The Nerve-net of Metridium senile: Artifacts and the Nerve-net

1961 ◽  
Vol s3-102 (58) ◽  
pp. 143-156
Author(s):  
E. J. BATHAM ◽  
C.F. A. PANTIN ◽  
E. A. ROBSON
Keyword(s):  
Nervous System ◽  
Nerve Cells ◽  
Muscle Fibres ◽  
Nerve Net ◽  
Metridium Senile ◽  
Staining Methods ◽  
Epithelial Layers

The present paper follows an account of the structure of the nervous system of Metridium senile(L.). Conflicting statements about the actinian nervous system in the earlier literature made it necessary to assess the results of previous workers critically. Several of their methods have now been repeated and compared with our results after using more specific techniques. The criteria for distinguishing nerve-cells from nonnervous elements in actinians are discussed. Mesogloeal fibres, amoebocytes, nematocyst threads, and muscle-fibres may on occasion be confused with nerve-cells, and deteriorating nerve-cells may also have a misleading appearance. Gross artifacts may be reduced by the use of special staining methods, and on the basis of this work the results of several earlier authors have been re-interpreted. It is concluded that the nervous system in the mesenteries and column of Metridium follows the epithelial layers and does not penetrate the mesogloea.

A Comparison of the Nervous Systems of two Sea-Anemones, Calliactis parasitica and Metridium senile

1961 ◽  
Vol s3-102 (59) ◽  
pp. 319-326
Author(s):  
ELAINE A. ROBSON
Keyword(s):  
Methylene Blue ◽  
Nervous System ◽  
Conduction System ◽  
Nerve Cells ◽  
Bipolar Cells ◽  
Retractor Muscle ◽  
Sea Anemones ◽  
Nerve Net ◽  
Metridium Senile ◽  
Calliactis Parasitica

The properties of the actinian nervous system are known mainly from physiological experiments on Calliactis parasitica (Couch), and from histological work on Metridium senile (L.). The structure of the nerve-net in the mesenteries of Calliactis is now shown to resemble in general that in Metridium. Methylene blue stains a network of bipolar cells over the retractor muscle, together with sense-cells, and unlike Metridium, multipolar nerve-cells. The nerve-net over the radial surface of the mesentery is similarly much sparser. The distribution of nerve-cells and sense-cells in the column also resembles that in Metridium. Experiments on Metridium show that as in Calliactis, the rate of conduction in the mesenteries is greater than in other parts of the anemone. The column, including the sphincter region, conducts more slowly. It is thus shown that the presence of a well developed nerve-net over the retractors is associated with the development of fast tracts in the through-conduction system, and of rapid, facilitated contractions of the retractor muscles, in both species of anemone.

scholarly journals The Nerve-Net of the Sea-Anemone Metridium Senile: the Mesenteries and the Column

1960 ◽  
Vol s3-101 (56) ◽  
pp. 487-510
Author(s):  
E. J. BATHAM ◽  
C. F. A. PANTIN ◽  
E. A. ROBSON
Keyword(s):  
Methylene Blue ◽  
Reciprocal Inhibition ◽  
Nerve Cells ◽  
Sea Anemone ◽  
Nerve Net ◽  
Metridium Senile ◽  
Physiological Evidence ◽  
Staining Methods

The actinian nerve-net has been examined in the mesenteries and column of Metridium senile (L.) after staining with silver and with methylene blue. Modified staining methods are described. The synaptic nature of the junctions between bipolar nerve-cells, of their expanded terminations over the muscle-field, and of their contacts with the neurites of sense-cells is reviewed. The neurites always run in the space between the epithelium and underlying muscle. They follow the distribution of the main contractile systems, including the passage of circular fibres beneath the mesenteries. The richerinnervation of the retractor surface of a mesentery compared to the radial is correlated with the ability of this hypertrophied muscle to contract rapidly. The distribution of nerve-cells and sense-cells in the mesenteries and column is related to physiological evidence concerning the through-conduction pathways, facilitated and slow contractions, and other aspects of the behaviour of Metridium. It is concluded that although features such as reciprocal inhibition in the column are still unexplained, there is as yet no histological or physiological evidence for double innervation of the musclesin this anemone. The terminations of sensory neurites, on musclefibres or elsewhere, have not yet been seen in any actinian

