Head and Neck Development Flashcards
1
Q
Pharyngeal arches
A
- 5 arches (1, 2, 3, 4, and 6) separated by a pharyngeal cleft on the outside (ectoderm) and a pharyngeal pouch on the inside (endoderm)
- Each arch has an artery, a nerve, cartilage, and mesenchyme
- Each pharyngeal nerve (a cranial nerve) is mixed- it has motor and sensory components
2
Q
First pharyngeal arch
A
- Has 2 subdivisions: the maxillary process (innervated by V2) and the mandibular process (V3)
- The frontonasal process (FNP) is anterior midline of the first arch (but its own structure) and is innervated by V1 (opthalmic)
3
Q
Innervation of arches 2, 3, 4, and 6
A
- Arch 2 from VII
- Arch 3 from IX
- Both arches 4 and 6 from X
4
Q
Carniofacial muscles
A
- Derived from paraxial mesoderm, but not from somites
- Maintain their early innervation pattern once it is established
- Some migrate w/ the migrating arch, some do not
- But can always trace the arch a muscle rose from by its innervation
5
Q
Pharyngeal arch cartilage
A
- 1st arch cartilage: template for formation of mandible and maxilla
- 2nd arch cartilage: supporting elements for jaw
- 3rd-6th arch cartilage: supporting elements for neck and larynx
6
Q
Pharyngeal mesenchyme
A
- Mesoderm and neural crest origin
- Mesoderm is source of cranial vascular endothelium and striated muscle
- Neural crest is the source of the dura, most of the vascular smooth muscle
- Cranial bones (and vascular smooth muscle) come from both
7
Q
Formation of palate
A
- Mandibular processes fuse in the midline
- Maxillary processes do not fuse at first, but are initially separated by the distal end of the FNP- intermaxillary segment (FNP is origin of philtrum of upper lip)
- FNP forms the primary palate (anterior 4 incisors)
- The palatal shelves from the maxillary processes form the secondary palate
- The primary palate and the anterior portion of the secondary palate become ossified to form the hard palate
- The remaining non-ossified portion is the soft palate
- Cleft palate: failure in fusion btwn the palatal shelves
- Cleft lip: failure in fusion of intermaxillary segment w/ either or both maxillary processes
8
Q
Formation of nasal cavity
A
- First forms by invagination from the surface ectoderm
- Innervated by CN V
- Nasal septum grows down the roof of the cavity and fuses w/ the superior side of the palate to divide the cavity in 2
9
Q
Formation and innervation of the oral cavity
A
- Oropharyngeal membrane is the only location of a direct contact btwn ectoderm and endoderm (no mesoderm btwn)
- This transition of ectoderm to endoderm lies w/in the oral cavity, anterior to the 1st pouch
- This is also the transition of sensory innervation from CN V (ectoderm) to CN IX (endoderm)
10
Q
Formation and innervation of the tongue
A
- Anterior 2/3 of the tongue forms from tongue buds derived from the 1st arch (ectodermal, CN V)
- The 3rd arch displaces the 2nd arch to the outside, and then creates the posterior 1/3 of the tongue (endodermal, CN IX)
- The very posterior end of the tongue derived from the 4th arch (endodermal, CN X)
- These nerves are only for somatosensory axons, special sensory taste axons run through slightly different pathways
- Special sensory taste in the anterior 2/3 of the tongue is from CN VII (2nd arch)
- Special sensory taste in posterior 1/3 is the same as somatosensory (CN IX and CN X, from arch 3 and 4 respectively)
11
Q
Muscles of the tongue
A
- Derived from the anterior-most (occipital) cerivcal somites, which migrate into the tongue (not pharyngeal muscles- not from pharyngeal arches)
- Tongue muscles are innervated by CN XII prior to migration and carry the innervation w/ them
12
Q
Development of the ear 1
A
- External ear (auricle) forms from 3 pairs of swellings outside the 1st (mandibular) and 2nd arches
- Inner ear is derived from surface ectoderm called otic placode, which buds off and moves inward (now otic vesicle)
- Otic placode originates btwn arches 2 and 3 and thus is not pharyngeal
- The otic vesicle acquired CN VIII innervation, corresponding to its position btwn arches 2 and 3 (which are innervated by CN VII and IX, respectively)
13
Q
Development of the ear 2
A
- External auditory meatus is derived from the 1st pharyngeal cleft (ectoderm)
- The tympanic cavity and auditory tube and derived from the 1st pharyngeal pouch (endoderm)
- Ear drum forms at the interface of the 1st pouch and the 1st cleft, so it has both ectodermal (V3) and endodermal (IX) innervation
- Not related to oropharyngeal membrane, since the eardrum does contain mesoderm
14
Q
Development of the thyroid
A
- Forms from the dorsal surface of what will become the tongue, just behind the junction of the 1st and 3rd arches (thus is endodermal)
- It descends through the tongue and migrates to straddle the larynx
- The connection to the dorsal surface of the tongue is the thyroglossal duct, which atrophies as the thyroid reaches the larynx
15
Q
Fate of pharyngeal pouches and clefts
A
- 1st pouch and cleft are involved in ear development
- All other clefts are irrelevant
- 2nd pouch-> palatine tonsils
- 3rd pouch-> inferior parathyroids and thymus
- 4th pouch-> superior parathyroids and ultimobranchial bodies
