Pharyngeal Apparatus PDF

Pharyngeal Apparatus What is included in the pharyngeal apparatus? Pharyngeal (branchial) arches o Lined by ectoderm on the outside, Mesoderm core ▪ Paraxial mesoderm: Muscles ▪ Neural crest cells: Skeletal component and associated connective tis...

Pharyngeal Apparatus What is included in the pharyngeal apparatus? Pharyngeal (branchial) arches o Lined by ectoderm on the outside, Mesoderm core ▪ Paraxial mesoderm: Muscles ▪ Neural crest cells: Skeletal component and associated connective tissue ▪ Lateral plate mesoderm: Cartilage of arch 4 and 6Have nerve, artery, and cartilage o Lined by endoderm* on the inside Pharyngeal clefts (grooves) Pharyngeal pouches (endoderm) Pharyngeal membranes Thyroid and tongue development Except for arch 1 What is Epithelial-mesenchymal interactions? Endoderm signals to overlying ectoderm (1) and ectoderm signals to underlying neural crest (2) What are the characteristics of pharyngeal arches? Form in weeks 4 to 5 Five pharyngeal arches, numbered craniocaudally (1, 2, 3, 4, 6) Outer lining = ectoderm Core = Paraxial mesoderm, neural crest cells, and lateral plate mesoderm Each arch contains: An artery, Cartilage, and a cranial nerve Inner lining = endoderm. Except first arch List migration of neural crest cells to the pharyngeal apparatus. P1: Midbrain and rhombomeres 1-2 P2: Rhombomere 4 P3: Rhombomeres 6-7  P4: Rhombomeres 6-7 P6: Rhombomeres 6-7 What are the skeletal components of the pharyngeal arches? Some bones form directly from cartilage Other bones form from intramembranous ossification of neural crest cells What is the muscle and nerve supply for each arch? Paraxial mesoderm, and neural crest cells make up the core mesenchyme of the arches Arches 1-3 come from unsegmented paraxial mesoderm Arches 4 and 6 come from somites 1-5 Muscles of the tongue also migrate from somites 1-5 Arch 1: CN V Trigeminal Arch 2: CN VII Facial Arch 3: CN IX Glossopharyngeal Arch 4: CN X Vagus Arch 6: CN XII Hypoglossal Musculature: o Developing muscles migrate and do not always attach to bone and cartilage from their own pharyngeal arch o The nerve supply to each arch innervates the muscles that arise from that arch regardless of how far they migrate What are the skeletal components of first pharyngeal arch (mandibular)? Maxillary process o Maxillary cartilage (regresses) o Maxilla, zygomatic, palatine, lacrimal, vomer, and squamous part of temporal bones form from NCCs Mandibular process o Meckel’s cartilage: ▪ Malleus and incus  ▪ Anterior ligament of the malleus and sphenomandibular ligament o Mandible forms from migration of NCCs ▪ Micrognathia – mandibular hypoplasia What is the pharyngeal arch 1 innervation? Cranial nerve V (trigeminal nerve) o Sensory innervation: ophthalmic (V1), maxillary (V2), mandibular(V3) branches; supplies the skin of the face o Motor innervation: mandibular branch (V3); supplies the muscles of mastication What is the muscle formation from arch 1? Muscles of mastication: (Temporalis, masseter, medial and lateral pterygoids) Tensor veli palatini (not shown –soft palate) Tensor tympani (not shown –decreases tympanic membrane response to sound) Anterior belly of the digastric Mylohyoid What are the skeletal components of the second pharyngeal arch (hyoid)? Reichert cartilage: o Stapes (ossicle) o Styloid process of the temporal bone o Stylohyoid ligament: (suspends hyoid bone) o Lesser horn and upper body of the hyoid bone What are the nerves and muscles from pharyngeal arch? Cranial nerve VII, Facial innervates o Muscles of facial expression (buccinator, auricularis, frontalis, platysma, orbicularis oris and oculi)  o Stapedius (not shown – tympanic cavity) o Stylohyoid o Posterior belly of the digastric o Provides special sensory (taste) innervation for anterior 2/3 of tongue What are the skeletal components and innervation of the third pharyngeal arch? Skeletal component: Lower body and greater horn of the hyoid bone Mesoderm forms stylopharyngeus muscle Innervated by glossopharyngeal nerve IX What are the characteristics for the fourth and sixth pharyngeal arch? Paraxial mesoderm forms muscles of the larynx & pharynx o Cricothyroid, Constrictors of pharynx, Levator veli palatini, Intrinsic muscles of larynx, and Skeletal muscles of the upper esophagus Cartilages fuse to form the larynx Sensory innervation by CN X Vagus Most tongue muscles are