Ultrastructure of the organ of Bellonci in the hypogean isopod Stenasellus virei boui Magniez (Crustacea, Asellota)

1992 ◽  
Vol 70 (1) ◽  
pp. 129-135
Author(s):  
Adriana Pitzalis ◽  
Christian Juberthie
Keyword(s):  
Glial Cells ◽  
Basal Body ◽  
Spatial Arrangement ◽  
Central Core ◽  
Sensory Cells ◽  
The Core ◽  
Ultrastructural Morphology

The ultrastructure of the organ of Bellonci in the hypogean isopod Stenasellus virei boui was investigated. There are two organs located anterodorsally, one on each side of the cephalon. Each organ consists of a wall surrounding a cavity with a central core irregular in shape. The bordering wall contains some glial cells and the inner dendritic segments of 25–28 sensory cells, each one bearing two cilia. Each cilium has a typical 9 + 0 axoneme, a basal body, and a long straight ciliary root that is at a right angle to the basal body; the cilium branches out into tubules that usually contain 1 microtubule, occasionally 2 or more. The ciliary tubules are gathered in three or four long bundles and are not linked to the core. The ciliary connections appear to be both conical and cylindrical. The ultrastructural morphology (polarization of the cilia, spatial arrangement of the bundles and central core) suggests that this organ can record directional stimuli.

The density variation of the earth's central core*

1942 ◽  
Vol 32 (1) ◽  
pp. 19-29
Author(s):  
K. E. Bullen
Keyword(s):  
Pure Iron ◽  
Outer Boundary ◽  
Density Variation ◽  
Central Core ◽  
Good Precision ◽  
Wide Margin ◽  
The Core ◽  
The Earth ◽  
The Mean ◽  
Published Paper

ABSTRACT A detailed analysis of the problem of the earth's density variation has been extended to the earth's central core. It is shown that in the region between the outer boundary of the core and a distance of about 1400 km. from the earth's center the density ranges from 9.4 gm/cm.3 to 11.5 gm/cm.3 within an uncertainty which, if certain general assumptions are true, does not exceed 3 per cent. The density and pressure figures are, moreover, compatible with the existence of fairly pure iron in this part of the earth. The result for the earth's outer mantle as given in a previously published paper, together with those in the present paper, are found to give with good precision the density distribution in a region occupying 99 per cent of the earth's volume. Values of the density within 1400 km. of the earth's center are subject, however, to a wide margin of uncertainty, and there appears to be no means of resolving this uncertainty for the present. The most that can be said is that the mean density in the latter region is greater than 12.3 gm/cm.3 and may quite possibly be several gm/cm.3 in excess of this figure. In the present paper figures are also included for the variation of gravity and the distribution of pressure within the central core. The gravity results are shown to be subject to an appreciable uncertainty except within about 1000 km. of the outer boundary of the core, but the pressure results are expected to be closely accurate at all depths.

scholarly journals THE ULTRASTRUCTURE OF THE SENSORY HAIRS AND ASSOCIATED ORGANELLES OF THE COCHLEAR INNER HAIR CELL, WITH REFERENCE TO DIRECTIONAL SENSITIVITY

1966 ◽  
Vol 29 (3) ◽  
pp. 497-505 ◽  
Author(s):  
Arndt J. Duvall ◽  
Åke Flock ◽  
Jan Wersäll
Keyword(s):  
Guinea Pig ◽  
Hair Cell ◽  
Basal Body ◽  
Organ Of Corti ◽  
Sensory Cells ◽  
Directional Sensitivity ◽  
Inner Hair Cell ◽  
Lateral Line Organ ◽  
Sensory Hairs ◽  
Line Organ

From the apical end of the inner hair cell of the organ of Corti in the guinea pig cochlea protrude four to five rows of stereocilia shaped in a pattern not unlike the wings of a bird. In the area devoid of cuticular substance facing toward the tunnel of Corti lies a consistently present centriole. The ultrastructure of this centriole is similar to that of the basal body of the kinocilium located in the periphery of the sensory hair bundles in the vestibular and lateral line organ sensory cells and to that of the centrioles of other cells. The physiological implications of the anatomical orientation of this centriole are discussed in terms of directional sensitivity.

