Head and Neck development Flashcards
Folding of embryo forms these two structures
primitive mouth (stomodeum) and forgut
What forms on either side in the floor of the pharynx during formation of foregut and stomodeum
Five pairs of pharyngeal arches
What do the pharyngeal arches consist of?
Mesodermal core covered by ectoderm, and lined by pharyngeal endoderm (EXCEPT the first)
Each arch appears as a swelling containing a cartilaginous rod form by?
Neural crest cells
Sequential swellings are separated by constrictions caused by these invaginations of the ectoderm. How many?
Pharyngeal clefts, 4
Evaginations of the endoderm. How many?
Pharyngeal pouches, 4
The narrow, constricted areas between clefts and pouches.
Pharyngeal membranes
In more primitive vertebrates, the membranes between clefts and pouches function for/form?
Gill slits or functioning gills. This doesn’t occur in humans, and are no longer necessary for breathing and filter feeding. Freed for other uses.
Muscle precursors derive from?
Paraxial somitomeres (recall paraxial mesoderm forms somites which go on to form myotome, dermatome, and sclerotome)
Arch 1 correlates with which CN?
CN V (Trigeminal, both)
Arch 2 correlates with which CN?
CN VII (Facial, both)
Arch 3 correlates with which CN?
CN IX (glossopharyngeal, both)
Arch 4 and 6 correlate with which CN?
CN X (Vagus, both)
Each cartilaginous rod that has migrated into the arch from rhombomeres make up these 4 important structures:
embryonic hindbrain, muscle precursors, aortic arch artery, and associated nerve
Transiently divided segment of the developing neural tube, within the hindbrain region in the area that will eventually become the rhombencephalon
Rhombomere, appear as a series of constricted swellings in the neural tube
What does the primitive mouth area is lined by what derived epithelium?
Ectodermal
The epithelial layer of the pharynx is derived from?
Endoderm
In humans the first arch cartilages persist as the Palatopterygoquadrate bars and Meckle’s cartilage (from maxilla and mandible process, respectively). What do their upper ends become?
The incus and malleus bones of the middle ear
Membrane bone from the neural crest mesenchyme develops and surrounded the remaining first arch cartilage to form these 4 bones:
Maxillary, Mandibular, zygomatic (cheek bones), and squamous temporal bones.
The first arch somitomeric mesoderm yields these 5 muscles:
- Muscles of mastication
- Tensor tympani
- Tensor veli palatini
- Anterior belly of digastric
- Mylohyloid
Second arch cartilage gives rise to these 3 bones:
- lesser cornu and upper rim of hyoid bone
- third ossicle of middle ear (stapes)
- styloid process
Muscles associated with second arch (4)
All muscles of facial expression including:
- platysma
- stylohyoid
- stapedius
- posterior belly of digastric
Third arch cartilage gives rise to this bone:
Greater cornu and lower rim of hyoid bone
The only muscle developed from third arch
Stylopharyngeous (innervated by CN IX)
What does the artery of the third arch give rise to?
Common carotid and base (first part) of the internal carotid
What do the fourth and sixth arches develop into? (1 with 5 parts)
laryngeal cartilage:
- thyroid
- cricothyroid
- arytenoid
- coniculate
- cuneiform
Muscles derived from the fourth arch mesoderm (3)
- Pharyngeal constrictors
- Cricothyroid
- levator veli palatine + other palatal muscles
Muscles derived from the sixth arch (2)
- intrinsic muscles of larynx
2. striated muscle of esophagus
Primary nerve [of vagus nerve] of the fourth arch derivative
superior laryngeal branch of vagus nerve
Innervation of the sixty arch muscles are from which nerve?
Recurrent laryngeal branch of the vagus nerve
The vagus nerve also contributes to innervation of the soft palate and pharyngeal constrictors through its contributions to what?
The pharyngeal plexus
What happens to the fifth arch?
In humans, it either never forms or is rudimentary and disappears
The first pharyngeal pouch expands to form these two structures
- Tubotympanic recess- gives rise to tympanic cavity of the middle ear
- Pharyngotympanic tube (eustachian tube/auditory tube) connecting the middle ear cavity and nasal pharynx
What does the pharyngeal membrane between the first clefts and pouches form?
The tympanic membrane (eardrum)
What does the second pouch form?
The palatine tonsils
The third pouch gives rise to what two regions?
A solid dorsal region and a hollow elongated ventral region
Where does the thymus originate from?
Ventral regions of the third pouches
Solid cords that break their connection with the pharynx migrate bilaterally and eventually form what?
