THE FINE STRUCTURE OF MOTOR ENDPLATE MORPHOGENESIS

The fine structure of the developing neuromuscular junction of rat intercostal muscle has been studied from 16 days in utero to 10 days postpartum. At 16 days, neuromuscular relations consist of close membrane apposition between clusters of axons and groups of myotubes. Focal electron-opaque membrane specializations more intimately connect axon and myotube membranes to each other. What relation these focal contacts bear to future motor endplates is undetermined. The presence of a group of axons lying within a depression in a myotube wall and local thickening of myotube membranes with some overlying basal lamina indicates primitive motor endplate differentiation. At 18 days, large myotubes surrounded by new generations of small muscle cells occur in groups. Clusters of terminal axon sprouts mutually innervate large myotubes and adjacent small muscle cells within the groups. Nerve is separated from muscle plasma membranes by synaptic gaps partially filled by basal lamina. The plasma membranes of large myotubes, where innervated, simulate postsynaptic membranes. At birth, intercostal muscle is composed of separate myofibers. Soleplate nuclei arise coincident with the peripheral migration of myofiber nuclei. A possible source of soleplate nuclei from lateral fusion of small cells' neighboring areas of innervation is suspected but not proven. Adjacent large and small myofibers are mutually innervated by terminal axon networks contained within single Schwann cells. Primary and secondary synaptic clefts are rudimentary. By 10 days, some differentiating motor endplates simulate endplates of mature muscle. Processes of Schwann cells cover primary synaptic clefts. Axon sprouts lie within the primary clefts and are separated from each other. Specific neural control over individual myofibers may occur after neural processes are segregated in this manner.

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The fine structure of the cecal epithelium of Megalodiscus temperatus

Canadian Journal of Zoology ◽

10.1139/z73-068 ◽

1973 ◽

Vol 51 (4) ◽

pp. 457-460 ◽

Cited By ~ 10

Author(s):

Gerald P. Morris

Keyword(s):

Fine Structure ◽

Basal Lamina ◽

Secretory Activity ◽

Muscle Cells ◽

Cell Types ◽

Basal Region ◽

Cell Type ◽

Thorium Dioxide ◽

Homogeneous Matrix ◽

Mononucleate Cell

The cecal epithelium of Megalodiscus temperatus (Stafford 1905) contains two cell types. Although the major component of the epithelium is a syncytium there are also isolated, small, mononucleate cells located in the basal region. The mononucleate cells are always in contact with the underlying basal lamina and show no signs of secretory activity. The lumenal surface is extended in the form of numerous long, closely packed, cylindrical microvilli with tapering tips. Each microvillus may be up to 25 μ long and possesses a central fibrillar core. The cytoplasm of the cecal syncytium contains numerous Golgi complexes which produce membrane-delimited granules containing a dense, homogeneous matrix. These granules appear to be releasing their contents either at the lumenal surface or immediately beneath it. The base of the cecal syncytium but not that of the mononucleate cell type is penetrated by numerous projections of underlying muscle cells. No evidence of endocytotic activity by the cecum can be detected by incubation in thorium dioxide.

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The digestive tract of actinotroch larvae (Lophotrochozoa, Phoronida): anatomy, ultrastructure, innervations, and some observations of metamorphosis

Canadian Journal of Zoology ◽

10.1139/z10-075 ◽

2010 ◽

Vol 88 (12) ◽

pp. 1149-1168 ◽

Cited By ~ 14

Author(s):

Elena N. Temereva

Keyword(s):

