scholarly journals FINE STRUCTURE AND MORPHOGENIC MOVEMENTS IN THE GASTRULA OF THE TREEFROG, HYLA REGILLA

1965 ◽  
Vol 24 (1) ◽  
pp. 95-116 ◽  
Author(s):  
Patricia C. Baker
Keyword(s):  
Fine Structure ◽  
Granular Material ◽  
Cell Body ◽  
Dense Layer ◽  
Intercellular Spaces ◽  
Hyla Regilla ◽  
Mesodermal Cell ◽  
Nucleus Plus ◽  
Distal Surface ◽  
Contraction And Expansion

The blastoporal groove of the early gastrula of the treefrog, Hyla regilla, was examined with the electron microscope. The innermost extension of the groove is lined with invaginating flask- and wedge-shaped cells of entoderm and mesoderm. The distal surfaces of these cells bear microvilli which are underlain with an electron-opaque layer composed of fine granular material and fibrils. The dense layer and masses of vesicles proximal to it fill the necks of the cells. In flask cells bordering the forming archenteron the vesicles are replaced by large vacuoles surrounded by layers of membranes. The cells lining the groove are tightly joined at their distal ends in the region of the dense layer. Proximally, the cell bodies are separated by wide intercellular spaces. The cell body, which is migrating toward the interior of the gastrula, contains the nucleus plus other organalles and inclusions common to amphibian gastrular cells. A dense layer of granular material, vesicles, and membranes lies beneath the surface of the cell body and extends into pseudopodium-like processes and surface undulations which cross the intercellular spaces. A special mesodermal cell observed in the dorsal lining of the groove is smaller and denser than the surrounding presumptive chordamesodermal cells. A long finger of cytoplasm, filled with a dense layer, vesicles and membranes, extends from its distal surface along the edge of the groove, ending in a tight interlocking with another mesodermal cell. Some correlations between fine structure and the mechanics of gastrulation are discussed, and a theory of invagination is proposed, based on contraction and expansion of the dense layer and the tight junctions at distal cell surfaces.

scholarly journals THE AXON HILLOCK AND THE INITIAL SEGMENT

1968 ◽  
Vol 38 (1) ◽  
pp. 193-201 ◽  
Author(s):  
Sanford L. Palay ◽  
Constantino Sotelo ◽  
Alan Peters ◽  
Paula M. Orkand
Keyword(s):  
Plasma Membrane ◽  
Fine Structure ◽  
Granular Material ◽  
Internal Structure ◽  
Electron Micrographs ◽  
Initial Segment ◽  
Special Function ◽  
Structural Features ◽  
Dense Layer ◽  
Axon Hillock

Axon hillocks and initial segments have been recognized and studied in electron micrographs of a wide variety of neurons. In all multipolar neurons the fine structure of the initial segment has the same pattern, whether or not the axon is ensheathed in myelin. The internal structure of the initial segment is characterized by three special features: (a) a dense layer of finely granular material undercoating the plasma membrane, (b) scattered clusters of ribosomes, and (c) fascicles of microtubules. A similar undercoating occurs beneath the plasma membrane of myelinated axons at nodes of Ranvier. The ribosomes are not organized into Nissl bodies and are too sparsely distributed to produce basophilia. They vanish at the end of the initial segment. Fascicles of microtubules occur only in the axon hillock and initial segment and nowhere else in the neuron. Therefore, they are the principal identifying mark. Some speculations are presented on the relation between these special structural features and the special function of the initial segment.