Paleoeskimo Occupations of Central and High Arctic Canada

1976 ◽  
Vol 31 ◽  
pp. 15-39 ◽  
Author(s):  
Robert McGhee
Keyword(s):  
Temporal Distribution ◽  
High Arctic ◽  
Central Core ◽  
Hudson Bay ◽  
Arctic Canada ◽  
The Core ◽  
The Past ◽  
Archaeological Collections ◽  
Distribution Of Components ◽  
Cultural Discontinuities

Most of our knowledge regarding the Paleoeskimos of Arctic Canada is derived from the “core area” of Paleoeskimo occupation, a rough circle of some 1,000 km diameter including the coasts of Fury and Hecla Strait, Hudson Bay, and Hudson Strait. This is the area in which Dorset culture was first recognized, the source of most of our larger collections, and the area where continuity of development throughout the Paleoeskimo sequence has been demonstrated (Meldgaard 1962; Taylor 1968a; Maxwell 1973). The number and size of archaeological collections from this area suggest that it supported a larger Paleoeskimo population than did other regions of Arctic Canada, while the temporal distribution of components and continuities of style suggests that the region was occupied continuously throughout the Paleoeskimo period.In the fringe areas surrounding this central core, continuous occupation has not yet been demonstrated through any major segment of the Paleoeskimo sequence. Work in these fringe areas has rapidly progressed during the past decade, and it now seems certain that most of the temporal gaps and cultural discontinuities are not the result of poor archaeological sampling but reflect a situation of sporadic occupation occurring at different times in different regions. One of the striking features of the Paleoeskimo population was its propensity for expanding and retracting its geographical range, and this is the phenomenon which this paper will attempt to document. The primary aim of the paper is to sort out who lived where and when; a secondary aim is to suggest how they may have got there and what happened to them.

scholarly journals Multifrequency Study of Periodic Nulling and Subpulse Drifting in Pulsar J2048−1616

2021 ◽  
Vol 923 (2) ◽  
pp. 259
Author(s):  
Z. Wang ◽  
Z. G. Wen ◽  
J. P. Yuan ◽  
N. Wang ◽  
J. L. Chen ◽  
...  
Keyword(s):  
Spectral Analysis ◽  
Radio Telescope ◽  
Pulse Sequences ◽  
Single Pulse ◽  
Central Core ◽  
Central Component ◽  
Pulse Emission ◽  
Physical Mechanisms ◽  
The Core ◽  
Fluctuation Rate

Abstract We have carried out a detailed study of single-pulse emission from the pulsar J2048−1616 (B2045−16), observed at 732, 1369, and 3100 MHz frequencies using the Parkes 64 m radio telescope. The pulsar possesses three well-resolved emission components, with the central component resembling core emission. The single pulses show the presence of two distinct periodic modulations using fluctuation spectral analysis. About 12% nulls are found to create alternating bunches of nulls and bursts in a quasiperiodic manner with longer periodicities of 83, 28, and 14 rotational periods for simultaneous observations at 732 and 3100 MHz. At 1369 MHz, the quasiperiodic nulling is detected, as well, to modulate across the entire profile both in the core and conal components simultaneously with a fluctuation rate of about 50 rotational periods, and the nulling fraction is estimated to be around 10%. Additionally, the quasiperiodic modulations are significantly dependent on time. In addition to nulling, the pulsar also presents subpulse drifting in the single-pulse sequences with shorter periodicity. The subpulse drifting is presented in the conal components and is absent in the central core emission. The leading component is modulated in longitude with a period of three pulses. The trailing component remains phase stationary within the pulse window but periodically modulates in amplitude with a period of three pulses. Finally, possible physical mechanisms are discussed.

Photoinactivation of the giant neuropil glial cells in the leech Hirudo medicinalis: effects on neuronal activity and synaptic transmission

1996 ◽  
Vol 76 (5) ◽  
pp. 2861-2871 ◽  
Author(s):  
J. Schmidt ◽  
J. W. Deitmer
Keyword(s):  
Synaptic Transmission ◽  
Glial Cells ◽  
Neuronal Activity ◽  
Lucifer Yellow ◽  
Hirudo Medicinalis ◽  
Membrane Properties ◽  
Sensory Cells ◽  
Chemical Synapse ◽  
Segmental Ganglion ◽  
Retzius Cells