Fine Structure ◽

Digestive Tract ◽

Basal Lamina ◽

Muscle Cells ◽

Proximal Part ◽

Neurosecretory Cells ◽

Structure And Function ◽

Fine Structure And Function ◽

Phoronopsis Harmeri ◽

And Function

The digestive tract of actinotroch consists of the vestibulum, oesophagus, stomach with stomach diverticulum, midgut, and proctodaeum. Monociliate muscle cells resting on the basal lamina of the oesophagus form its circular musculature. The epithelium of the cardiac sphincter contains axonal tracts and neurosecretory cells. Glandular, secretory, and digestive cells form the epithelium of the stomach and stomach diverticulum. The epithelium of the midgut is biciliate. The proctodaeum is divided into two parts, differing in fine structure and function. Individual serotonian and FMRFamide neurons and fibers occur in the oesophagus, cardiac sphincter, and midgut, as well as surrounding the anus. In larvae of Phoronopsis harmeri Pixell, 1912 during metamorphosis, the larval oesophagus gives rise to the juvenile oesohagus, the upper portion of the stomach stretches and transforms into prestomach, the stomach diverticulum moves into the stomach and then is digested, the larval stomach becomes the juvenile stomach, the midgut gives rise to the pyloric region, and the proctodaeum transforms into the ascending branch of the juvenile digestive tract. The data do not support the views that the proximal part of adult digestive tract forms from the ectodermal epithelium of the dorsal and ventral epidermis of the larva or that the telotroch enters the intestine during metamorphosis.

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Globular and asymmetric acetylcholinesterase in frog muscle basal lamina sheaths.

The Journal of Cell Biology ◽

10.1083/jcb.102.3.762 ◽

1986 ◽

Vol 102 (3) ◽

pp. 762-768 ◽

Cited By ~ 12

Author(s):

M Nicolet ◽

M Pinçon-Raymond ◽

F Rieger

Keyword(s):

Basal Lamina ◽

Acetylcholine Receptors ◽

Muscle Fibers ◽

Frog Muscle ◽

Motor Endplate ◽

Molecular Forms ◽

Nonionic Detergent ◽

Plasmic Membrane ◽

Triton X

After denervation in vivo, the frog cutaneus pectoris muscle can be led to degenerate by sectioning the muscle fibers on both sides of the region rich in motor endplate, leaving, 2 wk later, a muscle bridge containing the basal lamina (BL) sheaths of the muscle fibers (28). This preparation still contains various tissue remnants and some acetylcholine receptor-containing membranes. A further mild extraction by Triton X-100, a nonionic detergent, gives a pure BL sheath preparation, devoid of acetylcholine receptors. At the electron microscope level, this latter preparation is essentially composed of the muscle BL with no attached plasmic membrane and cellular component originating from Schwann cells or macrophages. Acetylcholinesterase is still present in high amounts in this BL sheath preparation. In both preparations, five major molecular forms (18, 14, 11, 6, and 3.5 S) can be identified that have either an asymmetric or a globular character. Their relative amount is found to be very similar in the BL and in the motor endplate-rich region of control muscle. Thus, observations show that all acetylcholinesterase forms can be accumulated in frog muscle BL.

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Human facial muscles: Dimensions, motor endplate distribution, and presence of muscle fibers with multiple motor endplates

The Anatomical Record ◽

10.1002/(sici)1097-0185(199710)249:2<276::aid-ar15>3.0.co;2-l ◽

1997 ◽

Vol 249 (2) ◽

pp. 276-284 ◽

Cited By ~ 57

Author(s):

Wolfgang Happak ◽

Ji Liu ◽

Georg Burggasser ◽

Amanda Flowers ◽

Helmut Gruber ◽

...

Keyword(s):

Muscle Fibers ◽

Motor Endplate ◽

Motor Endplates ◽

Facial Muscles

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The ability of an epithelium to survive removal of the basal lamina by enzymes: Fine structure and content of sodium and potassium of the midgut epithelium of the larva of Tenebrio molitor after withdrawal of the basal lamina by elastase—A short note

Tissue and Cell ◽

10.1016/0040-8166(87)90057-7 ◽

1987 ◽

Vol 19 (1) ◽

pp. 65-70 ◽

Cited By ~ 6

Author(s):

Bodil M. Koefoed

Keyword(s):

Fine Structure ◽

Basal Lamina ◽

Short Note ◽

Tenebrio Molitor ◽

Midgut Epithelium ◽

Sodium And Potassium

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Terminal Schwann cells elaborate extensive processes following denervation of the motor endplate

