Ultrastructure of the circumoral nerve ring and the radial nerve cords in holothurians (Echinodermata)

Zoomorphology ◽  
2006 ◽  
Vol 125 (1) ◽  
pp. 27-38 ◽  
Author(s):  
Vladimir S. Mashanov ◽  
Olga R. Zueva ◽  
Thomas Heinzeller ◽  
Igor Yu. Dolmatov
Keyword(s):  
Radial Nerve ◽  
Nerve Ring ◽  
Nerve Cords

Echinoderm Nervous System

2018 ◽  
Author(s):  
Carlos A. Díaz-Balzac ◽  
José E. García-Arrarás
Keyword(s):  
Nervous System ◽  
Radial Nerve ◽  
Regulatory Networks ◽  
Nerve Ring ◽  
Neural Net ◽  
System P ◽  
Embryonic Nervous System ◽  
Body Wall Muscles ◽  
Areas Of Interest ◽  
Nerve Cords

The nervous system of echinoderms has been studied for well over a century. Nonetheless, the information available is disparate, with in-depth descriptions for the nervous component of some groups or of particular organs while scant data is available for others. The best studied representatives to date are the nervous system of echinoid embryos and larva, and the adult holothurian nervous system. Although described sometimes inaccurately as a neural net, the echinoderm nervous system consists of well-defined neural structures. This is observed since early embryogenesis when activation of the anterior neuroectoderm gene regulatory networks initiate the formation of the embryonic nervous system. This system then undergoes expansion and differentiation to form the larval nervous system, which is centered on the ciliary bands. This “simpler” nervous system is then metamorphosed into the adult echinoderm nervous system. The adult echinoderm nervous system is composed of a central nervous system made up of a nerve ring connected to a series of radial nerve cords. Peripheral nerves extending from the radial nerve cords or nerve ring connect with the peripheral nervous system, located in other organs or effectors including the viscera, podia, body wall muscles, and connective tissue. Both the central and peripheral nervous systems are composed of complex and diverse subdivisions. These are mainly characterized by the expression of neurotransmitters, namely acetylcholine, catecholamines, histamine, amino acids, GABA, and neuropeptides. Other areas of interest include the amazing regenerative capabilities of echinoderms that have been shown to be able to regenerate their nervous system components; and the analysis of the echinoderm genome that has provided essential insights into the molecular basis of how echinoderms develop an adult pentaradial symmetry from bilaterally symmetric larvae and the role of the nervous system in this process.

The enteric nervous system of echinoderms: unexpected complexity revealed by neurochemical analysis

2001 ◽  
Vol 204 (5) ◽  
pp. 865-873
Author(s):  
J.E. Garcia-Arraras ◽  
M. Rojas-Soto ◽  
L.B. Jimenez ◽  
L. Diaz-Miranda
Keyword(s):  
Nervous System ◽  
Enteric Nervous System ◽  
Digestive Tract ◽  
Radial Nerve ◽  
Digestive System ◽  
Nerve Ring ◽  
Point Of View ◽  
Distinct Component ◽  
Future Studies ◽  
Neurochemical Analysis

Echinoderms are one of the most important groups of metazoans from the point of view of evolution, ecology and abundance. Nevertheless, their nervous system has been little studied. Particularly unexplored have been the components of the nervous system that lie outside the ectoneural and hyponeural divisions of the main nerve ring and radial nerve cords. We have gathered information on the nervous components of the digestive tract of echinoderms and demonstrate an unexpected level of complexity in terms of neurons, nerve plexi, their location and neurochemistry. The nervous elements within the digestive system consist of a distinct component of the echinoderm nervous system, termed the enteric nervous system. However, the association between the enteric nervous system and the ectoneural and hyponeural components of the nervous system is not well established. Our findings also emphasize the importance of the large lacunae in the neurobiology of echinoderms, a feature that should be addressed in future studies.

On the nervous system of Saccoglossus cambrensis (Enteropneusta)

1952 ◽  
Vol 236 (634) ◽  
pp. 315-354 ◽  
Keyword(s):  
Fine Particles ◽  
Basal Layer ◽  
Superficial Layer ◽  
Nerve Ring ◽  
Cell Nuclei ◽  
Nerve Fibres ◽  
Giant Axons ◽  
Almost Everywhere ◽  
Peristaltic Contractions ◽  
Nerve Cords