The anatomy of the nervous system in the genus Gerris (Hemiptera-Heteroptera)

1961 ◽  
Vol 244 (708) ◽  
pp. 65-102 ◽  
Keyword(s):  
Nervous System ◽  
Close Association ◽  
Muscle Fibres ◽  
Functional Regions ◽  
Corpora Pedunculata ◽  
Staining Methods ◽  
Degree Of Condensation ◽  
The Many ◽  
The One ◽  
Object Of Study

The most successful methods used in this study were Palmgren’s silver-on-the-slide technique, the rapid silver nitrate method of Golgi, and a method that has seldom been applied to insect material, the Golgi-Cox mercuric chloride method. A way of preparing sections of adult hardened insects by infiltrating with wax prior to softening with chlorinated acetic acid and nitric acid was also employed. The nervous system of Gerris shows a high degree of condensation in that all the segmental neuromeres are fused. This characteristic of the nervous system may be associated with the disposition of the one hundred and twenty-two pairs of muscles. The nerves of the head are specialized in association with the complex mouthparts. There are distinct stylet and labral ganglia, and peripheral interconnexions between some of the nerves. The posterior labral nerve was traced to the principal salivary gland. The reticulum described by Baptist (1941) as of a nervous nature was shown to consist of fine muscle fibres: the much finer nerve fibres were also stained in silver preparations. The many separate nerves of the prothorax reflect the unspecialized nature of this segment as compared with the meso- and metathorax in which most of the fibres are gathered into a few nerve trunks. The coalesced neuromeres of the abdominal region give rise to a pair of posterior nerve trunks connected with small ganglia or lateral bodies lying near the spiracles. These ganglia appear similar to the structures described by Landois & Thelen (1867), as controlling spiracular movements in Cossus . Rough estimates of the number of cells in different parts of the nervous system were correlated with the percentage success of staining methods, and specialization of the neuromeres. The form and arrangement of neurones within the optic and protocerebral centres of Gerris conforms for the most part to the patterns worked out in other insects, though there do not seem to be as many different types of internuncial neurone in the optic lobes of Gerris as exist in Apis or Calliphora (Cajal & Sanchez 1915). The corpora pedunculata are connected through a dorsal glomerulus with the deutocerebrum, the glomerulus having the form of a loose meshwork of fine fibres rather than of a distinct calyx. The deutocerebrum is indistinctly divided into anterior and posterior glomeruli, as described in Apis by Sanchez (1936). The form and size of the elements composing the somewhat enigmatic posterior glomerulus in Gerris supports the view that this is a motor centre. The close association between the maxillary and mandibular nerves is to some extent reflected in the internal organization of these neuromeres. Separate ventral areas could be distinguished, but ganglionic boundaries were indistinct. The large labral centre shows many of the features of a trunk ganglion. The pattern of neurones in the thoracic and abdominal centres could be compared in detail with the pattern described by Zawarzin (1924) in the larva of Aeschna . There are three unusually large internuncials with processes in this region, and cell bodies in the protocerebrum and suboesophageal centres. It is suggested that they form part of a dual physiological system controlling the motor centres of the thorax (Roeder 1953). The mesothoracic centre was made a special object of study as representative of the thoracic neuromeres. The fibre tracts are clearly marked and can be seen to correspond to functional regions within the centre. The alary nervous system of the mesothorax was investigated in some detail in both winged and wingless forms of Gerris . In the flying forms dorsal and ventral tracts can be distinguished, associated with motor and sensory regions of the mesothoracic neuropile respectively. In forms without wing muscles or fully developed wings the dorsal tract is absent or vestigial and the ventral tract is clearly reduced. The abdominal neuromeres are very closely compacted so that they tend to lose their identity. The ventral longitudinal tracts are unusually well developed and this may be correlated with the importance of the sensory areas.

