China
Africa
Explore chapters and articles related to this topic
Mitochondrial Dysfunction and Hearing Loss
Published in Shamim I. Ahmad, Handbook of Mitochondrial Dysfunction, 2019
This part is also associated with first and second branchial arches, the cavity and auditive tube have their origin in an expansion of the pharyngeal pouches; for this reason these areas have epithelium from endodermic origin; otherwise the tympanic membrane has tissues from the 3 germinal layers. Around the sixth week there is a mesenchymal condensation whose origin was the neural crest; this condensation will start the ossicles of the ear. It is until the last stages of gestation that the unnecessary mesenchyme completely disappears, due to the process of reabsorption and programmed cell death and the ossicles stay suspended inside the cavity. The somitomeres develops the muscle cells related to the first and second arches, that include the tensor tympani and stapedius muscles.6,7
Formation of the Cranial Base and Craniofacial Joints
Published in D. Dixon Andrew, A.N. Hoyte David, Ronning Olli, Fundamentals of Craniofacial Growth, 2017
Although cranial somitomeres do not condense to form somites and their presence has been doubted, the current consensus is that they do exist. They appear serially homologous to somites derived from trunk mesoderm, forming whorls of mesenchymal cells and giving some validity to the much-debated concept of vertebrate head segmentation (Alberch and Kollar, 1988; Jeffs and Keynes, 1990). In view of the accepted transient nature of somitomeres in the head of the embryo, an alternative view is that, although the caudal part of the developing skull shows this segmental pattern, the rostral part, which is unsegmented, is not homologous to trunk structures. Thus it has been suggested that the fore-part of the head represents a new development in vertebrate evolution, the “New Head” hypothesis (Gans and Northcutt, 1983; Northcutt and Gans, 1983).
Thyroid-Stimulating Hormone Receptor Expression on Primary Cultured Human Extraocular Muscle Myoblasts
Published in Current Eye Research, 2018
Hee-Young Choi, HyeShin Jeon, Jae Wook Yang, Jeong Hyo Ahn, Jae Ho Jung
Extraocular muscles (EOMs) differ from other skeletal muscles in several respects. In the embryo, EOM develop from somitomeres rather than from conventional mesoderm.1 Furthermore, EOMs are innervated by cranial nuclei rather than by spinal cord motor neurons, and contain atypical fiber types that express patterns of myosin heavy chain not observed in fast or slow twitch muscle fibers.2,3 From a disease perspective, EOMs are unaffected in Duchenne muscular dystrophy, despite the widespread damage observed in all other skeletal muscle types during the course of this disease,4 and are also unaffected by aging.5 However, EOMs are affected by certain diseases, such as, myasthenia gravis, congenital fibrosis syndrome, and thyroid-associated ophthalmopathy (TAO). TAO (also referred to as Graves’s ophthalmopathy) is a component of an autoimmune process that can affect orbital fibroblasts and orbital connective tissue, and the underlying pathophysiology of TAO is believed to be due to an antibody-mediated reaction against thyroid-stimulating hormone receptor (TSHR) on orbit fibroblasts.6 Although autoantibodies, cytokines, and immune-inflammatory cells also contribute to TAO,7 TSHR is believed to be the main autoantigen in the TAO pathogenesis.