A layer of nerve fibres is present almost everywhere at the base of the epidermis. It consists of a very thin basal layer of irregularly arranged fibres, and generally a thicker, more superficial layer of orientated fibres, which forms the main nerve cords and subsidiary systems of smaller through-conducting bundles. In the proboscis there are numerous longitudinal bundles, an anterior nerve ring round the basal periphery and a nerve loop under the pre-oral ciliary organ. The neurocord appears to be a simple conducting tract. In the collar epidermis numerous bundles are formed posteriorly, connecting with the prebranchial nerve ring. In the trunk the size of the longitudinal cords and the distribution of the general plexus is related to the degree of development of the muscles and cilia. The gut is well equipped with nerve fibres anteriorly, where it is particularly muscular. Practically all the nerve-cell nuclei lie outside the plexus of nerve fibres. They are very numerous and widely distributed. A concentration of bipolar neurones (Hess’s cells) occurs at the proboscis tip. Cells regarded as sensory on histological grounds are abundant round the base of the proboscis and in the groove of the ciliary organ. Large unipolar neurones are concentrated in the neurocord, some possessing ‘giant’ axons, which run posteriorly or anteriorly. The cilia of the epidermis are the chief agents of locomotion, those of the trunk being capable of synchronized reversal. They are aided by peristaltic contractions of the longitudinal muscles, which are controlled by the main longitudinal nerve cords. Burrowing peristalsis is controlled by the dorsal nerve cord of the proboscis. Some reactions to light, to the presence of fine particles and to adrenaline are described. The proboscis is necessary for spontaneous and varied activity, but the considerable degree of co-ordination shown is not due to any localized centre but to a longitudinal reflex path involving the main nerve cords. Rapid contractions of the anterior end are probably due to the giant axons. The peculiarities of the neurocord are difficult to interpret, except as a result of degeneration and paedomorphosis. The greater part of the richly nervous epidermis may be compared with the vertebrate neural plate.

Immunocytochemical demonstration of a neuropeptide in Ascaris suum (Nematoda) using an antiserum to FMR Famide

Parasitology ◽  
1988 ◽  
Vol 97 (1) ◽  
pp. 81-88 ◽  
Author(s):  
T. R. B. Davenport ◽  
D. L. Lee ◽  
R. E. Isaac
Keyword(s):  
Central Nervous System ◽  
Nervous System ◽  
Peripheral Nervous System ◽  
Ascaris Suum ◽  
Nerve Ring ◽  
Immunocytochemical Technique ◽  
The Central Nervous System ◽  
Nerve Cords

SUMMARYA FMRFamide-like peptide has been detected in the nematode Ascaris suum, using the peroxidase-anti-peroxidase (PAP) immunocytochemical technique. Positive reactions were obtained in both the central nervous system and the peripheral nervous system of the worm, the strongest reactions being in the anterior nerve ring, the cephalic papillary ganglia, the lateral ganglia and the dorso-rectal ganglion. Immunoreactivity was observed along the length of the main nerve cords of the worm and, to a lesser extent, in the pharyngeal nerve cords. The possible role of this neuropeptide in the physiology of the nematode is discussed.

Immunocytochemical demonstration of neuropeptides in the central nervous system of the roundworm, Ascaris suum (Nematoda: Ascaroidea)

Parasitology ◽  
1993 ◽  
Vol 106 (3) ◽  
pp. 305-316 ◽  
Author(s):  
D. J. A. Brownlee ◽  
I. Fairweather ◽  
C. F. Johnston ◽  
D. Smart ◽  
C. Shaw ◽  
...  
Keyword(s):  
Central Nervous System ◽  
Nervous System ◽  
Peptide Yy ◽  
Ascaris Suum ◽  
Nerve Ring ◽  
Gonadotropin Releasing Hormone ◽  
Releasing Hormone ◽  
Indirect Immunofluorescence Technique ◽  
The Central Nervous System ◽  
Nerve Cords

SUMMARYThe localization and distribution of neuropeptides in the central nervous system of the pig roundworm, Ascaris suum, have been determined by an indirect immunofluorescence technique in conjunction with confocal microscopy. Antisera to 25 vertebrate peptides and two invertebrate peptides were used to screen the worm for immunoreactivity (IR). Immuno-staining was obtained with antisera to pancreatic polypeptide (PP), peptide YY (PYY), neuropeptide Y (NPY), gastrin, cholecystokinin (CCK), substance P (SP), atrial natriuretic peptide (ANP), salmon gonadotropin-releasing hormone (SGnRH), mammalian gonadotropin-releasing hormone (MGnRH), chromogranin A (CGA) and FMRFamide. The most extensive patterns of IR occurred with antisera to PYY, FMRFamide and gastrin. IR was evident in nerve cells and fibres in the ganglia associated with the anterior nerve ring and in the main nerve cords and their commissures; IR to FMRFamide also occurred in the posterior nerve ring. Immunostaining for the other peptides was confined to the nerve cords, with the number of immunoreactive nerve fibres varying from peptide to peptide.

scholarly journals Studies on the Myoneural Physiology of Echinodermata

1955 ◽  
Vol 32 (1) ◽  
pp. 59-69
Author(s):  
WALTER POPLE ◽  
D. W. EWER
Keyword(s):  
Radial Nerve ◽  
Nerve Ring ◽  
Delayed Response ◽  
High Frequencies ◽  
Nerve Tracts ◽  
Synaptic Junctions ◽  
Post Tetanic Potentiation ◽  
Frequency Of Stimulation ◽  
Nervous Conduction ◽  
Delayed Responses

