A freeze-etch study of the ultrastructure of red algal pit plugs

Summary Freeze-etch studies indicate that the fully-formed pit plug ofPalmaria palmata consists of a homogeneous plug core, a pair of plug caps, and associated membranes. A single cap membrane separates the two layers of each plug cap and is the only membrane found between the cytoplasm and the plug core. Due to the apparent junction of the plasmalemma and cap membranes, the plug core, along with the adjacent plug cap layer on either face of the core, is entirely membrane-bounded and essentially extracellular. Fracture faces of the cap membrane bear large populations of particles which are inconspicuous due to their low profile. The plasmalemma lining the plug core from cell to cell has numerous, very obvious particles on its fracture faces, more even than does the cytoplasmic plasmalemma.The relationship of the rhodophycean pit plug to the fungal septal pore plug is discussed.This report represents a portion of a thesis submitted in partial fulfillment of the requirements of a Master of Science degree, Cornell University, Ithaca, N.Y.     

Middle-ear development: II. Morphometric changes in the conducting apparatus of the chick.

The ontogeny of various middle-ear structures was examined in 11 groups of chicks between 10 days embryonic and adult. Measurements of the tympanic membrane surface area and height, columella length, and that of the columella footplate, annular ligament, and oval window area were obtained using video micrographs and computer digitization techniques. The oval window matures first at 53 days post-hatching, whereas the columella achieves adult size at 74 days. The tympanic membrane surface area is the last middle-ear variable studied to reach adult size (79 days post-hatch). The columella increases its length from 0.63 mm (10 days embryonic) to 2.73 mm in the adult. The tympanic membrane area expands by 280% whereas the columellar footplate area increases by 11x. As a result, the pressure amplification of the middle ear due to the tympanic membrane/columellar footplate area ratio improves by over 400%. These data further contribute to our understanding of the functional development of the middle ear.     

The coelocapitular sensillum,an antennal hygro- and thermoreceptive sensillum of the honey bee,Apis mellifera L.

Summary The sensillum coelocapitulum, a hygro- and thermoreceptive sensillum of the honey bee, Apis mellifera, was investigated by electron microscopy. The cuticular apparatus of the sensillum is a mushroomshaped protrusion, devoid of pores, set in a narrow cylindrical pit positioned centrally within a cuticular, shallow depression. There may be three or four receptor cells. Three receptor cells have unbranched sensory cilia, containing densely packed microtubules, which extend distally into the cuticular apparatus and completely fill its cavity. These connecting cilia are of the usual 9+0 type. The fourth receptor, if present, has a thin sensory cilium which terminates beneath the cuticular apparatus. Its connecting cilium has armed outer doublets. The outer cavity is formed by two enveloping cells and is completely sealed off. Lipid deposits are present within the cavity and the tormogen cell. The thecogen cell has scolopale rod-like structures around the inner cavity. Features common to the insect hygro- and thermoreceptive sensilla are discussed in comparison with those of other insects.     

Das tympanalorgan von Gryllus bimaculatus Degeer (saltatoria,gryllidae)

Zusammenfassung Das Tympanalorgan von Gryllus bimaculatus Degeer liegt an der lateralen Wand der vorderen Trachee and schließt sich unmittelbar an das Subgenualorgan an. Es besteht aus 3 eng beieinanderliegenden Abschnitten: dem proximalen Absehnitt (10–12 Scolopidien), den Scolopidien des hinteren Tympanalnervs (10–12 Scolopidien) and einem distalen Absehnitt (35–40 Scolopidien).Ein Scolopidium des Tympanalorgans besteht aus folgenden Zellen: einer bipolaren Sinneszelle, die sich nach distal in einen Sinnesfortsatz mit einem Sinnescilium fortsetzt, einer oder zwei Gliazellen, einer proximalen Hüllzelle, der Stiftzelle (= 1. Hüllzelle), der Kappenzelle (= 2. Hüllzelle) und der akzessorischen Zelle (= 3. Hüllzelle). Das Sinnescilium ist mit einem langen, sich aufspaltenden Wurzelfaden im Sinnesfortsatz verankert. An der Cilienbasis befinden sich zwei Basalkörper. Die Spitze des Ciliums reicht in einen Stiftkopf, der wie bei alien hemimetabolen Insekten nicht massiv ist. Unterhalb des Stiftkopfes erweitert sich die Cilie zu einer Ciliendilatation, deren Zentrum elektronendichtes Material enthält. Die Cilie verläuft in einem extrazellulären Raum, der durch Stützstrukturen innerhalb der Stiftzelle, den Wandrippen, aufrecht gehalten wird. Das Organ hat an der lateralen Wand des Beines eine schmale Anheftungsstelle; die Verankerung in der Epidermis erfolgt über die akzessorischen Zellen.

