Embryology of the Pharyngeal Arches and Ear

Question 1

what is gastrulation

Answer 1

formation of the trilaminar disc- happens in week 3

Question 2

what happens in gastrulation

Answer 2

invagination of the epiblast cells through the primitive streak to form the definitive endoderm and mesoderm

Question 3

what is the mesoderm organised into

Answer 3

paraxial, intermediate and lateral plates

Question 4

what is the neural crest derived from

Answer 4

the ectoderm

Question 5

what folding happens in the embry

Answer 5

lateral and craniocaudal

Question 6

what does the neural crest form

Answer 6

melanocytes, craniofacial cartilage and bone, smooth muscle, peripheral and enteric neurons and glia, sympathetic ganglia

Question 7

what do the pharyngeal arches form

Answer 7

much of the head an neck

Question 8

when do the pharyngeal arches form

Answer 8

arch 1- day 22
arch 2 +3- day 24
arch 4+6- day 29

Question 9

what is neuralation

Answer 9

formation of a round tube of neural cells

Question 10

what number of pharyngeal arch doesnt form in humans

Answer 10

number 5

Question 11

what are the three components of the pharyngeal apparatus

Answer 11

core pharyngeal arch
external pharyngeal cleft
internal pharyngeal pouch

Question 12

what are the roles of the clefts and arches

Answer 12

separates the arches

Question 13

what makes up the core pharyngeal arches

Answer 13

mesechymal tissue

Question 14

what makes up the external pharyngeal cleft

Answer 14

ectoderm (as clefts on the outside)

Question 15

what do the three germ layers form

Answer 15

ecto- central nervous system, peripheral nervous system, epithelia of eye, ear, nose, epidermis and appendages, mammary glands, enamel of teeth

meso- muscle, vasculature, lymph vessels, bone, connective tissue, kidneys, gonads

endo- epithial lining of GI and resp tracts, parenchyma of the tonsils liver thymus thyroid parathyroid pancreas, epithelial lining of bladder, tympanic cavity and antrum and auditary tube

Question 16

what makes up the internal pharyngeal pouch

Answer 16

endo (as on the inside)

Question 17

what makes up each pharyngeal arch

Answer 17

core mesenchyme derived from paraxial and lateral plate mesoderm

neural crest cells

cranial nerve component

artery (aortic arch arteries)

Question 18

in the pharyngeal arch what does the core mesenchyme make

Answer 18

musculature of the face

Question 19

in the pharyngeal arch what does the neural crest cells make

Answer 19

skeletal component of the face

Question 20

in the pharyngeal arch what does the cranial nerve component make

Answer 20

innervation both sensory or motor

Question 21

what nerves supply all the structures in the head and neck from pharyngeal arch 1

Answer 21

tigeminal nerve (V)- mandibular and maxillary divisions

Question 22

what nerves supply all the structures in the head and neck from pharyngeal arch 2

Answer 22

facial nerve VII

Question 23

what nerves supply all the structures in the head and neck from pharyngeal arch 3

Answer 23

glossopharyngeal nerve CN IX

Question 24

what nerves supply all the structures in the head and neck from pharyngeal arch 4 and 6

Answer 24

vagus

Question 25

what are the skeletal elements of the 1st pharyngeal arch

Answer 25

maxillary process (cranial portion): - maxilla - zygomatic bone - squamous portion of temporal bone mandibular process (caudal portion): - forms meckels cartilage - incus and malleus (ear ossicles) - mandible

Question 26

what are the muscles and nerves of the 1st pharyngeal arch

Answer 26

all musculature supplied by CNV3: - muscles of mastication - mylohyoid - anterior belly of digastric - tensor tympani - tensor veli palatini sensory supply to skin of face: - V1 (ophthalmic) - V2 (maxillary) - V3 (mandibular)

Question 27

what is the role of tensor tympani

Answer 27

dampens sound

Question 28

what are the skeletal elements of the 2nd arch

Answer 28

cartilage- reicherts cartilage skeletal derivatives: - stapes - styloid process of temporal bone - stylohyoid ligament - lesser horn of hyoid - upper part of hyoid body

Question 29

what are the muscle and nerve elements of the 2nd pharyngeal arch

Answer 29

all musculature supplied by CN VI (facial nerve): - Muscles of facial expression - posterior belly of digastric - stylohyoid - stapedius - auricular muscles (move ears)

