ANAT 2626 Before We Are Born Embryology Notes

ANAT 2626 Before We Are Born Embryology Notes - BEFORE WE...

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BEFORE WE ARE BORN Chapter 11, pg 151-167 Pharyngeal Arches -- develops as neural crest cells -- migrate from rhombomeres 2-7 -- 1 st pair primordium of the jaw -- contributions from rhombomere 2 -- pairs 1-4 are visible, 5 and 6 are rudimentary -- arches are separated by clefts, called pharyngeal grooves 1 st pharyngeal arch (mandibular arch) -- develops as 2 prominences: 1. maxillary prominence (smaller) -- gives rise to maxilla, zygomatic bone, and squamous part of temporal bone 2. mandibular arch -- forms mandible -- plays major role in development of face 2 nd pharyngeal arch (hyoid arch) -- major contribution to the hyoid bone -- pharyngeal arches support the lateral walls of the primordial pharynx -- the primordial pharynx is derived from the cranial part of the foregut -- primordial mouth = stomodeum Components of Pharyngeal Arches -- initially they are: -- a core of mesenchyme -- covered externally by ectoderm -- covered internally by endoderm -- migration of neural crest cells into the arches and their differentiation into mesenchyme produces the maxillary and mandibular prominences of the 1 st arch Fate of Pharyngeal Arches -- during the 5 th week of development, 2 nd pharyngeal arches enlarges and overgrows the 3 rd and 4 th arches, forming an ectodermal depression called the cervical sinus -- the 2 nd , 3 rd , and 4 th disappear, so too does the cervical sinus, eventually giving the neck a smooth contour -- components of typical pharyngeal arches: -- aortic arch arises from truncus arteriosis -- cartilaginous rod forms skeleton of arch
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-- muscular component differentiates into muscles of the head and neck -- nerve supplies the mucosa and muscles derived from arch Derivatives of Aortic Arches ** will be shown at the end of this test material Derivatives of the Pharyngeal Arch Cartilages * 1 st arch cartilage (Meckel’s cartilage) -- dorsal end becomes ossified to form 2 middle ear bones, the malleus and the incus -- middle part regresses, but its perichondrium forms the anterior ligament of malleus and the sphenomandibular ligament -- ventral end forms horseshoe shaped primordium of the mandible * 2 nd arch cartilage (Reichert’s cartilage) -- dorsal end ossifies to form the stapes of the middle ear and the styloid process -- ventral end ossifies to form the lesser cornu and superior part of the body of the hyoid * 3 rd arch cartilage -- ossifies to form the greater cornu and inferior part of the body of the hyoid * 4 th and 6 th arch cartilages -- fuse to form the laryngeal cartilages, except for the epiglottis -- the epiglottis is formed from mesenchyme of the 3 rd and 4 th pharyngeal arches Derivatives of Pharyngeal Arch Muscles (see Table11-1 in BWAB) 1 st arch muscles of mastication -- mylohyoid and anterior belly of digastric -- tensor tympani -- tensor veli palatine 2 nd arch muscles of facial expression -- stapedius -- stylohyoid -- posterior belly of digastric 3 rd arch stylopharyngeus 4 th and 6 th arch cricothyrooid -- levator veli palatine
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This note was uploaded on 11/22/2011 for the course ANAT 2626 taught by Professor Ronaldg.mayne during the Winter '11 term at Life Chiropractic College West.

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ANAT 2626 Before We Are Born Embryology Notes - BEFORE WE...

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