Embryology of Head & Neck Flashcards
Define Pharyngeal (brachial) apparatus:
- Surrounds developing foregut
- Source of mesenchymal tissue that will form the head & neck, face, palate & nasal cavity structures
- Target for migrating neural crest cells that differentiate into skeletal, muscular and neural structures
What are the parts of the pharyngeal apparatus?
- Arches
- Clefts
- Pouches
- Membranes
What are the pharyngeal arches?
Bars of mesenchyme covered with ectoderm externally and endoderm internally. Form around the developing gut tube (pharynx)
- Contribute to viscerocranium
- Five pairs
- Lateral plate mesoderm forms initial shape of pharyngeal arches
- Branch of aorta associated with each arch
What is present by weeks 4-5?
Primordial of head, neck, face, palate & nasal cavity
What are the pharyngeal clefts (grooves)?
- Four pairs
- Surface ectoderm - lined invaginations
- Form between the pharyngeal arches (depressions between the arches)
What are the pharyngeal pouches?
- EPITHELIAL
- Develop in cranial to caudal direction
- Four pairs
- Endoderm - lined pouches along the lateral walls of the pharyngeal gut
- Located opposite the pharyngeal clefts
What are the pharyngeal membranes?
- Separate the ‘pouches’ from the ‘clefts’
- Consist of ectoderm (externally), endoderm (internally) and mesenchyme in between
- Membranes do NOT break down in humans, so clefts and pouches do not communicate! [no gills]
What are the five facial prominences?
- 1 Frontonasal prominence
- 2 Maxillary prominences (first pharyngeal arch mesenchyme)
- 2 Mandibular prominences (first pharyngeal arch mesenchyme)
What cell types migrate into the arches as they are forming?
- Mesoderm from Somites & Somitomeres
- Neural Crest
- Nerves
Where does mesoderm from somites and somitomeres go?
Migrate into the arches
- Eye muscle precursors from occipital somites
- Forms most of skeletal muscle in head & parts of skull
- Tongue precursors from occipital somites
What do neural crest cells that migrate to the pharyngeal arches form?
-Skeletal elements of the head & parts of the PNS
What pharyngeal membrane do you need to know about?
1st Membrane!
What structure develops from the 1st pharyngeal membrane?
Tympanic Membrane (only membrane to persist - has 3 layers: endoderm, mesoderm, ectoderm)
How many pharyngeal clefts are there?
4!
What develops from the first pharyngeal cleft?
External auditory meatus (epithelial lining)
What develops from the second, third and fourth pharyngeal cleft?
Cervical Sinus
- Normally disappears
- Lateral cervical (branchial) cyst or fistula when it persists
What develops from the first pharyngeal pouch?
Tubotympanic recess —> becomes:
- Auditory tube (epithelial lining)
- Tympanic or middle ear cavity (epithelial lining)
- Mastoid air cells
What develops from the second pharyngeal pouch?
-Palatine tonsils
epithelial component
What develops from the third pharyngeal pouch?
- Thymus (ventral)
- Inferior Parathyroid Glands (dorsal)
What develops from the fourth pharyngeal pouch?
- Superior parathyroid glands (dorsal)
- Ultimobranchial bodies (ventral) -AKA parafollicular cells of thyroid
What are the pharyngeal arches?
First, Second, Third, Fourth and Sixth
What nerve innervates each of the 5 arches?
1st - Trigeminal Nerve (V3)
2nd - Facial Nerve (CN VII)
3rd - Glossopharyngeal Nerve (CN IX)
4th - Vagus Nerve (CN X) - Superior Laryngeal
6th - Vagus Nerve (CN X) - Recurrent Laryngeal
What skeletal parts arise from the first pharyngeal arch?
Maxillary prominence (upper jaw): -Maxilla -Zygomatic -Squamous part of temporal bone (intramembranous ossification) Mandibular prominence (lower jaw): -Malleus -Incus (endochondral ossification) -Anterior Ligament of Malleus -Spin of Sphenoid -Sphenomandibular ligament (all from Meckel's Cartilage)
What cartilage does the first arch skeleton develop from?
Meckel’s Cartilage
What muscles derives from the first pharyngeal arch?
“Tense, tense, chew, chew”
- Muscles of mastication (temporals, masseter)
- Mylohyoid
- Anterior belly of digastric
- Tensor tympani
- Tensor Veli Palatini
What skeletal components are from the 2nd pharyngeal arch?
-Stapes -Styloid process
-Stylohyoid Ligament
-Lesser cornu
-Upper body of hyoid bone
[All from Reichert’s cartilage]
What muscle components are from the 2nd pharyngeal arch?
- Muscles of facial expression
- Posterior belly of the digastric
- Stylohyoid
- Stapedius
What skeletal components are from the 3rd pharyngeal arch?
- Lower body of the hyoid bone
- Greater Cornu
What muscle is derived from the 3rd pharyngeal arch?