The Structure of the Nervous System in Velella

1960 ◽  
Vol s3-101 (54) ◽  
pp. 119-131
Author(s):  
G. O. MACKIE
Keyword(s):  
Nervous System ◽  
Open System ◽  
Closed System ◽  
Silver Staining ◽  
Sensory Cells ◽  
Nerve Fibres ◽  
Nerve Net ◽  
Two Systems ◽  
Staining Methods ◽  
Closed Systems

Silver staining methods have been applied to the nervous system of Velella. Two histologically distinct plexuses are described under the headings ‘open’ and ‘closed’ systems. The open system consists of neurones with fine processes which run for distances of up to 2 mm, retaining their independence ins pite of frequent contacts with other fibres. The fibres of the closed system are large and run together, forming a nerve-net in which neurofibrillar material from different neurones intermingles; it is provisionally to be regarded as a syncytium. A certain type of ‘fibre’ in this system is believed to arise secondarily by the drawing out of adhesion connexions into long strands. Free nerve-endings resembling growing-points occur in both systems. The two systems occur throughout the ectoderm, but in the invaginated ectoderm the open system is poorly developed. The functions of the two systems are not known, but the closed system is probably specialized for through-conduction. Neuro-sensory cells occur in the external ectoderm, making contact with fibres of both open and closed systems. No specialized endings have been found in a muscular region examined. No nerve-rings or centres have been found. Nerves are sparsely distributed in the endoderm, but they lie independently of one another and of ectodermal nerve-fibres crossing the mesogloea between the invaginated and external ectoderm layers.

The Structural and Physiological Nervous Unit

1897 ◽  
Vol 21 ◽  
pp. 182-189
Keyword(s):  
Nervous System ◽  
Sensory Nerve ◽  
Organ Of Corti ◽  
Nerve Cells ◽  
Muscle Fibres ◽  
Sensory Organs ◽  
Nerve Fibres

Up to a comparatively recent date, our conception of the nervous system was that it was built up of nerve cells and nerve fibres, more or less intimately bound together by a peculiar kind of tissue known as neuroglia. It was further supposed that, in the central nervous organs, nerve cells were linked together by processes passing from one cell to another, that sensory nerve fibres passed into, and were in their substance continuous with, nerve cells, and that motor fibres originated in nerve cells, and passed out to muscle fibres. It was also held that the elements of sensory organs, such as the retina or the organ of Corti, were organically connected with nerve cells in the cerebral organs. In short, the nervous system, as a whole, was held to be composed of cells and fibres closely connected together, so that the structure was like a vast web, the size of the meshes of which would vary according to the intricacy of the connections by which the various cellular elements were held together by nerve fibres. These histological conceptions were founded on the microscopical scrutiny of sections prepared by the older methods of hardening and staining, from the time of Lockhart Clarke to nearly the present day.The notions of physiologists, as is usually the case, were more or less in conformity with, and were influenced by, these histological conceptions. Nerve cells were supposed to be excited by nervous impulses, or to originate nervous impulses, and nervous impulses appeared to pass from cell to cell.

The musculature and nervous system of the plerocercoid larva of Dibothriorhynchus grossum (Rud.)

Parasitology ◽  
1941 ◽  
Vol 33 (4) ◽  
pp. 373-389 ◽  
Author(s):  
Gwendolen Rees
Keyword(s):  
Nervous System ◽  
Muscle Mass ◽  
Nerve Cells ◽  
The Body ◽  
Lateral Nerve ◽  
Posterior Median ◽  
The Brain ◽  
Ventral Muscle ◽  
Nerve Cords ◽  
Extrinsic Muscles

1. The structure of the proboscides of the larva of Dibothriorhynchus grossum (Rud.) is described. Each proboscis is provided with four sets of extrinsic muscles, and there is an anterior dorso-ventral muscle mass connected to all four proboscides.2. The musculature of the body and scolex is described.3. The nervous system consists of a brain, two lateral nerve cords, two outer and inner anterior nerves on each side, twenty-five pairs of bothridial nerves to each bothridium, four longitudinal bothridial nerves connecting these latter before their entry into the bothridia, four proboscis nerves arising from the brain, and a series of lateral nerves supplying the lateral regions of the body.4. The so-called ganglia contain no nerve cells, these are present only in the posterior median commissure which is therefore the nerve centre.

scholarly journals Synapsin I (protein I), a nerve terminal-specific phosphoprotein. I. Its general distribution in synapses of the central and peripheral nervous system demonstrated by immunofluorescence in frozen and plastic sections.

