Embryology Flashcards
How many branchial arches are there + how many branchial arches does the neck develop from
6
5
What is mesenchyme
Embryonic connective tissue
What 2 regions of the embryo is there no mesoderm and why is this
Head and tail region - to form a hole for the mouth and anus
Which germ layer are the somites derived from + what do they help develop
Paraxial mesoderm
Cranial skeleton
Where do branchial arches develop around
Around the future mouth and pharynx
What week gestation do pre-branchial arches form
4
What does each branchial arch contain (3)
A skeletal element
Artery
Nerve
Why does the neck only develop from 5 branchial arches when there’s 6 in total
Arch 5 disappears
How many mesenchymal processes does the face develop from + name them
5:
1 frontonasal process
2 maxillary processes
2 mandibular processes
1st branchial arch innervated by what nerve
CN V3
2nd branchial arch innervated by what nerve
Facial nerve
3rd branchial arch innervated by what nerve
Glossopharyngeal nerve
4th branchial arch innervated by what nerve
Superior laryngeal nerve (branch of vagus)
6th branchial arch innervated by what nerve
Recurrent laryngeal nerve (branch of vagus)
Cranial vault (neurocranium) formed of flat bones which is formed by what type of ossification
Membranous
Base of skull formed of irregular bones which is formed by what type of ossification
Endochondral
Viscerocranium (Facial skeleton) formed by what embryologically
Mesenchyme of branchial arches and sensory capsules
Name a congenital facial defect
Cleft lip + palate
What causes cleft lip
failure of fusion of the maxillary and medial nasal (frontonasal) processes (failure of formation primary palate)
What causes cleft palate
failure of fusion of the palatine shelves (failure of formation of the secondary palate)
Name a congenital abnormality of the head
Craniosynotosis
What is craniosynotosis
Skull bones fused too early
Which branchial arch is affected in treacher collins syndrome
1st branchial arch abnormality
Some cells at the crest of the neural fold (before fully becoming a closed tube) in the ectoderm midline separate to form what kind of cells
Neural crest cells - mix with mesoderm in the head and neck region of embryo
What 3 tissues make up branchial arches
Ectoderm
Mesoderm + neural crest cells
Endoderm
What branchial arch do the maxillary processes arise from
1st branchial arch mesoderm
What branchial arch do the mandibular processes arise from
1st branchial arch mesoderm
What tissue do the frontonasal processes arise from
Mesenchyme superior to future mouth
Describe how the face forms from the mandibular & frontonasal (medial nasal) processes (4)
- The 2 mandibular processes fuse in the midline
- Ectoderm thickens to form 2 NASAL PLACODES which push inwards (invaginates) to form NOSTRILS, thus separating the frontonasal process –> 2 LATERAL NASAL PROCESSES
- The nasal placodes migrate downwards and fuse, forming a MEDIAL NASAL PROCESS in the midline
- The medial nasal process further grows downwards and laterally to form a process called the PHILTRUM
Describe the formation of the palate (3)
- Medial nasal process grows downwards and forms the philtrum –> PRIMARY PALATE
- From the maxillary processes, 2 palatine shelves grow inwards
- The palatine shelves meet in the midline to form the SECONDARY PALATE
ORAL CAVITY AND NASAL CAVITY ARE NOW SEPARATE
Cleft lip is due to failure of fusion of what processes
Maxillary and medial nasal (frontonasal) processes
Cleft palate is due to failure of fusion of what processes
Palatine shelves (they fuse to form the secondary palate)
Structures arising from 1st branchial arch (4)
Anterior belly of digastric
Muscles of mastication -
Malleus + incus (of ossicle)
Anterior 2/3 tongue
Structures arising from 2nd branchial arch (4)
Muscles of facial expression
Posterior belly of digastric
Stapes
Suprahyoid muscles
Structures arising from 3rd branchial arch (3)
Lower hyoid bone
Infrahyoid muscles
Posterior 1/3 tongue
Structures arising from 4th branchial arch (2)
Thyroid cartilage
Larynx
Structures arising from 6th branchial arch (1)
Cricoid cartilage