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The tyrnpanic organ of Gryllus bimaculatus Degeer (saltatoria, gryllidae)

Summary The tympanic organ of Gryllus bimaculatus Degeer is situated at the lateral wall of the anterior trachea just distal to the subgenual organ. It consists of three groups of sensilla lying quite close together: the proximal part (10–12 scolopidia), the scolopidia of the posterior tympanic nerve (10–12 scolopidia), and a distal part (35–40 scolopidia).Each scolopophorous sensillum of the tympanic organ is composed of the following distinct cells: the bipolar sense cell, which narrows to form the dendrite with the cilium, one or two glial cells, the proximal enveloping cell, the scolopale cell (= 1st sheath cell), the cap cell (= 2nd sheath cell), and the accessory cell (= 3rd sheath cell). The cilium is anchored within the dendrite with a long root, which divides into numerous rootlets. There are two basal bodies at the base of the cilium. The tip of the cilium projects into the cap, which, as in all hemimetabol insects, is not solid. Proximal to the cap the cilium widens into a dilatation containing electron-dense material in the centre. The cilium passes through an extracellular space, which is maintained by supporting structures, the rods, lying in the scolopale cell. The organ is attached to the epidermis of the wall of the leg by means of the accessory cells.

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Abkürzungen A Anheftungsstelle - äK äu\ere Kante der kleinen Trachee - akZ akzessorische Zelle - Ax Axon - Bk Blutkanal - Bz Blutzelle Das Tympanalorgan von Gryllus bimaculatus Deg Cd Ciliendilatation - Cu Cuticula - D Desmosom - dBa distaler Basalkörper - De Dendritenerweiterung - Dm Deckmembran - Ep Epedermis - ER endoplasmatisches Reticulum - ETk Epithel des Trachealkörperehens - Ex Extrazellularraum - F Fettgewebe - Fc Femur - Fi Fibrillen - fiF fingerförmige Fortsätze - G Gliazelle - Go Golgi-Komplex - Hd Hemidesmosom - hSn hinterer des Subgenualnervs - hT hinteres Tympanum - hTl hintere Tympanalleiste - hTr hintere Trachee - iN integumentaler Nerv - K Kappenzelle - M Mündung der klemen Trachee - Mi Mitochondrium - Mk Muskelkanal - Mt Mikrotubulus - Mu Muskel - N Nucleus - Nt Neurotubulus - Pi Pigment - pBa proximaler Basalkörper - pHz proximale Hüllzelle - prA proximaler Abschnitt - S Suspensorium - Sc Sinnescilium - Se Sehne - Sf Sinnesfortsatz - Si Stift - Sk Stiftkopf - Sn Subgenualnerv - So Subgenualorgan - Stz Stiftzelle - Sz Sinneszelle - Tan Tarsalnerv - Tf Tonofibrille - Ti Tibia - Tin Tibialnerv - Tk Trachealkörperchen - Tn Tympanalnerv - To Tympanalorgan - Tsn Subgenualast des Tympanalnervs - V Vakuole - vSn vorderer - Ast des Subgenualnervs - vT vorderes Tympanum - vTl vordere Tympanalleiste - vTr vordere Trachee - W Wurzelfaden - Wr Wandrippe - Wu Wulst Dissertation im Fachbereich Biologie der Universität Mainz.Herrn Professor Dr. H. Risler bin ich für die Themenstellung und für die gewährte Unterstützung zu Dank verpflichtet. Herra Professor Dr. K. Schmidt danke ich für die Einführung in die elektronenmikroskopische Technik und für wertvolle Anregungen und Hinweise.     

