1. embryonic development

what happens on day 15 of embryonic development

the trilaminar disc forms - ectoderm, mesoderm, endoderm

what are the three germ layer and what do they give rise to

ectoderm - epidermis, nervous system, sensory system

mesoderm - bones, cartilage, connective tissue

endoderm - GI tract, lungs, glands, pancreas, liver

what is the stomodeum and what does it become

its a pit developing in the midline between the brain and heart and will eventually become the oral cavity

what gives rise to the branchial arches during the fourth week

clefts on the embryo

what structures are formed from the branchial arches

blood vessels, nerves, skeletal elements (including cartilage) and aortic arch vessels

what cartilage is formed by the 1st hyoid arch

Meckel’s cartilage

what cartilage is formed by the 2nd hyoid arch

Reichert’s cartilage

from which day do pharyngeal arches begin to develop

day 21 onwards

where do pharyngeal arches develop in the embryo

in the ventrolateral parts of the embryo

How many pharyngeal arches contribute to head and neck development?

Six arches (but the 5th arch is ignored in humans).

what separates the pharyngeal arches externally and internally

externally = clefts

internally = pouches (or cavities)

 What key components does each pharyngeal arch contain?

Its own nerve, artery, connective tissue, and muscle cells.

 What type of tissue fills each pharyngeal arch

mesenchymal tissue which is the primary collagen

What is the origin of mesenchyme in the pharyngeal arches

It comes from paraxial and lateral plate mesoderm.

What type of cells migrate into the pharyngeal arches?

Neural crest cells

what do neural crest cells form in the pharyngeal arches

all tissues - it’s the primitive spinal cord (from the neural tube)

stomodeum formation?

a depression in the ectodermal surface forming the future face and mouth and its continuous with the primitive gut tube

what does arch 1 divide into

a dorsal maxillary process that’s dorsal and a ventral mandibular process that’s ventral = the primitive bones

what bones are derived from the mandibular arch

maxilla

mandible

zygomatic bone

squamous part of temporal bone

malleus (middle ear bone)

incus (middle ear bone)

what ligaments are derived from the mandibular arch

sphenomandibular ligament

anterior ligament of malleus

what muscles are derived from mandibular arch

all muscles of mastication: masseter, temporalis, medial pterygoid, lateral pterygoid

and:

• mylohyoid

• anterior belly of digastric

• tensor tympani

• tensor veli palatini

what nerve is derived from mandibular arch

trigeminal nerve (CN V)

what is the blood supply of the mandibular arch

maxillary artery (a branch of external carotid artery)

which nerve is typically anaesthetised during dental procedures

the trigeminal nerve

what does the first pharyngeal cleft and first pharyngeal pouch develop into

cleft one: external auditory meatus

pouch one: the tubotympanic recess (in the inner ear)

what does the hyoid arch do as it grows

it grows quickly and inferiorly to cover the smaller arches forming the operculum

what is the operculum

a ‘lid’ formed by the hyoid arch that covers the smaller arches and creates a smooth covering of the neck

what bones does the hyoid arch give rise to

• stapes (middle ear bone)

• styloid process

• lesser horn of hyoid bone

what muscles are derived from the hyoid arch

• muscles of facial expression

• stapedius

• stylohyoid muscle

• posterior belly of digastric muscle

what ligaments are derived from the mandibular arch

the stylohyoid ligament

what artery is derived from the hyoid arch

the stapedial artery

what does the second cleft and pouch give rise to?

cleft = form the cervical sinus (a sinus with the 3rd and 4th clefts)

pouch = forms the lymphoid tissue → the palatine tonsils

at around starting which days of embryonic development do the first and second pharyngeal arches form

day 21 onwards

when do pharyngeal arches 3,4 and 6 start forming in embryonic development

day 28 onwards

How does Arch 3 compare to Arches 1 and 2 in terms of size and derivatives

Arch 3 is considerably smaller than Arches 1 and 2 and has fewer derivatives

what bones are derived from arch 3

greater horn of hyoid bone

what msucle derived from arch 3

stylopharyngeus muscle

what nerve derived from arch 3

glossopharyngeal (IX)

what artery derived from arch 3

common carotid and internal carotid

what do 3rd cleft and pouch form

cleft= incorporated into cervical sinus

pouch 3 = form the thymus gland (Lymphoid tissue) and inferior parathyroid glands

what muscles are derived from the 4th and 6th arch

4 = pharynx muscles except stylopharyngeus and soft palate

6 = larynx muscles

what nerves are derived from the 4th and 6th arch

4 = parts of aortic arch and subclavian artery

6 = contribute to pulmonary arteries

what do the 4th cleft and pouch give rise to

cleft = incorporated into the cervical sinus; it helps in it’s formation

pouch = contribute to parathyroid glands

what events occur in week 4 of facial development

• face starts developing from tissues surrounding the oral pit

• frontal processes form the forehead; the horizontal portion of the frontal bone

• the spatial layout around the oral pit:

  • above oral pit: frontal process forming the forehead

  • laterally: maxillary processes forming cheeks

  • below oral pit: mandibular arch forming lower jaw

what events occur at week 5 of facial development

frontal process evolves into frontonasal process → develop into nostrils

all structures start migrating towards the midline

what events occur at week 6 of facial development

• eyes and maxillary process move towards the front of face

• oral slit widens

• facial components develop: philtrum from medial nasal process and 2 maxillary + lateral nasal processes

• lips are formed by fusion of medial nasal process and maxillary process

• orbicularis oris muscle grows around pit

• nasolacrimal ducts begin to form

• auricular hillocks develop around the external ear canal (primitive ear)

what events occur at week 7 of facial development

• face takes on human appearance

• all structures have migrated to midline

• eyes approach the front of the face and are on the same horizontal plane as nostrils

• nostrils shift downwards

• ear hillocks fuse to form auricles

• ridges around eyes develop into eyelids

when do congenital malformations of face occur

at 4th week of development

what is craniofrontonasal syndrome characterised by

• broad forehead

• hypertelorism

• early fusion of cranial sutures

• nasal fissure, cleft lip and/ or palate

• facial and palatal fissures

what is teacher collins syndrome characterised by

• incomplete orbits

• micrognathia

• alteration of tympanic bones

• alterations in ear formation

what is golden-haar syndrome characterised by

• micrognathia

• no ATM formation

• ear malformations and facial fissures

• unilateral facial underdevelopment

what is pierre-robin syndrome characterised by

• micrognathia

• cleft palate

• cardiac defects

• underdeveloped mandible