2.2 - development of H&N (pharyngeal arches + derivatives)

Question 1

what are pharyngeal arches? what are they also known as?

Answer 1

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

Question 2

what do the pharyngeal arches form?

Answer 2

future head and neck

Question 3

what does each arch contain?

Answer 3

a large mesenchyme core (with some neural crest cells that migrate in)

Question 4

what is each arch covered by?

Answer 4

ectoderm on its external surface

Question 5

what is between each arch on the ectoderm external surface?

Answer 5

pharyngeal groove / pharyngeal cleft

Question 6

what happens to the pharyngeal clefts?

Answer 6

eventually disappear except the first, bewteen the 1st and 2nd arches

Question 7

what does the 1st pharyngeal cleft become?

Answer 7

external auditory meatus of the ear

Question 8

what does the external ear itself arise from?

Answer 8

from swellings, which form around the entrance to the meatus

Question 9

what is the external ear called?

Answer 9

auricle

Question 10

what is the internal surface of each pharyngeal arch covered by?

Answer 10

endoderm

Question 11

what does the internal surface of each pharyngeal arch face?

Answer 11

faces into the primitive gut tube

covered by endoderm

Question 12

what are pharyngeal pouches?

Answer 12

similar pattern of grooves (as seen on the external surface) is seen between each arch on the inner surface

Question 13

what arises from the pharyngeal pouches?

Answer 13

a number of important glandular structures:
parathyroids
thymus
tonsils

Question 14

what are the pharyngeal Arches (cranial neural tube) and their Grooves (clefts) and Pouches (endoderm) collectively known as?

Answer 14

pharyngeal apparatus

Question 15

how many pharyngeal arches are there?

Answer 15

theoretically 6 (1-6)
but the 5th doesn't form in humans

Question 16

what is the biggest arch?

Answer 16

1st

arches get progressively smaller in size from 1-6

Question 17

which arches are not as readily visible? compared to which?

Answer 17

4th + 6th are not as readily visible as the first 3

Question 18

what is from / associated with each arch?

Answer 18

cartilage, nerve + artery

Question 19

where does the cartilage associated with each arch arise as?

Answer 19

as a cartilage bar in each pharyngeal arch

Question 20

what will the cartilage bar in each pharyngeal arch subsequently become?

Answer 20

a skeletal element of the head and neck

Question 21

which cartilaginous bar is largest?

Answer 21

the cartilaginous bar of the 1st pharyngeal arch

Question 22

what is the cartilaginous bar of the 1st pharyngeal arch known as?

Answer 22

Meckel’s cartilage

Question 23

what does Meckel’s cartilage give rise to?

Answer 23

mandible, malleus, incus bones

Question 24

what do the 4th and 6th arches give rise to?

Answer 24

thyroid, arytenoids, cricoids (remain cartilaginous)

Question 25

which cranial nerves are associated with the pharyngeal arches?

Answer 25

5, 7, 9, 10

V, VII, IX, X

Question 26

where do the cranial nerves associated with the pharyngeal arches arise from? innervate?

Answer 26

the lowest part of the brainstem

innervate the pharyngeal arches

Question 27

what do the structural derivatives of each pharyngeal arch be innervated by?

Answer 27

the particular cranial nerve associated with that arch

Question 28

what does each pharyngeal arch also become associated with?

Answer 28

an aortic arch blood vessel (runs through the mesenchyme of each pharyngeal arch)

Question 29

what does the recurrent laryngeal nerve of the vagus become looped under?

Answer 29

the arch of aorta (on the left side)
subclavian artery (on the right side)

Question 30

why does the recurrent laryngeal nerve of the vagus become looped under the aoAorta (L) and subclavian (R)?

Answer 30

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

Question 31

where does the facial skeleton arise from?

Answer 31

frontal prominence + 1st pharyngeal arch

Question 32

where do the muscles of mastication derive from? innervation?

Answer 32

1st pharyngeal arch

innervated by trigeminal nerve (CN V)

Question 33

what is significant of CN V (trigeminal)?

Answer 33

principal sensory nerve of the head

Question 34

what are muscles of facial expression derived from? innervation?

Answer 34

2nd pharyngeal arch

facial nerve innervation (CN VII)

Question 35

why do muscles of mastication and facial expression have different innervation despite being topographically related?

Answer 35

difference in pharyngeal arch derivative

facial: 2nd arch
mastication: 1st pharyngeal arch

Question 36

what does the 6th pharyngeal arch give rise to?

Answer 36

intrinsic muscles of the larynx