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Macromolecular Absorption From The Digestive Tract In Young Vertebrates
Published in Károly Baintner, Intestinal Absorption of Macromolecules and Immune Transmission from Mother to Young, 2019
It is more or less possible to reconstruct the absorptive process if, after the first feeding, samples are taken periodically for electron microscopic examination. In the precolostral piglet, the nuclei tend to be localized in the apical third of the enterocyte, and the Golgi apparatus is found subnuclearly.1337 The cells take up colostrum through the intermicrovillus pores into the ACS, then pass it to the subapical vacuoles which fuse into a single or several large eosinophilic droplets. As formulated by Staley,1360 “...the engorged end-pieces detach from the tubules, coalesce with other free end-pieces and eventually form vacuoles large enough to be seen by the light microscope.” If plenty of colostrum is available, the eosinophilic droplet may enlarge to cell size. The elevation of intracellular pressure may stop the further uptake of colostrum (Figure 47) until emptying of the vacuolar content. Payne and Marsh1120 called this phenomenon the “all or none law.” However, if the colostrum is taken up at a slower rate, the cell may carry out all the steps of transmission simultaneously.
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Published in Anton Sebastian, A Dictionary of the History of Medicine, 2018
Lucas, Keith (1879–1916) English neurophysiologist, born in Greenwich, and educated at Trinity College, Cambridge. Lecturer and Fellow of Trinity College Cambridge. He described the ‘all or none law’, that a given stimulus evokes a maximum contraction or no contraction at all in muscles. Together with his pupil, Lord Edgar Douglas Adrian (1889–1977), he showed the same principle in motor nerve fibers. His The Conduction of the Nervous Impulse was prepared by Adrian and published posthumously in 1917.
Solving The Mystery Of The Nerve Impulse
Published in Andrew P. Wickens, A History of the Brain, 2014
In 1912, a young Cambridge student with an exemplary first class degree in Natural Sciences called Edgar Douglas Adrian, joined Lucas’s laboratory to investigate whether nerve impulses followed the all-or-none law. Much inconsistent evidence had emerged concerning the possibility. One objection had come from the discovery that the electrical strength of an action potential weakened if passed through a cooled or anaesthetised section of nerve fibre. This implied a graded or partial response was possible – at least in some instances. To determine whether this was indeed the case, Adrian exposed a small segment of frog nerve to alcohol vapour, and then followed the passage of a nerve impulse along the fibre. The results showed that while the alcohol ‘block’ produced a decrement in the force of the signal, it was only short-lasting. In other words, the nervous impulse was like a burning train of gunpowder: as long as its embers were not totally extinguished, it would be recharged back to its full ‘strength’. This supported the all-or-none law. It also showed the flow of energy along a nerve fibre was not a passive process. Rather, there appeared to be a self-regenerative mechanism at work allowing the full force of the impulse to be reinstated.
Biomechanical analysis of the clinical characteristics of enlarged vestibular aqueduct syndrome with Mondini malformation
Published in Acta Oto-Laryngologica, 2020
Jia-Wei Han, Lin Wang, Hui Zhao, Shi-Ming Yang
Figure 3(A) shows the distal end of the vestibular aqueduct and endolymphatic sac. The endolymphatic sac is usually divided into three parts: proximal, intermediate and distal. This intermediate part has also been called rugose part due to its remarkable appearance with mucosal folds. These mucosal folds protruding into the lumen are as mobile as waterweeds. Therefore, when the endolymph flows to the distal part of the endolymphatic sac normally, its kinetic energy is small, the folds will deform with the direction of fluid movement, and the endolymph can pass through. However, when the change of cerebrospinal fluid pressure gives the endolymph more kinetic energy, these folds will rapidly deform and block the lumen on account of the rugose part’s narrow diameter, to prevent the countercurrent of the endolymph from affecting the homeostasis of the membranous labyrinth system. In conclusion, we believe that the rugose part has its function of ‘valve’. Figure 3(B) is a schematic diagram of the relevant structure when the vestibular aqueduct is enlarged. From the diagram, we found that with the enlargement of the vestibular aqueduct, these mucosal folds are not in contact with each other, and thus the valve function is no longer present. When the ‘valve’ is lost, it means that the change of cerebrospinal fluid pressure can directly damage the function of hearing and balance through the endolymph countercurrent. Furthermore, the expanded endolymphatic sac exacerbates the above process. Clinically, patients with EVA will suffer temporary or permanent hearing loss and vestibular dysfunction when encountering precipitating events that can cause changes in cerebrospinal fluid pressure, such as strenuous physical exercise, head trauma, severe long-term cough. And this clinical manifestation can also be explained by the above theory. Besides, the ‘valve’ appears to conform to the all-or-none law. That also explains that some authors found that the clinical manifestations of patients were not related to the extent of enlargement of the vestibular aqueduct [6]. As discussed above, we conclude that the ‘valve’ in the rugose part of the endolymphatic sac and the loss of its function under pathological conditions are the premise of researching the pathological mechanism of Enlarged Vestibular Aqueduct (EVA) syndrome from the perspective of biomechanics.