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Anatomy.10
Development of Head & Neck
| Question | Answer |
|---|---|
| When does development of the face & its related tissues begin to form? | During the fourth week. |
| What embryonic layers are involved in facial development? | All threee layers. (ectoderm, mesoderm, & endoderm) |
| What does the facial development include? | The formation of the primitive mouth, mandibular arch, maxillary process, frontonasal process, & nose. |
| What processes does facial development depend on? | The five facial processes: the single frontonasal process, the paired maxillary processes & the paired mandibular processes. |
| What does the frontonasal process become? | The upper portion of the face. |
| What does the maxillary process become? | The middle portion of the face. |
| What does the mandibular process become? | The lower portion of the face. |
| What is the time period of facial development? | It starts in the fourth week and will be completed later in the twelfth week within the fetal period. |
| How do most of the facial tissues develop? | By fusion of swellings or tissues on the same surface of the embryo. |
| Describe fusion. | A cleft of groove is created by growth, morphogenesis & differentiation. These grooves are eliminated because adjacent mesenchyme grows & merges beneath the external ectoderm. |
| What direction in relation to the cranial base does the face grow? | overall growth is in a inferior & anterior directon. |
| What is the stomodeum? | The primitive mouth, which initially appears as a shallow depression in the embryonic surface. |
| What is the oropharyngeal membrane? | It is a temporary membrane, consisting of external ectoderm overlying endoderm. It separates the stomodeum from the primitive pharynx. |
| What happens when the oropharyngeal membrane disintegrates? | The depth of the primitive mouth increases & allows access from the internal primitive pharynx to the outside fluids. |
| What will the stomodeum become? | The oral cavity. |
| What will become the teeth and associated tissues? | The oral epithelium. |
| After formation of the stomodeum what two bulges of tissue appear inferior to the primitive mouth? | The two mandibular processes. |
| What does the mandibular process consist of? | A core of mesenchyme partially formed by neural crest cells that migrate to the facial region & covered externally by ectoderm & internally by endoderm. |
| Mandibular arch. | The formation of the two mandibular processes that fuse at the midline. |
| Meckel's cartilage | Cartilage that forms during the growth of the mandibular arch. It forms on each side of the mandibular arch. |
| What happens to Meckel's cartilage? | Most of it disappears as the bony mandible forms. |
| What happens to a portion of Meckel's cartilage? | It participates in the formation of the middle ear bones. (malleus, incus, and stapes) |
| What does the mandibular arch become? | The lower lip, mandible, mandibular teeth & associated tissues. |
| What does part of the perichondrium surrounding Meckel's cartilage become? | Ligaments of the jaws and middle ear. |
| What does the mesoderm of the mandibular arch form? | The muscles of mastication, some palatal muscles & suprahyoid muscles. |
| The muscles derived from the mandibular arch are innervated by what nerve? | The trigeminal nerve. (aka...the nerve of the 1st arch, the cranial nerve) |
| What is at the most cephalic end of the embryo, and is the cranial boundary of the stomodeum? | The frontonasal process-a bulge of tissue in the upper facial area, it is formed from mesenchyme near the brain. |
| What structures will the frontonasal process become? | forehead, bridge of the nose |
| Placodes? | Rounded areas of specialized thickened ectoderm found at the location of developing special sense organs. Located on the outer surface. |
| Name the three types of placodes & what they become. | lens placodes-eyes, otic placodes-internal ear, nasal placodes-nose |
| What is formed as a depression in the center of each nasal placode? | Nasal pits |
| What do nasal pits develop into? | The nasal cavities. |
| medial nasal processess | The middle portion of the tissue growing around the nasal placodes-they look like two crescent-shaped swellings. |
| What is formed when the medial nasal processes fuse together externally? | The middle portion of the nose & center portion of the upper lip and the philtrum region |
| What is formed when the medial nasal processes fuse together internally? | it grows inferiorly on the inside of the stomodeum to form the intermaxillary segment (or premaxillary segment) |
| What does the intermaxillary segment later form? | The maxillary incisors & associated tissues, the primary palate & the nasal septum. |
| What are the two crescent-shaped swelling on the outer portion of the nasal pits? | The lateral nasal processes |
| What do the two lateral nasal processes form? | The alae, or sides of the nose. |
| What is formed by the fusion of the lateral nasal, maxillary & medial nasal processes? | the nares, or nostrils |
| What is formed from the mandibular arch superiorly & anteriorly on each side of the stomodeum? | The maxillary process |