innervated by CNXII, except palatoglossus CNX What are the Muscular, Neural, and Skeletal Derivatives of the Pharyngeal Arches? Arch 1: muscles of mastication, CN V, Meckel’s cartilage, malleus, incus Arch 2: muscles of facial expression, CN VII, upper body & lesser horn of hyoid, Reichert cartilage, stapes, styloid process of temporal bone Arch 3: stylopharyngeus muscle, CN IX, lower body & greater horn of hyoid Arch 4&6: pharyngeal muscles, CN X & XII, (thyroid and cricoid cartilage) What are the derivatives of the pharyngeal endoderm? First pouch – middle ear and auditory (eustachian) tube Second pouch – palatine tonsils Third pouch – inferior parathyroid glands and thymus Fourth pouch – ultimopharyngeal body – superior parathyroid glands and C cells of the thyroid Midline structures: tongue and thyroid What is the pharyngeal pouch 1? Tubotympanic recess forms epithelial lining of auditory tube and middle ear cavity Connection between the middle ear and the pharynx First pharyngeal membrane forms tympanic membrane What is the pharyngeal pouch 2? Endoderm gives rise to palatine tonsil epithelium and tonsillar fossa Invasion of mesoderm aids in formation of the primordial tonsil Lymphatic tissue invades later in fetal development What is the pharyngeal pouch 3? Has a dorsal and a ventral “wing” Dorsal region o inferior parathyroid glands Ventral region o thymus Both parathyroid glands and thymus migrate in a caudal and medial direction to their final locations What is the pharyngeal pouch 4? Dorsal region forms the superior parathyroid glands Ventral region forms the ultimopharyngeal body to form the parafollicular cells (C-cells) of the thyroid gland What are the Pharyngeal Clefts/Grooves & Pharyngeal Membranes? External auditory meatus forms from an invagination of cleft 1* Tympanic membrane is formed by first pharyngeal membrane Mesenchyme of arch 2 grows over clefts 2-3 and meets up with the epicardial ridge to cover cleft 4 which forms the cervical sinus More recent evidence suggests this may be from an invagination of the pharyngeal arch 2 outgrowth. What are the derivatives of the pharyngeal pouches and clefts? Pouch 1: tubotympanic recess Pouch 2: palatine tonsils Pouch 3: inferior parathyroid glands and thymus Pouch 4: superior parathyroid glands and C-cells of thyroid What are the characteristic of the thyroid gland? Thyroid diverticulum develops from the midline of the second pharyngeal arch at the foramen cecum Descends to its final position over the superior tracheal rings  Pharyngeal mesoderm induces ventral midline endoderm at the foramen cecum Begins as a thickened plate of endoderm and becomes the thyroid diverticulum Gland incorporates mesenchyme and buds off the foramen cecum Thyroglossal duct – strand of thyroid diverticulum that ultimately (usually) breaks down What are the locations of ectopic thyroid tissues? How is the tongue developed? Anterior two thirds (body) of the tongue form from pharyngeal arch 1 Root of the tongue is from arch 3 (and some arch 4) Terminal sulcus marks division between ectoderm and endoderm Connective tissue and vasculature come from neural crest cells The muscles of the tongue mainly migrate from occipital somites Complex innervation Oral tongue: o 1 median lingual swelling o 2 lateral lingual swellings Pharyngeal tongue: o Copula (2nd arch) gets overgrown by hypopharyngeal eminence (3rd & 4th arches) o Third arch mesoderm overgrows lateral second arch mesoderm o No second arch contribution to adult tongue What is the sensory innervation of the tongue? Epithelium of anterior two-thirds derived from first pharyngeal arch (CN V) Epithelium of posterior one-third mostly from third pharyngeal arch (CN IX) and some from 4th (CN X)  CN VII, IX, and X innervate the taste buds What is the motor innervation of the tongue muscles? Vagus X and Hypoglossal XII Note: Both typical and atypical developmental patterns are illustrated here. Do not memorize fistulas or aberrant/persistent locations for glands/cords What are the skeletal structures of the head and neck? Bone and cartilage form from mesenchyme Facial skeleton (blue) – neural crest cells Bones of cranium (red) – paraxial mesoderm Cartilage of larynx (yellow) – lateral plate mesoderm What is the early development of the facial processes/ prominences? Frontonasal process: Forehead, Optic vesicles, Nose and nasal septum, Philtrum of