The Function and Fine Structure of the Cephalic Airflow Receptor in Schistocerca Gregaria

1966 ◽  
Vol 1 (4) ◽  
pp. 463-470
Author(s):  
D. M. GUTHRIE
Keyword(s):  
Fine Structure ◽  
Cell Body ◽  
Schistocerca Gregaria ◽  
Tube Wall ◽  
Sense Organ ◽  
Hair Shaft ◽  
Sensory Axons ◽  
Steady Rate ◽  
Neuron Cell Body ◽  
Tormogen Cell

Electron micrographs of parts of the sense organ showed that the dendritic axis consisted of a large and a small envelope containing microtubules as their main inclusion. The envelopes are supported by a thick-walled tube believed to be part of the Ist-tier sheath cells. The small envelope is segregated from the large envelope near its apex by a fold of the tube wall. The packing of the neurotubular array within the small envelope is both more dense and more regular than within the large envelope. The tube is separated by an extracellular space from the trichogen-tormogen cell. Sections through the apex of the dendrite reveal a homogeneous cap unlikely to be part of a structure continued into the upper region of the hair shaft. No ciliary structures were visible within the dendrite, whose microtubules pass into the neuron cell body proximally. Sections through the neuron cell body reveal branched mitochondria, and numerous microtubules. Rates of discharge in sensory axons from these hair organs produced by deflexion of the hair shaft were found to be within the range 300-100 impulses/sec. There is an initial phase of rapid adaptation which gives place to a steady rate. It is suggested that the fine structure of the receptor may indicate mechano-electrical transduction at a more proximal level than is believed to be the case in some other types of receptor. The diaphragms that support the hair shaft laterally can be seen to be composed of fine cuticular strands.

scholarly journals Inversion of force lines in fiber-reinforced jammed granular material

2021 ◽  
Vol 44 (4) ◽  
Author(s):  
Pavel S. Iliev ◽  
Falk K. Wittel ◽  
Hans J. Herrmann
Keyword(s):  
Fine Structure ◽  
Granular Material ◽  
Fiber Reinforced ◽  
Dynamic Simulations ◽  
Contact Networks ◽  
Particle Contact ◽  
Rigid Particles

Abstract Freestanding columns, built out of nothing but loose gravel and continuous strings can be stable even at several meters in height and withstand vertical loads high enough to severely fragment grains of the column core. We explain this counter-intuitive behavior through dynamic simulations with polyhedral rigid particles and elastic wire chains. We evaluate the fine structure of the particle contact networks, as well as confining forces and reveal fundamental intrinsic differences to the well-studied case of confining silos. Graphic abstract

Fine Structure of the Hindgut of Armadillidium Vulgare

1971 ◽  
Vol 29 ◽  
pp. 414-415
Author(s):  
Laura Herold ◽  
G. M. Vernon ◽  
E. R. Witkus
Keyword(s):  
Fine Structure ◽  
Epithelial Cell ◽  
Cell Layer ◽  
The Other ◽  
Apical Region ◽  
Luminal Surface ◽  
Intercellular Spaces ◽  
Armadillidium Vulgare ◽  
Epithelial Cell Layer ◽  
Peripheral Cytoplasm

An ultrastructural study of the hepatopancreatic ducts and the hindgut of the terrestrial isopod, Armadillidium vulgare, reveals the presence of a single epithelial cell layer lined with cuticle. The cells of the duct lack the microvilli characteristic of the hepatopancreas and exhibit fewer apical infoldings than the cells of the hindgut. Basal infoldings, on the other hand, are common and relatively deep. Mitochondria are more abundant in the apical region of the cell than in the basal part. Bands of microtubules are present in the peripheral cytoplasm, and most of the microtubules run vertically in the cell from the luminal surface to the base (see fig. 1). Single membrane bounded vesicles of varying size were observed. These bodies contain moderately electron dense granular material. At the luminal surface the lateral membranes of adjacent cells are linked together by septate desmosomes. From the septate desmosome to the base of the cell there are relatively large intercellular spaces alternating with intermediate junctions or zona adherens.

