The Pharyngeal Arches and Cranial Nerves Flashcards
Describe the basic layout of pharyngeal arches, pouches clefts and grooves.
On the outer neck of the embryo are the arches, which are ridge like structures separated by clefts.
Inside the neck are corresponding ridges but they are called pouches and are separated by grooves
Which germ layer are pharyngeal arches and pharyngeal pouches derived from individually?
Pharyngeal arches: endoderm
Pharyngeal pouches: ectoderm
How many pharyngeal arches are there and how are they numbered?
There are 5 numbered 1,2,3,4,6 (the 1st and 2nd arches are the largest)
What is found inside each arch?
Nerve, artery, vein
Some mesenchymal tissue of varying origin: some is mesodermal and goes on to form muscle, some is from the neural crest and goes onto form bone or cartilage
What are the 3 vesicles of the neural tube?
Forebrain, midbrain, hindbrain (plus a long tail forming the spinal cord)
How many cranial nerves are there?
12
How many cranial nerves are from the forebrain, midbrain and hindbrain?
Forebrain: 2
Midbrain and hindbrain: 10
What cranial nerve supplies the 1st pharyngeal arch and what does it innervate?
5th cranial nerve: trigeminal nerve
Supplies the muscles off mastication and the sensory innervation of the face
What cranial nerve supplies the 2nd pharyngeal arch and what does it innervate?
7th cranial nerve: facial nerve
Supplies the muscles of facial expression
What cranial nerve supplies the 3rd pharyngeal arch and what does it innervate?
9th cranial nerve: glossopharyngeal nerve
Sensory innervation of the tonsils, middle ear, posterior 1/3rd of the tongue and the pharynx
What cranial nerve supplies the 4th and 6th pharyngeal arches?
10th cranial nerve: vagus nerve
4th PA: superior laryngeal nerve
6th PA: recurrent laryngeal nerve
What cartilage develops in the 1st pharyngeal arch?
Meckels cartilage: forms from the mandibular process of the 1st pharyngeal arch (there are 2 processes, the maxillary and the mandibular because the 1st arch is so big).
Meckels cartilage forms the template for the mandible, which forms from membranous ossification.
What cartilage develops in the 2nd pharyngeal arch?
Reicherts cartilage:
- contributes to the middle ear formation
- forms the hyoid cartilage and the styloid process
What cartilage develops in the 4th and 6th pharyngeal arches?
Laryngeal cartilages: (all contribute to speech)
- epiglottis
- thyroid
- cricoid
- arytenoid
Where does the aortic sac lie in the fetus?
The floor of the pharynx
State the names of the future arteries in each pharyngeal arch.
PA1 and PA2: arteries disappear
PA3: inner carotid artery
PA4: arch of the aorta L, and brachiocephalic R
PA6: pulmonary arch
How many pouches does the human embryo have?
4 (the 5th is underdeveloped)
What lines the pharyngeal pouches?
Endoderm
What organs/tissues does the 1st pouch give rise to?
Eustation tube and middle ear
What organs/tissues does the 2nd pouch give rise to?
Palatine tonsil
What organs/tissues does the 3rd pouch give rise to?
Dorsally: inferior parathyroid
Ventrally: thymus
What organs/tissues does the 4th pouch give rise to?
Dorsally: superior parathyroid
Ventrally: thyroid chief cells
What happens to the 2nd pharyngeal arch and how does this effect the clefts?
The 2nd PA grows down covering all other arches except the 1st
How can cysts or fistulae form from the arches?
If the cervical sinus is obliterated cysts and fistulae can appear along the anterior border of the SCM.
