Motor neurons of the laryngeal nerves

The present study was undertaken to determine the relationship between the motor neurons of the superior and recurrent laryngeal nerves within the nucleus ambiguus. The retrograde transport of horseradish peroxidase was utilized to identify the motor neurons subsequent to its application to the proximal transected end of the superior and recurrent laryngeal nerves. Labeled superior laryngeal motor neurons were distributed ventrolaterally in the rostral portion of the nucleus. The recurrent laryngeal motor neurons were distributed throughout the nucleus with two distinct populations: a rostral group and a caudal group. The rostral group overlaps the motor neurons of the superior laryngeal nerve. The caudal group occupies that portion of the nucleus that is classically described for the recurrent laryngeal nerve. Additional superior laryngeal nerve labeled perikarya were found in the dorsal motor nucleus of the vagus. This study defines the rostral distribution of the recurrent laryngeal nerve motor neurons and suggests that this rostral group is a component of the neuroanatomical substrate that is involved in the co-activation of the laryngeal abductors controlling the laryngeal aperture.     

喉返神经在颈部的应用解剖研究

目的　为在甲状腺手术中避免误伤喉返神经提供解剖学基础。方法　对 5 0具 (男 3 0具 ,女 2 0具 )成人尸体解剖喉返神经和甲状腺下动脉之间的关系进行解剖观测。结果　喉返神经平均横径为 ( 1.93± 0 .3 5 )mm。喉返神经入喉支以 2～ 5干型为多见 ,占 70 .0 0 %。甲状腺下动脉的直径为 ( 2 .61± 0 .2 3 )mm。喉返神经和甲状腺下动脉之间的关系 ,左右均有明显差异。结论　喉返神经横径平均在 ( 1.93± 0 .3 5 )mm之间 ;喉返神经在甲状腺峡平面分支的最为常见 ;神经位于动脉主干之后的为多见 ,占 5 4.0 0 % ;神经位于动脉前及动脉分支之间的例数相近 ,左侧神经位于动脉之后的多见 ,而右侧神经位于动脉之前的多见 ,左右有明显差异 ,为临床颈部外科手术时参考。     

Intrathoracic blood supply of the left vagus and recurrent laryngeal nerves

Abstract The arteries and veins of the left vagus (VN) and left recurrent laryngeal (RLN) nerves from the thoracic inlet to the subaortic region are described following vascular casting with red colored latex in 6 adult fresh non-embalmed cadavers. In all specimens the anterior bronchoesophageal artery supplied at least one vessel to the VN and RLN in the subaortic region. For the RLN other arterial sources were arteries arising from the aortic arch in 1 specimen, the subclavian artery in 3 specimens, the first intercostal artery in 1 specimen, and the inferior thyroid artery in all specimens. For the VN other arterial sources were arteries arising from the aortic arch in 2 specimens and the inferior thyroid artery in 1 specimen. For both the VN and RLN the veins were located under the pleura and directed towards the internal thoracic vein anteriorly and the thoracic intercostal veins posteriorly. In conclusion, the inferior thyroid artery at the thoracic inlet for the RLN and the anterior bronchoesophageal artery are the more consistent vessels supplying the VN and RLN. Vascular damage occurring during mediastinal lymph node excision to the VN and RLN, especially in the subaortic region, may explain postoperative vocal fold paralysis.     

Motor nerves of salivary myoepithelial cells in dogs

1. The pressures in the ducts of the parotid and submaxillary glands were recorded in dogs under chloralose-urethane anaesthesia. A single stimulus applied to the parasympathetic nerve regularly caused a pressure rise of short duration. Usually it did not evoke secretion.2. In both glands a single stimulus applied to the vagosympathetic trunk usually caused a pressure response of short duration. It had no secretory effect.3. In the parotid gland, repetitive vagosympathetic stimulation caused a sustained increase of pressure in the duct, usually without inducing secretion.4. In the submaxillary gland, repetitive vagosympathetic stimulation caused a sustained pressure rise, even when the secretory response had been abolished by propranolol.5. It is concluded that the salivary myoepithelial cells of dogs are supplied with fibres from both sympathetic and parasympathetic divisions of the autonomic nervous system and both can cause the cells to contract.     

Responses of primate spinothalamic tract neurons to electrical stimulation of hindlimb peripheral nerves.