-Stylopharyngeus
What skeletal components are derived from the fourth and sixth arch?
Thyroid Cartilage
Cricoid Cartilage
What muscles are derived from the 4th pharyngeal arch?
- Muscles of soft palate (except tensor veil palatini)
- Muscles of pharynx (except stylopharyngeus)
- Cricothyroid
- Cricopharyngeus
What muscles are derived from the 6th pharyngeal arch?
- Intrinsic muscle of larynx (except cricothyroid)
- Striated (upper) muscle of esophagus
What innervates the palatoglossal muscle? Motor or sensory?
Palatoglossus (Vagus Nerve, CN X) - Motor
What does motor innervation for almost all tongue muscles?
Hypoglossal Nerve (CN XII)
What provides general sensory information to the 4th arch/middle back of tongue?
Internal Laryngeal Nerve (CN X)
What provides general and special sensory information to the 3rd arch (back 1/3 of tongue & vallate papillae)?
Glossopharyngeal Nerve (CN IX)
What supplies general sensory information to the anterior 2/3 of the tongue?
Lingual Nerve (V3)
What supplies special sensory information to the anterior 2/3 of the tongue?
Chorda tympani (CN VII) -taste afferents
What supplies general & special visceral sensory information (GI, heart, etc.) from the epiglottis?
Vagus Nerve (CN X)
What part of the tongue develops from 1st arch mesenchyme?
Anterior 2/3 of tongue (oral part)
-From median tongue bud and two distal tongue buds (these overgrow and fuse)
What part of the tongue develops from 2nd arch mesenchyme?
Copula
-3rd arch overgrows 2nd arch, so arch 2 doesn’t contribute to tongue mucosa
What part of the tongue develops from 3rd arch mesenchyme?
Posterior 1/3 (root of pharyngeal part)
-Hypobranchial eminence
What part of the tongue develops from 4th arch mesenchyme?
- Hypobranchial eminence
- Epiglottis
- Extreme posterior tongue
What do myoblasts become?
Most tongue muscles are derived from them (they migrate with hypoglossal nerve from occipital myotomes)
What is the terminal sulcus?
Boundary between anterior 2/3 and posterior 1/3 of tongue
-Former position of buccopharyngeal membrane
Where can you have stenosis or atresia (narrowed/closed off)?
- Ear Canal
- Nasal Passage
- Larynx
- Esophagus
- Trachea
Where can you have clefts?
- Ear pit
- Nasal masses
- Face
- Lip
- Palate
- Larynx
- Tracheal-Esophageal
What are some vestigial structures that were supposed to be obliterated but persisted?
- Thyroglossal duct
- Branchial cleft
What is caused by a deficiency of neural crest cells migrating into the first pharyngeal arch?
Treacher Collns Syndrome & Pierre Robin Syndrome
What are the symptoms and cause of Treacher Collins Syndrome?
- Mandibulofacial dysostosis
- Abnormal development of structures derived from the first arch
- Hypoplasia of upper & lower jaw; external & middle ear deformities, palate & eyelid defects
- Conductive hearing loss
- Autosomal dominant and/or teratogenic cause
What can the face look like for a child with Treacher Collins?
- Eyelid Malformation
- Hypoplastic Cheek and Jaw
- External Ear malformation and low-set
- “Fishmouth” appearance
What is Pierre Robin Syndrome?
- Deficiency of neural crest cells migrating into the arch
- Abnormal development of structures derived from the first arch
- Micrognathia + large, posteriorly placed tongue ->airway obstruction (glossoptosis)
- U-shaped cleft palate problems
What causes Pierre Robin Syndrome?
Genetic and/or environmental etiology
What can be used in severe cases of Pierre Robin syndrome?
- Distraction osteogenesis (pulling mandible apart to induce bone growth) (mandibular lengthening) is employed
- May need tracheostomy to maintain airway while mandibular lengthening is occurring
- 1/8,500 births
What is the function of the inferior and superior parathyroid glands?
Increase blood Ca2+
What is the function of the Ultimobranchial bodies?
Decrease blood Ca2+ (Calcitonin)
What is DiGeorge Syndrome?
- Genetic and/or environmental causes (micro deletion of Chr. 22q11.2)
- No thymus or parathyroids (diminished immunity, hypocalcemia)
- Failure of neural crest migration into arches –> 3rd & 4th pouch failure & hypoplasia of 1st arch (cleft palate, low set ears, poor feeding, delayed speech)
- Heart defects, poor circulation, poor muscle tone
What are the “CATCH-22” Symptoms of DiGeorge Syndrome?
Cardiac Abnormalities Abnormal facies Thymic aplasia Cleft palate Hypocalcemia 22 - deletion/abnormality of chromosome 22
What happens when the cervical sinus (from the 2nd, 3rd & 4th clefts) persists?
It is called a lateral cervical (branchial) cyst or fistula