Histophysiological observations on the external auditory meatus,middle, and inner ear of the weddell seal (Leptonychotes weddelli)

The external auditory meatus, middle, and inner ear of the deep-diving Weddell seal (Leptonychotes weddelli) were studied with light microscopic, histological, and histochemical techniques in order to contribute to the open discussion on the orientation of this seal in the darkness of the deep Antarctic seas. The external auditory meatus is characterized by a well-developed venous plexus, single apocrine ceruminous, and numerous holocrine sebaceous glands and an incomplete tube of elastic cartilage. The tympanic membrane is comprised of two layers of radially and concentrically arranged collagen fibers and by elastic fibers which are concentrated in the outer part of the ear drum. The tympanic cavity is lined by a pseudostratified prismatic ciliated epithelium with goblet cells; a plexus of wide venous vessels marks the subepithelial lamina propria. The cochlea is about 10 mm high and forms about two and a half turns. The richly pigmented stria vascularis is well vascularized, while the cell-rich prominentia spiralis contains only single small blood vessels. The organ of Corti contains one row of inner and three rows of outer hair cells. Cells of Hensen, Claudius, and Boettcher are present. The basilar membrane is of comparatively uniform simple structure and is composed of abundant glycoproteins, proteoglycans, collagenous fibers, and the loose tissue of the tympanal layer. The spiral ligament is built up by abundant proteoglycans and a complex system of radial and concentric collagen fibers; close to the osseous wall of the bony cochlea it contains fine elastic fibers. The inner zone of the osseous wall of the cochlea strikingly contains hyaline cartilage. The thin lamina spiralis ossea is covered by a limbus spiralis with interdental cells secreting the lamina tectoria, which has a fibrous texture and contains glycoproteins and negatively charged components. J. Morphol. 234:25–36, 1997. © 1997 Wiley-Liss, Inc.     

Development of the discharge apparatus in the fungus Entophlyctis

Correlative light and electron microscopic observations were used to reconstruct the morphological events involved in the development of the discharge apparatus of Entophlyctis zoosporangia. A discharge plug formed as vesicles containing fibrillar material fused with the plasma membrane and deposited their matrices between the plasma membrane and zoosporangial wall. At the apex of the enlarging plug, the zoosporangial wall lost its microfibrillar appearance, became diffuse, and left an inoperculate discharge pore. The discharge plug exuded through this pore and then expanded into a sphere which rested at the tip of the discharge papilla or tube. After the release of the discharge plug, the number of fibrilla containing vesicles decreased and abundant endoplasmic reticulum appeared in the cytoplasm below the plug. Granular material then accumulated at the interface of the discharge plug and the plasma membrane. This was the endo-operculum. A single layer of endoplasmic reticulum subtended the area of plasma membrane which the endo-operculum covered. Later, dictyosomes appeared in the cytoplasm below the endo-operculum. Fusion of Golgi vesicles with the plasma membrane below the endo-operculum coincided with the initiation of cytoplasmic cleavage. This sequence of events indicates that, unlike the discharge plug, the endo-operculum does not originate by vesicular addition of preformed material.     

Classification of Different Tympanic Membrane Conditions Using Fused Deep Hypercolumn Features and Bidirectional LSTM

