequential contractions of the pcp and pyloric muscles to constrict or dilate a number of their attached ossicles.Several modulatory input fibres in the stomatogastric nerve, activated via stimulation of the superior or inferior oesophageal nerve (son, ion), prime or trigger the cyclic motor outputs. The son inputs induce distinct effects on the cardiac and pcp-pyloric pattern generators, while the ion inputs, via the oesophageal ganglion, excite only the pcp-pyloric generator.On the basis of anatomical and physiological observations, the possible functions of motor neurons involved in the pcp-pyloric cycle are described with reference to opening of the pcp and pyloric channels.This stomatogastric nervous system inSquilla is compared to that in decapods which has been well analyzed.Abbreviations CG commissural ganglion - ion inferior oesophageal nerve - lvn lateral ventricular nerve - OG oesophageal ganglion - pep posterior cardiac plate - son superior oesophageal nerve - STG stomatogastric ganglion - stn stomatogastric nerve - ivn inferior ventricular nerve     

Myonic makeup of the muscles innervated by the vagus nerve

Histochemical investigation on succinic dehydrogenase activity and morphometric studies have demonstrated certain differences in the dog sublingual group of muscles. The thyreohyoid and sternohyoid muscles innervated by spinal nerves possess three types of myons differing in succinic dehydrogenase activity and in the area of transversal section. The cricothyreoid muscle and the superior pharyngeal constrictor obtaining their motor innervation from the vagus nerve are composed of unitypical muscular fibres with nearly the same areas of transversal section and high enzymic activity. The differences noted should be explained by different sources of motor innervation.     

Laryngeal influences on breathing pattern and posterior cricoarytenoid muscle activity

Receptors responding to transmural pressure, airflow, and contraction of laryngeal muscles have been previously identified in the larynx. To assess the relative contribution of these three types of receptors to the reflex changes in breathing pattern and upper airway patency, we studied diaphragmatic (DIA) and posterior cricoarytenoid muscle (PCA) activity in anesthetized dogs during spontaneous breathing and occluded efforts with and without bypassing the larynx. Inspiratory duration (TI) was longer, mean inspiratory slope (peak DIA/TI) was lower, and PCA activity was greater with upper airway occlusion than with tracheal occlusion (larynx bypassed). Bilateral section of the superior laryngeal nerves eliminated these differences. When respiratory airflow was diverted from the tracheostomy to the upper airway the only change attributable to laryngeal afferents was an increase in PCA activity. These results confirm the importance of the superior laryngeal nerves in the regulation of breathing pattern and upper airway patency and suggest a prevalent role for laryngeal negative pressure receptors.     

Influence of nerve supply on hand electromyography coherence during a three-digit task

Intermuscular coupling has been investigated to understand neural inputs to coordinate muscles in a motor performance. However, little is known on the role of nerve innervation on intermuscular coupling. The purpose of this study was to investigate how the anatomy of nerve distribution affected intermuscular coupling in the hand during static grip. Electromyographic (EMG) signals were recorded from intrinsic and extrinsic muscles while subjects performed a static grip. Coherence was computed for muscle pairs innervated by either the same or different nerves. The results did not support the hypothesis that muscles sharing the same nerve exhibit greater coupling than muscles innervated by different nerves. In general, extrinsic muscle pairs displayed higher coherence than intrinsic pairs. The results suggest that intermuscular coupling in a voluntary motor task is likely modulated in a functional manner and that different nerves might transport common neural inputs to functionally coupled muscles.     

The superior laryngeal nerve and the superior laryngeal artery

Length, diameter and anastomoses of the nervus vagus and its ganglion inferius were measured 44 halved heads. On the average, 8.65 fiber bundles of the vagus nerve leave the retro-olivary area. In the area of the jugular foramen is the near superior ganglion of the 10th cranial nerve. In this area were found 1.48 (mean value) anastomoses with the 9th cranial nerve. 11.34 mm below the margo terminalis sigmoidea branches off the ramus internus of the accessory nerve which has a length of 9.75 mm. Further anastomoses with the 10th cranial nerve were found. The inferior ganglion of the 10th nerve had a length of 25.47 mm and a diameter of 3.46 mm. Five mm below the ganglion the 10th nerve had a width of 2.9 and a thickness of 1.5 mm. The mean length of the superior sympathetic ganglion was 26.6 mm, its width 7.2 and its thickness 3.4 mm. In nearly all specimens anastomoses of the superior sympathetic ganglion with the ansa cervicalis profunda and the inferior ganglion of the 10th cranial nerve were found. The superior laryngeal nerve branches off about 36 mm below the margo terminalis sigmoidea. The width of this nerve was 1.9 mm, its thickness 0.8 mm on the right and 1.0 mm on the left side. The division in the internal and external rami was found about 21 mm below its origin. Between the n. vagus and thyreohyoid membrane the ramus internus had a length of 64 mm, the length of external ramus between the vagal nerve and the inferior pharyngeal constrictor muscle was 89 mm. Its mean length below the thyreopharyngeal part was 10.7 mm, 8.6 branchlets to the cricothyroid muscle were counted. The superior laryngeal artery had its origin in 80% of cases in the superior thyroideal artery, in 6.8% this vessel was a branch of the external carotid artery. Its average outer diameter was 1.23 mm on the right side and 1.39 mm on the left. The length of this vessel between its origin and the thyreohyoid membrane was 34 mm. In 7% on the right side and in 13% on the left, the superior laryngeal artery reached the larynx through a foramen thyreoideum. Ranges of diameters and lengths of vessels and nerves in the larynx are given.     