Movement, Fine Structure, and Fusion of Pseudopods of an Enclosed Amoeba, Difflugiella Sp

1972 ◽  
Vol 10 (2) ◽  
pp. 563-583
Author(s):  
J. L. GRIFFIN
Keyword(s):  
Fine Structure ◽  
Cell Body ◽  
Activity Cycle ◽  
Different Types ◽  
Anterior Extension

In Difflugiella sp., strain F-20, a small amoeba enclosed in a flexible mantle, pseudopods extended through a mouth or aperture and seemed to function only for movement and feeding. Pseudopods from different cells fused on contact and cell clumps shared common pseudopods and moved in a co-ordinated way. During locomotion, pseudopods or pseudopod complexes usually exhibited an activity cycle of 3 phases: anterior extension with the tip firmly adhering; stable hold as other pseudopods advanced; and flaccid posterior retraction. While distal adhesive tips advanced, proximal unattached parts of pseudopods simultaneously shortened as the cell body advanced. Microtubules were numerous in pseudopods within the mouth but extended for only 1-2 µm into pseudopods up to 20-30 µm long. Microfilaments were present where pseudopods adhered to the substratum, to the mantle, or to bacteria and were also associated with pinocytotic invaginations. Pseudopod ground plasm was either reticulate or amorphous; no axial rods or aligned filaments related to pseudopod rigidity were seen. Simultaneous pseudopod adhesion, extension, and proximal shortening apparently account for locomotion or cell body translation of Difflugiella. While some similarities to other amoeboid systems were noted, the need for detailed studies on different types of organisms or cells is emphasized.

The behavior of chick gastrula mesodermal cells under the unidirectional tractive force parallel to the substrata

1995 ◽  
Vol 108 (2) ◽  
pp. 557-567 ◽  
Author(s):  
R. Toyoizumi ◽  
S. Takeuchi
Keyword(s):  
Cell Body ◽  
Magnetic Force ◽  
Single Cells ◽  
Attachment Site ◽  
Leading Edge ◽  
Time Lapse ◽  
Tractive Force ◽  
Citrate Buffer ◽  
Mesodermal Cell ◽  
Significance Level

Advancement of leading lamellae of a migratory cell inevitably causes a strain inside the cell body. We investigated the effect of the tension arisen inside a mesodermal cell on its behavior by pulling the cell body unidirectionally along the substratum. Chick gastrula mesodermal cells, known as highly migratory, were dissociated into single cells in sodium citrate buffer, conjugated with paramagnetic beads activated by tosyl-residue (4.5 microns in diameter) and seeded onto coverglasses coated with fibronectin. After the cells spread on the substratum and protruded cellular processes in all directions, they were exposed to a non-uniform magnetic field by a magnet. Thus the cells bearing the beads were pulled with a force in the order of 10(−10) N. The behavior of such cells was recorded with a time-lapse video taperecorder and assessed quantitatively. Shortly after the magnetic force was applied, the beads stuck to the cells were aligned in tandem along the line of magnetic force at the site for the magnet. Subsequently, they frequently came to extend their leading lamella precisely counter to the traction on the line of the beads. Observation with scanning electron microscope revealed that a large part of the beads attached to the cells were wrapped in the cell membrane. In this condition, the cells were stretched locally between the attachment site of the beads and adhesion plaques beneath the leading edge, which was formed in a direction away from the traction. It was proved statistically that such cells tended to locomote away from the magnet at the 0.1% significance level with Hotelling's T2-test. In contrast, the mesodermal cells free of the artificial traction in three kinds of control experiments did not show such a preference in the direction of locomotion. These results proved that migratory cells tended to move in the direction away from the tractive force parallel to the substratum, suggesting that advancement of a leading lamella is accelerated when it is stretched along the direction of projection by a mechanical force of sufficient strength. Implication of this finding to the mechanism of cell locomotion will be discussed.

Some Aspects of the Cytology of Polycelis nigra

1961 ◽  
Vol s3-102 (59) ◽  
pp. 295-317
Author(s):  
R. J. SKAER
Keyword(s):  
Fine Structure ◽  
Epithelial Cells ◽  
Basement Membrane ◽  
Muscle Fibre ◽  
Cell Body ◽  
Basal Body ◽  
Sense Organs ◽  
Gland Cells ◽  
Secretion Granules ◽  
Undifferentiated Cells

