2.2 - development of H&N (pharyngeal arches + derivatives) Flashcards
what are pharyngeal arches? what are they also known as?
sequence of ridges that form in the lateral walls of the embryonic pharynx, towards the cranial end of the neural tube
known as brachial arches
what do the pharyngeal arches form?
future head and neck
what does each arch contain?
a large mesenchyme core (with some neural crest cells that migrate in)
what is each arch covered by?
ectoderm on its external surface
what is between each arch on the ectoderm external surface?
pharyngeal groove / pharyngeal cleft
what happens to the pharyngeal clefts?
eventually disappear except the first, bewteen the 1st and 2nd arches
what does the 1st pharyngeal cleft become?
external auditory meatus of the ear
what does the external ear itself arise from?
from swellings, which form around the entrance to the meatus
what is the external ear called?
auricle
what is the internal surface of each pharyngeal arch covered by?
endoderm
what does the internal surface of each pharyngeal arch face?
faces into the primitive gut tube
covered by endoderm
what are pharyngeal pouches?
similar pattern of grooves (as seen on the external surface) is seen between each arch on the inner surface
what arises from the pharyngeal pouches?
a number of important glandular structures:
parathyroids
thymus
tonsils
what are the pharyngeal Arches (cranial neural tube) and their Grooves (clefts) and Pouches (endoderm) collectively known as?
pharyngeal apparatus
how many pharyngeal arches are there?
theoretically 6 (1-6) but the 5th doesn't form in humans
what is the biggest arch?
1st
arches get progressively smaller in size from 1-6
which arches are not as readily visible? compared to which?
4th + 6th are not as readily visible as the first 3
what is from / associated with each arch?
cartilage, nerve + artery
where does the cartilage associated with each arch arise as?
as a cartilage bar in each pharyngeal arch
what will the cartilage bar in each pharyngeal arch subsequently become?
a skeletal element of the head and neck
which cartilaginous bar is largest?
the cartilaginous bar of the 1st pharyngeal arch
what is the cartilaginous bar of the 1st pharyngeal arch known as?
Meckel’s cartilage
what does Meckel’s cartilage give rise to?
mandible, malleus, incus bones
what do the 4th and 6th arches give rise to?
thyroid, arytenoids, cricoids (remain cartilaginous)
which cranial nerves are associated with the pharyngeal arches?
5, 7, 9, 10
V, VII, IX, X
where do the cranial nerves associated with the pharyngeal arches arise from? innervate?
the lowest part of the brainstem
innervate the pharyngeal arches
what do the structural derivatives of each pharyngeal arch be innervated by?
the particular cranial nerve associated with that arch
what does each pharyngeal arch also become associated with?
an aortic arch blood vessel (runs through the mesenchyme of each pharyngeal arch)
what does the recurrent laryngeal nerve of the vagus become looped under?
the arch of aorta (on the left side) subclavian artery (on the right side)
why does the recurrent laryngeal nerve of the vagus become looped under the aoAorta (L) and subclavian (R)?
as the embryo develops, structures start to derive from the pharyngeal arches and much of the arrangement of the aortic arch blood vessels is lost
where does the facial skeleton arise from?
frontal prominence + 1st pharyngeal arch
where do the muscles of mastication derive from? innervation?
1st pharyngeal arch
innervated by trigeminal nerve (CN V)
what is significant of CN V (trigeminal)?
principal sensory nerve of the head
what are muscles of facial expression derived from? innervation?
2nd pharyngeal arch
facial nerve innervation (CN VII)
why do muscles of mastication and facial expression have different innervation despite being topographically related?
difference in pharyngeal arch derivative
facial: 2nd arch
mastication: 1st pharyngeal arch
what does the 6th pharyngeal arch give rise to?
intrinsic muscles of the larynx