The responses of spinothalamic tract neurons were studied by extra- and intracellular recordings from the lumbosacral spinal cord in anesthetized rhesus monkeys (Macaca mulatta). The neurons were identified by antidromic activation from the contralateral diencephalon. They were then classified by the mildest form of mechanical stimulation applied to the ipsilateral hindlimb. The effects of electrical stimulation of the nerve(s) supplying the receptive field were investigated. Graded electrical stimulation revealed that the threshold responses of spinothalamic tract neurons excited by weak mechanical stimuli occurred when the largest afferent fibers were activated. On the other hand, neurons that required intense mechanical stimulation for their excitation tended to have higher thresholds to electrical stimulation. Some spinothalamic tract cells were shown to receive monosynaptic excitatory connections from peripheral nerve fibers, although polysynaptic connections may generally be more important. An input from unmyelinated afferent fibers was demonstrated. It is concluded the primate spinothalamic tract neurons receive a rich convergent input from a variety of cutaneous receptors. The experiments provide some evidence for the most likely types of receptors.     

Expression of catecholamine-synthesizing enzymes in paraganglionic and ganglionic cells in the laryngeal nerves of the rat

Summary The rat recurrent and superior laryngeal nerves with adjacent connective tissue were examined by immunohistochemical techniques for localization of the catecholamine-synthesizing enzymes tyrosine hydroxylase, dopamine--hydroxylase and phenylethanolamine-n-methyltransferase. Most of the cells in the paraganglia of the recurrent and superior laryngeal nerves showed an intense tyrosine hydroxylase-like immunoreactivity. A few paraganglionic cells exhibited dopamine--hydroxylase-like immunoreactivity while none of the cells displayed phenylethanolamine-n-methyltransferase-like immunoreactivity. Some of the ganglionic cells in the recurrent and superior laryngeal nerves showed dopamine--hydroxylase-like immunoreactivity whilst these cells never showed tyrosine hydroxylase- or phenylethanolamine-N-methyltransferase-like immunoreactivity. The arterioles were supplied with plexuses of nerve fibres showing tyrosine hydroxylase- and dopamine--hydroxylase-like immunoreactivity. The results indicate that dopamine is the major catecholamine located in the laryngeal nerve paraganglia and show that ganglionic cells in the recurrent and superior laryngeal nerves show immunolabelling for one of the enzymes in the catecholamine synthetic pathway, dopamine--hydroxylase.     

Interrelationships between the innervations from the laryngeal nerves and the pharyngeal plexus to the inferior pharyngeal constrictor

Purpose

The inferior constrictor is innervated by the pharyngeal plexus and the external and recurrent laryngeal nerves. The communication between these nerves may influence the innervations. However, the relations of their anastomoses with the innervations have been unclear. This gross anatomical study re-examined the configuration of the inferior constrictor and investigated the variations of the anastomoses and the innervations of the constrictor to clarify their interrelationships.

Methods

The inferior constrictor and the branches of the superior and recurrent laryngeal nerves and the pharyngeal plexus were examined under a binocular microscope in 30 Japanese cadavers.

Results

The inferior constrictor consisted of the oblique fibers from the thyroid and cricoid cartilages and the horizontal ones from the cricoid. The oblique fibers were innervated by the pharyngeal plexus from the dorsal and ventral surfaces. The external laryngeal nerve gave twigs to the oblique fibers and the cricothyroid from the lateral surface. The recurrent laryngeal nerve supplied the horizontal fibers from the ventral surface. The internal laryngeal nerve sometimes and the main trunk of the superior laryngeal nerve rarely supplied the upper oblique fibers. The communicating branches between the laryngeal nerves and the pharyngeal plexus sometimes gave twigs to the constrictor from the dorsal surface.

Conclusions

The innervations to the inferior constrictor from the laryngeal nerves and the pharyngeal plexus are classified into some types based on their branching patterns and anastomoses, suggesting that the dysfunctions of the laryngopharyngeal region vary according to the positional relationships between the affected part and the innervations types.     

Morphology and electrophysiology of superior laryngeal nerve afferents and postsynaptic neurons in the medulla oblongata of the cat.