The triclad, Polycelis nigra, has been found to be fully cellular. Gland-cells, undifferentiated cells, and the cell-bodies of muscle-cells, make up the parenchyma. The fine structure of the component cells of the parenchyma, nervous, and excretory systems, testis, pharynx, and epidermis is described. Acidophil secretion granules, produced by certain parenchymatous gland-cells, have a characteristic, doubly-banded ultrastructure which is not invariably associated with the property of adhesiveness. The parenchymatous cell-body of the muscles is often up to 10 µ. from the musclefibre, to which it is joined by tenuous cytoplasmic connexions. The muscle-fibre itself consists of coarse and fine sets of hexagonally arranged myofilaments, but is unhanded. The basement membrane of the epidermis is composed of fine, banded fibrils, apparently randomly arranged in the plane of the membrane. Permeating the epidermis at a level just above the basement membrane is a system of extracellular spaces, which may have a hydrostatic function and assist in the extrusion of secretion granules. Epidermal sense organs, whose fine structure resembles the basal body of the cilia, are considered to have a functionally significant distribution on the surface of the animal. The rhabdites have been shown to develop in special cells of the parenchyma. Such rhabdite-forming cells, together with their contained rhabdites, have been found apparently passing through the basement membrane of the epidermis. As all the epidermal epithelial cells contain rhabdites, it is suggested that the epidermis as a whole is renewed by centrifugal migration of rhabdite-forming cells. The rhabdites themselves appear to consist of arginine and some tyrosine, together with a purine, probably adenine. They may be an excretory product.

Fine structure of Tyloses in three species of the Myrtaceae

1967 ◽  
Vol 15 (1) ◽  
pp. 25 ◽  
Author(s):  
RC Foster
Keyword(s):  
Fine Structure ◽  
Granular Material ◽  
Double Layer ◽  
Layered Structure ◽  
Outer Layer ◽  
Secondary Wall ◽  
Pit Membrane ◽  
Ray Cell

The tylosis wall in Eucalyptus obliqua L'Herit. is shown to be composed of two microfibrillar layers. The outer layer (T1), with randomly orientated microfibrils, is covered with amorphous granular material. The inner layer (T2) is multilamellate. In sclerosed tyloses of E. miniata A. Cunn., each lamella of T2 is composed of many layers of microfibrils. Simple pits, delineated by circumferentially orientated microfibrils, are found in both sclerosed and non-sclerosed tyloses. The tylosis in E. obliqua is shown to arise from a two-layered structure formed within the secondary wall of the ray cell. This layer extends into the pit chamber, covering the pit membrane on the ray side. Following the breakdown of the vestures and the pit membrane, this double layer bulges out into the vessel to form the tylosis.

Ultrastructural Analysis Of The Aseptate Gregarine Pterospora, A Parasite of The Bamboo Worm Axiothella Mucosa.

1999 ◽  
Vol 5 (S2) ◽  
pp. 1274-1275
Author(s):  
Stephen C. Landers
Keyword(s):  
Fine Structure ◽  
Cell Body ◽  
Cytoplasmic Streaming ◽  
The Body ◽  
Ultrastructural Analysis ◽  
State University ◽  
University Campus ◽  
Sodium Cacodylate ◽  
Main Cell

The gregarine Pterospora is a parasite found in the body cavities of bamboo worms (Polychaeta: Maldanidae). The gamont stage of Pterospora has a bizarre structure with a main cell body and multiple posterior cytoplasmic extensions (Fig. 1). The cells are found in pairs within the coelom of the host and move by cytoplasmic streaming as they fill and empty their posterior extensions. Reports of this parasite in the literature are few (see references 1 & 2 for a review) and no ultrastructural details have been published regarding the genus. This study examines the fine structure of the gamont stage with particular emphasis on the structure of the pellicle.The maldanid worm Axiothella mucosa was collected by shovel in St. Andrew Bay, Florida and returned to the Troy State University campus. Pterospora spp. gamonts were pipetted from minced setigers of the worms and fixed in 3% glutaraldehyde buffered with 0.05M sodium cacodylate, pH 7.5, for 1-6 hours.

Sign in / Sign up

Export Citation Format

Share Document