Branchial arches

Question 1

branchial arches definition

Answer 1

a series of externally visible anterior tissue bands lying under the brain that give rise to the structures of the head and neck

Question 2

what day does pharyngeal arch development begin?

Answer 2

day 21

Question 3

what does cranial neurulation form?

Answer 3

anterior portion of the neural tube forms the three main parts of the brain:

forebrain- prosencephalon, midbrain- mesencephalon and the hindbrain, rhombencephalon

Question 4

explain further embryology of the brain

Answer 4

the structures initially appear just under the neural tube closures as bulges called brain vesicles in a pattern specified by anterior-posterior patterning genes such as Hox genes

the brain vesicles divide into more subdivisions

prosencephalon into telencephalon and diencephalon

rhombencephalon into metencephalon and myelencephalon and rhombomeres

neural crest cells form ganglia above each rhombomere, where neural circuits that control respiration, heart rate and production of most cranial nerves occurs

Question 5

what forms the embryonic pharynx?

Answer 5

the pharyngeal arches, their pouches and clefts

Question 6

germ layer origin of the different structures

Answer 6

branchial arches

• endoderm forms pharyngeal pouch- endoderm pouches out of foregut
• ectoderm forms pharyngeal cleft
• inside is filled with neural crest cells and mesoderm

Question 7

structure of embryonic pharynx

Answer 7

formed of 5 branchial arches, arranged in 5 bilateral pairs

I, II, III, IV and XI, NO X

Question 8

ectodermal eventual structures

Answer 8

neural tube-brain and eye

ectodermal places- sense organs

surface ectoderm- outer ear

Question 9

endodermal eventual structures

Answer 9

internal structures, endocrine glands such as thyroid and thymus

Question 10

mesodermal eventual structures

Answer 10

muscles, skeletal structures

Question 11

neural crest structures

Answer 11

skeleton, cartilage

Question 12

what will each branchial arch give rise to?

Answer 12

a nerve, a rod of cartilage, muscles and an artery

Question 13

what does the 1st arch form?

Answer 13

2 processes, the maxillary and mandibular swelling

Question 14

from cleft to pouch, what is the order of nerve, artery and cartilage?

Answer 14

nerve, cartilage and artery

Question 15

where is the first arch located?

Answer 15

between the stomodeum and first pharyngeal groove

Question 16

stomodeum definition

Answer 16

depression between the brain and pericardium of the embryo, the primitive mouth

Question 17

what does the maxillary process become?

Answer 17

the maxilla and palate, alisphenoid

palatopterygoquadrate bar of cartilage forms here, preceding the bone

Question 18

what does the mandibular process become?

Answer 18

the mandible and muscles of mastication

Meckel’s cartilage forms in the mesoderm and eventually regresses to form the incus and malleus of the middle ear

Question 19

difference in formation of upper and Lowe jaw

Answer 19

the mandibular process becomes ossified using Meckel’s cartilage as a template but the maxillary does not arise from direct ossification of Meckel’s cartilage

Question 20

examples of muscles of mastication

Answer 20

masseter, medial and lateral pterygoid muscles and temporalis

Question 21

explain the innervation of the first branchial arch

Answer 21

branches of the trigeminal nerve innervates the structures derived from the first arch

the trigeminal nerve runs along the cranial side of the arch, called the post trematic nerve of the arch

each arch also receives a branch from the nerve of the succeeding arch called the pre traumatic nerve which runs along the caudal border

in the human embryo, double innervation is only seen in the first arch

pre-trematic-chorda tympani, branch of the facial nerve

mandibular nerve- post trematic

Question 22

where is double innervation reflected?

Answer 22

the nervous supply of the anterior two thirds of the tongue are derived from the first arch

Question 23

two types of skeleton in the skull

Answer 23

neurocranium- brain case

viscerocranium- facial skeleton

Question 24

how does the malleus form?

Answer 24

forms from Meckel’s cartilage by endochondral ossification

Question 25

how does the incus form?

