Embryology Part 2 Flashcards
How many brachial arches are there?
Six arches each possessing its own cartilage, nerves, vascular supply and muscles
First two are highly developed, the rest are poorly developed, The fifth atrophies
Which major structures compose the first mandibular arch?
Posterior portion of upper lip and cheeks
Posterior portion of the maxilla
Posterior 2/3 of the hard palate
Entire lower lip, mandibular arch and body of the tongue
Which structures are composed of Meckel’s cartilage? Which brachial arch is it a part of?
First brachial arch
Mental symphysis
Malleus and incus
Sphenomandibular ligament
What are the muscles of mastication? Which arch are they formed from?
Mandibular arch
Temporalis, masseter, medial and lateral pterygoid
What other muscles form from the first mandibular arch?
Anterior belly of the digastric muscle – Elevates the hyoid bone and mylohyoid muscle that forms the floor of the mouth
Tensor veli Palatine- soft palate
Tensor tympani-Tympanic membrane
Which nerve innervates all of the tissues of the face tongue and teeth?
Trigeminal nerve
Which major structure forms from the 2nd/hyoid arch?
Root of the tongue
What is Reichert’s cartilage and what Originates from it??
A continuous cartilaginous formation in the second brachial arch
 stapes/ear
Styloid process of temporal bone
Lesser cornu of the hyoid
Superior aspect of body of hyoid
Which muscles are formed from the second brachial arch?
Muscles of facial expression
Stapedius muscle
Styloid muscle
Posterior belly of the digastric
Which cranial nerve innervates the second brachial arch?
7th/facial
What major structure forms from the third brachial arch?
Posterior third of the tongue/root
Which cranial nerve innervates the third brachial arch?
9th/glossopharyngeal
Major structure of the fourth arch
Copula
Major structure of the sixth arch
Epiglottic eminence
What forms the oral cavity when the ectoderm invaginate’s?
Stomodeum
What is the first branchial arch divide into?
Posterior 2/3 of the maxillary process and the entire mandibular arch
Which direction does the mandibular process grow in? What does it form?
Grows medially and fuses at the midline
Forms the entire mandible/lower jaw and alveolar arch. Entire lower lip and lower cheeks
Which direction does the maxillary process grow? What does it form?
Grows mediately but does not meet
Formed the lateral sides of the upper lip, upper cheeks, lateral sides of the maxilla/alveolar bone. Lateral sides of the hard palate
(posterior 2/3)
How does the lateral nasal process grow and what does it form?
Grows laterally and fuses with the maxillary process
Forms the alae of the nose and nasal labial sulcus
How does the medial nasal process grow and what does it form?
Grows medially, inferiorly, interiorly and fuses
Forms the columella and tip of the nose, nasal septum
Inter-maxillary segment/pre-maxilla
How does the inter-maxillary segment/globular process grow and what does it form?
Grows inferiorly
Forms the philtrum of upper lip- Lateral borders fuse with the posterior 2/3 of the upper lip
When is fusion of the facial process is complete?
Complete by week eight
Between which weeks do the eyes form and migrate medially on face?
Is form at week six and migrate medially on the face at week 12
When do the ears form and where? When do they migrate superiorly onto the head?
Ears form on the low side of the neck at week eight and migrate onto the head at week 12
During which weeks does formation of the pre-maxilla/primary palate occur (anterior 1/3)?
Starts at week six and completes by week 12
What happens during primary palate formation during weeks five and six? What is formed?
Inter-maxillary segment/inferior aspect grows downward from right and left sides and fuses at the midline.
Forms the interior 1/3 of the alveolar ridge and hard palate
What happens during week seven of primary palate formation?
Lateral sides of the pre-maxilla fuse with the lateral Palatine shelves
What would failure of fusion of the maxillary process with the lateral borders of the center portion of the philtrum result in?
Cleft lip- week8
What happens during week six of secondary palate formation?
Lateral Palatine shelves form from the medial aspects of the maxilary processes
Grow mediallu than inferiorly due to tongue development
What happens during week seven of secondary pallet formation?
Tongue drops, Palatine shelves elevate and grow mediately and meet
What happens during week eight of secondary palate formation?
Palatine shelves start to fuse at the midline and form the posterior 2/3 of the hard palate
What happens during week 12/3rd month of secondary palate formation
Palate forms and fusion is complete
What does the secondary palate and pre-maxilla fusing with the inferior aspect of the nasal septum give rise to?
Gives rise to the nasal cavities and developing paranasal sinuses
When does tongue formation occur? Where does this occur and from which brachial arch?
Occurs from weeks 4 to 8 in the floor of the pharynx. Develops mainly from the first brachial arch but also from the second and third as well as a small portion from the fourth and sixth
What part of the tongue forms from the first brachial arch?
