Prenatal Development of the Head and Neck PDF

Created by Turbolearn AI Focus on What You Can Control Focus on the things that you can control. Don't waste your time and energy on what has already happened. Instead, think about what you can do from now moving forward. Organize Your Sock Drawer and Your Study Strat...

Created by Turbolearn AI Focus on What You Can Control Focus on the things that you can control. Don't waste your time and energy on what has already happened. Instead, think about what you can do from now moving forward. Organize Your Sock Drawer and Your Study Strategies Organize your sock drawer Engage in high-yield study strategies for anatomy and other courses Prenatal Development of the Head and Neck In the next two lectures, we will explore the prenatal development of the head and neck to make sense of some of the complex anatomy and interesting patterns of motor and sensory innervation. Ode to a Placode There once was a flat sheet of cells that were stumpy and ugly as hell. But one day, they arose, stood tall on their toes, and declared they were the best cells of all. Presumptuously, they cried that their lineage was high, and right proudly, they bragged of their codes. But soon it was clear, they weren't like the ear, and they were nixed in their dreams as placodes. Semantics, they screamed. Please maintain our dreams. But their pleas were unheeded and late. And now to this day, in repast, they must lay as a misconstrued flat neural plate. By TD Sadler Preview of Head and Neck Development Nasal placode: future opening of the nasal cavity, nostrils Stomatium: future opening of the oral cavity EAM ExternalAuditoryMeatus: outer ear hole Auricular hillock: future auricle Page 1  Created by Turbolearn AI Structure Description Nasal placode Future opening of the nasal cavity, nostrils Stomatium Future opening of the oral cavity EAM ExternalAuditoryMeatus Outer ear hole Auricular hillock Future auricle Development of the Head and Neck The head and neck develop from a combination of ectodermal placodes, pharyngeal arches, and neural crest cells. Ectodermal placodes: give rise to special sensory organs and structures, such as the ear, nose, and eye Pharyngeal arches: give rise to cartilaginous structures, such as the skull and other cartilages Neural crest cells: give rise to many structures, including the facial skeleton and related structures Overview of Head and Neck Development Stage Description a Tube within a tube design, neural tube hasn't closed off yet Emergence of pharyngeal arches, condensations of mesenchyme with an b outer covering of ectoderm and inner lining of endoderm c Pharyngeal arches reach towards the midline d 6 pharyngeal arches form, 2 of which will regress e Development of the head and neck continues Germ Layers and Their Final Derivatives Ectoderm: gives rise to special structures, such as the skin, nervous system, and sensory organs Endoderm: gives rise to epithelial linings of tubes, such as the digestive system and respiratory system Mesoderm: gives rise to muscles, bones, and connective tissue Page 2  Created by Turbolearn AI Germ Layer Final Derivatives Ectoderm Skin, nervous system, sensory organs Endoderm Epithelial linings of tubes, digestive system, respiratory system Mesoderm Muscles, bones, connective tissue Note: Neural crest cells are an important player in head and neck development, particularly in facial development and anomalies.## Pharynx and Cranial Development Cranium Structure The cranium can be divided into two parts: Facial component visceralcranium: contains organs Neurocranium: directly surrounds and supports the brain Embryonic Skull Development Structure Germ Layer Origin Facial skeleton Neural crest cells Vault and cranial base Paraxial mesoderm Laryngeal cartilages Lateral plate mesoderm Pharyngeal Arches The pharyngeal arches are a crucial part of cranial development. Neural crest cells migrate from the neural tube to form these arches. "Remember, those neural crest cells started after the neural tube was formed. They were part of that ectoderm, that neural ectoderm that then break off and then migrate into different parts of the body." The pharyngeal arches give rise to various structures, including: Page 3  Created by Turbolearn AI Maxilla Temporal bones Mandible Styloid process Hyoid bone Auditory ossicles Laryngeal cartilages Pharyngeal Arch Structure A pharyngeal arch consists of: Mesenchyme connectivetissue Ectoderm outerlayer Endoderm innerlayer Artery and related vein Cartilaginous rod Muscle Sensory or motor nerves Pharyngeal Arch Development The pharyngeal arches develop from cranial to caudal, with 6 pairs forming. One arch regresses, leaving 5 distinct arches. Here's a lateral view of a human embryo from weeks 4 to 5, showing the development of the pharyngeal arches: Arch 1, 2, and 3 form Clefts form on the outside Pouches form on the inside withinthepharynx Note: The term "brachial" may be used in older texts or by seasoned clinicians, but we'll use the term "pharyngeal arch" as it relates to the throat.