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Biomedical subjects

J L Cobb

Publications and source records attributed to J L Cobb.

At least 55 records · Page 3Linked to original sources
PubMed1978

An ultrastructural study of the dermal papulae of the starfish, Asterias rubens, with special reference to innervation of the muscles.

The ultrastructure of the dermal papulae of a starfish (Asterias rubens) is consistent with a respiratory function. The present study has shown no regions specialized for excretory mechanisms. The papulae consist of an outer ectodermal epithelium of sensory, support and gland cells and a small basiepithelial nerve plexus. A true basement membrane lies underneath the epithelium and regularly arranged longitudinal muscle bundles lie within the connective tissue. The coelomic cavity of the papulae is lined with ciliated endothelial cells, which overlie an irregular layer of circular muscles. A system of canals that are not lined by cells occurs at the base of the papulae with the circular muscles. The longitudinal and circular muscles show a different gross morphological arrangement and innervation. This paper proposes that there are "skeletal" and "visceral" types of smooth muscle in echinoderms and discusses this proposal at length.

Animals↗
PubMed1977

An ultra-structural study of the gills of Echinus esculentus.

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.

Animals↗
PubMed1977

Anatomical studies of simple invertebrate synapses utilizing stage rotation election microscopy and densitometry.

The radial nerve cords of starfish and the central ganglia of a gastropod mollusc were examined for the presence of chemical synapses. No structures with the degree of specialization of synapses in the vertebrate CNS were observed. Presumed chemical synapses, which possessed slight but variable paramembrane densities, were examined with a tilting stage. This showed that such densities were frequently due to overlap of vesicle and axon membrane within the section, which were resolved at the correct angle of tilt. Many structures resembled demonosomes. The necessity for care in interpreting the structure of chemical synapses in vertebrates is emphasized.

Animals↗
PubMed1975

Nerve-ending specializations in the central ganglia of Planorbis corneus.

The neuropile in the central ganglia of Planorbis corneus was studied by electron microscopy, using different fixatives. Several types of specialization were observed in the membranes of adjacent axonal processes, varying from only slight membrane thickenings to structures resembling desmosomes. Specialized structures similar to the 'spinule complexes' in mammalian brain are widely distributed in certain areas of neuropile. They consist of a small projection which invaginates a neighbouring neurone; the membranes are closely apposed and there is associated electron-dense material. The problem of identifying chemical synapses in this tissue is discussed. Many axonal processes are varicose, and it is suggested that varicosities may also be sites of transmitter release.

Animals↗
PubMed1973

Electrophysiology of cardiac function in teleosts: cholinergically mediated inhibition and rebound excitation.

1. A study has been made on the responses of the plaice (Pleuronectes platessa) heart, isolated and in situ to differential vagal stimulation using intra- and extracellular recording electrodes. The effects of direct application of acetylcholine and catecholamines and their respective blocking agents are also reported.2. Vagal stimulation at 7 Hz totally inhibits heart beat whilst stimulation at 2-3 Hz accelerates it. Both these effects are blocked by atropine (10(-6) g/ml.). Bretylium (10(-5) g/ml.) and pronethalol (10(-6) g/ml.) have no effect upon either response to vagal stimulation.3. On cessation of prolonged inhibitory vagal stimulation there is a marked increase in the heart rate, and in quiescent hearts one or two beats are initiated after stimulation.4. Vagal stimulation gives rise to a hyperpolarization in atrial cells. It is proposed that all the excitatory effects of vagal stimulation are due to rebound excitation from an inhibitory hyperpolarization. At high frequencies the hyperpolarizations summate to give rise to total inhibition. At lower frequencies of stimulation the heart beat is increased to rates dependent on interaction between the time course of the hyperpolarization and the refractory period of the heart. Both effects are cholinergically mediated.5. The rebound excitation in response to vagal stimulation (post-vagal tachycardia) persists in response to stimulation of the atrial myocardium in the presence of atropine (10(-6) g/ml.) and bretylium (10(-5) g/ml.). It is therefore suggested that this is a response of the muscle cell membrane to vagal stimulation and is not nerve-mediated.

Acetylcholine↗