Anterior 2/3 (body) Of tongue
Which swellings merge together to form the body of the tongue?
Tuberculum impar
Lateral lingual swellings
What forms the median lingual sulcus?
Fusion of the lateral lingual swellings and corresponding deep fibrous band
What fuses together to form the root of the tongue?
Copula and epiglottic eminence
Which arches does the posterior 1/3 of the tongue form from?
Second and third with a small portion from the fourth and sixth
What is the sulcus terminalis?
March the fusion between the body and the route of the tongue. V-shaped roof on the dorsal surface, Apex points posteriorly
What is the foramen cecum?
Origin of the thyroid gland
When will tongue formation infusion be complete by?
Week eight
What effect on the developing fetus can alcohol consumption have?
Fetal alcohol syndrome
Growth efficiencies and mental disabilities. Similar facial features to children with down syndrome
What effect on development does the use of tetracycline during pregnancy have?
Has affects during tooth development. Can affect primary or permanent teeth causing intrinsic yellow to gray brown stain
What effect can polychlorinated biphenyl’s have on the developing fetus?
Growth deficiencies and mental disabilities. Small premium, impaired visual recognition, poor short-term memory, low verbal skills
 Infections that can affect the fetus
Rubella- cataracts, cardiac defects and deafness
Syphilis – hutchinson incisors and mulberry molars, blindness, deafness and paralysis
Effects of radiation on the embryo or fetus
What was deficiencies and mental disabilities: cell death commicromosome damage, delayed mental and physical growth
Congenital defects affecting the Dentition
Down syndrome, epodermal dysplasia, treacher-Collins syndrome
What effect does down syndrome have on the dentition?
Hypertrophy of lingual papillae
High incidence of periodontal disease, delayed eruption, hypodontia, microdontia
What effect does ectodermal dysplasia have on the dentition?
Hypodontia and loss of alveolar ridge. Protuberant lips with loss of vertical dimension due to alveolar bone loss
What effect does Treacher Collins syndrome have on the Dentition?
High vaulted palate, palatal clefts and malocclusions
What causes spinal bifida?
Neural tube defect, failure of neural tube to fuse
What causes a cleft lip?
Partial or complete failure of inter-maxillary segment and maxillary process to fuse
Unilateral or bilateral
Most common in males
What causes a cleft chin?
Failure of depression to fill in at mandibular midline
What causes an oblique facial cleft?
Failure of lateral nasal process and maxillary process to merge
Void in nasolacrimal Groove
What causes macrostomia and microstomia?
Failure of closure or over closure of maxillary and mandibular processes
Exceptionally large or small mouth opening
What causes Fordyce granules?
Entrapment of sebaceous glands during fusion of maxillary and mandibular processes
Entrapped ectopic sebaceous glands located at retromolar areas, labial mucocutaneous junctions and commissures
What causes a cleft palate?
Premaxilla and/or secondary palate fail to fuse with the nasal septum and/or failure of pre-maxilla to fuse with secondary palate in canine area
What is the appearance and treatment of cleft palate?
Crippling communication between oral cavity and nasal cavity; may be partial or complete
May involve the maxillary ridge, bilateral or unilateral with displaced or missing teeth
What causes a cleft uvula?
Uvula fails to completely fuse at the midline
What causes a median maxillary/anterior alveolar cleft?
Pre-maxilla fails to completely fuse at the midline forming a very large diastema that may be fixed with orthodontics
What is Bifid tongue?
Cleft in tip of tongue caused by the lateral lingual swelling‘s failing to merge in the midline
What is microglossia?
Under development/hypertrophy of musculature of the tongue
What is macroglossia?
Over development/hypertrophy of musculature of the tongue
What is aglossia?
Absence of the tongue
Defect involving the first, second and third brachial arches
What is ankyloglossia?
Very short lingual Frenum
Individual cannot lift tongue to roof of mouth
What may cause fissural cysts of the oral region?
During fusion of embryonic processes, epithelial cell rests may become entrapped. Entrapped cells have the potential to form cysts
Nasopalatine cyst
Lies near or in the incisive canal
Median Palatine cyst
Lies on the fusion line between the lateral palatine shelves of the maxillary process
Globulomaxillary cyst
Lies on the fusion line between the pre-maxilla and the maxillary process (between lateral and canine)
Dermoid/epidermoid cyst
Lies in the floor of the mouth. Submandibular or sublingual areas
Brachial cleft cyst
Usually lies between the second and third brachial arches. Below the angle of the mandible, along the interior border of the SCM)
What are the muscles of mastication? Which arch are they formed from?
Mandibular arch
Temporalis, masseter, medial and lateral pterygoid