1983 ◽  
Vol 96 (5) ◽  
pp. 1337-1354 ◽  
Author(s):  
P De Camilli ◽  
R Cameron ◽  
P Greengard
Keyword(s):  
Nervous System ◽  
Detailed Examination ◽  
Specific Protein ◽  
Nerve Cells ◽  
General Distribution ◽  
Synapsin I ◽  
Nervous Systems ◽  
Synaptic Region ◽  
Specific Localization ◽  
Peripheral Nervous Systems

Synapsin I (formerly referred to as protein I) is the collective name for two almost identical phosphoproteins, synapsin Ia and synapsin Ib (protein Ia and protein Ib), present in the nervous system. Synapsin I has previously been shown by immunoperoxidase studies (De Camilli, P., T. Ueda, F. E. Bloom, E. Battenberg, and P. Greengard, 1979, Proc. Natl. Acad. Sci. USA, 76:5977-5981; Bloom, F. E., T. Ueda, E. Battenberg, and P. Greengard, 1979, Proc. Natl. Acad. Sci. USA 76:5982-5986) to be a neuron-specific protein, present in both the central and peripheral nervous systems and concentrated in the synaptic region of nerve cells. In those preliminary studies, the occurrence of synapsin I could be demonstrated in only a portion of synapses. We have now carried out a detailed examination of the distribution of synapsin I immunoreactivity in the central and peripheral nervous systems. In this study we have attempted to maximize the level of resolution of immunohistochemical light microscopy images in order to estimate the proportion of immunoreactive synapses and to establish their precise distribution. Optimal results were obtained by the use of immunofluorescence in semithin sections (approximately 1 micron) prepared from Epon-embedded nonosmicated tissues after the Epon had been removed. Our results confirm the previous observations on the specific localization of synapsin I in nerve cells and synapses. In addition, the results strongly suggest that, with a few possible exceptions involving highly specialized neurons, all synapses contain synapsin I. Finally, immunocytochemical experiments indicate that synapsin I appearance in the various regions of the developing nervous system correlates topographically and temporally with the appearance of synapses. In two accompanying papers (De Camilli, P., S. M. Harris, Jr., W. B. Huttner, and P. Greengard, and Huttner, W. B., W. Schiebler, P. Greengard, and P. De Camilli, 1983, J. Cell Biol. 96:1355-1373 and 1374-1388, respectively), evidence is presented that synapsin I is specifically associated with synaptic vesicles in nerve endings.

scholarly journals VI. —Anaphylaxis and anaphylatoxins

1923 ◽  
Vol 211 (382-390) ◽  
pp. 273-315 ◽  
Keyword(s):  
Central Nervous System ◽  
Nervous System ◽  
Guinea Pig ◽  
Anaphylactic Shock ◽  
The Body ◽  
Muscle Fibres ◽  
Direct Stimulation ◽  
Fundamental Conception ◽  
The Central Nervous System ◽  
Stimulation Of