lip, Premaxilla and primary palate, and Rostral boundary of stomodeum o Medial nasal process (x2) o Lateral nasal process (x2)  o Stomodeum – primitive mouth o Oropharyngeal membrane –boundary between stomodeum and primitive pharynx (boundary between ectoderm and endoderm) o Frontonasal prominence o Nasal (olfactory) placodes – thickened regions of ectoderm that will give rise to the nasal pits Two maxillary processes: Secondary palate, Soft palate, Lateral upper lip, and Lateral boundary of stomodeum o Maxillary processes proliferate and move medially ▪ Fuse with medial nasal processes o Medial nasal processes fuse to form intermaxillary segment ▪ Intermaxillary segment: Philtrum of lip, Medial upper jaw (premaxilla), Primary palate, and Nasal septum o Nasolacrimal groove – boundary between lateral nasal process and maxillary process Two mandibular processes: Lower lip, jaw, and Caudal boundary of stomodeum What is Elimination of furrows vs Fusion of process? Elimination of furrows: o Proliferation of mesenchyme fills in furrows o Incomplete filling can result in a cleft Fusion of processes: o Requires proliferation of mesenchyme o Requires apoptosis of epithelial tissue o Disruptions can result in clefts What is the process of the development of the jaw and hard palate? Primary palate o Intermaxillary segment – fusion of the medial nasal processes that forms in the 5th to 6th week of development o Labial component: Forms the philtrum of the lip o Upper jaw component: Forms premaxilla of upper jaw o Palatal component: Forms the primary palate Secondary palate o Development: ▪ 6th to 12th week of development ▪ Primary palate has formed (yellow) ▪ Palatine (palatal) shelves: Downward growth of maxillary processes  ▪ Palatine shelves initially in depressed position and flank the elevated tongue o Formation: ▪ Palatine shelves fuse in an anterior-to-posterior direction ▪ Incisive foramen marks the midline division between the primary palate and secondary palate ▪ Palate fusion completes in week 12 of development: Epithelial seam between shelves breaks down Cleft lip and palate o Cleft lip – failure of maxillary process and medial nasal process (rarely: medial nasal processes) to fuse. Labial component only o Cleft lip and palate – includes palate o Why does it happen? ▪ Insufficient NCC proliferation in the: maxillary processes, intermaxillary segment, and disrupted growth in secondary palate ▪ Failure of epithelial seam to break down o What are the types of clefts? ▪ Incisive foramen – anatomical landmark that divides anterior and posterior cleft congenital anomalies ▪ Anterior cleft: unilateral cleft (A) bilateral cleft between primary and secondary palate (B) Failure of one or both lateral palatine shelves to fuse with intermaxillary segment ▪ Posterior cleft: lack of fusion of palatine shelves, can result in cleft uvula (C) Failure of palatine shelves to fuse with each other (and the nasal septum) o What is the division of the nasal and oral cavity? ▪ At 5-7 weeks the primary palate forms, but nasal cavity is open to oral cavity ▪ At 8-12 weeks, the secondary palate forms and fuses at the midline, dividing the nasal and oral cavities ▪ By 9 weeks, the nasal septum has also divided the nasal cavity o Why does cleft palate occur? ▪ Failure of primary and secondary palate to fuse ▪ Failure of secondary palate to fuse with itself ▪ Failure of nasal septum to fuse with secondary palate What is the process of the nose, nasal cavity, and oral cavity? Development of nasal cavity o Nasal placodes invaginate to form nasal pits o Frontonasal process gives rise to medial and lateral nasal processes o Nasal septum is a downward growth of the medial nasal processes (intermaxillary segment) that fuses with the palate o Maxillary processes grow medially and compress the medial nasal prominences toward the midline o The cleft between maxillary process and medial nasal process fills in Formation of the nasal cavity o Oronasal membrane initially separates nasal pits from oral cavity but later ruptures o Primitive choanae connect each nasal chamber to the oral cavity o Ectodermal epithelium becomes the olfactory epithelium Nasolacrimal (Naso-optic) Groove o Located at the junction between the lateral nasal process and maxillary process o Solid cord of ectoderm sinks into underlying mesenchyme o Cavitates to give rise to the nasolacrimal duct