Answer 25

forms from maxilla, paletoptreygoquadrate bar

Question 26

blood supply of first arch

Answer 26

first aortic arch, which partially persists as the maxillary artery

Question 27

what is the frontonasal prominence?

Answer 27

cranial region that contains neural crest cells form the midbrain and forebrain

Question 28

what structures originate from the 2nd branchial arch?

Answer 28

muscles of facial expression, styloid process and stapes

Question 29

what cartilage is present + how is it different to Meckel's?

Answer 29

Reichert's cartilage unlike Meckel's it does not constitute a continuous element and is instead formed of two distinct cartilaginous segments joint together by a faint layer of mesenchyme

Question 30

what are stapes + how are they formed?

Answer 30

bone in the middle ear which is involved in the conduction of sound vibrations to the inner ear the ends of the cartilage ossify to form the stapes of the middle ear before being incorporated into the middle ear cavity lightest and smallest bone in the body

Question 31

what is the styloid process + how is it formed?

Answer 31

a process that extends from the temporal bone endochondral ossification of Reichert's cartilage

Question 32

what muscles are formed?

Answer 32

frontalis- muscle the covers part of the forehead, lifts eyebrows orbicularis oculi- muscle that closes the eyelids orbicularis oris- complex of muscles that encircle the mouth buccinator- forms the anterior part of the wheel auricularis- three muscles surrounding the outer ear

Question 33

innervation of structures from 2nd arch

Answer 33

facial nerve

Question 34

blood supply from 2nd arch

Answer 34

2nd aortic arch which gives origin to the stapedial artery in some muscles but atrophies in humans

Question 35

what structures are formed from the 3rd arch?

Answer 35

stylopharyngeal muscle, hyoid bone

Question 36

explain formation of stylopharyngeal muscle + function

Answer 36

long slender muscle arising from the medial side of the base of the styloid temporal process and inserted into the posterior border of the thyroid cartilage elevates the larynx and pharynx, used for vocalisation and swallowing

Question 37

explain formation of hyoid + function

Answer 37

second pharyngeal arch gives rise to the lesser Cornu of the hyoid and the upper part of the body of the hyoid the cartilage of the third arch forms the greater Cornu and lower body becomes ossified from six centres, ossification of greater corpus begins towards the end of fatal development, hyoid body shortly afterwards and lesser Cornu until 1-2 years of age neural crest cells contribute allows a wider range of tongue, pharyngeal and laryngeal movements by bracing these structures alongside each other to produce variation

Question 38

innervation of third arch

Answer 38

glossopharyngeal nerve

Question 39

structures of IX arch

Answer 39

pharyngeal and laryngeal muscles, laryngeal cartilages

Question 40

what muscles are formed + function?

Answer 40

cricothyroid muscle- tensor muscle of the larynx aiding phonation all intrinsic muscles of the soft palate, except the tensor veli palatini- involved in swelling, breathing and moving the uvula

Question 41

what cartilages are formed + functions?

Answer 41

thyroid cartilage- hyaline cartilage structure that sits in front of the larynx and above the thyroid, protects the vocal cords, pitch of voice epiglottic cartilage- bends back during swallowing, prevent the food bolus from falling into the trachea

Question 42

explain thyroid cartilage structure in more detail

Answer 42

Two halves of cartilage that meet at a peak called the laryngeal prominence, Adam's apple super thyroid notch is at the midline above the prominence articulates with the cricoid, changing angles relevant to the cricoid causes changes in pitch

Question 43

what innervates these structures?

Answer 43

the superior laryngeal and the recurrent laryngeal branches of the vagus nerve

Question 44

what innervates the tensor veli palatini + why?

Answer 44

trigeminal nerve, as it originates from the first pharyngeal arch

Question 45

what does the 6th arch form?

Answer 45

laryngeal muscles, cricoid cartilage

Question 46

which muscles?

