Embryology Flashcards
What do the pharyngeal arches develop into?
much of the face and neck
When do the pharyngeal arches develop?
weeks 4 and 5
What are the pharyngeal arches in humans?
arches 1,2,3,4 and 6
In what sequence do the pharyngeal arches develop?
cranial-caudal
Why don’t you have all the arches present at one time?
as they develop in a cranial-caudal sequence, by the time 4 and 6 are developing, 1 will have regressed
What does each pharyngeal arch consist of?
core of mesenchyme; neural crest cels; cranial nerve component; artery
What does the core of mesenchyme develop into?
musculature of face and neck
What do the neural crest cells develop into?
skeletal components of the face
What are the arches separated externally by?
deep pharyngeal clefts
What are the arches separated internally by?
pharyngeal pouches
What is the lining of the pharyngeal cleft?
ectoderm
What is the lining of the pharyngeal pouches?
endoderm
What nerve is associated with the 1st arch?
maxillary and mandibular divisions of trigeminal
What nerve is associated with the 2nd arch?
facial nerve
What nerve is associated with the 3rd arch?
glossopharyngeal (9)
What nerve is associated with arches 4 and 6?
vagus
What branch of the vagus is associated with arch4?
superior laryngeal
What branch is associated with arch 6?
recurrent laryngeal
What are the 2 skeletal components of the 1st arch?
maxillary process and mandibular process
What develops from the maxiallry process of the 1st arch?
maxilla; zygomatic and part of temporal bone
What develops from the mandibular process of the 1st arch?
incus; malleus and mandible
What type of cartilage is found within the mandibular process?
Meckel’s cartilage- developing type of cartilage that the mandible develops alongside
What are the muscles formed from arch1?
muscles of mastication; anterior belly of digastric; mylohyoid; tensor tympani and tensor palatini
What does the mylohyoid form most of?
floor of mouth
What nerve supplies the msucles from arch 1?
V3
What are the skeletal components of the 2nd arch?
stapes; process of temporal bone and stylohyoid ligamnet; lesser horn and upper parto f body of hyoid
What are the muscles formed from arch 2?
muscles of facial expression; stapedius; stylohyoid; posterior belly of digastric and auricular muscles
What are the auricular muscles used for?
moving the ears- not really used in humans
What nerve supplies the muscles of arch 2?
facial nerve
What is the skeletal component of arch 3?
greater horn and lower part of body of hyoid
What muscle is formed from arch 3?
stylopharyngeus
What is the skeletal component of arches 4 and 6?
laryngeal cartilages eg thyroid and cricoid cartilages
What are the muscles of arch 4?
cricothyroid; levator palatini; pharyngeal constrictors
What nerve supplies the msucles of arch 4?
vagus- superior laryngeal; pharngeal plexus
What are the muscles formed by arch 6?
intrinsic laryngeal
What nerve supplesi the intrinsic laryngeal muscle?
recurrent laryngeal nerve
What does the 1st cleft develop into?
external auditory meatus
What do the 2nd-4th clefts devlop into?
lose contact with outside and form the cervical sinus which usually disappears
What develops from the 1st pouch?
middle ear; eustachian tube; tympanic membrane
What develops from the 2nd pouch?
palatine tonsil- will be invaded by lots of lymphoid tissue
What develops from the 3rd pouch?
inferior parathyroid gland; thymus
What develops from the 4th pouch?
superior parathyroid glands; ultimobranchial body (c cells of thyroid gland)
What do C cells produce?
calcitonin
What does the thyroid develop from?
a proliferation of the tongue
How does the thyroid descend down into the neck?
anterior to the gut tube
How do the inferior parathyroid glands migrate from above the superior glands to their place?
the thymus migrates, pulling the inferior parathyroid glands down with it, then pulls away from the thymus when passing the thyroid
What is an otic placode?
thickening of the ectoderm which give rise to structures of the ear- one on each side
What do the otic placodes overly?
the hindbrain
What happens to the otic placodes?
thye invaginate and form a pit and then a vesicle
What do the otic vesicles give rise to?
inner ear
What is the statoacoustic ganglion and how does it relate the forming of otic vesicles?