Journal of Neurocytology ◽

10.1007/bf01206897 ◽

1992 ◽

Vol 21 (1) ◽

pp. 50-66 ◽

Cited By ~ 121

Author(s):

M. L. Reynolds ◽

C. J. Woolf

Keyword(s):

Schwann Cells ◽

Motor Endplate ◽

Terminal Schwann Cells

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Yolk transport in the ovarian follicle of the hen (Gallus domesticus): lipoprotein-like particles at the periphery of the oocyte in the rapid growth phase

Journal of Cell Science ◽

10.1242/jcs.39.1.257 ◽

1979 ◽

Vol 39 (1) ◽

pp. 257-272 ◽

Cited By ~ 1

Author(s):

M.M. Perry ◽

A.B. Gilbert

Keyword(s):

Basal Lamina ◽

Granulosa Cells ◽

Plasma Membranes ◽

Ovarian Follicle ◽

Cell Loss ◽

Coated Vesicles ◽

Morphological Alteration ◽

Tissue Preparation ◽

Very Low Density Lipoproteins ◽

Thin Sections

Thin sections of the oocyte periphery and surrounding granulosa layer from 1–5 day preovulatory follicles were examined by transmission electron microscopy. With the use of certain procedures in tissue preparation, notably the tannic acid method, numerous particles in the range of 15–40 nm with a mean diameter of 27 nm were observed in both extra- and intracellularly. The particles were abundant in the granulosa basal lamina, in the spaces between the granulosa cells and in the perivitelline space. They appeared to adhere to the oolemma as a continuous double layer which was also observed to line the coated vesicles, 200–350 nm in diameter, invaginating from the oolemma. The layer of particles was not found on the plasma membranes of the granulosa cells, nor were particles present within the cells. In the peripheral cytoplasm of the oocyte the yolk spheres, ranging upwards from 250 nm diameter, were membrane-bound and contained tightly packed particles similar to those on the oolemma. Bodies displaying features intermediate between coated vesicles and yolk spheres suggested that, on entry into the cell, loss of the cytoplasmic coat and obliteration of the vesicular lumen gave rise to nascent yolk spheres which then fused together to form the larger spheres. The extracellular layer, coated vesicles and smaller yolk spheres were absent in oocytes fixed after a 10-min delay. The evidence indicated that 27-nm particles were transferred from the basal lamina to the oocyte surface via the intergranulosa cell channels, incorporated into the cell by adsorptive endocytosis and then transferred to the yolk spheres with little morphological alteration. The identity of the particles with very low density lipoproteins, the major components of the yolk solids, was discussed.

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Structure and innervation of the swim bladder musculature in the weakfish, Cynoscion regalis (Teleostei: Sciaenidae)

Canadian Journal of Zoology ◽

10.1139/z82-253 ◽

1982 ◽

Vol 60 (8) ◽

pp. 1955-1967 ◽

Cited By ~ 39

Author(s):

R. Dana Ono ◽

Stuart G. Poss

Keyword(s):

Sarcoplasmic Reticulum ◽

Muscle Fiber ◽

Muscle Fibers ◽

Postsynaptic Membrane ◽

Motor Endplate ◽

Central Core ◽

Swim Bladder ◽

Motor Endplates ◽

Cynoscion Regalis

The striated swim bladder muscles of the weakfish Cynoscion regalis are deep red in color but cannot be classified histologically as having typical red fibers. The muscle fibers are homogeneous and average 29.6 ± 5.3 μm in diameter, one-fifth the diameter of the adjacent hypaxialis fibers. Each muscle fiber contains thin, ribbonlike myofibrils which are radially arranged around a central core of mitochondria, glycogen, and sarcoplasmic reticulum. Myofibrils are extremely regular in pattern. Triads occur at the Z line. Numerous mitochondria and muscle nuclei are located at the periphery of each muscle fiber. The muscle fibers are multiply innervated with motor endplates distributed along their entire lengths. Well-developed folding of the postsynaptic membrane, not previously reported in fishes, is present at the motor endplate.

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