Objectives: Middle ear inflammatory diseases are global health problem that can have serious consequences such as hearing loss and speech disorders. The high cost of medical devices such as oto-endoscope and oto-microscope used by the specialists for the diagnosis of the disease prevents its widespread use. In addition, the decisions of otolaryngologists may differ due to the subjective visual examinations. For this reason, computer-aided middle ear disease diagnosis systems are needed to eliminate subjective diagnosis and high cost problems. To this aim, a hybrid deep learning approach was proposed for automatic recognition of different tympanic membrane conditions such as earwax plug, myringosclerosis, chronic otitis media and normal from the otoscopy images.Materials and methods: In this study we used public Ear Imagery dataset containing 880 otoscopy images. The proposed approach detects keypoints from the otoscopy images and following the obtained keypoint positions, extracts hypercolumn deep features from 5 different layers of the VGG 16 model. Classification of tympanic membrane conditions were realized by feeding the deep hypercolumn features to Bi-LSTM network in the form of non-time related data.Results: The performance of the proposed model was evaluated in three different color spaces as Red-Green-Blue (RGB), Hue-Saturation-Value (HSV) and Haematoxylin-Eosin-Diaminobenzidine (HED). The proposed model achieved acceptable results in all color spaces, moreover it showed a very successful performance in classifying tympanic membrane conditions especially in RGB space. Experimental studies showed that the proposed model achieved Acc of 99.06%, Sen of 98.13% and Spe of 99.38%.Conclusion: As a result, a robust model with high sensitivity was obtained for classification of tympanic membrane conditions and it was shown that Bi-LSTM network, which is generally used with time-related data, could also be used successfully with non-time related data for diagnosis of tympanic membrane conditions.     

RHODOPHYCEAN PIT PLUGS: AN ULTRASTRUCTURAL SURVEY WITH TAXONOMIC IMPLICATIONS

The fine structure of pit plugs was examined in 63 species of red algae representing 34 families. The number of plug cap layers was found to be a taxonomically reliable character when tested against a recent revision of the Rhodymeniales which established the order Palmariales. In a broader survey involving all the orders of red algae possessing pit plugs, three basic plug cap configurations were detected. These differ in having one, two, or no plug cap layers. Some taxa have plug caps in which the outer cap layer is greatly elaborated, however, this layer was shown to be positionally and cytochemically identical, thus probably homologous, to the outer cap layer of the typical two-layered plug cap. The pit plug character confirms the validity of the order Palmariales and indicates that the Nemaliales and Cryptonemiales are heterogeneous assemblages. Revision of these groups along lines indicated by the plug character is supported by significant features of morphology and reproduction. These correlations lead us to propose that Rhodophysema and Coriophyllum be transferred to the Palmariales, that the Gelidiales be resurrected, that the Bonnemaisoniales (including the Naccariaceae) is deserving of recognition, that the Batrachospermaceae be raised to a higher rank which will also receive the Lemaneaceae and the Thoreaceae, and that the Corallinaceae and Hildenbrandiaceae both be raised to ordinal status.     

ABSENCE OF CAP MEMBRANES AS A CHARACTERISTIC OF PIT PLUGS OF SOME RED ALGAL ORDERS1

The current general model of the organization of a fully developed rhodophycean pit plug includes a cap membrane associated with each end of the plug. Continuity of the plasmalemma and cap membrane results in the plug core being extracellular. However, routine ultrastructural methods have not convincingly demonstrated cap membranes in the Bangiales or the Corallinales. In this study, a variety of fixation regimes that enhance membrane contrast were used in an attempt to detect cap membranes in representatives of these two orders. Although cap membranes were readily and clearly demonstrable by these methods in a representative of an order previously known to have cap membranes, they could not be detected in members of the Bangiales or Corallinales. Should the absence of cap membranes prove to be an invariant feature of these two orders, presence or absence of cap membranes will constitute a new character for phylogenetic analysis. It is proposed that the ancestral character state of red algal pit plugs was a homogeneous plug without caps and without cap membranes.     

ABSENCE OF CAP MEMBRANES AS A CHARACTERISTIC OF PIT PLUGS OF SOME RED ALGAL ORDERS1

The current general model of the organization of a fully developed rhodophycean pit plug includes a cap membrane associated with each end of the plug. Continuity of the plasmalemma and cap membrane results in the plug core being extracellular. However, routine ultrastructural methods have not convincingly demonstrated cap membranes in the Bangiales or the Corallinales. In this study, a variety of fixation regimes that enhance membrane contrast were used in an attempt to detect cap membranes in representatives of these two orders. Although cap membranes were readily and clearly demonstrable by these methods in a representative of an order previously known to have cap membranes, they could not be detected in members of the Bangiales or Corallinales. Should the absence of cap membranes prove to be an invariant feature of these two orders, presence or absence of cap membranes will constitute a new character for phylogenetic analysis. It is proposed that the ancestral character state of red algal pit plugs was a homogeneous plug without caps and without cap membranes.     