1. The general characteristics of circumoral nervous conduction in Cucumaria have been studied by the use of preparations consisting of the retractor muscles and radial nerves of two adjoining radii joined by a sector of circumoral nerve ring and by the use of similar preparations of all five retractor muscles and the complete circumoral nerve ring. 2. The characteristics of the responses of muscles stimulated by way of circumoral nerve tracts are as follows: the muscles respond with a quick and a delayed response; the magnitude of these responses depends upon the intensity of stimulation applied to an adjoining radial nerve, but is unaffected by frequency of stimulation up to a rate of 10 s./sec.; at high frequencies of stimulation both quick and delayed responses are depressed; the conduction velocity of impulses releasing quick and delayed responses is of the same order; the delayed response may show a prolonged facilitation previously analogized with post-tetanic potentiation. In these characteristics the muscular responses to impulses conducted in the circumoral nerve tracts are similar to those found to impulses conducted in the radial nerve tracts alone. 3. When, in a preparation of the five-retractor muscles, a radial nerve is stimulated, the muscles of radii nearer the stimulated nerve contract more strongly than those of radii further away. 4. Evidence is presented in favour of the view that this ‘decremental’ effect is dependent upon the geometrical arrangement of the fibre tracts in the circumoral nerve. The effect is not dependent upon frequency-sensitive synaptic junctions nor upon proprioceptive relays.

Acetylcholinesterase and synapses in the nervous system of Phocanema decipiens (Nematoda): a histochemical and ultrastructural study

1976 ◽  
Vol 54 (5) ◽  
pp. 752-771 ◽  
Author(s):  
S. L. Goh ◽  
K. G. Davey
Keyword(s):  
Nervous System ◽  
Electron Microscope ◽  
Enzymatic Activity ◽  
Ultrastructural Study ◽  
Neuromuscular Junctions ◽  
Nerve Ring ◽  
Synaptic Contacts ◽  
Longitudinal Nerve ◽  
Specific Inhibitors ◽  
Nerve Cords

The nervous system of Phocanema decipiens was examined histochemically for acetylcholinesterases (EC 3.1.1.7) using the acetylthiocholine method with specific inhibitors (eserine and diisopropylfluorophosphate) and different substrates (butyrylthiocholine and acetylthiocholine). The enzymes, which are localized mainly as small discrete granules, are found in the nerve ring, the six longitudinal nerve cords, and the three pharyngeal nerves. With the electron microscope, these neurons are found to contain presumptive cholinergic synaptic contacts with aggregations of small lucent vesicles in the presynaptic axons. In the nerve ring, such synapses are observed in axoaxonal, neuromuscular and axoglial cell contacts. The longitudinal nerve cords have neuromuscular junctions similar to those observed in other nematodes. In the four sublateral nerve cords, the alternating regions with and without synaptic contacts correspond to the discontinuous histochemical pattern of enzymatic activity. The pharyngeal nerves have axoaxonal and axooesophageal musculature synapses. In most of the synapses, some large dense or dense-core vesicles are found intermingled with the small lucent vesicles. This coexistence of different vesicles is discussed in the light of the cholinergic link hypothesis, whereby acetylcholine is initially released to facilitate the release of other neurotransmitters.

Sensitivity to light and the reactions to changes in light intensity of the Echinoid Diadema Antillarum Philippi

1954 ◽  
Vol 238 (655) ◽  
pp. 187-220 ◽  
Keyword(s):  
Nervous System ◽  
Light Intensity ◽  
Radial Nerve ◽  
Diadema Antillarum ◽  
Entire Surface ◽  
Degree Of Dispersion ◽  
Tube Feet ◽  
Nerve Cords

The reactions of Diadema antillarum to directional illumination and changes in light intensity are described, and the responses of the spines, tube feet and pedicellariae are reviewed, and shown to depend on a process of adjustment, so that light- and dark-adapted phases can be recognized. The responses of the spines to decreases in light intensity are examined in detail and shown to be reflexes, the receptive surface for which extends over the entire surface of the test but not the spines. The degree of sensitivity is correlated with the degree of dispersion of the pigment in superficial melanophores. The areas with most melanin (tube feet and ambulacral margins) are most sensitive, the so-called ‘eyes’ appearing to be least sensitive. The radial nerve cords and their branches appear to be affected by changes in light intensity. No morphologically or histologically differentiated receptors have yet been found, and it is suggested that the nervous system may be influenced directly by light. The findings are reviewed in relation to existing knowledge of the similar phenomena in other animals, and a comparison made between the entire surface of Diadema and certain features of the photoreceptive surface in highly differentiated eyes.

scholarly journals Neuronal Birth Dating in the Radial Nerve Cords of Holothuria glaberrima: A Search For Neurogenesis

2008 ◽  
Vol 22 (S1) ◽  
Author(s):  
Angel Ricardo Maldonado‐Soto ◽  
Jose Enrique San Miguel‐Ruiz ◽  
Jose Enrique Garcia‐Arraras
Keyword(s):  
Radial Nerve ◽  
Holothuria Glaberrima ◽  
Nerve Cords
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