The thorax, fuse into a single gland
Where does the inferior parathyroid gland originate from?
The dorsal region of the third pouch
Which pouch in addition to the third pouch has dorsal and ventral regions?
The fourth pouches
What two important structures does the fourth pouch form?
- Superior parathyroid (dorsal)
2. Ultimobranchial body (ventral)
Of neural crest origin, these cells give rise to the calcitonin secreting C cells of the parafollicular thyroid
Ultimobranchial body (small organ found in the neck region)
The last 3 pharyngeal clefts usually disappear and become covered by the second arch, however the first cleft becomes these two structures:
- external acoustic meatus (ear canal)
2. External layer of tympanic membrane
This develops by proliferation of cells in the floor of the pharynx between the first and second pouches
Thyroid gland
The most common congenital malformation of the head and neck
Unilateral cleft lip (failure of one of maxillary prominence to fuse with medial nasal prominence of same side)
Cleft palate, a defect distinct from cleft lip, is usually classified as anterior or posterior, distinguishable by their relationship to what?
The incisive foramen
First arch syndrome, the lumping together of first arch, is usually a result from failure of what?
Failure of neural crest cells to migrate into the arch
DiGeorge Syndrome
complex constellation of anomalies caused by deletion of chromosome 22 (first arch anomalies, immunological deficiencies with thymus, deficiencies of thyroid and parathyroid glands, cardiovascular anomalies)
Common denominator for DiGeorge syndrome
Impaired neural crest migration into the third and fourth arches
The hard palate is formed in how many stages?
2
This segment contributes to the upper lip (philtrum) and a jaw component carrying the incisor teeth, forming the triangular primary palate
Intermaxillary segment (has deep palatal compartments)
What forms the secondary palate?
Formed by paired outgrowth of the maxilla
Ventrally, what undergoes endochondrial ossification to form the hard palate?
Mesenchymal condensations
Posteriorly, what condenses to form the soft palate?
Myogenic mesenchyme
Expansion of the face continues after birth by development and expansion of
paransal sinuses
Paransal sinues (air filled spaces) develop as diverticular of the lateral nasal wall and invade and expand within which 4 bones?
- Maxillary
- Ethmoid
- Sphenoid
- Frontal
Mandibulofacial dysostosis, genetic basis, inherited as autosomal dominant (first arch syndrome)
Treacher Collins
The tongue develops from which arch?
1, 3, and 4
What forms the intrinsic and extrinsic muscles of the tongue?
migrating occipital somite mesoderm
What innervate the muscles in tongue derived from occipital somites?
hypoglossal nerve CN XII
The mucosa of the anterior two-thirds of the tongue receives general sensory innervation from which nerve?
CN V
The posterior third of the tongue received its innervation for both general and taste from which nerve?
CN IX (glossophyrangeal)
A small area on the dorsal most part of the root or pharyngeal part of tongue receives general and taste sensation from?
superior laryngeal branch of CN X (vagus)
Taste to the anterior two-thirds is from what nerve?
Chorda tympani branch of CN VII (facial)
Most recent evidence is that taste buds form independtly in this, but survive only if what are present?
Form in lingual epithelium, need nerves to survive
All “glossus” muscles (muscles of palate) are innervated by CN XII, except for this muscle
Palatoglossus
The five facial swellings
An unpaired frontonasal prominence on anterior end of developing embryo, and paired maxillary and mandibular prominences (form from growth and division of the paired first pharyngeal arches)
The five prominences form this major facial feature
The nose
What forms the bridge of the nose?
The frontonasal prominence
Formation of the tongue
Pharyngeal arches 1, 3, and 4
The thyroid develops from an invagination of the tongue endoderm between what two structures? Later indicated by what foramen?
Tuberculum impar and copula linguae. Foramen cecum
Through where does the thyroid migrate to its porper position?
Thyroglossal duct
Unilateral cleft lip can result from these two factors:
- maxillary prominence fails to fuse with medial nasal prominence
- underlying somitomeric mesoderm and neural crest fail to expand, resulting in a “persistent labial groove”
What does the intermaxillary segment form?
The philtrum of the lip, the incisors (4), and the primary palate
Palatine shelves
outgrowths of maxillary prominences
The secondary palate forms from outgrowths of these structures
palatine shelves, maxillary promimences
palatine shelves project downward on either side of tongue but later attain a horizontal postition and fuse along the ________ to form the ______
palatine raphe, secondary palate
Where do the primary and secondary palates fuse? to form what?
incisive foramen, definitive palate
