ISSN:0741-0581    

DOI:10.1002/jemt.1060150202

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractThe cochleas of four human fetuses ranging 22–25 weeks gestation were studied by scanning electron microscopy (SEM) for the purpose of obtaining a better understanding of the nerve fiber arrangement in the human ear. After critical point drying, the specimens were dissected and the floor of the tunnel of Corti and the outer wall of Nuel's space were exposed for observation. Upper cochlear turns, especially the apical turn, seemed to be still immature.Observed nerve fibers were classified into three types:1Spiral fibers: Fibers traveling basalward and following the shape of the cochlea were found in both the tunnel of Corti and Nuel's space and believed to be the afferent nerves responsible for innervating the outer hair cells2Radial fibers: radiating outward from the osseous spiral lamina—one such radial fiber transversing high in the tunnel space (supposedly the efferent nerve servicing the outer hair cells), and another sort of radial fiber (found crossing the tunnel floor), the nature of which was uncertain.3Irregular fibers: Consisting of thin, randomly running fibers within the cochlea. The destination of these fibers was not determined, but possibly they represent transitory nerve branchings of afferent or more probably efferent nerves, which would later regress during maturat

ISSN:0741-0581    

DOI:10.1002/jemt.1060150203

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractThis paper brings together the most recent findings concerning the development of human fetus cochlear hair cells, as observed using transmission and scanning electron microscopy (TEM and SEM). Specific attention is drawn to the formation of synapses and the growth of stereocilia. In both types of hair cells, synaptogenesis begins before ciliogenesis (week 10 of gestation versus week 12). In the inner hair cell (IHC), an adultlike stage is seen around week 15 for synapses, but not before week 22 for stereocilia. In the outer hair cell (OHC), both synapses and stereocilia are not yet fully mature at week 22. Classic gradients of maturation are found: a base‐to‐apex gradient, and an IHC‐to‐OHC gradient. By comparing these results with the anatomical and functional data on cochlear development in laboratory mammals, the onset of cochlear function in the human fetus can be estimated to occur around week 18. The completion of cochlear maturation based upon the same anatomical criteria should occur about 10 week

ISSN:0741-0581    

DOI:10.1002/jemt.1060150204

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractWe have compared the biochemical expression of cholinergic enzymes with the morphological differentiation of efferent nerve fibers and endings in the cochlea of the postnatally developing mouse. Choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) are present in the newborn cochlea at specific activities 63% and 25%, respectively, of their mature levels. The relative increases in ChAT, in AChE, and in its molecular forms over the newborn values start about day 4 and reach maturity by about day 10. The biochemical results correlate well with the massive presence of nerve fibers stained immunocytochemically for ChAT and AChE or enzymatically for AChE in the inner and outer hair cell regions. Ultrastructural studies, however, indicate the presence of only few vesiculated fibers and endings in the inner and outer hair cell regions. The appearance of large, cytologically mature endings occurs only toward the end of the third postnatal week. The discrepancy may be resolved in the electron microscope using the enzymatic staining for AChE. Labeling is seen on many nonvesiculated fibers and endings in the hair cell regions, suggesting that the majority of the efferent fibers in the perinatal organ may be biochemically differentiated but morphologically immature. The results may imply that the efferents to inner and outer hair cells develop earlier than indicated by previous ultrastructural studies. Moreover, the pattern of development suggests that in the cochlea, as in other tissues, the biochemical differentiation of the efferent innervation may precede the morphological maturation.

ISSN:0741-0581    

DOI:10.1002/jemt.1060150205

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractThe development of the spiral ganglion in the cat, the rat, and the mouse was studied by electron microscopy, from fetal stages in the cat and from birth in the rodent. In the earliest stages, a single population of ganglion cells is present. Immature spiral ganglion neurons possess small perisomatic processes that seem to disappear with development, before the myelination ganglion cells are surrounded by one or two layers of Schwann cell processes. With maturation, the Schwann process increases in number around the perikaryon and its processes, which leads to the onset of myelination. The onset of myelination of the cell body processes is asynchronous. The perikaryon may be delayed in myelination by several days. Moreover, ganglion neurons from a given region of the cochlea do not myelinate simultaneously. The differentiation of two types of fibers in the intraganglionic spiral bundle and the first appearance of TII neurons occurs around birth in the cat and a few days after birth for the rat and the mouse. The distinction of TII cells is possible due to characteristic accumulation of neurofilamentous structures in the cytoplasm.

