Intro/Embryology Flashcards
what happens during gastrulation (week 3)?
formation of trilaminar disc
invagination of epiblast cells through the primitive streak to form the definitive endoderm and mesoderm
mesoderm is then organised into 3 main groups
- paraxial
- intermediate
- lateral plate
what is the neural crest?
group of cells arising from ectoderm at the margins of the neural tube which eventually break off and move around the body to give rise to several structures
what 2 types of folding occur in development of embryo?
lateral folding
craniocaudal folding
what are pharyngeal arches?
remnants of fish gills (present in all vertebrates)
form much of the head and neck in human
what arches are present and when do they develop>
all arches develop in week 4 and 5 arch 1 = day 22 2 + 3 = day 24 4 + 6 = day 29 (no 5th arch)
development occurs in which direction?
cranial to caudal
what are the 3 components of the pharyngeal apparatus?
core pharyngeal arch (mesenchymal tissue)
external pharyngeal cleft (ectoderm)
internal pharyngeal pouch (endoderm)
what separates the arches?
clefts and pouches
what is contained within each pharyngeal arch?
core of mesenchyme derived from paraxial and lateral plate mesoderm = forms musculature of the face neural crest cells = skeletal components of the face cranial nerve component = innervation (sensory or motor) artery (aortic arch arteries)
what nerves supply the pharyngeal apparatus?
arch 1 = trigeminal nerve (V2 and V3 divisions)
arch 2 = facial nerve
arch 3 = glossopharyngeal nerve
arch 4 = superior laryngeal branch of vagus
arch 6 = recurrent laryngeal branch of vagus
what are the 2 portions of the 1st arch?
maxillary process (cranial portion) mandibular portion (caudal portion)
what does the maxillary process form?
maxilla
zygomatic bone
squamous portion of temporal bone
what does the mandibular portion form?
Meckels cartilage
incus and malleus (ear ossicles)
mandible
what muscles does the first arch give rise to?
all musculature supplied by CN V3
- muscles of mastication
- anterior belly of digastric
- mylohyoid
- tensor tympani
- tensor veli palatini
what sensory nerves does the 1st arch give rise to?
V1
V2
V3
what is reichert’s cartilage?
cartilage of 2nd arch
all skeletal derivatives of 2nd arch develop from this
list the 5 skeletal derivatives of the 2nd arch?
stapes (ear ossicle) styloid process of temporal bone stylohyoid ligament lesser horn of hyoid upper part of hyoid body
what muscles are derived from the 2nd arch?
all muscles supplied by CN VII
- muscles of facial expression
- posterior belly of digastric
- stylohyoid
- stapedius
- auricular muscles
what skeletal components are derived from the 3rd arch?
greater horn of hyoid
lower part of hyoid bone
what muscles are derived from 3rd arch?
stylopharyngeus
longitudinal pharyngeal muscle
what nerve is associated with 3rd arch?
glossopharyngeal (CN IX)
what skeletal components are derived form arch 4 and 6?
laryngeal cartilages
what muscles are derived from arch 4?
cricothyroid
levator veli palatine
pharyngeal constrictor
what muscle is derived from arch 6?
intrinsic laryngeal muscle
what nerves supply arches 4 and 6?
4 = superior laryngeal branch of vagus (pharyngeal plexus) 6 = recurrent laryngeal nerve
what structure does the 1st cleft form?
external acoustic meatus
what structure does 2nd - 4th cleft form?
cervical sinus (usually disappears)
what is a branchial fistula?
congenital abnormality due to persistence of branchial apparatus remnants
what does the 1st pharyngeal pouch form?
middle ear
tympanic membrane
eustachian tube
what does the 2nd pharyngeal pouch form?
palatine tonsil
what does the 3rd pouch form?
upper wing = inferior parathyroid gland
lower wing = thymus
what does the 4th pouch?
superior parathyroid gland ultimobranchial body (thyroid gland/C-cells)
what is the ultimobranchial body?
collection of C cells (produces calcitonin?)
function of inner ear?
balance (semi-circular canals)
hearing (organ of corti)
2 components of middle ear?
tympanic cavity
ossicles
2 components of external ear?
external auditory meatus
auricle
what is the otic placode?
thickening of the ectoderm on the outer surface of a developing embryo from which the ear develops
what does the otic placode do?
otic placode invaginates in to form otic pit
otic pit encloses forming a otic vesicle
what does the otic vesicle form?
inner ear
what does the pars superior/utricular portion of the otic vesicle form?
semi-circular canals
what does the pars-inferior/saccular portion of otic vesicle form?
cochlear
when do the semi-circular canals form and how?
week 6
flattened outpocketings of utricular part of otic vesicles
central part of the walls appose each other and break down forming a central canal
- add picture
what are ampullare in semi-circular canals?
bulges at each end of each semi-circular canal
dilates end = crus ampullare (X3)
non-dilated end = crus nonampullare (X2)
crista ampullaris found within the ampullare
what is the crista ampullaris?
sensory cells for balance
vestibular fibres of CN VIII
how does the cochlear duct develop?
grows in spiral between weeks 6-8
surrounding mesenchyme becomes cartilaginous
what structures surround the cochlear duct?
lateral side = connected to bone via spiral ligament
medial = bony section = modiolus
space above = scala vastibuli
space below = scala tympani
what is the organ of corti?
sensory organ in the cochlea
otocyst?
another name for vesicle
how do the ossicles form?
mesenchyme condenses forming ossicles
how does the external ear develop?
dorsal part of 1st pharyngeal cleft
at month 3 - epithelial cells proliferate to form meatal plug
plug dissolves in month 7 and contributes to the eardrum
what is the auricular hillocks?
group of 6 mesenchymal proliferations surrounding 1st pharyngeal cleft (3 from arch 1, 3 from arch 2)
how does the auricular hillocks form the external ear?
hillocks fuse to form definitive auricle
external ears initially in the lower neck and then ascend due to the development of the mandible
