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Embryology
Structures, NCCs, placodes
| Question | Answer |
|---|---|
| What tissue type are the embryonic pouches? | Endoderm (foregut) |
| When do pharyngeal pouches form? | 4 pouches during 4/5th wk |
| What do each of the pharyngeal pouches form? | 1st -> primitive tympanic cavity, Eustachian tube, 2nd -> palatine tonsils, 3rd dorsal -> inferior parathyroid glands, 3rd ventral -> thymus (T cell maturation), 4th dorsal -> superior parathyroid glands, 4th ventral -> ultimobranchial body (C cells) |
| When do parathyroid glands finish migrating? | Migrate from pharyngeal dorsal pouch 3/4 by wk 7 |
| What tissue type are the embryonic clefts? | Ectoderm invaginates to meet tip of pouches and form clefts |
| What do pharyngeal clefts form? | 1st -> EAM, 2/3/4th -> cervical sinus obliterating in wk 10 |
| What happens if cervical sinus fails to obliterate? | Remnants of clefts 2-4 form cervical cysts along anterior SCM border -> painful w/ possible infections |
| What tissue type are the pharyngeal arches? | Bars of mesodermal tissue btwn pouches |
| What types of structures do the pharyngeal arches form? | Paraxial mesoderm derivative forms artery/muscle -> migrates to final positions but remain innervated by cranial nerve of origin, neural crest derivative forms bone/cartilage |
| When do pharyngeal arches form? | 5 arches from day 22 -> arches 1-4, 6 -> 5th arch not readily seen externally (non-existent/regresses) |
| 1st pharyngeal arch artery and cranial nerve? | Maxillary artery, CN Vb/c |
| 1st pharyngeal arch muscles? | Muscles of mastication, mylohyoid muscle, ant belly of digastric, tensor tympani, tensor veli palatini |
| 1st pharyngeal arch skeletal structures/ligaments? | Meckel's cartilage -> malleus, maxillary cartilage -> short limb of incus, alisphenoid, maxilla, zygomatic, hard palate, vomer, squamous temporal bone, ant malleus ligament, sphenomandibular ligament |
| 2nd pharyngeal arch artery and cranial nerve? | Stapedial artery, CN VII |
| 2nd pharyngeal arch muscles? | Muscles of facial expression, stylohyoid muscle, post belly of digastric, stapedius, platysma |
| 2nd pharyngeal arch skeletal structures/ligaments? | Stapes, long limb of incus, styloid process, lesser horn/upper body of hyoid bone, stylohyoid ligament |
| 3rd pharyngeal arch artery and cranial nerve? | Common carotid artery, proximal ICA, CN IX |
| 3rd pharyngeal arch muscles, skeletal structures/ligaments? | Stylopharyngeus muscle, greater cornu/lower body of hyoid bone |
| 4th pharyngeal arch artery and cranial nerve? | Aortic arch, proximal subclavian artery, CN X - superior laryngeal branch |
| 4th pharyngeal arch muscles, skeletal structures/ligaments? | Cricothyroid muscle, levator veli palatini, pharyngeal constrictors, laryngeal cartilages xcp epiglottis |
| 6th pharyngeal arch muscles, artery, cranial nerve? | Intrinsic laryngeal muscles, striated oesophageal muscles, ductus arteriosus artery, proximal pulmonary arteries, CN X - recurrent laryngeal branch |
| 1st pharyngeal arch divisions? | Maxillary (dorsal) and mandibular (ventral) prominences |
| What does dorsal 1st pharyngeal arch form? | Maxillary prominence -> maxilla, zygomatic bone, vomer, short limb of incus |
| What does ventral 1st pharyngeal arch form? | Mandibular prominence -> temporal bone, malleus, mandible |
| What structures contribute to tongue formation? | Tongue muscles from migrating myoblasts from occipital somites (2-5) to tongue primordium -> CN XII, pharyngeal arches 1-4 contribute to developing tongue |
| Where and what is the foramen caecum? | Midline on dorsal tongue surface at apex of terminal sulcus -> marks boundary btwn ant 2/3 and post 1/3 of tongue, location of developing thyroid gland |
| What is the thyroglossal duct? | Connection btwn original thyroid position (foramen caecum) and final position (wk 7) -> persistent duct -> fluid accumulation/infection -> cyst -> midline neck mass below hyoid bone that moves upon swallowing -> can become cancerous/abscess |
