15. Pharyngeal Arch Development (Dennis) Flashcards
What muscles come from the fourth arch?
What cranial nerve innervates them?
Cricothyroid, levator veli palatini and the constrictors of the pharynx.
CN X
What is a cervical cyst?
remnant of the cervical sinus and or 2nd pharyngeal groove
persists and forms enlarging, cyst in neck, inferior to angle of mandible
They are typically asymptomatic until they get larger and fill with fluid and cellular debris.
Pharyngeal Arch Components
NCC-derived mesenchyme-All CT in head, including dermis and smooth muscle
Paraxial Mesoderm-forms sleketal and facial musculature from PA
Lateral Plate Mesoderm-angioblasts differentiate into endothelium for BV
Prechordal plate mesoderm-extraocular musculature (obicularis oculi)
What general structures are found in each pharyngeal arch?
What forms the body of the hyoid bone?
Hypopharyngeal eminence (from PA 3 and PA 4)
What is responsible for the formation of the maxillary and mandibular components of pharyngeal arch 1?
Neural crest cell migration into the area.
What is the “cervical sinus?”
A depression in ectoderm caused by PA 2 overgrowing PA 3 and PA 4. This leads to a common pharyngeal groove “sinus” for pharyngeal grooves 2,3, and 4.
Fistula occurs when a canal opens into the tonsillar sinus into the external side of the neck-persistent parts of 2nd groove and pouch.
What muscles come from the second arch?
What cranial nerve innervates them?
Stapedius and the muscles of facial expression.
CN VII
What embryological structure gives rise to the distal internal carotid?
Extensions of the dorsal aortae.
From what does the thyroid gland develop?
A median thickening in the endoderm of the primordial pharynx.
What is Treacher-Collins syndrome?
What is the cause?
(Mandibulofacial dysostosis)
Treacher-Collins syndrome (mandibulofacial dysostosis)
• Malar hypoplasia w/ down-slanting palpebral fissures, defects
of lower eyelids, deformed external ears, & sometimes middle
& internal ears
• Autosomal dominant disorder; mutations in Treacher Collins–
Franceschetti syndrome 1 gene (TCOF1)
• Encodes for the protein TREACLE, involved in ribosome
biogenesis
• Truncated in TCS leading to ↑↑ apoptosis of cranial NCC
What is Meckel’s cartilage?
What is it’s function?
The cartilage of pharyngeal arch 1.
Used as a model for osteoblasts to form the mandible. After the mandible is created, Meckel’s cartilgae will degenerate.
Also, two nodules break off and serve as a precursor from the malleus and incus.
What is formed by the cartilage of the third pharyngeal arch?
Greater cornu of the hyoid bone.
What embryological layer gives rise to the thyroid parafollicular cells (C Cells)?
Neural crest cells
The majority of the developing pharyngeal arches are what type of tissue?
Neural crest cells.