Formation of the middle ear: recent progress on the developmental and molecular mechanisms

The middle ear allows animals to hear while moving in an aerial medium. It is composed of a cavity harbouring a chain of three ossicles that transmit vibrations produced by airborne sound in the tympanic membrane into the inner ear, where they are converted into neural impulses. The middle ear develops in the branchial arches, and this requires sequential interactions between the epithelia and the underlying mesenchyme. Gene-inactivation experiments have identified genes required for the formation of different middle ear components. Some encode for signalling molecules, including Endothelin1 and Fgf8, probable mediators of epithelial-mesenchymal interactions. Other genes, including Eya1, Prx1, Hoxa1, Hoxa2, Dlx1, Dlx2, Dlx5, and Gsc, are most likely involved in patterning and morphogenetic processes in the neural crest-derived mesenchyme. Mechanisms controlling formation of a functional tympanic membrane are also discussed. Basically, the tympanic ring, which serves as support for the tympanic membrane, directs invagination of the first pharyngeal cleft ectoderm to form the external acoustic meatus (EAM), which provides the outer layer of the membrane. Gsc and Prx1 are essential for tympanic ring development. While invaginating, the EAM controls skeletogenesis in the underlying mesenchyme to form the manubrium of the malleus, the link between the membrane and the middle ear ossicles.     

An ultra-structural study of the gills of Echinus esculentus

Summary The ultrastructure of the gills of Echinus esculentus is described using transmission electron microscopy. The gills are covered by typical epithelial cells overlying a collagenous basement membrane. The coelomic lumen of the gills is thrown into a series of irregular grooves and ridges which are formed by long narrow cells from each of which projects a single cilium. There is a layer of muscle cells lying underneath these cells adjacent to the basement membrane. They are innervated by axons containing large granular vesicles and the significance of this innervation is discussed in terms of neuromuscular junctions in general within the echinoderms. This study shows that the main function of the gills is excretory and describes three apparent systems whereby excretory products and necrotic coelomocytes are removed.     

Occurrence of plasmodesmata between differentiating vessels and other xylem cells inSorbus torminalis L. Crantz and their fate during xylem maturation

Summary The development of pit-pairs between differentiating xylem cells has been examined by transmission electron microscopy in young shoots ofSorbus torminalis. In some vessel-to-tracheid pits, as well as in previously studied intertracheid pits, a thickening of the pit membrane containing branched plasmodesmata was observed. A secondary wall-like cap was deposited over the thickening prior to cytoplasmic autolysis; some plasmodesmata, parallel to the plane of section, appeared to perforate the cap. At the end of the cell maturation stage, the central part of the primary wall thickening was hydrolysed, while the cap, including plasmodesmata remnants, appeared unaltered. In half-bordered pit-pairs between a parenchyma cell and a vessel or a tracheid, similar structures could be observed beside the conducting elements. When the vessel or tracheid matured, sealing of the pit membrane plasmodesmata resulted from the formation of a protective layer on the parenchyma-side rather than from the deposition of a cap on the conducting cell-side. These observations provide the first information on the presence of symplasmic connections in pits between differentiating vessels and neighbouring xylem cells. InS. torminalis, xylem differentiation is probably highly coordinated within a symplasmic domain; the persistence of such connections may account for the lack of specialization ofSorbus wood.     

