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Biomedical subjects

C Gans

Publications and source records attributed to C Gans.

At least 37 records · Page 2Linked to original sources
PubMed1983

Narial closure in toads; which muscles?

Narial closure in frogs never involves intrinsic narial muscles; rather it is effected by action of the M. submentalis, a muscle of the lower jaw. None of more than 40 species of frogs examined showed any strained muscles in the snout, anterior to the eyes. Direct stimulation of all the relevant muscles, as well as electromyography with simultaneous measurement of air flow at the nostrils, confirms Gaupp's hypothesis that the muscular displacement of the M. submentalis is transmitted via bones and cartilages of the snout to close the nares.

Animals↗
PubMed1983

The genesis of neural crest and epidermal placodes: a reinterpretation of vertebrate origins.

Vertebrate body organization differs from that of other chordates in a large number of derived features that involve all organ systems. Most of these features arise embryonically from epidermal placodes, neural crest, and a muscularized hypomere. The developmental modifications were associated with a shift from filter-feeding to more active predation, which established advantages for improved gas exchange and distribution. Active predation involved more efficient patterns of locomotion and led to a major reorganization of the pharynx, to elaboration of the circulatory, digestive, and nervous systems, and to special sense organs. Most of the organs that derive from epidermal placodes and neural crest may have arisen phylogentically from epidermal nerve plexus of earlier chordates. Supportive tissues such as cartilage, bone, dentine, and enamel-like tissues probably arose in association with several of the new vertebrate sense organs and only secondarily provided mechanical support. The development of armor appears to have occurred late in vertebrate evolution. Finally, the origin of a postotic skull and axial vertebrae appears to be associated with the origin of the gnathostomes.

Animals↗
PubMed1982

Functional morphology of lingual protrusion in marine toads (Bufo marinus).

Bufo marinus catches its prey by stiffening the intrinsic muscles of the tongue, rapidly flipping the tongue out of the mouth. High-speed cinematography synchronized with computer-analyzed electromyograms (EMGs)shows that during the flip the tongue is supported by the M. genioglossus medialis and that this muscle stiffens into a rod when stimulated. Coincident stiffening of the transversely arranged M. genioglossus basalis provides a wedge under the anterior tip of this rod. Stiffening of the M. submentalis depresses the mandibular symphysis and brings the dentary tips together. The M. submentalis also acts on the wedge of the basalis to raise and rotate the rigid rod of the medialis over the symphysial attachment. The tip of this lingual rod carries along the pad and soft tissues of the tongue. The lingual pad, positioned the posterodorsal portion of the resting tongue, rotates during eversion so that its dorsal surface impacts onto the prey object. Retraction starts by contraction of the elongate, parallel fibers of the M. hyoglossus; this retracts the medical sulcus of the pad and holds the prey by a suction cup-like effect. The extensibility of the buccal membranes allows the pad to be retracted first; it reaches the posterior portion of the buccal cavity before the still-rigid, backward rotating M. genioglossus has reached the level of the symphysis. Protraction of the hyoid facilitates the extension of the M. hyoglossus. The M. sternohyoideus only retracts the hyoid and stabilizes it when the tongue starts to pull posteriorly; it does not assist tongue protrusion. The Mm. petrohyoideus and omohyoideus show only incidental activity, and the M. depressor mandibulae participate in mouth opening but is not otherwise involved in the flip. Previous hypotheses of the flipping mechanism are reviewed and evaluated.

Animals↗
PubMed1980

Electromyograms are repeatable: precautions and limitations.

Electromyograms recorded by bipolar, fine wire electrodes placed into anatomically equivalent sites in skeletal muscles of vertebrates are repeatable when the animals use the muscles in a similar way. Repeatability applies to the number of spikes recorded from a given site and to their average amplitude as well as to the root-mean-square value, though the values obtained for these descriptors differ among muscles, and perhaps fascicles, of particular animals even when the animals are performing equivalent actions. Tests suggest that these results are not affected by the nature of most kinds of recording equipment. Also, substantial differences in electrode tip configuration and wire diameter induce relatively minor, less than 8 percent, differences in electrode resistance and impedance. Doubling the length of the fine wire leads produces less than an 8 percent (15 percent when the length is tripled) effect; however, the effect of electrode material may be as much as 85 percent in resistance and 20 percent in impedance. Reports of nonreproducibility or variability of electromyograms apparently result mainly from anatomically inexact placement into physiologically and histochemically different fascicles of compound muscles, from recordings of muscles that are active at very low levels, and perhaps from comparison among recordings of muscles that really differ in their activity level.

Action Potentials↗
PubMed1980

Quantitative assay of electromyograms during mastication in domestic cats (Felis catus).

Mastication has been studied by cinematography with synchronized electromyography (computer quantified and analyzed), while unanesthetized, freely feeding cats (Felis catus) were reducing equivalent-sized chunks of raw and cookded beef and cooked chicken. Cats reduce food on one side at a time, and their chewing cycles show horizontal and anteroposterior deflections. Food objects are shifted from side to side by lateral jerks of the head and movements of the tongue. During the opening phase, the lower jaw is rotated relatively straight downward, and the digastric muscles are active in bilateral symmetry. Near the end of opening, the head jerks upward, both zygomaticomandibulares start to fire, and opening acceleration of the mandible decreases. Closing starts with horizontal displacement of the mandibular canines toward the working side, accompanied by asymmetrical activities from the working side deep temporalis and the balancing side medial pterygoid, as well as a downward jerk of the head. As closing proceeds the mandibular canines remain near the working side and the working side zygomaticomandibularis and deep masseter are very active. Near the end of closing, the mandibular canine on the working side moves toward the midline, and adductors, digastrics, and lateral pterygoids of both sides are active. The adductors of the working side are generally more active than those of the balancing side. During a reduction sequence, the number and shape of the masticatory cycles, as well as movements of the head, during a reduction sequence are affected significantly by food type. As reduction proceeds, the duration of bite and the muscular activity (as characterized by number and amplitude of spikes) change significantly among muscles of the working and balancing sides. The adductors of the working side are generally most active when cats chew raw beef, less for cooked beef, and least for cooked chicken. In general, the adductor activity reflect food consistency, whereas that of the digastrics and lateral pterygoids reflects more the vertical and lateral displacements of the mandible. Statistical analysis documents that the methods of electrode insertion and test give repeatable results for particular sites in different animals. Thus, it should be possible to compare these results with those produced while other mammals are masticating.