Question 30

what are the skeletal elements of the 3rd pharyngeal arch

Answer 30

greater horn pf hyoid bone | lower part of hyoid bone

Question 31

what are the muscle and nerve elements of the 3rd pharyngeal arch

Answer 31

stylopharyngeus longitudinal pharyngeal muscle supplied by the glossopharyngeal nerve

Question 32

what are the skeletal elements of the 4th and 6th pharyngeal arch

Answer 32

laryngeal cartilages

Question 33

what are the muscle elements of the 4th pharyngeal arch

Answer 33

- cricothyroid - levator veli palatini - pharyngeal constrictors

Question 34

what are the muscle elements of the 6th pharyngeal arch

Answer 34

intrinsic laryngeal muscles (moves vocal chords)

Question 35

what are the nerve elements of the 4th and 6th pharyngeal arch

Answer 35

both supplied by vagus nerve arch 4- superior laryngeal nerve, pharyngeal plexus arch 6- recurrent laryngeal nerve

Question 36

what does the 1st pharyngeal cleft form

Answer 36

external acoustic meatus

Question 37

what do the 2-4th pharyngeal clefts form

Answer 37

lose contact with outside and form the cervical sinus

Question 38

what can happen if pharyngeal cleft 2 doesnt form properly

Answer 38

creates branchial sinus- bacteria can get in | can get internal fistulas

Question 39

what does the 1st pharyngeal pouch form

Answer 39

middle ear, tympanic membrane, eustachian tube

Question 40

what does the 2nd pharyngeal pouch

Answer 40

palatine tonsil

Question 41

what does the third pharyngeal pouch form

Answer 41

inferior parathryoid gland | thymus

Question 42

what does the fourth pharyngeal pouch form

Answer 42

``` superior parathyroid gland ultimobranchial body (thyroid gland/ C-cells) ```

Question 43

what is the path of the thymus

Answer 43

Thymus lies on anterior mediastinum mostly then moves outwards. As embryo starts to develop it will track its way down the way to thorax, unite with contralateral side and form thymus gland. Drags ifnferior parathyroid gland with it and develops over superior parathyroid gland which is derived from 4th pouch. Thyroid gland descending down Thymus drags down and drags parathyroid gland and lodges self in back of thyroid

Question 44

what are the parts of the inner ear and what do they do

Answer 44

balance (semicircular canals) | hearing (organ of corti)

Question 45

what makes up the middle ear

Answer 45

tympanic cavity | ossicles

Question 46

what makes up the external ear

Answer 46

external auditory meatus | auricle (pinna)

Question 47

what makes the otic placodes

Answer 47

ectoderm

Question 48

how do the otic vesicles form

Answer 48

otic placode- otic pit- otic vesicle

Question 49

what do the otic vesicles make

Answer 49

the inner ear

Question 50

what gives rise to the semicircular canals

Answer 50

utricular portion

Question 51

what gives rise to the cochlear

Answer 51

saccular portion

Question 52

what is endolymph and perilymph

Answer 52

endo fluid inside the membranous labyrinth of the ear peri fluid inbetween the membranous labyrinth of the ears

Question 53

how do the semicircular canals form

Answer 53

at week 6 utricular portion starts to flatten itself out. Central area moves in. starts to create rings.

Question 54

what is the crus ampullare

Answer 54

dilated end of the semicircular canals

Question 55

what is the crus nonampullare

Answer 55

non dilated end of the semicircular canals

Question 56

what is the crista ampullaris

Answer 56

within the ampulla of the semicircular canals contains: sensory cells for balance vestibular fibres CN VIII

Question 57

how does the cochlear duct develop

Answer 57

grows in spiral at weeks 6-8 surrounding mesenchyme becomes cartilagenous

Question 58

how many coils of the cochlea

Answer 58

2.5

Question 59

where is sound mostly conducted in the cochlear

Answer 59

organ of corti

Question 60

what forms the oval window

Answer 60

neural crest cells

Question 61

what forms the external auditory meatus

Answer 61

dorsal part of first pharyngeal cleft

Question 62

how is the external ear developed

Answer 62

Month 3 – epithelial cells proliferate to form Meatal Plug Plug dissolves in month 7 and contributes to eardrum 6 mesenchymal proliferations (3 from arch 1, 3 from arch 2) surround 1st pharyngeal cleft Hillocks fuse to form definitve Auricle External ears initially in lower neck Ascend due to development of mandible

Question 63

what forms the internal layer of the external ear

Answer 63

tubotympanic recess

Question 64

what makes the intermediate layer of the external ear

Answer 64

neural crest cells

Question 65

what forms the external cartilage of the ear

Answer 65

neural crest cells