Embryology Flashcards
What is the direction of development?
cranial to caudal
What are the three parts of the arches?
- External pharyngeal cleft is from ectoderm: nervous system, skin
- Internal pharyngeal pouch is from the endoderm: lining of respiratory and digestive tracts
- Core pharyngeal arch is from the mesenchymal tissue
What does each arch have?
- mesenchyme core: from paraxial and lateral plate mesoderm
- neural crest cells: migrate into the pharyngeal arches and form the cartilaginous and skeletal portions of the arches
- cranial nerve
- artery: aortic arch arteries
What is the nerve supply to each of the arches?
1st arch- CNV (maxillary and mandibular divisions of trigeminal)
2nd arch- CNVII (facial)
3rd arch- CNIX (glossopharyngeal)
4th and 6th arch- CNX (vagus and branches)
What are the skeletal derivatives of the 1st arch?
- This will split into a mandibular and maxillary process
- Maxillary process: will become the maxilla, zygomatic bone and squamous portion of temporal bone
- Mandibular process: Meckel’s cartilage, this will become the incus and the malleus and the mandible
What are the muscle derivatives of the 1st arch?
The maxillary portion of the trigeminal is not motor but mandibular is motor so become the
- Muscles of mastication
- Anterior belly of the digastric
- Mylohyoid
- Tensor tympani
- Tensor veli palatini
Sensory is the maxillary and mandibular divisions of CNV
What are the skeletal derivatives of the 2nd arch?
- Stapes
- Styloid process of temporal bone
- Stylohoid ligament
- Lesser horn of hyoid
- Upper part of hyoid
What are the muscle derivatives of the 2nd arch?
- Muscles of facial expression
- Posterior belly of digastric
- Stylohyoid
- Stapedius
- Auricular muscles
What are the skeletal derivatives of the 3rd arch?
- Greater horn of the hyoid bone
- Lower part of the body of the hyoid bone
What are the muscle derivatives of the 3rd arch?
- Stylopharyngeus
- Longitudinal pharyngeal muscle
What are the skeletal derivatives of the 4th and 6th arches?
Laryngeal cartilages so thyroid and cricoid
What are the muscle derivatives of the 4th and 6th arches?
- 4Levator veli palatini
- 4Cricothyroid
- 4Pharyngeal constrictors
- 6Intrinsic laryngeal
What is the nerve supply to the 4th and 6th arches?
Vagus= arch 4 is superior laryngeal and pharyngeal plexus and 6 is recurrent laryngeal
What does the 1st cleft become?
- External acoustic meatus
Dual innervation by the two supplies of the tympanic membrane
What does the 2nd-4th clefts become?
- Lose contact with outside and form the cervical sinus
What does the 1st pouch become?
- Middle ear
- Tympanic membrane
- Eustachian tube
A point is created and there is mesenchymal condensation which leads to the ossicles being formed
What does the 2nd pouch become?
- Palatine tonsils
What does the 3rd pouch become?
- Inferior parathyroid gland (then descends below after)
- Thymus
What does the 4th pouch become?
- Superior parathyroid gland
- Ultimobranchial body
What are cervical/branchial cysts/fistulas?
- along the anterior border of the sternocleidomastoid
- not seen in birth and enlarges in childhood
- swelling in the neck
- external branchial fistula is attachment to outside
- internal branchial fistula are less common which connect to the palatine tonsils
What is the process of tongue development?
- 4th week by two lateral swellings and one midline swelling
- 4 CN supply the tongue
- anterior mucosa is CNV3 and posterior is CNIX
- base of the tongue can get taste from the vagus nerve
- V of the tongue by the vallate papillae marks the boundary between anterior 2/3rd and posterior 1/3rd of the tongue
- When the thyroid tissue migrates down, it can lead to accessory glands or remnants where it moved
What are the five facial swellings?
present from week 4
- Frontonasal prominence: ectodermal thickenings here for the nasal placodes
- Maxillary prominence x2
- Mandibular prominence x2
Stomodeum forms the primitive oral cavity
What do nasal placodes deepen to cause?
forms two areas within each placode medial and lateral nasal swellings
When does the eye begin to develop?
week 6