Functional differentiation of superior laryngeal nerve afferents in cats

Electrophysiological characteristics of superior laryngeal nerve fibers and reflex responses in respiratory motor nerves and the recurrent nerve were investigated in acute experiments on cats under superficial pentobarbital anesthesia. Analysis of the compound action potential in the superior laryngeal nerve revealed three distinct groups of afferent fibers subserving different functions: group A, responsible for proprioceptive mechanisms of coordination of activity of the laryngeal muscles; group A(₃), responsible for feedback mechanisms between the receptor apparatus of the mucous membrane and muscles of the larynx and bulbar respiratory neurons, and group A, responsible for the development of protective respiratory reflexes.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 16, No. 6, pp. 777–783, November–December, 1984.     

The Sense Organs and Ventral Ganglion of Sagitta (Chaetognatha)

This paper describes some features of the chaetognath nervous system from ultrastructural observations and observations on material stained with specific techniques for nervous tissue, and from records of the activity of the locomotor muscles and ventral ganglion. Sensory cells grouped on the ventral surface of the head bear ciliary processes (some with multiple tubules), and are probably in connexion with the central nervous system by their own axons, unlike the sensory cells of the hair fan vibration receptors of head and body. The ventral ganglion is motor to the locomotor muscles of the body, and controls the rhythmic locomotor activity of the animal. Electrical events associated with contraction of these muscles are compound non-overshooting spike-like potentials. The ventral ganglion contains several large nerve fibres constant in position and connexions in different individuals. Some of these arise from cells in the ganglia of the head, and pass to the ventral ganglion, others from cells within the ventral ganglion, and probably supply the ciliary hair fan receptors of the body, whilst the motor axons issuing from the ventral ganglion are smaller in diameter. The ganglion is arranged on a ladder-like plan, and axons of the lateral cell bodies cross the central neuropil transversely before they contribute to the longitudinal tracts or pass out in the radial nerves. Synapses in the neuropil contain 30–40 nm electron lucent vesicles; the transmitter is unknown, but is unlikely to be either acetylcholine or l -glutamate. Occasional larger electron dense vesicles up to 70 nm in diameter are also found within nerve fibres of the neuropil. It is concluded that the arrangement of the peripheral nervous system is unlike that of several groups which have been suggested as related to chaetognaths.     

Quantitative electron-microscopy analysis of cranial nerves III, IV, and VI and of the extrinsic eye muscles in fog.

A comparative study of the quantitative data of the frog extraocular muscles and the cranial nerves that innervate them was performed. Oculorotatory muscles contain muscle fibres of at least 4 types which are arranged in heterogeneous layers. The zonal arrangement of the muscles does not occur on the cross-sections in the vicinity of muscle insertions. In these regions only two muscle fibre types are present and the total number of fibres is smaller by 70% than in the central region of the muscle. Most numerous are muscle fibres in the rectus inferior muscle, while the smallest number of fibres is found in rectus interior muscle. Three distinct types of nerve fibres are distinguished according to the following criteria: occurrence and thickness of myelin sheath, fibre diameter and ratio "g". The fibres with thin myelin sheaths indicate small diameters (1-5--6- mum) and their ratio "g" equals 0-82 +/- 0-08. They constitute about 30% of the myelinated fibres in the nerve supply of the oculorotatory muscles and about 14% in the supply of the retractor bulbi muscle. Both the value of the ratio "g" and a greater number of these fibres in the nerve supply of the muscles that contain slow contracting muscle fibres indicate that they are rather slow conducting nerve fibres. The range of the diameters of the fibres with thick myelin sheaths is greater (3-5--13-5 mum) and their "g" equals 0-66 +/- 0-06. These fibres constitute about 70% of the myelinated ones in the nerve supply of the oculorotatory muscles and 86% in the supply of the retractor bulbi muscles. The value of the ratio "g" in these fibres indicates that they are fast contracting ones. The smallest diameters are found in the myelinated fibres (0-5--1-7 mum). These fibres occur frequently in all the examined nerves; they constitute 36--47% of the total number of all the nerve fibres. The frog extraocular muscles are characterized by an abundal nerve supply which is reflected in the low innervation ratio (1:4--1:5). On the distal cross-section of nerves the number of nerve fibres is greater than on the proximal ones. Ganglionic neurons occur sporadically around the nerves; in the nerve III synaptic contacts between two neurons were observed.     

