LEC-11 Neuroembryology (Head & Neck Development) Flashcards
What happens in week 2 of development?
- Formation of trophoblast
- Cytotrophoblast
- Syncytiotrophoblast
- Bilmanar disk formation (from embryoblast)
- Epiblast
- Hypoblast
- Two cavities
- Amniotic
- Chorionic
- Two extraembryonic mesoderm layers
- Somatopleuric
- Splanchnopleuric
What happens in week 3 of development?
- Gastrulation
- Neurulation
- Cephalocaudal and lateral folding
What does the endoderm give rise to?
- Epithelial lining
- Pharyngeal pouches
What does the mesoderm give rise to?
- Notochord (nucleus pulposus)
- Somites
- Sclerotome (bone and cartilage)
- Dermatome (dermis)
- Myotome (muscles)
What does the ectoderm give rise to?
- Neural tube (CNS-motor neurons, preganglionic ANS)
- Neural crest (PNS-postganglionic ANS)
- Epithelial component of skin (glands, invaginations)
- Stomodeum (lining of future oral cavity)
- Nasal pit, external auditory meatus
- Thickens to form placodes (olfactory, lens and optic)
What is the auricle of the external ear derived from?
1st and 2nd pharyngeal arch
What is the external auditory canal derived from?
1st pharyngeal cleft
What is the pharyngotympanic tube derived from?
1st pharyngeal pouch
What is the cervical sinus derived from?
2nd, 3rd, and 4th pharyngeal grooves merge to form it
Eventually disappears
What is the trigeminal (V) nerve derived from?
1st pharyngeal arch
What is the facial (VII) nerve derived from?
2nd pharyngeal arch
What is the glossopharyngeal (IX) nerve derived from?
3rd pharyngeal arch
What is the vagus (X) nerve derived from?
4th and 6th pharyngeal arch
What does the 5th pharyngeal arch become?
It is vestigial and doesn’t develop
The muscles of mastication are supplied by what pharyngeal arch?
1st arch (CN V)
The muscles of facial expression are supplied by what pharyngeal arch?
2nd arch (CN VII)
The stylopharyngeus muscle is supplied by what pharyngeal arch?
3rd arch (CN IX)
The laryngeal muscles are supplied by what pharyngeal arch?
4th arch (CN X)
The pharyngeal muscles are supplied by what pharyngeal arch?
6th arch (CN X)
What arch is responsible for the Malleus, Incus, (sphenoMandibular lig.), and disappearing of the rest of Meckel’s cartilage?
1st arch
What arch is responsible for the Stapes, Styloid process, Superior half of hyoid, and Stylohyoid ligament?
2nd arch
What arch is responsible for the inferior half of body and greater horn of hyoid?
3rd arch
What arch is responsible for the thyroid and epiglottic cartilages of larynx?
4th arch
What arch is responsible for the laryngeal cartilages (cricoid, arytenoid, corniculate)?
6th arch
What does the 1st pharyngeal pouch form?
- Pharyngotympanic tube
- Middle ear
What does the 2nd pharyngeal pouch form?
Palatine tonsil (epithelial crypts)
What does the 3rd pharyngeal pouch form?
- Inferior parathyroid gland (migrates inferiorly)
- Thymus
What does the 4th pharyngeal pouch become?
- Superior parathyroid glands
- Ultimobranchial body (C cells of thyroid gland)
In regards to the development of the face, what does the first pharyngeal arch become?
- Has both maxillary and mandibular parts
- Surrounds stomodeum (so has ectoderm on outside and inside)
- Become upper and lower jaw regions
What is the frontonasal process?
The mesenchyme around the forebrain that develops into the “rest of the face” that isn’t derived from the 1st pharyngeal arch
What are the nasal placodes and what do they form?
Part of the frontonasal process that invaginate to form medial and lateral swellings on either side of the nasal pits
What does the medial swelling (from nasal placodes) form?
Intermaxillary segment
What does the lateral swelling (from nasal placodes) form?
Nasolacrimal groove
How is the nasolacrimal duct formed?
From the extension of the nasolacrimal groove (that is the cleft between the lateral nasal swelling and maxillary part of first arch)
How is the palate formed?
From the fusion of the pirmary palate (intermaxillary segment) and secondary palate (maxillary part of first pharyngeal arch)
How is a cleft lip formed?
From the failure of the medial nasal and maxillary prominences to fuse with each other
How is a cleft palate formed?
From the failure of the palatine processes to fuse with each other
How is the anterior 2/3 of the tongue formed?
From the two lateral lingual swellings (that arise from the 1st pair of pharyngeal arches)
How is the posterior 1/3 of the tongue formed?
From the two caudal lingual swellings (that arise from the 3rd and 4th pair of pharyngeal arches)
From what structure are taste buds (on anterior 2/3 of tongue) derived from?
From and overgrowth of the 2nd pair of pharyngeal arches
What are somitomeres?
7 segments that the paraxial mesoderm is organized into (form head region mesenchyme)
What are somites?
The further organization of somitomeres that form the rest of the body
How many somites are formed by the end of week 5?
~42-44 pairs
How many somites are left after some disappear during development?
~36-38 pairs (3 occipital, 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 3-5 coccygeal)
When do the first pair of somite appear and what is the rate at which more are formed?
- First Pair: Day 20
- Rate: 3 pairs/day in a craniocaudal sequence
What is resegmentation?
- Migration and subsequent fusion of the caudal half of each sclerotome towards the cephalif half of the subjacent sclerotome
- Results in spinal nerves exiting vertebral column through intervertebral foramina
What is hemivertebrae?
- Unilateral defects in formation of sclerotomes
- Causes congenital scoliosis of vertbebral column
What do defects in resegmentation result in?
- Fused vertebrae which also causes congenital scoliosis of vertebral column