The larval ocelli of Golfingia misakiana (Sipuncula, Golfingiidae) and of a pelagosphera of another unidentified species

 The inverse cerebral ocelli of the pelagosphera larva of Golfingia misakiana and of another unidentified larva are composed of two or three sensory cells and one supportive pigmented cell. The sensory cells bear an array of microvilli as well as a single cilium with poor undulation of its membrane; the photoreceptive organelles are regarded as the rhabdomeric type. A striking feature of these cells is the cores, which extend within the microvilli from the tip into the midregion of the cell. It is suggested that these structures are identical with the submicrovillar cisternae found in the cerebral inverse eyes of larvae of Polychaeta. The findings allow the conclusion that in the pelagosphera of the Sipuncula, contrary to the teleplanic veliger larvae of Gastropoda, a lengthy pelagic cycle is not correlated with the development of a ciliary photoreceptor. Additionally, it is assumed that the pigment cup ocelli in larvae of Sipuncula are homologous with the cerebral inverted pigment cup ocelli of larvae of Polychaeta. Accepted: 19 March 1997     

Microvascular networks in tympanic membrane, malleus periosteum, and annulus perichondrium of neonatal mongrel dog: a vasculoanatomic model for surgical considerations

India-ink-imaged blood-vessel networks in cleared tympanic membranes and adnexa from ten neonatal dogs were examined microscopically and photographed. The major significance of the study lies in documentation of a dual source of arterial supply, a bilaminar relationship of arterial and venous plexuses intrinsic to the tympanic membrane, and a consistent major venous pathway relative to a definite locus (pars flaccida of the membrane). Illustration of all three types of blood pathways (arteries, veins, and capillaries) provides new vasculoanatomic data that are essential to ear surgery, specifically--to myringotomies and myringoplasties. A comparison was made between dog and human tympanic membrane structures and their arterial supplies. Close similarities suggested that dog tympanic membrane might serve as a suitable model for development of innovative surgical procedures and as a model for rehearsal of difficult techniques. The results of this investigation provide a valuable caveat to otologists.     

The Behavior and Fine Structure of the Dorsal Bristles of Euplotes minuta,E. aediculatus,and Stylonychia mytilus (Ciliata,Hypotrichida)1

ABSTRACT. Studies of the bristle (dorsal) cilia of Euplotes minuta. E. aediculatus, and Stylonychia mytilus by light and electron microscopy indicate that these cilia do not beat metachronously in any of the species. The bristle cilia in Stylonychia may beat actively, but those in Euplotes stand erect or are bent in different directions with the flow of water. The duration and degree of bending appear correlated with the duration and velocity of the water current. The fine structure of the bristle complex is similar in both Euplotes species and like other reports of Euplotes in the literature. The complex consists of paired kinetosomes, the anterior bearing a short cilium containing four to six rows of fibrous balls (lasiosomes) oriented along the anterior surface of the axoneme, the posterior lacking a cilium but with a small cap. Microtubular ribbons are associated with the paired kinetosomes, and a collar with a pronounced alveolar ring underneath the pellicular membrane tightly surrounds the cilium at the opening of the bristle pit. The bristle complex in S. mytilus differs from that of Euplotes and other hypotrichs in that it has a single kinetosome in interphase cells and, attached to the kinetosome, a prominent fibrous structure (parakinetosomal body). Microtubules are attached to the parakinetosomal body. As in Euplotes, the bristle unit is surrounded by mucocyst-like organelles (ampules). Observations of behavior and fine structure suggest that the dorsal bristles may be sensory, perhaps responding to stimuli from water currents, although other functions are possible, too.     

Root apical organization inArabidopsis thaliana 1. Root cap and protoderm

Summary We investigated the development of the root cap and protoderm inArabidopsis thaliana root tips.A. Thaliana roots have closed apical organization with the peripheral root cap, columella root cap and protoderm developing from the dermatogen/calyptrogen histogen. The columella root cap arises from columella initials. The initials for the peripheral root cap and protoderm are arranged in a collar and the initiation event for these cells occurs in a sequential pattern that is coordinated with the columella initials. The resulting root cap appears as a series of interconnected spiraling cones. The protoderm, in three-dimensions, is a cylinder composed of cell files made up of packets of cells. The number of cell files within the protoderm cylinder increases as the root ages from one to two weeks. The coordinated division sequence of the dermatogen/calyptrogen and the increase in the number of protoderm cell files are both features of post-embryonic development within the primary root meristem.Abbreviations RCP root cap/protoderm - CI columella initial - PI protoderm initial     

