Branchial Arches Flashcards
How many branchial arches are there?
5 (1,2,3,4,6)
Why is there no 5th branchial arch?
It fails to develop and doesn’t become anything.
When do the branchial arches appear?
Week 4-5.
What separates all of the branchial arches?
Separated by pouches on the inside and branchial clefts on the outside.
How does the palate form?
Primary palate forms from front-nasal process (medial-nasal process).
Secondary palate forms from palatal shelves of the maxillary process (1st pharyngeal arch) which fuse at the palatine raphe (midline).
What structures does the primary palate give rise to?
Incisors and bone.
What structures does the secondary palate give rise to?
- Hard palate (including maxilla and palatine bones).
- Soft palate (including
extrinsic muscles: tensor veli palatini, levator ve
li palatini, palatoglossus, palatopharyngeus,
musculus uvulae). - Teeth (canines to molars).
When do nasal processes fuse?
7th week
What happens if there are defects in the fusion of the fronto-nasal processes and palatal shelves of maxillary processes?
Cleft palate/lip
What does the 1st branchial arch form?
Maxillary process and mandibular process
What nerve innervates the 1st branchial arch?
V3 of trigeminal (CN V)
Where is the Meckel’s cartilage located?
In the mandible. Mostly disappears except the incus and the malleus (of the middle ear).
What muscles are formed from the 1st branchial arch?
Muscles of mastication.
What can arise from abnormalities in the 1st branchial arch?
Treacher Collins Syndrome (underdeveloped face).
Pierre Robin Sequence (underdeveloped mandible, cleft palate).
What does the 2nd branchial arch form?
Hyoid arch:
- Stapes.
- Styloid process.
- Upper part of hyoid bone.
- Lesser cornu.
What nerve innervates the 2nd branchial arch?
CN VII - facial
What muscles are formed from the 2nd branchial arch?
Muscles of facial expression
What does the cartilage of the 3rd branchial arch form?
- Greater cornu.
- Lower part of hyoid bone.
What muscles are formed from the 3rd branchial arch?
Stylopharyngeus muscle
What nerve innervates the 3rd branchial arch?
CN IX - glosspharyngeal
What does the cartilage of the 4th branchial arch form?
Laryngeal cartilages, e.g. thyroid.
What muscles are formed from the 4th branchial arch?
Pharyngeal constrictor muscles (inferior, superior, middle).
What nerve innervates the 4th branchial arch?
CN X - vagus (superior laryngeal branch)
What does the cartilage of the 6th branchial arch form?
Laryngeal cartilages, e.g. cricoid.
What muscles are formed from the 6th branchial arch?
Intrinsic laryngeal muscles.
What nerve innervates the 6th branchial arch?
CN X - vagus (recurrent laryngeal branch)
What lines the brachial clefts?
Ectoderm
Which branchial cleft forms a structure in the adult?
1st branchial cleft.
Where is the 1st branchial cleft located?
Between the 1st and 2nd branchial arches.
What does the 1st branchial cleft form?
External auditory canal/meatus.
What is the meatal plug?
Epithelial plate of cells formed by the ectoderm at the bottom of the cleft at month 3.
Why is there only 1 branchial cleft?
The mesenchyme from the 2nd arch expands and fuses with the 6th arch, blocking off other clefts. Therefore, all other clefts obliterate during development.
What happens if there is incomplete fusion of the 2nd and 6th branchial arch?
Branchial sinus (small hole in the neck).
What are the consequences of a branchial sinus?
Formation of cysts or fistulas which can damage the facial nerve.
What lines branchial pouches?
Endoderm.
What does the 1st branchial pouch form?
Tubotympanic recess
What does the 2nd branchial pouch form?
Palatine tonsils
What does the 3rd branchial pouch form?
Inferior parathyroid gland and thymus.
What does the 4th branchial pouch form?
Superior parathyroid glands.
What does the 5th branchial pouch form?
Ultimobranchial body (incorporated into thyroid).
Which duct is commonly lost?
Thyroglossal duct.
What happens if the Thyroglossal duct remains?
It can cause a thyroglossal cyst.
What is connected by the Thyroglossal duct?
The developing thyroid gland to the wall.
What does the distal portion of the 1st branchial pouch form?
Primitive tympanic cavity (middle ear)
What does the proximal region of the 1st branchial pouch form?
Eustachian tube.
Which branchial arches are involved in tongue development?
1st arch - anterior 2/3 tongue
3rd and 4th arch - posterior 1/3 of tongue
Which cells give rise to tongue muscles?
Myogenic cells (when they migrate from the occipital somite via the hypoglossal chord).
Where do the tongue muscles originate from?
Mesoderm and occipital somites.
What is a somite?
Body region formed during development.
It forms segmented vertebrae and associated tendons/muscles.
What is ankyloglossia?
Tongue tie.
What causes ankyloglossia?
Mesenchyme failing to regress so tongue is attached to floor of mouth.
