embryology Flashcards
pharyngeal apparatus
embryological component which gives rise to much of head and neck structures
what does the pharyngeal apparatus consist of
arches, pouches, grooves and membranes
how many arches are there
6 but 5 regresses early so only 5 functional
development of arches
- Develop in week 4 and 5
○ Arch 1 - day 22
○ Arch 2 + 3 - day 24
Arch 4 + 6 - day 29
components of each pharyngeal arch
- Core of mesenchyme derived from paraxial and lateral plate mesoderm, which gives rise to the musculature
- Neural crest cells which give rise to the connective tissues and smooth muscle
- Cranial nerve component which gives rise to innervation (sensory or motor)
Artery (aortic arch arteries)
first arch characteristics
trigeminal nerve
dorsal forms maxilla and zygomatic bone
Ventral; mandibular process, and part of temporal bone- squamous part - flat part of temporal bone
forms incus and malleus ear ossicles
second arch charactersitcs
reichert cartilage
Forms third ossicle and part of temporal bone and part of hyoid bone
facial nerve
third arch characteristcs
rest of hyoid bone
stylopharyngeus muscle
glossopharyngeal nerve
4th and 6th arches nerve
vagus nerve
what are the clefts
external depressions between arches
what does the first cleft give rise to
invaginates in and gives rise to the external acoustic meatus
what do the 2nd, 3rd and 4th clefts form
looses contact with the outside and forms the cervical sinus (usually obliterates)
what are cervical custs and fistuals due to
failure of obliteration of the 2nd to 4th cleft
clinical charactertistcs of cysts and fistulas
- Typically found along the anterior border of the sternocleidomastoid
- Often not seen at birth, only enlarges during childhood
Can be asymptomatic or can become infected
developmental events of first pouch
tympanic membrane
middle ear
eustachian tube
developmental events of 2nd pouch
palatine tonsil
developmental events of 3rd pouch
inferior parathyroid gland
thymus
4th pouch developmental events
superior parathyroid gland
ultimobrachial body - tyroid gland/ c cells
development of the tongue
- Usually appears in 4th week by two lateral swellings and one midline swelling
- More midline swellings then form - copula and epiglottal
- Anterior mucosa derived from CN V3
- Posterior mucosa derived from CN IX
Myoblasts originates from occipital somites and receive innervation from CN XII
what arch contributes to facial expression
pharyngeal arch 2