## Pharyngeal Arches and their Derivatives ️ In this section, we will explore the pharyngeal arches, their derivatives, and the structures that arise from them. Page 4  Created by Turbolearn AI Coronal Section of the Pharynx A coronal section of the pharynx shows the arrangement of structures within the pharyngeal arches. Pharyngeal Arches and their Derivatives Arch Derivatives 1st Mandible, 2 of 3 auditory ossicles malleusandincus Mandibular Stapes, styloid process, stylohyoid ligament, lesser horn, and part of 2nd the body of the hyoid 3rd Inferior portion of the body of the hyoid, greater horns 4th Upper portion of the thyroid cartilage 6th Inferior portion of the thyroid cartilage, cartilages of the larynx Muscles related to the Arches Arch Muscle Group Muscles 1st Muscles of Mastication Temporalis, Masseter, Mylohyoid Muscles of Facial Muscles of facial expression, Posterior 2nd Expression digastric, stylohyoid 3rd Stylopharyngeus 4th and Muscles of the Pharynx and Muscles in the pharynx and larynx 6th Larynx Cranial Nerves Associated with the Arches Arch Muscle Group Cranial Nerve 1st Muscles of Mastication V3 Mandibulardivision 2nd Muscles of Facial Expression VII F acialnerve 3rd IX Glossopharyngealnerve 4th and 6th Muscles of the Pharynx and Larynx X V agusnerve Page 5  Created by Turbolearn AI Summary The pharyngeal arches give rise to various structures in the head and neck, including bones, cartilages, muscles, and nerves. The derivatives of each arch are closely related to the muscles and cranial nerves associated with that arch.## Pharyngeal Arches and Cranial Nerves Each pharyngeal arch is associated with: A cranial nerve A muscle or group of muscles that share similar functions Skeletal components, including bone or cartilage Anomalies of Pharyngeal Arches Treacher Collins Syndrome MandibulofacialDystosis A first arch anomaly, characterized by: Hypoplastic bones underdevelopedorsmaller Smaller mandible lowerpartoftheface Recessed cheeks External ear anomalies: Auricle not developed normally External auditory meatus atretic notpresent Conduction deafness due to lack of auditory ossicles malleusandincus Issues with eyes, pupils, and trachea Pierre Robin Sequence A first arch anomaly, characterized by: Micronathia smallmandible Cleft palate Glossotosis droopingtongue Issues with breathing, suckling, and feeding due to cleft palate Hearing problems due to atretic external auditory meatus Page 6  Created by Turbolearn AI DiGeorge Syndrome A 3rd and 4th arch anomaly, characterized by: Absence of thymus and parathyroid glands Issues with thyroid function Anomalous facial features: Shorter upper lip philtrum Lower-set ears Notching in the auricle Clefts within the nose and palate Pharyngeal Pouches and Clefts Pharyngeal pouches are formed from endoderm and contribute to specific structures, while pharyngeal clefts are formed from ectoderm and contribute to other structures. Pharyngeal Pouches Pouch Derivative Structure Number External auditory meatus, auditory tube, and part of the tympanic 1 cavity 2 Tonsils 3 Parathyroid glands 4 Thymus Pharyngeal Clefts Cleft Number Derivative Structure 1 External auditory meatus 2-4 Obliterated, overgrown by tissue from arch 2 Relationships between Pharyngeal Arches, Pouches, and Clefts Page 7  Created by Turbolearn AI Pharyngeal Arches Pharyngeal Pouches Pharyngeal Clefts 1st arch Pouch 1 Cleft 1 2nd arch Pouch 2 Cleft 2 3rd arch Pouch 3 Cleft 3 4th arch Pouch 4 Cleft 4 Note: This table shows the relationships between pharyngeal arches, pouches, and clefts, but does not imply a direct connection between them.## Cervical Fistula or Cyst Developmental Background Developmental anomalies in the pouches and clefts can lead to structural issues in newborns, pediatric patients, or even adults. Cervical Fistula or Cyst Formation Normally, second arch tissue grows over the second, third, and fourth clefts. However, if this growth is incomplete, remnants of these clefts can form: Benign fluid-filled cysts Fistulas connectionswiththeoutsideofthebody Characteristics Located primarily along the anterior border of the sternocleidomastoid muscle lateralneck May be small and undetectable or large and fluid-filled Can be drained outpatient Typically, nontender fluid-filled masses May compress structures in the lateral neck, including: Jugular veins Carotid Nerves Page 8  Created by Turbolearn AI Imaging CT or axial section can help identify cervical cysts Example image: large fluid-filled mass in the lateral neck, between internal and external jugular veins Important Notes Cervical cysts can be a potential source of compression on surrounding structures Understanding pouches and clefts is crucial for identifying and addressing developmental anomalies Practice Question "What is the typical location of a cervical fistula or cyst?" Answer: Along the anterior border of the sternocleidomastoid muscle lateralneck Blank Chart for Note-Takers Structure Description Second arch tissue Second, third, and fourth clefts Cervical cyst Sternocleidomastoid muscle Please fill in the chart to reinforce your understanding of the material! Page 9