Intra-axonal recordings were made from 24 afferent fibres of the superior laryngeal nerve in and around the nucleus tractus solitarius, in 26 pentobarbitone-anaesthetized cats. Conduction velocity ranged from 15 to 38 m/s. Four afferents were injected with horseradish peroxidase. They showed dense terminal arborization in the region of the ventral and ventrolateral subnuclei of the nucleus tractus solitarius, both rostral and caudal to the obex. Six other intra-axonal recordings were thought to originate from axons of neurons postsynaptic to superior laryngeal afferents; one of these was injected with horseradish peroxidase and showed a similar arborization pattern to that of the afferent axons. In the same region, intracellular recordings were made from 124 neurons which responded to superior laryngeal nerve stimulation with excitatory postsynaptic potentials (mean latency 2.7 +/- 1.0 ms). Ninety-nine of these neurons were thought to receive a monosynaptic input. The stimulation threshold evoking these responses was similar to that which inhibited phrenic nerve discharge. Eleven of the monosynaptically excited neurons were injected with horseradish peroxidase. They had fusiform or stellate somata and simple dendritic trees, radiating mainly in the transverse plane. In one experiment, in which both a superior laryngeal nerve afferent fibre and a neuron were labelled, afferent terminal varicosities were found in close apposition with the postsynaptic membrane of the injected neuron. Four of 14 (29%) tested neurons could be antidromically activated from the C3 spinal segment. The stimulus thresholds and onset latencies of the responses of superior laryngeal nerve afferents and medullary neurons to stimulation of the superior laryngeal nerve are consistent with their involvement in the reflex inhibition of respiratory neurons evoked by superior laryngeal nerve stimulation.     

Reactions of neurons of the mediodorsal nucleus of the thalamus to the stimulation of peripheral nerves

The reactions of neurons of the associative mediodorsal nucleus of the thalamus to a solitary stimulation of the radial, sciatic, and splanchnic nerves were studied in conditions of an acute experiment in anesthetized and immobilized cats. There were 91.85, 90.56, and 81.35% reactive neurons, respectively. They were mainly concentrated in the parvocellular division of the nucleus. A high degree of convergence (82.6%) of somatic and visceral signals was found and their interaction was of the reciprocal blocking type.Translated from Fiziologicheskii Zhurnal SSSR imeni I. M. Sechenova, Vol. 76, No. 11, pp. 1528–1537, November, 1990.     

Training in intraoperative neuromonitoring of recurrent laryngeal nerves reduces the risk of their injury during thyroid surgery

IntroductionEven though incidence of recurrent laryngeal nerve palsy (RLNP) is low, it affects importantly the quality of life of patients and remains one of main medicolegal litigation problems in surgery. Intraoperative neuromonitoring (IONM) has become widely accepted tool helping in recurrent laryngeal nerve identification, however no clear association of IONM with RLNP rate has been demonstrated. The aim of our study was to assess whether training in IONM influences rates of RNLP after thyroid surgery as an independent factor.Material and methodsWe analysed retrospectively 1235 patients who underwent thyroidectomy at the 1st Department of General and Endocrine Surgery, Medical University of Bialystok. Possible risk factors for RLNP were evaluated: application or not of IONM, the extent of surgery or thyroid pathology in correlation with surgeons’ experience in IONM (trained or untrained).ResultsThere were 2351 nerves at risk (NAR) and 39 RNLP were diagnosed after thyroid surgery (1.66%). Surgeons trained in IONM performed 52.2% of all operations (1200 NAR) with 7 RLNP (0.58%), whereas not-trained had 32 RLNP for 1151 NAR (2.8%; p < 0.001). After 182 thyroidectomies (357 NAR) guided by IONM (14.7%) 3 RLNP were observed (0.84%) vs. 36 palsies per 1994 NAR without IONM (1.81%; p = 0.189). The highest danger of RLNP was reported after reoperations and the lowest after subtotal thyroidectomies. We found no association between thyroid pathology and RLNP rate.ConclusionsAccording to our study training in IONM decreases chances of RLNP especially during total or near total thyroidectomy.     

Distribution of NADPH-diaphorase-positive nerves in the uterine cervix and neurons in dorsal root and paracervical ganglia of the female rat.

Nitric oxide synthase (NOS) was selectively stained in nerve fibers of the uterine cervix and neurons of the paracervical (PG) and dorsal root ganglia (DRG) by NADPH diaphorase histochemistry. In the cervix, numerous NADPH-diaphorase-positive nerve fibers were observed in the myometrium, endometrium and around arteries. In addition, a subpopulation of neurons within ganglia that innervate the cervix, i.e., the PG and DRG, were NADPH-diaphorase positive; thus the fibers in the cervix could be sensory and/or autonomic. NADPH-diaphorase/NOS localization identifies sites where nitric oxide (NO) can be synthesized. Since NO relaxes vascular and nonvascular smooth muscle, the prevalence and anatomical localization of NADPH-diaphorase-positive fibers suggest that they could influence functions of the uterine cervix.