The statoacoustic ganglion give rise to sensory cells in the ear, breaks away from the placode as the vesicle develops
What does the utricular portion of the otic vesicle give?
semicircular canals
What does the saccular portion of the otic vescicle give rise to?
cochlea
What connects the utricular and saccular portions of the vesicle?
utriculosaccular duct
How do the semicircular canals develop?
there are flattened outpocketings of utricular part, the cnetral part of these walls appose each other and break down, leaving tubes aroudn the outside
What is the dilated end of the semicircular canals called?
crus ampullare
What is the non-dilated end of the semicircular canals called?
crus-nonampullare
What is found within the ampullae?
crista ampullaris which contains sensory cells for balance and vestibular fibres of CN8
When does the cochlear duct grow?
between weeks 6 and 8
What happens to the surrounding mesenchyme in the cochlea between weeks 6-8?
becomes cartilaginous and ossifies nad forms cavities
How does the organ of Corti develop?
develops from the cochlear duct, develops tectorial membrane and then 3 rows of outer hair cells and 1 row of innter hair cells
How is the tectorial membrane involved in hearing?
movement of hair on the membrane creates APs
What does the middle ear develop from ?
1st pharyngeal pouch
What is the mesenchymal condensation formed from?
1st and 2nd pouches
What does the 1st pouch develop into?
develops a small swelling to form the primitive tympanic cavity
What happens with the primitive tympanic cavity and the mesenchymal condensation?
3 ossicles develop in the condensation as the mesenchyme breaks down, the cavity encroaches upon these
What coats the 3 ossiclaes of the middle ear?
endoderm- ligaments attaching the bones in place
What does the EAM develop from?
1st pharyngeal cleft
What do the epithelial cells at the 1st phayngeal cleft develop into?
Meatal plug which then contributes the the eardrum
How is the auricle formed?
6 mesenchymal proliferations from arch 1 and 2 which surrpound the 1st pharyngeal cleft in auricular hillocks.
where do the the auricles initially develop and why do they move?
in the neck, move due to the devleopment of the mandible
What facial structures does arch1 give rise to?
maxilla, mandible, zygomatic and temporal squamous bones; muscles of mastication
What facial structures does arch 2 give rise to?
muscles of facial expression
What gives rise to the upper and mid-facial features?
proliferating mesechyme associated with the forebrain
What cells give rise to the skeletal components?
neural crests
Waht nerve is associated with arch1?
V
What nerve is associated with arch2?
VII
What nerve is associated with arch 3?
IX
Waht nerve is assocaited with arches 4 and 6?
vagus
What are the 5 facial swellings present from week 4?
frontonasal prominence; 2 maxillary prominences and 2 mandibular prominences
What is the future opneing of the mouth called?
stomodeum
How do the facial swelling develop?
aroun the stomodeum
What is present laterally in the frontonasal prominces?
nasal placodes
What are the 4 nasal swellings that develop in the frontonasal prominence in week 5?
2 medial and 2 lateral nasal swellings
How do the nasal swellings develop?
the nasal placodes begin to invaginate, tissue surrounding invagination begins to swell
Where does the nasolacrimal groove lie?
between the maxillary prominence and the lateral nasal prominence
Where do the eyes develop in relation to the nasal swellings?
lateral
How do the medial nasal swelling and maxillary prominences join together?
maxillary prominence puts pressure on nasal wellings moving them medially, as this happens the medial swelling develops downwards to medial edge of maxillary prominence to join together
Hwo does the nasolacrimal duct form?
ectoderm proliferates to form a solic epithelial cord which detaches from the ectoderm and canalises to form the duct
What forms the upper lip?
2 medial nasal prominences and 2 maxillary promences
What forms the lower lip?
mandibular prominences
What forms the bridge and nasal septum of the nose?
frontonasal prominence
What forms the crest and tip of the nose?
medial nasal prominences
What forms the alae of the nose?
lateral nasal prominences
What gives the intermaxillary segment?
fusion of medial nasal promiences
What is the intermaxillary segmnet?
primary palate
What does the labial protion of the intermaxillary segment give rise to?
philtrum of upper lip
What does the upper jaw of the intermaxillary segment give rise to?
carries 4 incisors
What does the palatal component of the intermaxillary segment give rise to?
forms primary palate
What are the palatine shelves derived from?
maxillary promineneces
What happens during week 7 of the devleopment of the secondary palate?
shelves ascend to horizontal position as tongue moves down (were on either side of tongue); fuse together to form secondary palate and fuse with primary palate anteriorly
What is found at the meeting of the primary and the 2 sides of the secondary palates?
incisive foramen
What happens during week 6 with the nasal cavities?
nasal pits deepen and penetrate into underlying mesenchyme
What separates the nasal pits from the oral cavity during week 6?
oronasal membrane
What happens to the oronasal membrae and what does this result in?
breaks down so the oral and nasal cavities are one
What is the communication between the nasal and oral cavities called?
primitive choanae
When does the definitive choanae arise?
with the secondary palate- so communication is behind that