Answer 46

all intrinsic muscles of the larynx apart from the Cricothyroid muscle

Question 47

innervation of the 6th arch?

Answer 47

vagus nerve

Question 48

pharyngeal cleft derivatives

Answer 48

between first and second arch- the outer ear

Question 49

what happens to the other clefts?

Answer 49

second arch grows over them

Question 50

pharyngeal pouch derivatives

Answer 50

pouch 1- middle ear + Eustachian tube pouch 2- tonsils pouch 3- thymus and inferior parathyroid pouch 4- superior parathyroid

Question 51

trigeminal nerve sensory and motor innervation

Answer 51

motor to muscles of mastication sensory to skin of face, facial and oral mucosa, anterior 2/3rds of tongue

Question 52

facial nerve sensory and motor innervation

Answer 52

muscles of facial expression sensory taste from anterior 2/3rds

Question 53

explain initial blood supply then changes

Answer 53

each branchial arch is supplied by one aortic arch neural crest cells than involved in remodelling

Question 54

explain stages of facial development

Answer 54

1. the maxillary and mandibular processes surround the stomodeum along with the frontonasal prominence at 4-4.5 weeks 2. a series of individualised tissue swellings give rise to the different parts of the face, called facial processes. The frontonasal process gives rise to: - a pair of medial nasal processes - a pair of lateral nasal processes 3. nasal placodes, two ectodermal thickenings appear on the frontonasal process, the lateral nasal and medial nasal swellings that surround the placodes appear on the process 4. as the swellings grow forward, the nasal placodes remain relatively stationary, giving the impression that they invaginate, eventually become the nasal pits 4. the maxillary process grows rapidly and joins the medial and lateral nasal processes, forming the philtrum of the upper lip. The nasolacrimal groove lies between the lateral process fused to the maxillary process and will form he nasolacrimal duct 5. merging occurs where the grooves between two facial processes are eliminated. The tissues in the groove grow more rapidly by proliferating more until the groove becomes shallower and it smooths out 6. the maxillary process forms the cheeks, primary palate and medial part of the nose

Question 55

what can go wrong if merging does not occur?

Answer 55

a facial cleft is left, different types depending where fusion went wrong oblique- side bilateral- two median- middle

Question 56

palate definition

Answer 56

tissue between nasal and oral cavities

Question 57

what forms the definitive palate?

Answer 57

the primary palate and secondary palate

Question 58

formation of the primary palate

Answer 58

1. medial and lateral nasal processes come into contact and then the medial and maxillary processes come together, pinching some epithelium between them 2. this sheet of epithelium is composed of future nasal epithelium superiorly and future oral epithelium inferiorly 3. the two layers of epithelium are then pulled apart, making mesenchyme between medial nasal and maxillary processes, forming the primary plate core 4. posterior behind the primary plate, the nasal epithelium continues to touch the oral epithelium, forming the oronasal membrane 5. the oronasal membrane cells eventually stop undergoing mitosis which rips open the membrane resulting in an opening connecting the nasal cavity and oral cavity called the primitive choanae (two, one for each nasal cavity)

Question 59

development of the secondary palate

Answer 59

1. as the face grows in the anterograde-posterior dimension, the primary palate soon becomes too short to provide adequate separation between the nasal cavities and the oral cavity, thus a secondary palate must form 2. the medial walls of the maxillary processes product a pair of thin medial extensions called the palatal processes 3. they initially grow vertically, downward and parallel to the lateral surfaces of the tongue 4. as the tongue begins to contract and move and the lower jaw drops, the palatal processes rapidly rotate upward to a horizontal position and fuse with each other with the primary plate

Question 60

where else can clefts form?

Answer 60

any site where merging or fusion occurs palate and tongue

Question 61

what is DiGeorge syndrome?

Answer 61

deletion of a small segment of chromosome 22, around 30-40 genes, autosomal dominant leads to defects such as congenital heart disease, defects in the palate, learning difficulties and neuromuscular problems with closure- veropharyngeal inadequacy