Embryology of the Pharyngeal Arches and Ear Flashcards
what is gastrulation
formation of the trilaminar disc- happens in week 3
what happens in gastrulation
invagination of the epiblast cells through the primitive streak to form the definitive endoderm and mesoderm
what is the mesoderm organised into
paraxial, intermediate and lateral plates
what is the neural crest derived from
the ectoderm
what folding happens in the embry
lateral and craniocaudal
what does the neural crest form
melanocytes, craniofacial cartilage and bone, smooth muscle, peripheral and enteric neurons and glia, sympathetic ganglia
what do the pharyngeal arches form
much of the head an neck
when do the pharyngeal arches form
arch 1- day 22
arch 2 +3- day 24
arch 4+6- day 29
what is neuralation
formation of a round tube of neural cells
what number of pharyngeal arch doesnt form in humans
number 5
what are the three components of the pharyngeal apparatus
core pharyngeal arch
external pharyngeal cleft
internal pharyngeal pouch
what are the roles of the clefts and arches
separates the arches
what makes up the core pharyngeal arches
mesechymal tissue
what makes up the external pharyngeal cleft
ectoderm (as clefts on the outside)
what do the three germ layers form
ecto- central nervous system, peripheral nervous system, epithelia of eye, ear, nose, epidermis and appendages, mammary glands, enamel of teeth
meso- muscle, vasculature, lymph vessels, bone, connective tissue, kidneys, gonads
endo- epithial lining of GI and resp tracts, parenchyma of the tonsils liver thymus thyroid parathyroid pancreas, epithelial lining of bladder, tympanic cavity and antrum and auditary tube
what makes up the internal pharyngeal pouch
endo (as on the inside)
what makes up each pharyngeal arch
core mesenchyme derived from paraxial and lateral plate mesoderm
neural crest cells
cranial nerve component
artery (aortic arch arteries)
in the pharyngeal arch what does the core mesenchyme make
musculature of the face
in the pharyngeal arch what does the neural crest cells make
skeletal component of the face
in the pharyngeal arch what does the cranial nerve component make
innervation both sensory or motor
what nerves supply all the structures in the head and neck from pharyngeal arch 1
tigeminal nerve (V)- mandibular and maxillary divisions
what nerves supply all the structures in the head and neck from pharyngeal arch 2
facial nerve VII
what nerves supply all the structures in the head and neck from pharyngeal arch 3
glossopharyngeal nerve CN IX
what nerves supply all the structures in the head and neck from pharyngeal arch 4 and 6
vagus
what are the skeletal elements of the 1st pharyngeal arch
maxillary process (cranial portion):
- maxilla
- zygomatic bone
- squamous portion of temporal bone
mandibular process (caudal portion):
- forms meckels cartilage
- incus and malleus (ear ossicles)
- mandible
what are the muscles and nerves of the 1st pharyngeal arch
all musculature supplied by CNV3:
- muscles of mastication
- mylohyoid
- anterior belly of digastric
- tensor tympani
- tensor veli palatini
sensory supply to skin of face:
- V1 (ophthalmic)
- V2 (maxillary)
- V3 (mandibular)
what is the role of tensor tympani
dampens sound
what are the skeletal elements of the 2nd arch
cartilage- reicherts cartilage
skeletal derivatives:
- stapes
- styloid process of temporal bone
- stylohyoid ligament
- lesser horn of hyoid
- upper part of hyoid body
what are the muscle and nerve elements of the 2nd pharyngeal arch
all musculature supplied by CN VI (facial nerve):
- Muscles of facial expression
- posterior belly of digastric
- stylohyoid
- stapedius
- auricular muscles (move ears)
what are the skeletal elements of the 3rd pharyngeal arch
greater horn pf hyoid bone
lower part of hyoid bone
what are the muscle and nerve elements of the 3rd pharyngeal arch
stylopharyngeus
longitudinal pharyngeal muscle
supplied by the glossopharyngeal nerve
what are the skeletal elements of the 4th and 6th pharyngeal arch
laryngeal cartilages
what are the muscle elements of the 4th pharyngeal arch
- cricothyroid
- levator veli palatini
- pharyngeal constrictors
what are the muscle elements of the 6th pharyngeal arch
intrinsic laryngeal muscles (moves vocal chords)
what are the nerve elements of the 4th and 6th pharyngeal arch
both supplied by vagus nerve
arch 4- superior laryngeal nerve, pharyngeal plexus
arch 6- recurrent laryngeal nerve
what does the 1st pharyngeal cleft form
external acoustic meatus
what do the 2-4th pharyngeal clefts form
lose contact with outside and form the cervical sinus
what can happen if pharyngeal cleft 2 doesnt form properly
creates branchial sinus- bacteria can get in
can get internal fistulas
what does the 1st pharyngeal pouch form
middle ear, tympanic membrane, eustachian tube
what does the 2nd pharyngeal pouch
palatine tonsil
what does the third pharyngeal pouch form
inferior parathryoid gland
thymus
what does the fourth pharyngeal pouch form
superior parathyroid gland ultimobranchial body (thyroid gland/ C-cells)
what is the path of the thymus
Thymus lies on anterior mediastinum mostly then moves outwards.
As embryo starts to develop it will track its way down the way to thorax, unite with contralateral side and form thymus gland. Drags ifnferior parathyroid gland with it and develops over superior parathyroid gland which is derived from 4th pouch.
Thyroid gland descending down
Thymus drags down and drags parathyroid gland and lodges self in back of thyroid
what are the parts of the inner ear and what do they do
balance (semicircular canals)
hearing (organ of corti)
what makes up the middle ear
tympanic cavity
ossicles
what makes up the external ear
external auditory meatus
auricle (pinna)
what makes the otic placodes
ectoderm
how do the otic vesicles form
otic placode- otic pit- otic vesicle
what do the otic vesicles make
the inner ear
what gives rise to the semicircular canals
utricular portion
what gives rise to the cochlear
saccular portion
what is endolymph and perilymph
endo fluid inside the membranous labyrinth of the ear
peri fluid inbetween the membranous labyrinth of the ears
how do the semicircular canals form
at week 6 utricular portion starts to flatten itself out. Central area moves in. starts to create rings.
what is the crus ampullare
dilated end of the semicircular canals
what is the crus nonampullare
non dilated end of the semicircular canals
what is the crista ampullaris
within the ampulla of the semicircular canals
contains:
sensory cells for balance
vestibular fibres CN VIII
how does the cochlear duct develop
grows in spiral at weeks 6-8
surrounding mesenchyme becomes cartilagenous
how many coils of the cochlea
2.5
where is sound mostly conducted in the cochlear
organ of corti
what forms the oval window
neural crest cells
what forms the external auditory meatus
dorsal part of first pharyngeal cleft
how is the external ear developed
Month 3 – epithelial cells proliferate to form Meatal Plug
Plug dissolves in month 7 and contributes to eardrum
6 mesenchymal proliferations (3 from arch 1, 3 from arch 2)
surround 1st pharyngeal cleft
Hillocks fuse to form definitve Auricle
External ears initially in lower neck
Ascend due to development of mandible
what forms the internal layer of the external ear
tubotympanic recess
what makes the intermediate layer of the external ear
neural crest cells
what forms the external cartilage of the ear
neural crest cells