Animals↗
PubMed1979

Muscle fiber regeneration after transplantation: prediction of structure and physiology from electromyograms.

Digitized electromyographic activity of transplanted extensor digitorum longus (EDL) muscles in cats differs from that of control EDL and anterior tibialis muscles lying adjacent to transplanted EDL muscles. In autotransplanted muscles, the cross-sectional area of the fibers shows a negative correlation with mean spike frequency and a positive correlation with mean amplitude. The mean frequency-amplitude products correlate with isometric tetanic tensions.

Action Potentials↗
PubMed1978

Air flow in snake ventilation.

Ventilation in resting, unrestrained Boa constrictor, Python regius and Thanmophis s. sirtalis was monitored using various combinations of a closed Kopfkappe (head chamber), intratracheal pressure catheters, strain gauges around the trunk, and a flow meter connected to one of the nostrils. Records of intratracheal pressure with and without closing the Kopfkappe show that the latter device induces artifacts in the normal ventilatory pattern. Flow meter readings from quiescent snakes indicate that ventilation is biphasic (outflow-inflow-pause) rather than triphasic (outflow-inflow-outflow-pause), while simultaneous pressure and strain gauge records are variably tri- or quadriphasic.

Animals↗
PubMed1976

Studies on ventilation of Caiman crocodilus (Crocodilia: Reptilia).

The ventilatory mechanics of freely moving Caiman crocodilus were studied by cinefluorescopy and electromyography. The buccal oscillations serve only to flush the internal nares in olfaction. Ventilations are coincident with abdominal oscillations. The larynx ordinarily lies adpressed to the internal nares so that the posterior buccal chamber is excluded from the path of air flow during ventilation and does not contribute to respiratory dead space. The pulmonary pressures may be variably polyphasic and the tracheal flows diphasic. Exhalation involves an anterior shift of the liver by action of the transverse abdominal muscles, while inhalation proceeds due to contraction of the diaphragmatic muscle pulling the liver caudad. The various costal muscles facilitate air flow by shifting the position of the ribs. They also play a role in fixation of the flexible rib cage so that it resists the aspirating and compressing actions of the hepatic piston. The pattern of muscular activity shifts as the trunk is immersed; expiration becomes passive and inspiration requires increased muscular effort. The ribs, instead of changing position with each breath are comparatively fixed by the costal muscles, while changes in the volume of the pleural cavity are caused almost exclusively by movements of the hepatic piston.

Alligators and Crocodiles↗
PubMed1976

The caecilian ear: further observations.

The structure of the ear is examined in two species of caecilians, Ichthyophis glutinosus and I. orthoplicatus, and the sensitivity to aerial sounds is assessed in terms of the electrical potentials of the cochlea. The results are in general agreement with previous reports on other caecilian species.

Action Potentials↗
PubMed1976

Ear and hearing in Sphenodon punctatus.

Observations on Sphenodon punctatus have revealed new features of the anatomy of the ear,and measurements in a living specimen by means of cochlear potentials show the form and level of this ear's performance in sound reception. For an animal lacking an external ear opening and a functional tympanic membrane, the sensitivity of from 100-900 Hz is surprisingly good in low tones with peak response around 200-400 Hz. The inner ear is well developed, with a tectorial membrane connected to a tectorial plate that extends throughout the cochlea. The best region of sensitivity agrees well with the main frequency components of the animal's vocalizations.

Action Potentials↗
PubMed1975

Muscle activity in rat locomotion: movement analysis and electromyography of the flexors and extensors of the elbow.

Footfall patterns and time sequence of activity are described for white rats conditioned to run freely in an activity wheel (which they drive). Motion is described in terms of soft contact, hard contact, soft contact, and flip phases. Duration of stride decreases and length of stride increases from walk to trot to canter to gallop. Myographic analysis shows that the brachialis has a major tonic function after it fires strongly during the flip phase and during much of the hard contact phase. Animals running at canter or gallop show major asymmetries between forelimb muscles on the first paw and on the lead paw sides.

Animals↗
PubMed1975

The amphisbaenian ear: Blanus cinereus and Diplometopon zarudnyi.

Observations on the structure and function of the ear in amphisbaenians have been extended to two new species: to Blanus cinereus of the family Amphisbaenidae and Diplometopon zarudnyi of the family Trogonophidae. Blanus, considered one of the most primitive of this group of reptiles, shows a distinctive form of sound-receptive mechanism. The usual extracolumella is lacking, and the columella attaches to a cartilaginous plate beneath the skin posterior to the facial area. Diplometopon zarudnyi, a highly modified trogonophid, shows a columella and extracolumella of massive dimensions, with considerable calcification of the latter process. Cochlear potential measurements revealed the levels of auditory sensitivity in these species. A peculiar feature is the degree of stability of the ear's responses in the presence of large variations in body temperature.

Animals↗