Mechanisms of Hearing Loss after Blast Injury to the Ear

Given the frequent use of improvised explosive devices (IEDs) around the world, the study of traumatic blast injuries is of increasing interest. The ear is the most common organ affected by blast injury because it is the body’s most sensitive pressure transducer. We fabricated a blast chamber to re-create blast profiles similar to that of IEDs and used it to develop a reproducible mouse model to study blast-induced hearing loss. The tympanic membrane was perforated in all mice after blast exposure and found to heal spontaneously. Micro-computed tomography demonstrated no evidence for middle ear or otic capsule injuries; however, the healed tympanic membrane was thickened. Auditory brainstem response and distortion product otoacoustic emission threshold shifts were found to be correlated with blast intensity. As well, these threshold shifts were larger than those found in control mice that underwent surgical perforation of their tympanic membranes, indicating cochlear trauma. Histological studies one week and three months after the blast demonstrated no disruption or damage to the intra-cochlear membranes. However, there was loss of outer hair cells (OHCs) within the basal turn of the cochlea and decreased spiral ganglion neurons (SGNs) and afferent nerve synapses. Using our mouse model that recapitulates human IED exposure, our results identify that the mechanisms underlying blast-induced hearing loss does not include gross membranous rupture as is commonly believed. Instead, there is both OHC and SGN loss that produce auditory dysfunction.     

Biomechanics of the tympanic membrane

The tympanic membrane is a key component of the human auditory apparatus which is a complex biomechanical system, devoted to sound reception and perception. Over the past 30 years, various bioengineering approaches have been applied to the ear modeling and particularly to the middle part. The tympanic membrane, included in the middle ear, transfers sound waves into mechanical vibration from the ear canal into the middle ear. Changes in structure and mechanical properties of the tympanic membrane due to middle ear diseases or damages can deteriorate sound transmission. An accurate model of the tympanic membrane, which simulates the acoustic-mechanical transmission, could improve clinical surgical intervention. In this paper a detailed survey of the biomechanics and the modeling of the tympanic membrane focusing on the finite element method is conduced. Eight selected models are evaluated and compared deducing the main features and most design parameters from published models, mainly focusing on geometric, constraint and material aspects. Non-specified parameters are replaced with the most commonly employed values. Our simulation results (in terms of modal frequencies and umbo displacement), compared with published numerical and experimental results, show a good agreement even if some scattering appears to indicate the need of further investigation and experimental validation.     

Whispers from vestigial nubbins: Arrested development provokes trait loss in toads

Despite the use of acoustic communication, many species of toads (family Bufonidae) have lost parts of the tympanic middle ear, representing at least 12 independent evolutionary occurrences of trait loss. The comparative development of the tympanic middle ear in toads is poorly understood. Here, we compared middle ear development among two pairs of closely related toad species in the genera Atelopus and Rhinella that have (eared) or lack (earless) middle ear structures. We bred toads in Peru and Ecuador, preserved developmental series from tadpoles to juveniles, and examined ontogenetic timing and volume of the otic capsule, oval window, operculum, opercularis muscle, columella (stapes), and extracolumella in three‐dimensional histological reconstructions. All species had similar ontogenesis of the otic capsule, oval window, operculum, and opercularis muscle. Moreover, cell clusters of primordial columella in the oval window appeared just before metamorphosis in both eared and earless lineages. However, in earless lineages, the cell clusters either remained as small nubbins or cell buds in the location of the columella footplate within the oval window or disappeared by juvenile and adult stages. Thus, columella growth began around metamorphosis in all species but was truncated and/or degenerated after metamorphosis in earless species, leaving earless adults with morphology typical of metamorphic anurans. Shifts in the timing or expression of biochemical pathways that regulate the extension or differentiation of the columella after metamorphosis may be the developmental mechanism underlying convergent trait loss among toad lineages.