Class Notes (809,509)
Canada (493,754)
Brock University (11,930)
Biology (1,611)
BIOL 2P95 (35)

Head and Neck

10 Pages
Unlock Document

Brock University
Dirk De Clercq

Embryology: Head and Neck Begins at start of fourth week Neural crest (cells at junction between surface ectoderm and neural plate) deposits in cranial region as neural folds form • mesenchyme of head: paraxial mesoderm (somitomeres and somites) + neural crest • while in neural folds, neural crest cells receive precise info (via HOX gene code) as to where to go after they leavepopulate very specific region of head • some neural crest cells (along rhombomere 3 and 5), receive instructions from MSX-2 genes to commit suicide to produce gaps to prevent mixing of neural crest cell population • free gaps produce clefts between the upper arches = branchial grooves or branchial clefts neural crest = bones of face and anterior skull mesoderm: posterior bones and base of skull laryngeal cartilages in neck: lateral plate mesoderm mesoderm from primitive streak accumulates on both sides of midline; head region: not completely segmentedsomitomeres • seven somitomeres • form from cranial to caudal sequence • from region of prosencephalon to occipital region • each one associated with specific portion of cranial neural plate; forebrain, midbrain and hindbrain presaged by one or more somitomeres o somitomeres tell neural tube segment what to become • somitomeres set up initial organization of brain and form all voluntary muscle of head and neck • scaffold or patterning of muscles determined by connective tissue of head a neck (neural crest) somitomere primitive brain subdivision cranial nerve craniofacial muscle Origin Craniofacial muscles Innvervation Somitomere 1,2 Sup., med., ventral recti CN III Somitomere 3 Sup. Oblique CN IV Somitomere 4 Jaw-closing mm. CN V Somitomere 5 Lat. Rectus CN VI Somitomere 6 Jaw-opening mm. CN VII nd Other 2 arch mm. Somitomere 7 Stylopharyngeus CN IX Somites 1,2 Intrinsic laryngeals CN X Somites 2-5 Tongue mm. CN XII (Note: Raymond has replaced a table image with equivalent text) hindbrain undergoes further segmentation: rhombomeres; each has unique genetic identity pharyngeal (branchial, visceral) arches (six arches, #5 is degenerate) • lateral swellings on either side of head th • apparent during 5 week • result of local proliferation of neural crest cell populations as they take position • made up of mesenchyme • delineated from each other by pharyngeal grooves, covered by ectoderm (external) and by pharyngeal pouches, lined by endoderm (internal) • closing membranes (ectoderm/endoderm contact points) seal off archesno mixing • each arch has unique genetic identityspecific cartilages and bones • with connective tissue in place, somitomeres and occipital somites can organize the formation of the voluntary musculature associate with their respective connective tissues Summary of info, thus far: • each segment of neural tube has unique genetic identity (HOX)carried into pharyngeal arches through neural crest cellssome cells die to for grooves • coordinate brain and facial development Aortic arch arteries • pharyngeal arches initially serve as conduits for aortic arch arteries o arteries migrate thru path of least resistance: mesenchyme • early in embryogenesis, pattern of arterial supply is symmetrical, but each pair of arch arteries has different fates; some arteries grow, some degenerate • (Note: Raymond has replaced a table image with equivalent text below) Aortic arch 1t Maxillary a. 2d Stapedius a. 3d Carotid a. th Proximal subclavian a. (right), aortic arch (left) 5 None 6th Pulmonary a. Cranial Nerve • each pharyngeal arch associated with specific cranial nerve • CN emerge from specific regions of brain and supply pharyngeal arch with neural crest that came from same region (same HOX code) • To know which arch a muscle came from, know the CN (Raymond has removed a table image from the original document) Pharyngeal pouchesglands/organs • 5 pairs • first pouch o auditory tube o comes in contact with epithelial lining of first pharyngeal cleftfuture EAM o distal portiontympanic cavity (lining will become eardrum) o proximal portionauditory tube • second pouch o forms buds that penetrate surrounding