Laryngeal nerve activity during pulse emission in the CF-FM bat,Rhinolophus ferrumequinum

Summary The activity of the external (motor) branch of the superior laryngeal nerve (SLN), innervating the cricothyroid muscle, was recorded in the greater horseshoe bat,Rhinolophus ferrumequinum. The bats were induced to change the frequency of the constant frequency (CF) component of their echolocation signals by presenting artificial signals for which they Doppler shift compensated. The data show that the SLN discharge rate and the frequency of the emitted CF are correlated in a linear manner.Abbreviations SLN Superior laryngeal nerve - RLN Recurrent laryngeal nerve - DCS Doppler compensation system - CF Constant frequency - FM Frequency modulation Supported by grants of the Deutsche Forschungsgemeinschaft (DFG), Az.: Schu 390/1, /2 and SFB 45We are indebted to Dipl.-Ing. H. Zöller for providing the computer programs. We want to thank H. Hahn and A. Polotzek for technical help.     

Water stimulation of the posterior oral cavity induces inhibition of gastric motility

The response of gastric motility to the administration of water and saline in the larynx and epiglottis was investigated in urethan-chloralose anesthetized rats. Administration of water inhibited motility of the distal stomach, but 0.15 M NaCl did not induce the inhibitory response. Bilateral sectioning of the superior laryngeal nerve (SLN) abolished the inhibitory response induced by water. Bilateral cervical vagotomies abolished the inhibitory responses, although spinal transection did not affect the inhibitory response. These inhibitory responses have been observed in immobilized animals. The degree of inhibition by water and hypotonic saline was negatively correlated with the sodium concentration. In contrast, the degree of inhibition to hypertonic saline was positively correlated with the sodium concentration. The proximal stomach also showed a reduction in intragastric pressure in response to the administration of water. These findings suggest that water-responsive afferent neurons in the SLN suppress gastric motility via the vagal efferent nerve.     

Influences from laryngeal afferents on expiratory bulbospinal neurons and motoneurons

The purpose of this study is to analyze the reflex effects of laryngeal afferent activation on respiratory patterns in anesthetized, vagotomized, paralyzed, ventilated cats. We recorded simultaneously from the phrenic nerve, T10 internal intercostal nerve, and single bulbospinal expiratory neurons of the caudal ventral respiratory group (VRG). Laryngeal afferents were activated by electrical stimulation of the superior laryngeal nerve (SLN) or by cold-water infusion into the larynx. Both types of stimuli caused inhibition of phrenic activity and facilitation of internal intercostal nerve activity, indicating expiratory effort. The activity of 46 bulbospinal expiratory cells was depressed during SLN electrical stimulation, and 13 of them were completely inhibited. In 44 of 56 neurons tested, mean firing frequency (FFmean) was decreased in response to cold-water infusion and 8 others responded with increased FFmean; in the remaining 4 neurons, FFmean was unchanged. Possible reasons for different neuronal responses to SLN electrical stimulation and water infusion are discussed. We conclude that bulbospinal expiratory neurons of VRG were not the source of the reflex motoneuronal expiratory-like activity produced by SLN stimulation. Other, not yet identified inputs to spinal expiratory motoneurons are activated during this experimental condition.     

