Branchial arches Flashcards
branchial arches definition
a series of externally visible anterior tissue bands lying under the brain that give rise to the structures of the head and neck
what day does pharyngeal arch development begin?
day 21
what does cranial neurulation form?
anterior portion of the neural tube forms the three main parts of the brain:
forebrain- prosencephalon, midbrain- mesencephalon and the hindbrain, rhombencephalon
explain further embryology of the brain
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
what forms the embryonic pharynx?
the pharyngeal arches, their pouches and clefts
germ layer origin of the different structures
branchial arches
- endoderm forms pharyngeal pouch- endoderm pouches out of foregut
- ectoderm forms pharyngeal cleft
- inside is filled with neural crest cells and mesoderm
structure of embryonic pharynx
formed of 5 branchial arches, arranged in 5 bilateral pairs
I, II, III, IV and XI, NO X
ectodermal eventual structures
neural tube-brain and eye
ectodermal places- sense organs
surface ectoderm- outer ear
endodermal eventual structures
internal structures, endocrine glands such as thyroid and thymus
mesodermal eventual structures
muscles, skeletal structures
neural crest structures
skeleton, cartilage
what will each branchial arch give rise to?
a nerve, a rod of cartilage, muscles and an artery
what does the 1st arch form?
2 processes, the maxillary and mandibular swelling
from cleft to pouch, what is the order of nerve, artery and cartilage?
nerve, cartilage and artery
where is the first arch located?
between the stomodeum and first pharyngeal groove
stomodeum definition
depression between the brain and pericardium of the embryo, the primitive mouth
what does the maxillary process become?
the maxilla and palate, alisphenoid
palatopterygoquadrate bar of cartilage forms here, preceding the bone
what does the mandibular process become?
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
difference in formation of upper and Lowe jaw
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
examples of muscles of mastication
masseter, medial and lateral pterygoid muscles and temporalis
explain the innervation of the first branchial arch
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
where is double innervation reflected?
the nervous supply of the anterior two thirds of the tongue are derived from the first arch
two types of skeleton in the skull
neurocranium- brain case
viscerocranium- facial skeleton
how does the malleus form?
forms from Meckel’s cartilage by endochondral ossification
how does the incus form?
forms from maxilla, paletoptreygoquadrate bar
blood supply of first arch
first aortic arch, which partially persists as the maxillary artery
what is the frontonasal prominence?
cranial region that contains neural crest cells form the midbrain and forebrain
what structures originate from the 2nd branchial arch?
muscles of facial expression, styloid process and stapes
what cartilage is present + how is it different to Meckel’s?
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
what are stapes + how are they formed?
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
what is the styloid process + how is it formed?
a process that extends from the temporal bone
endochondral ossification of Reichert’s cartilage
what muscles are formed?
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
innervation of structures from 2nd arch
facial nerve
blood supply from 2nd arch
2nd aortic arch which gives origin to the stapedial artery in some muscles but atrophies in humans
what structures are formed from the 3rd arch?
stylopharyngeal muscle, hyoid bone
explain formation of stylopharyngeal muscle + function
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
explain formation of hyoid + function
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
innervation of third arch
glossopharyngeal nerve
structures of IX arch
pharyngeal and laryngeal muscles, laryngeal cartilages
what muscles are formed + function?
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
what cartilages are formed + functions?
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
explain thyroid cartilage structure in more detail
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
what innervates these structures?
the superior laryngeal and the recurrent laryngeal branches of the vagus nerve
what innervates the tensor veli palatini + why?
trigeminal nerve, as it originates from the first pharyngeal arch
what does the 6th arch form?
laryngeal muscles, cricoid cartilage
which muscles?
all intrinsic muscles of the larynx apart from the Cricothyroid muscle
innervation of the 6th arch?
vagus nerve
pharyngeal cleft derivatives
between first and second arch- the outer ear
what happens to the other clefts?
second arch grows over them
pharyngeal pouch derivatives
pouch 1- middle ear + Eustachian tube
pouch 2- tonsils
pouch 3- thymus and inferior parathyroid
pouch 4- superior parathyroid
trigeminal nerve sensory and motor innervation
motor to muscles of mastication
sensory to skin of face, facial and oral mucosa, anterior 2/3rds of tongue
facial nerve sensory and motor innervation
muscles of facial expression
sensory taste from anterior 2/3rds
explain initial blood supply then changes
each branchial arch is supplied by one aortic arch
neural crest cells than involved in remodelling
explain stages of facial development
- the maxillary and mandibular processes surround the stomodeum along with the frontonasal prominence at 4-4.5 weeks
- 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 - 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
- as the swellings grow forward, the nasal placodes remain relatively stationary, giving the impression that they invaginate, eventually become the nasal pits
- 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
- 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
- the maxillary process forms the cheeks, primary palate and medial part of the nose
what can go wrong if merging does not occur?
a facial cleft is left, different types depending where fusion went wrong
oblique- side
bilateral- two
median- middle
palate definition
tissue between nasal and oral cavities
what forms the definitive palate?
the primary palate and secondary palate
formation of the primary palate
- medial and lateral nasal processes come into contact and then the medial and maxillary processes come together, pinching some epithelium between them
- this sheet of epithelium is composed of future nasal epithelium superiorly and future oral epithelium inferiorly
- the two layers of epithelium are then pulled apart, making mesenchyme between medial nasal and maxillary processes, forming the primary plate core
- posterior behind the primary plate, the nasal epithelium continues to touch the oral epithelium, forming the oronasal membrane
- 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)
development of the secondary palate
- 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
- the medial walls of the maxillary processes product a pair of thin medial extensions called the palatal processes
- they initially grow vertically, downward and parallel to the lateral surfaces of the tongue
- 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
where else can clefts form?
any site where merging or fusion occurs
palate and tongue
what is DiGeorge syndrome?
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