1. We studied the effects of photoinactivation of neuropil glial (NG) cells of the leech Hirudo medicinalis on neuronal activity and synaptic transmission. Each segmental ganglion contains two of these giant glial cells, which are electrically and dye coupled. 2. One of the two NG cells in an isolated segmental ganglion was filled with the dye Lucifer yellow (LY). Subsequent irradiation of the ganglion with laser light (440 nm) to photolyze LY caused irreversible depolarization of both NG cells. The NG cells that were filled with LY depolarized from -73 +/- 1.1 (SE) mV to -22 +/- 2.4 mV within 25 +/- 2.8 min of continuous irradiation (n = 22). The other NG cell, which was not directly filled with LY, depolarized with some delay. 3. Photoinactivation of the NG cells caused an irreversible depolarization of Retzius neurons and noxious (N) sensory cells by a mean of 14 mV (n = 36) and 9 mV (n = 24), respectively. In addition, the input resistance was reduced by 54% in Retzius cells and by 34% in N cells. Spikes could not be evoked in Retzius cells after the inactivation of the NG cells, either by intracellular current injection or by electrical nerve stimulation. Similarly, anterior pagoda neurons, annulus erector neurons, and the excitor neurons of the ventrolateral circular muscles became inexcitable. However, N cells, heart interneurons, and most of the heart motor neurons, touch cells, and pressure cells could still generate spontaneous or evoked action potentials. 4. Photoinactivation of the NG cells impaired the electrical connection between the two Retzius neurons. The electrical coupling was completely eliminated in six of eight cell pairs and reduced by 66% in two others. 5. Photoinactivation of the NG cells in the 3rd and 4th segmental ganglion caused a complete block of the chemical synapse between reciprocal inhibitory heart interneurons in these ganglia; the bursting rhythm either stopped or changed to a tonic activity, whereas inhibitory postsynaptic potentials could not be recorded in either heart interneuron anymore. 6. Laser irradiation alone had no effect on neuronal activity and synaptic transmission. Addition of glutathione (10 mM) and ascorbic acid (10 mM) to the saline to bind extracellular radicals that might be produced by the irradiation did not suppress the effects caused by photoinactivation of NG cells. 7. Elevation of bath K+ concentration to 12 mM, acidification of the saline to pH 5.5, and alkalinization to pH 8.5 for 6 min each did not mimick the effects on membrane properties of Retzius cells as produced by inactivation of NG cells. The results suggest some role of glial cells in the maintenance of neuronal activity and electrical and chemical synaptic transmission.

scholarly journals On the Primary Importance of Pulsars with Five-Component Profiles

1992 ◽  
Vol 128 ◽  
pp. 195-200 ◽  
Author(s):  
Joanna M. Rankin
Keyword(s):  
Central Core ◽  
Emission Region ◽  
Physical Parameters ◽  
Core Component ◽  
The Core ◽  
Component Class

AbstractSome 15 members of the class of profiles with five components have been identified. These profiles have a central core component and two pairs of conal outriders, thus exhibiting the highest degree of formal complexity observed. No good examples of pulsars with six or more profile components are known.Members of the five-component class have very similar physical parameters and emission-region geometries. An analysis of their emission geometry indicates both that the core and conal beams scale as P–1/2 and that the 1-GHz conal emission comes from a height of some 100-200 km.

scholarly journals Early evolution of radial glial cells in Bilateria

2017 ◽  
Vol 284 (1859) ◽  
pp. 20170743 ◽  
Author(s):  
Conrad Helm ◽  
Anett Karl ◽  
Patrick Beckers ◽  
Sabrina Kaul-Strehlow ◽  
Elke Ulbricht ◽  
...  
Keyword(s):  
Nervous System ◽  
Glial Cells ◽  
Radial Glia ◽  
Early Evolution ◽  
Sensory Cells ◽  
Last Common Ancestor ◽  
Radial Glial Cells ◽  
Antibody Staining ◽  
Transmission Electron ◽  
Radial Glial

Bilaterians usually possess a central nervous system, composed of neurons and supportive cells called glial cells. Whereas neuronal cells are highly comparable in all these animals, glial cells apparently differ, and in deuterostomes, radial glial cells are found. These particular secretory glial cells may represent the archetype of all (macro) glial cells and have not been reported from protostomes so far. This has caused controversial discussions of whether glial cells represent a homologous bilaterian characteristic or whether they (and thus, centralized nervous systems) evolved convergently in the two main clades of bilaterians. By using histology, transmission electron microscopy, immunolabelling and whole-mount in situ hybridization, we show here that protostomes also possess radial glia-like cells, which are very likely to be homologous to those of deuterostomes. Moreover, our antibody staining indicates that the secretory character of radial glial cells is maintained throughout their various evolutionary adaptations. This implies an early evolution of radial glial cells in the last common ancestor of Protostomia and Deuterostomia. Furthermore, it suggests that an intraepidermal nervous system—composed of sensory cells, neurons and radial glial cells—was probably the plesiomorphic condition in the bilaterian ancestor.