ISSN:0741-0581    

DOI:10.1002/jemt.1060150206

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractFreeze‐fracture analysis of adult spiral ganglion cells of CBA/CBA mice revealed two types of membrane specializations. Most cells (type I) had a smooth surface and were surrounded by Schwann cells. Type II spiral ganglion cells showed numerous membrane specializations with well‐delineated indentations similar to those previously found on hair cells adjacent to afferent and efferent nerve endings. Immunomorphological analysis (using well‐defined monoclonal antibodies directed against different subclasses of intermediate filament proteins) revealed a unique co‐expression of neurofilaments, vimentin and cytokeratins in spiral ganglion cells of 8‐to 22‐week hu

ISSN:0741-0581    

DOI:10.1002/jemt.1060150207

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractSpiral and Scarpa's (vestibular) ganglia of female C57BL/6 mice, ranging in age from 1.5 to 32 months, were examined by light and electron microscopy. The spiral ganglia of C57BL/6 mice undergo sweeping neuronal losses. Based on cytological characteristics that repeat themselves in both young and old mice, we divided perikaryal demyelination and degeneration of spiral ganglia into four arbitary stages: (1) incipient demyelination, myelin sheaths begin to loosen and unravel; (2) contact, the partially demyelinated perikarya abut as the extracellular matrix disappear; (3) clumping, clusters of naked perikarya clump together, cytoplasmic processes surround the exterior of the clump; and (4) resorption, the clumps gradually disintegrate, leaving at completion large, fluid‐filled spaces and few cellular remnants. In Scarpa's ganglia, a small number of neurons demyelinate and clump, but none degenerate or undergo resorptio

ISSN:0741-0581    

DOI:10.1002/jemt.1060150208

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractThe fine structure of both the afferent and efferent hair cell synapses in the sensory epithelium of guinea pig organ of Corti was examined by freeze‐fracture electron microscopy. In the afferent synapse, barlike aggregates of intramembrane particles (IMPs) of about 10 nm in diameter were seen on the P‐face of the afferent presynaptic membrane directly beneath the presynaptic dense projection which is located in the active zone of the presynaptic membrane. Small and large depressions have been seen on the presynaptic membrane. The former were observed in the proximity of the barlike aggregates, while the latter were observed some distance from the aggregate. In outer hair cells, IMPs of about 10 nm in diameter were seen on the P‐face of the afferent postsynaptic membrane at a density of 3,000/μm2.In the efferent synapse, many aggregates composed of from several to tens of large IMPs of 13 nm in diameter were observed on the presynaptic membrane. These aggregates were localized to small membrane depressions, which tended to be deeper as particle number per aggregate increased.Dense populations of IMPs of about 9 nm in diameter were observed on the P‐face of the efferent postsynaptic membrane at a density of 4,000/μm2. A fenestrated subsynaptic cistern completely covers the efferent postsynaptic membrane. Moreover, the subsynaptic cistern spans several efferent postsynaptic membranes when efferent synapses are gathered in a group.In the afferent and efferent synapses of hair cells, specializations of the synaptic membranes were represented by marked aggregates characteristic of IMPs. In the efferent synapse, IMP movement inside the synaptic membrane was proposed in relationship to retrival of synaptic vesicle membrane. Structural relationship between the subsynaptic cistern and efferent postsynaptic membrane was

ISSN:0741-0581    

DOI:10.1002/jemt.1060150209

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractInnervations of inner and outer hair cells of the organ of Corti of the human cochlea were studied by serial section electron microscopy. At the base of inner hair cells, presumed afferent fibers were of varying size and demonstrated synaptic specialization consisting of a presynaptic body, vesicles, and asymmetrical synaptic membrane specialization. Two types of neurons, vesiculated presumably efferent and nonvesiculated presumably afferent, synapsed at the base of outer hair cells. The synaptic specialization of afferent fibers included presynaptic body, vesicles, and asymmetrical membrane thickening, whereas efferent synapses demonstrated presynaptic vesicles and a subsynaptic cisterna. Some presumably afferent nerve terminals formed a reciprocal synapse with outer hair cells in both the human and the chimpanzee. Such a synaptic relationship demonstrated morphologic specialization consistent with both hair cell‐to‐neuron and neuron‐to‐hair cell transmission between the same outer hair cell and nerve terminal. The innervation density of inner and outer hair cells and the comparative anatomy of the afferent and efferent innervation are di

ISSN:0741-0581    

DOI:10.1002/jemt.1060150210

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

ISSN:0741-0581    

DOI:10.1002/jemt.1060150201

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY