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Organisation of the body: embryology > Branchial arches > Flashcards

Branchial arches Flashcards

1
Q

branchial arches definition

A

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

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2
Q

what day does pharyngeal arch development begin?

A

day 21

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3
Q

what does cranial neurulation form?

A

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

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

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4
Q

explain further embryology of the brain

A

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

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5
Q

what forms the embryonic pharynx?

A

the pharyngeal arches, their pouches and clefts

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6
Q

germ layer origin of the different structures

A

branchial arches

  • endoderm forms pharyngeal pouch- endoderm pouches out of foregut
  • ectoderm forms pharyngeal cleft
  • inside is filled with neural crest cells and mesoderm
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7
Q

structure of embryonic pharynx

A

formed of 5 branchial arches, arranged in 5 bilateral pairs

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

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8
Q

ectodermal eventual structures

A

neural tube-brain and eye

ectodermal places- sense organs

surface ectoderm- outer ear

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9
Q

endodermal eventual structures

A

internal structures, endocrine glands such as thyroid and thymus

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10
Q

mesodermal eventual structures

A

muscles, skeletal structures

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11
Q

neural crest structures

A

skeleton, cartilage

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12
Q

what will each branchial arch give rise to?

A

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

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13
Q

what does the 1st arch form?

A

2 processes, the maxillary and mandibular swelling

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14
Q

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

A

nerve, cartilage and artery

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15
Q

where is the first arch located?

A

between the stomodeum and first pharyngeal groove

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16
Q

stomodeum definition

A

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

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17
Q

what does the maxillary process become?

A

the maxilla and palate, alisphenoid

palatopterygoquadrate bar of cartilage forms here, preceding the bone

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18
Q

what does the mandibular process become?

A

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

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19
Q

difference in formation of upper and Lowe jaw

A

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

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20
Q

examples of muscles of mastication

A

masseter, medial and lateral pterygoid muscles and temporalis

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21
Q

explain the innervation of the first branchial arch

A

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

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22
Q

where is double innervation reflected?

A

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

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23
Q

two types of skeleton in the skull

A

neurocranium- brain case

viscerocranium- facial skeleton

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24
Q

how does the malleus form?

A

forms from Meckel’s cartilage by endochondral ossification

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25
Q

how does the incus form?

A

forms from maxilla, paletoptreygoquadrate bar

26
Q

blood supply of first arch

A

first aortic arch, which partially persists as the maxillary artery

27
Q

what is the frontonasal prominence?

A

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

28
Q

what structures originate from the 2nd branchial arch?

A

muscles of facial expression, styloid process and stapes

29
Q

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

A

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

30
Q

what are stapes + how are they formed?

A

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

31
Q

what is the styloid process + how is it formed?

A

a process that extends from the temporal bone

endochondral ossification of Reichert’s cartilage

32
Q

what muscles are formed?

A

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

33
Q

innervation of structures from 2nd arch

A

facial nerve

34
Q

blood supply from 2nd arch

A

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

35
Q

what structures are formed from the 3rd arch?

A

stylopharyngeal muscle, hyoid bone

36
Q

explain formation of stylopharyngeal muscle + function

A

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

37
Q

explain formation of hyoid + function

A

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

38
Q

innervation of third arch

A

glossopharyngeal nerve

39
Q

structures of IX arch

A

pharyngeal and laryngeal muscles, laryngeal cartilages

40
Q

what muscles are formed + function?

A

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

41
Q

what cartilages are formed + functions?

A

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

42
Q

explain thyroid cartilage structure in more detail

A

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

43
Q

what innervates these structures?

A

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

44
Q

what innervates the tensor veli palatini + why?

A

trigeminal nerve, as it originates from the first pharyngeal arch

45
Q

what does the 6th arch form?

A

laryngeal muscles, cricoid cartilage

46
Q

which muscles?

A

all intrinsic muscles of the larynx apart from the Cricothyroid muscle

47
Q

innervation of the 6th arch?

A

vagus nerve

48
Q

pharyngeal cleft derivatives

A

between first and second arch- the outer ear

49
Q

what happens to the other clefts?

A

second arch grows over them

50
Q

pharyngeal pouch derivatives

A

pouch 1- middle ear + Eustachian tube

pouch 2- tonsils

pouch 3- thymus and inferior parathyroid

pouch 4- superior parathyroid

51
Q

trigeminal nerve sensory and motor innervation

A

motor to muscles of mastication

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

52
Q

facial nerve sensory and motor innervation

A

muscles of facial expression

sensory taste from anterior 2/3rds

53
Q

explain initial blood supply then changes

A

each branchial arch is supplied by one aortic arch

neural crest cells than involved in remodelling

54
Q

explain stages of facial development

A
  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
  5. 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
  6. 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
  7. the maxillary process forms the cheeks, primary palate and medial part of the nose
55
Q

what can go wrong if merging does not occur?

A

a facial cleft is left, different types depending where fusion went wrong

oblique- side
bilateral- two
median- middle

56
Q

palate definition

A

tissue between nasal and oral cavities

57
Q

what forms the definitive palate?

A

the primary palate and secondary palate

58
Q

formation of the primary palate

A
  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)
59
Q

development of the secondary palate

A
  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
60
Q

where else can clefts form?

A

any site where merging or fusion occurs

palate and tongue

61
Q

what is DiGeorge syndrome?

A

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

Organisation of the body: embryology (11 decks)

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