| What does the maxillary process consist of? | It is formed from mesenchyme provided by neural crest cells. (neuromesenchyme or ectomesenchyme) |
| What will the maxillary process become? | the midface, including the side of the upper lip, cheeks, secondary palate (palatal shelves), posterior portion of the maxilla, max canines, post teeth & assoc. tissue, zygomatic bones & portions of the temporal bones. |
| What is formed by the fusion of the maxillary processes & the mandibular arch? | labial commissures |
| How is the upper lip formed? | From the fusion of the two maxillary processes with each medial nasal process. |
| What is formed from the fusion of each maxillary process with the lateral nasal process? | Nasolacrimal cord |
| What does the nasolacrimal cord become? | the nasolacrimal duct |
| What is developing during the same time of the development of the face? | the neck |
| What is formed from the anterior portion of the foregut? | The primitive pharynx |
| What does the branchial apparatus (or pharyngeal apparatus) consists of? | branchial arches, branchial grooves & membranes & pharyngeal pouches |
| What are branchial arches? | Six pairs of U-shaped bars with a core of mesenchyme. |
| What are branchial arches made of? | They have a core of mesenchyme, covered externally by ectoderm & lined internally by endoderm. |
| What does each paired branchial arch contain? | developing cartilage, nerve, vascular, & muscular components within it's mesodemal core. |
| What do the branchial arches support? | The lateral walls of the primitive pharynx. |
| Which branchial arches form the neck? | The lower four pairs of arches. |
| What is the name of the second branchial arch? | Hyoid arch |
| What is the name of the cartlidge within the hyoid arch? | Reichert's cartilage |
| What does part of the Reichert's cartilage become? | middle ear bone, a process of temporal bone, and portions of the hyoid bone & ligament of the hyoid bone |
| What does the mesoderm of the hyoid arch form? | muscles of facial expression, middle ear muscles & suprahyoid muscles |
| The muscles derived from the hyoid arch are intervated by what nerve? | the facial nerve (seventh cranial nerve) |
| What is the name of the third branchial arch? | Neither the third, fourth or sixth branchial arches are named. |
| Where is the fifth branchial arch? | The fifth branchial arches are so rudimentary that they are absent in humans or are included with the fourth branchial arches. |
| What is the cartilage associated with the third branchial arches? | The 3rd, 4th & 6th arches have cartilage but they do not have names. |
| What is the cartilage of the 3rd branchial arch responsible for? | The formation of portions of the hyoid bone. |
| What muscle is derived from the mesoderm of the 3rd branchial arches? | the pharyngeal muscle |
| What nerve innervates the 3rd branchial arch? | the glossopharyngeal nerve (9th cranial nerve) |
| What are the cartilages associated with the 4th & 6th branchial arches responsible for? | They are associated with the formation of the laryngeal cartilages. |
| What muscles are derived from the mesoderm of the 4th & 6th branchial arches? | larynx and pharynx |
| What nerve innervates the 4th & 6th branchial arch? | vagus (10th cranial nerve) |
| What are branchial grooves? | Also called pharyngeal grooves, they are external grooves found between the branchial arches. |
| What do the branchial grooves form? | The first groove forms the external auditory meatus(ear canal). The last four are obliterated to give the neck a smooth contour. |
| What is the first branchial membrane or pharyngeal membrane? | It is a double-layered membrane that consists of the ectoderm of the branchial groove and the endoderm of the branchial pouch. |
| What does the first branchial membrane become? | It develops into the tympanic membrane. (ear drum) |
| What do the 2nd, 3rd & 4th branchial membranes become? | nothing they are just temporary structures of the embryo. |
| What are the balloon like structures between the branchial arches? | Pharyngeal pouches |
| What do the first pharyngeal pouches become? | The auditory tubes & tympanic cavities. |
| What do the second pharyngeal pouches & walls become? | palatine tonsillar tissue |
| What do the third & fourth pharyngeal pouches give rise to? | thymus & parathyroid glands |
| What is the palate formed from? | Two separate embryonic structures--the primary palate & the secondary palate. |
| Name the stages of development of the palate. | The formation of the primary palate. The formation of the secondary palate. The completion of the palate |
| Where does the nasal septum grom from? | from the fused medial nasal processes |
| What causes the paired nasal cavity & single oral cavity in the fetus to become completely separate? | The fusion of the nasal septum with the final palate. |
| What does the tongue develop from? | From independent swellings located internally on the floor of the primitive pharynx, formed by teh first four branchial arches. |
| The body of the tongue develops from...? | The first branchial arch. |
| The base of the tongue develops from...? | The second, third, & fourth branchial arches. |
Created by:
llgalby