mesenchyme o palatine tonsil o structure infiltrated by lymphatic tissue • third pouch o forms thymus and inferior parathyroid glands o as thymus descends into thoracic region, pulls inferior parathyroid glands with it o inferior parathyroid glands become embedded into gland • fourth pouch o superior parathyroid glands o as thyroid gland moves caudally, glands attach to dorsal surface • fifth pouch o utlimobranchial body o regulates calcium levels in blood o embedded into thyroid gland when pulled caudally pharyngeal clefts/grooves • initially, four clefts exist • only one gives rise to definite structure • 1 pharyngeal cleft penetrates underlying mesenchyme and forms EAM o bottom of EAM forms lateral aspect of tympanic cavity • 2 cleft o undergoes active proliferation and overlaps remaining clefts o merges with ectoderm of lower neckremaining cleft have no contact with outside o temporarily, clefts form cervical sinus, but disappears Tongue development • tongue=groupthf muscles covered by mucosa • appears at 4 week • formed by endoderm and mesoderm of 1 – 4 archth • mesoderm from occipital somites (NOT somitomeres); precursor muscle cells migrate to region of tongue; innervated by GSE component of XII cranial nerve • mucosa: anterior endoderm lining the first four pharyngeal arches; innervation depends on arch derivation o anterior and posterior separated by a terminal sulcus • midpoint of sulcus: foramen cecum position of thyroid outgrowth o mucosa of anterior 2/3 of tongue comes from first archCN V o mucosa of posterior 1/3 of tongue comes from third and 4 archCN IX, X o special taste of anterior 2/3CN VII o Special taste of posterior 1/3CN X • Tongue freed from floor of mouth by extensive degeneration of underlying tissue o Midline frenulum anchors tongue to floor of mouth Thyroid Gland • Arises from foramen cecum • Descends along front of pharyngeal gut • Remains connected to tongue by narrow canal: thyroglossal duct (obliterated later) • Descends just caudal to laryngeal cartilages • Functions during early fetal period Facial development • Nose o At time of anterior neural tube closure, mesenchyme around forebrain, frontonasal prominence (FNP), has smooth rounded extended contour o Nasal placodes (thickening of surface ectoderm to become peripheral neural tissue) develop on frontolateral aspects of FNP o Mesenchyme swells around nasal placodemedial and lateral nasal prominence (nasomedial and nasolateral processes) o Nasal prominencesnose • Mouth o Stomadeum (primitive oral cavity) forms between frontonasal prominence and first pharyngeal arch o First pharyngeal archdorsal maxillary prominence and ventral mandibular prominence o Maxillary prominence will merge with medial nasal prominences, pushing them closer to cause fusion  Fused medial nasal prominences will form midline of nose and midline of upper lip (philtrum) and primary palate (carries first four teeth) • Nasolacrimal structures o Maxillary and lateral nasal prominences separated by deep furrow: nasolacrimal groove o Ectoderm in floor of groove forms epithelial cord, detaches from overlying ectoderm  Epithelial cord canalizesnasolacrimal duct  Upper end widenslacrimal sac o After detachment of cord, maxillary and lateral nasal prominences merge with each othernasolacrimal duct runs from medial corner of eye to inferior meatus of nasal cavity o Maxillary prominences enlargecheeks and maxillae o Lateral nasal prominencesalae of nose Secondary Palate development • Main part of definitive palate formed by two shelf-like outgrowths from maxillary prominences • Outgrowths=palatine shelves th o Appear during 6 week o Directly obliquely downward on each side of tongue—moves down when mandible gets bigger o 7 week: ascend to attain horizontal position , fuse  secondary palate o anteriorly: shelves fuse with triangular primary palate (front 4 teeth) o incisive foramen: midline landmark b/w primary and secondary palate o at time palatine shelves fuse, nasal septum (outgrowth of median tissue of frontonasal prominence) grows down and joins cephalic aspect of newly formed palate Ear development • three distinct parts
More Less

Related notes for BIOL 2P95

Log In


Don't have an account?

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.