Comparison of central core and radially separated models of renal inner medulla

1995 ◽  
Vol 268 (4) ◽  
pp. F693-F697 ◽  
Author(s):  
J. F. Jen ◽  
H. Wang ◽  
R. P. Tewarson ◽  
J. L. Stephenson
Keyword(s):  
Mathematical Model ◽  
Partition Coefficient ◽  
Collecting Duct ◽  
Radial Diffusion ◽  
Central Core ◽  
Core Model ◽  
Continuous Transition ◽  
The Core ◽  
Vascular Space ◽  
Renal Inner Medulla

In this paper we describe the effect of partitioning exchange of ascending thin limb (ATL) and collecting duct (CD) between a central vascular space (CORE) and a radially separated capillary node (NODE) in a mathematical model of the concentrating mechanism of the renal inner medulla. A detailed description of the model has been provided [J. L. Stephenson, J. F. Jen, H. Wang, and R. P. Tewarson. Am. J. Physiol. 268 (Renal Fluid Electrolyte Physiol. 37): F680–F692, 1995]. We define a partition coefficient theta, which denotes the fractional exchange of CD and ATL with the NODE. Thus with theta = 0 we have a central core model, in which the ATL and CD exchange with the CORE only, and with theta = 1 we have a totally radially separated model, in which the ATL and CD exchange with the NODE only. Decreasing the partition coefficient from 1 to 0 effects a continuous transition from a totally radially separated model to a central core model. As this transition progresses with increasing exchange with the CORE, the osmolalities in all structures become nearly the same at the papilla, and the ability to transport salt uphill is lost. This is true even with no radial diffusion. However, radial diffusion and direct exchange with the CORE act synergistically in decreasing osmolality differences at the papilla and the capacity for convective uphill transport. These are lost in a more or less parallel way. There is, however, no significant concomitant change in concentrating ability. These results indicate that models with radial mixing of the interstitial vascular space are probably reasonably good approximations for the inner medulla.

scholarly journals A model for PSR J0437-4715

1996 ◽  
Vol 160 ◽  
pp. 213-214
Author(s):  
Janusz Gil ◽  
Agnieszka Krawczyk
Keyword(s):  
Magnetic Axis ◽  
Central Core ◽  
Polar Cap ◽  
Pulsar Emission ◽  
The Core ◽  
First Case ◽  
Central Column ◽  
The Mean ◽  
Multiple Component ◽  
Real Challenge

We present the modelling results of full polarization data of the PSR J0437-4715, recently published by Manchester & Johnston (1995). This pulsar presents a real challenge for pulsar modelling because of seven clear components in its mean profile. In terms of the conal model of pulsar emission this is the first case indicating three distinct cones surrounding the central core beam. We have attempted to model this pulsar and obtained a very satisfactory fit to the data. We succeded to reproduce the complexities of the multiple component profile and polarization properties.To model the radiation from PSR J0437-4715 we use the method presented in Gil et al. (1995 and references therein). We assume that subpulses in single pulses correspond to the subpulse-associated plasma columns distributed within the overall pulsar beam. Each column represents a gaussian intensity distribution. These columns rotate more or less regularly around the magnetic axis. The exception is the central column directed almost along the magnetic axis defined by the local surface magnetic pole. This column corresponds to the core beam and consequently to the core component in our model. Outer columns rotating at some distances from the core axis will form a number of coaxial conal beams corresponding to the conal profile components. Figure 1a represents a projection of the subpulse-associated columns onto the polar cap while Fig. lb represents schematically a corresponding multiconal structure of the average beam. The initial positions, the characteristic dimensions and the relative amplitudes of the subpulse spots (Fig. 1a) have been estimated from the mean profile (Fig. 2b). We assume that the subpulse spots are separated from each other by distances comparable with their sizes (Fig. 1a). The very large polar cap with the radiusrp= 1.4 · 104P−1/2cm ≈ 1900 m as compared with the characteristic subpulse spot dimensionD≈ 300 m allows three conal rings surrounding the central core beam (Fig. 1b).

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