In the study of the phenomena of anaphylaxis there are certain points on which some measure of agreement seems to have been attained. In the case of anaphylaxis to soluble proteins, with which alone we are directly concerned in this paper, the majority of investigators probably accept the view that the condition is due to the formation of an antibody of the precipitin type. Concerning the method, however, by which the presence of this antibody causes the specific sensitiveness, the means by which its interaction with the antibody produces the anaphylactic shock, there is a wide divergence of conception. Two main currents of speculation can be discerned. One view, historically rather the earlier, and first put forward by Besredka (1) attributes the anaphylactic condition to the location of the antibody in the body cells. There is not complete unanimity among adherents of this view as to the nature of the antibody concerned, or as to the class of cells containing it which are primarily affected in the anaphylactic shock. Besredka (2) himself has apparently not accepted the identification of the anaphylactic antibody with a precipitin, but regards it as belonging to a special class (sensibilisine). He also regards the cells of the central nervous system as those primarily involved in the anaphylactic shock in the guinea-pig. Others, including one of us (3), have found no adequate reason for rejecting the strong evidence in favour of the precipitin nature of the anaphylactic antibody, produced by Doerr and Russ (4), Weil (5), and others, and have accepted and confirmed the description of the rapid anaphylactic death in the guinea-pig as due to a direct stimulation of the plain-muscle fibres surrounding the bronchioles, causing valve-like obstruction of the lumen, and leading to asphyxia, with the characteristic fixed distension of the lungs, as first described by Auer and Lewis (6), and almost simultaneously by Biedl and Kraus (7). But the fundamental conception of anaphylaxis as due to cellular location of an antibody, and of the reaction as due to the union of antigen and antibody taking place in the protoplasm, is common to a number of workers who thus differ on details.

The Behaviour and Neuromuscular System of Gonactinia Prolifera, A Swimming Sea-Anemone

1971 ◽  
Vol 55 (3) ◽  
pp. 611-640
Author(s):  
ELAINE A. ROBSON
Keyword(s):  
Electrical Stimulation ◽  
Mechanical Stimulation ◽  
Motor Units ◽  
Nerve Cells ◽  
Sea Anemone ◽  
Neuromuscular System ◽  
Sea Anemones ◽  
Nerve Net ◽  
Local Contraction ◽  
Electric Shocks

1. In Gonactinia well-developed ectodermal muscle and nerve-net extend over the column and crown and play an important part in the anemone's behaviour. 2. Common sequences of behaviour are described. Feeding is a series of reflex contractions of different muscles by means of which plankton is caught and swallowed. Walking, in the form of brief looping steps, differs markedly in that it continues after interruptions. Anemones also swim with rapid tentacle strokes after contact with certain nudibranch molluscs, strong mechanical disturbance or electrical stimulation. 3. Swimming is attributed to temporary excitation of a diffuse ectodermal pacemaker possibly situated in the upper column. 4. From the results of electrical and mechanical stimulation it is concluded that the endodermal neuromuscular system resembles that of other anemones but that the properties of the ectodermal neuromuscular system require a new explanation. The size and spread of responses to electric shocks vary with intensity, latency is variable and there is a tendency to after-discharge. There is precise radial localization, for example touching a tentacle or the column causes it to bend towards or away from the stimulus. 5. A model to explain these and other features includes multipolar nerve cells closely linked to the nerve-net which would act as intermediate motor units, causing local contraction of the ectodermal muscle. This scheme can be applied to other swimming anemones but there is no evidence that it holds for sea anemones generally.

The Danger of B12 Deficiency in the Elderly

1998 ◽  
Vol 12 (4) ◽  
pp. 215-226 ◽  
Author(s):  
Margaret Wynn ◽  
Arthur Wynn
Keyword(s):  
Nervous System ◽  
Risk Factor ◽  
Heart Disease ◽  
Vitamin B12 ◽  
Vitamin B12 Deficiency ◽  
Pernicious Anaemia ◽  
The Elderly ◽  
Nerve Cells ◽  
Accelerated Ageing ◽  
B12 Deficiency

Vitamin B12 deficiency damages nerve cells and aggravates nervous system disorders even in the absence of evidence of anaemia. Prevalence of B12 deficiency increases with age especially over 65 and is frequently associated with Alzheimer's disease. Recent American surveys record a higher prevalence of B12 deficiency and of undiagnosed and untreated pernicious anaemia in the elderly than reported earlier. B12 deficiency is also reported to be a risk factor for heart disease, stroke and accelerated ageing.

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