Noradrenergic and peptidergic innervation of the mammary gland in the immature pig

The presence and pattern of coexistence of some biologically active substances in nerve fibres supplying the mammary gland in the immature pig were studied using immunohistochemical methods. The substances studied included: protein gene product 9.5 (PGP), tyrosine hydroxylase (TH), somatostatin (SOM), neuropeptide Y (NPY), galanin (GAL), calcitonin gene-related peptide (CGRP) and substance P (SP). The mammary gland was found to be richly supplied by PGP-immunoreactive (PGP-IR) nerve fibres that surrounded blood vessels, bundles of smooth muscle cells and lactiferous ducts. The vast majority of these nerves also displayed immunoreactivity to TH. Immunoreactivity to SOM was observed in a moderate number of nerve fibres which were associated with smooth muscles of the nipple and blood vessels. Immunoreactivity to NPY occurred in many nerve fibres associated with blood vessels and in single nerves supplying smooth muscle cells. Solitary GAL-IR axons supplied mostly blood vessels. Many CGRP-IR nerve fibres were associated with both blood vessels and smooth muscles. SP-IR nerve fibres richly supplied blood vessels only. The colocalization study revealed that SOM, NPY and GAL partly colocalized with TH in nerve fibres supplying the porcine mammary gland.     

The role of the superior laryngeal nerve in esophageal reflexes

The aim of this study was to determine the role of the superior laryngeal nerve (SLN) in the following esophageal reflexes: esophago-upper esophageal sphincter (UES) contractile reflex (EUCR), esophago-lower esophageal sphincter (LES) relaxation reflex (ELIR), secondary peristalsis, pharyngeal swallowing, and belch. Cats (N = 43) were decerebrated and instrumented to record EMG of the cricopharyngeus, thyrohyoideus, geniohyoideus, and cricothyroideus; esophageal pressure; and motility of LES. Reflexes were activated by stimulation of the esophagus via slow balloon or rapid air distension at 1 to 16 cm distal to the UES. Slow balloon distension consistently activated EUCR and ELIR from all areas of the esophagus, but the distal esophagus was more sensitive than the proximal esophagus. Transection of SLN or proximal recurrent laryngeal nerves (RLN) blocked EUCR and ELIR generated from the cervical esophagus. Distal RLN transection blocked EUCR from the distal cervical esophagus. Slow distension of all areas of the esophagus except the most proximal few centimeters activated secondary peristalsis, and SLN transection had no effect on secondary peristalsis. Slow distension of all areas of the esophagus inconsistently activated pharyngeal swallows, and SLN transection blocked generation of pharyngeal swallows from all levels of the esophagus. Slow distension of the esophagus inconsistently activated belching, but rapid air distension consistently activated belching from all areas of the esophagus. SLN transection did not block initiation of belch but blocked one aspect of belch, i.e., inhibition of cricopharyngeus EMG. Vagotomy blocked all aspects of belch generated from all areas of esophagus and blocked all responses of all reflexes not blocked by SLN or RLN transection. In conclusion, the SLN mediates all aspects of the pharyngeal swallow, no portion of the secondary peristalsis, and the EUCR and ELIR generated from the proximal esophagus. Considering that SLN is not a motor nerve for any of these reflexes, the role of the SLN in control of these reflexes is sensory in nature only.     

A comparative histochemical study of intrinsic laryngeal muscles of ungulates and carnivores

The intrinsic laryngeal muscles of the horse, donkey, sheep, ox, pig, dog and cat were examined for myosin ATPase, following acid and alkali pre-incubation, SDH and M-alphaGPDH activities. In all laryngeal muscles two fibre types, betaR and alphaR, belonging to slow and fast-contracting, fatigue-resistant motor units (types S and FR) were present in different proportions. The alphaW fibre type, belonging to fast-contracting and fatigue-resistant motor units was absent (type FF). The alphaR fibres of the dog and the cat were subdivided into groups by the various degrees of acid stable myosin ATPase, oxidative and glycolytic activities. In the ox and pig laryngeal muscles, the same fibres showed an atypical myosin ATPase activity, as high as the fast-contracting fibres but acid-resistant like the slow-twitch fibres. The most uniform muscle was the CAD, which was formed of a higher percentage of slow-twitch fibres than the other laryngeal muscles of the same species. Also the VE muscle was very uniform in the dog, horse and donkey but the fast-twitch fibres were by far the most numerous, the highest in fact among all the laryngeal muscles. In the TA muscle of the cat, sheep and ox, the percentage of fast-twitch fibres was very high in the rostral portion decreasing gradually towards the caudal portion. Thus it was possible to separate histochemically the TA muscle in the rostral (pars ventricularis) and caudal (pars vocalis) portions which are related to the VE and the VO muscles of the dog, horse and donkey. In the VO muscle the slow-twitch fibres are more numerous than in the VE. The two portions of the TA were not detected by histochemical methods in the pig. However, this muscle has the highest percentage of fast-twitch fibres. The qualitative and quantitative data presented in this paper together with the data reported in the literature, enable us to correlate morphological and functional aspects of fibre composition among the species.