Session 2 - Embryology of H&N Flashcards
At what week do pharyngeal arches develop?
4
How many pharyngeal arches are there? What are they numbered?
1-6, 5 pharyngeal arches. Number 5 is obliterated.
What 3 structures does each pharyngeal arch have associated with it?
Artery, nerve, and cartilage bar
Describe the formation of the nerual tube
- Notochord signals cause overlying ectoderm to thicken
- Edges elevate out of plane of the disk and curl towards each other, creating the neural tube.
What part of the neural tube forms the brain?
anterior end
Name the 4 functional regions of the neural tube
- Prosencephalon = forebrain
- Mesencephalon = midbrain
- Rhombencephalon = hindbrain
- Spinal cord
How many cranial nerves are there? Which cranial nerves are derived in the forebrain?
12 cranial nerves
1 and 2 derived in forebrain
What is the facial skeleton derived from?
Frontonasal prominence and 1st PA
Where are the muscles of mastication derived from?
PA1
Where are the muscles of facial expression derived from?
PA2
What are the derivatives of PA1 and 2?
1 - Facial skeleton and muscles of mastication
2 - Muscles of facial expression
What are the derivatives of PA 3 and 6?
3 - stylopharyngeus
6 - Intrinsic muscles of the larynx
What are the derivates of PA4?
Cricothyroid, levator palatini, constrictors of the pharynx
What is the name of cranial nerve:
a) V
b) VII
c) IX
d) X - 4th PA
e) X - 6th PA
a) trigeminal
b) Facial
c) glossopharyngeal
d) superior laryngeal
e) recurrent laryngeal
What are the sensory and motor innervations of CN V?
Sensory - Skin of face, lining of nose and mouth
Motor - Muscles of mastication, muscles derived form mandibular process
What are the sensory and motor innervations of CN VII?
Sensory - Taste buds in Anterior 2/3 of tongue
Motor - Muscles of facial expression, muscles derived from PA2
What are the sensory and motor innervations of CN IX?
Sensory - Posterior 1/3 of tongue
Motor - Stylopharyngeus muscle
What are the sensory and motor innervations of CN X (PA4)?
Motor innervation - cricothyroid, constrictors of pharynx
What are the sensory and motor innervations of CN X (PA6)?
Motor - Intrinsic muscles of the pharynx
What are the cartilage bars derived from PA1, 2, 4, and 6?
PA 1 - Meckels
PA 2 - Reicherts
PA 4 and 6 - Cartilages of larynx
What does the cartilage bar of PA1 develop into?
- PhA1 divides into maxillary and mandibular prominences
- Mandibular prominence develops the Meckel’s cartilage, composed of the Malleus and incus which provides a template for mandible formation via membranous ossification
What does PA2 cartilage bar develop into?
- Contributes to middle ear development via stapes
- Forms the styloid process and hyoid bone
What does the cartilage bar of the 4th and 6th PA devleop into?
- Mesenchyme of 4th and 6th arch forms the epiglottis
- Cartilage bars of 4th and 6th forms the thyroid, arytenoid, and cricoid cartilages
What does the PA3 cartilage bar develop into?
- Hyoid bone (great cornu and lower body)
What are the arterial derivatives of PA 1-6?
1-3 - common, internal and external carotid arteries and branches
4 - Aortic arch and part of right subclavian
6 - pulmonary arteries
Where does the aortic sac lie?
floor of the pharynx
What are the pharyngheal pouches? How many pairs do we have?
- Form on the endodermal side between the pharyngeal arches
- These form the lateral ectodermal surface of the neck region
- 4 pairs
What does the 1st pharyngeal pouch become?
Eustachian tube and middle ear cavity
What does the 2nd pharyngeal pouch become?
Crypts of palatine tonsil
What does the 3rd pharyngeal pouch become?
- Divides into dorsal and ventral
- Dorsal part - inferior parathyroid
- Ventral part - thymus
What does the 4th pharyngeal pouch become?
- Divides into dorsal and ventral part
- Dorsal - Superior parathyroid
- Ventral - Thyroid C cells
From where are the ossicels of the middle ear derived?
Meckels and reicherts
How many pharyngeal clefts are there and why?
Only 1st cleft remains as the 2nd arch grows down to cover the others.
What could happen if the cervical sinus is not obliterated?
cysts or fistulae can occur anywhere along anterior border of SCM