| Which laryngeal cartilages are NCC derived? | Epiglottis, thyroid cartilage (mostly NCC, small mesodermic contribution), cricoid and arytenoid are mesoderm derived |
| What do cardiac NCCs form? | Aorticopulmonary septum, non-endothelial components of aortic arches (pericytes, connective tissue, smooth muscle), mesenchymal components of thymus/parathyroid glands |
| What do cranial NCCs form? | Skull cartilage/bones, tooth pulp, odontoblasts (dentine), melanocytes, cranial sensory ganglia glia/somatosensory neurons, parasympathetic ganglia (III, VII, IX, X), nerve glia (olfactor ensheathing cells I glia), Schwann cells, forebrain dermis/meninges |
| What do vagal NCCs form? | Carotid/aortic bodies, aorticopulmonary septum, ENS neurons/glia |
| What do trunk NCCs form? | Melanocytes, DRG, sympathetic ganglia, adrenal medulla chromaffin cells, Schwann cells |
| Where is cardiac NCC fate mapping? | Caudal hindbrain (otic placode -> 3rd somites - 4/6th pharyngeal arches) -> cardiac outflow tract -> migration failure = persistent truncus arteriosus |
| Where is cranial NCC fate mapping? | Midbrain region -> invade face/pharyngeal arches to surround brain -> forms endocranium/facial skull bones |
| Where is vagal NCC fate mapping? | Caudal hindbrain -> invade heart/gut |
| What do Schwann cell precursors form? | Melanocytes, parasympathetic neurons, adrenal chromaffin C cells, carotid body glomus cells -> NCCs colonise peripheral nerves and are carried throughout body |
| Where is trunk NCC fate mapping? | Btwn vagal/sacral neural crest -> dorsolaterally (melanocytes), ventrolaterally (ant sclerotome) -> adrenal gland NA producing cells, sympathetic neurons, DRG |
| What are cranial neurogenic placodes? | Bilateral patches of thickened neurogenic surface ectoderm |
| What nerves are associated w/ placodes? | I (special sensory), V (somatosensory), VII (viscerosensory), VIII (special sensory), IX (viscerosensory), X (viscerosensory) |
| What does CN I placode form? | Olfactory placode -> special sensory neurons in entire olfactory epithelium, olfactory receptor neurons |
| What does CN V placode form? | Trigeminal placode -> some trigeminal ganglion somatosensory neurons (most from NCC) -> transmit somatosensory info from face/jaws -> trigeminal sensory nucleus |
| What does CN VII placode form? | Geniculate placode -> viscerosensory neurons (geniculate ganglion) transmit taste from ant 2/3 tongue -> solitary tract nucleus |
| What does CN VIII placode form? | Otic placode -> special sensory neurons of entire inner ear, cochlear/vestibular ganglia neurons, transmit hearing/balance info from IHCs to cochlear/vestibular nuclei |
| What does CN IX placode form? | Petrosal placode -> viscerosensory neurons in petrosal ganglion transmit taste from post 1/3 tongue/general pharynx viscera/carotid body/sinus chemo/mechanoreceptors -> solitary tract nucleus |
| What do CN IX NCC derived neurons form? | Superior IX ganglion -> NCC neurons transmit somatosensory from post 1/3 tongue, pharynx, Eustachian, middle ear -> trigeminal sensory nucleus |
| What do CN VII NCC derived neurons form? | Superior VII ganglion -> NCC neurons transmit somatosensory info from external ear -> trigeminal sensory nucleus |
| What does CN X placode form? | Nodose placode -> viscerosensory neurons transmit taste from epiglottic vallecula/general visceral pharynx/larynx/oesophagus/thoracic/abd viscera/aortic body/arch chemo/mechanoreceptor -> solitary tract nucleus |
| What do CN X NCC derived neurons form? | Superior X ganglion -> NCC neurons transmit somatosensory info from pharynx/larynx/tympanic membrane/EAM -> trigeminal sensory nucleus |
| What is function of cranial neurogenic placodes? | Derive some peripheral neurons -> other than olfactory placode, other placode-derived neurons delaminate from placode -> migrate -> coalesce w/ NCC-derived glia -> form ganglion |
| What is special about the 1-3rd arches? | All cartilages are NCC derived, 4th arch cartilages have mixed origin (thyroid is mostly NCC w/ some mesoderm, cricoid is mesoderm), 6th arch is all mesoderm derived |
Created by:
vykleung
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