Session 5- Development of the Head, Neck and Face Flashcards
what are the pharyngeal arches
sequence of ridges that form in the lateral walls of the embryonic pharynx towards the cranial end of the neural tube
when do the pharyngeal arches become apparent
4 weeks in
which clefts remain and what do they become
first - becomes external auditory meatus
what forms the auricle
swellings which form around the entrance to the meatus
what covers the external surface of the pharyngeal arches
ectoderm
what covers the internal surface of the pharyngeal arches
endoderm
how many arches are there
theoretically 6 but the 5th doesnt form in humans
whuch arch is biggest
1st and they get progressively smaller in size from 1-6
what is assciated with each arch
cartilage
artery
nerve
what does the cartilage bar become
skeletal element of the head and neck
what is teh cartilagenous bar in the 1st bar known is
meckles cartilage
largest
what does the Meckel’s cartilage become- derived from 1st arch
mandible
malleus
incus
what do the 4th and 6th arches give rise to
thyroid
arytenoids
cricoids
which cranial nerves associate with the pharyngeal arches
V
VII
IX
X
What is arch 1 associated with
V
What nerve is arch 2 associated with
VII
What is arch 3 associated with
IX
What is arch 4 associated with
vagus- superior laryngeal
What nerve arch 6 associated with
vagus- recurrent laryngeal nerve
what muscles are derived from the first arch
muscles of mastication
what muscles are derived from the second arch
Muscles of facial expression
what muscles are derived from the third arch
stylopharyngeus - muscle of pharynx
what muscles are derived from the 4-6arch
constrictor muscles of pharynx and muscles of soft palate
muscles of the larynx
striated muscle of upper oesophagus
where does the facial skeleton arise from
frontonasal prominene
what structure arises from pouch 1
pharyngotympanic (eustachian) tube and middle ear cavity
what structure arises from pouch 2
palatine tonsil
what structure arises from pouch 3
inferior parathyroid
thymus
what structure arises from pouch 4
superior parathyroid
c cells of thyroid
what are the 5 building blocks of the face
frontonasal prominence
2 maxillary prominences
2 mandibular prominences
what is teh frist evidence of face development
stomadaeum - a depression in the ectoderm on the ventral aspect of the head which is teh site of future mouth
how is the face created
the 5 prominences fold around the stomadaeum to create the face
what does the frontonasal prominence go on to form
forehead
bridge of nose
upper eyelids
centre of upper lip
what do teh 2 lateral paired maxillary prominence form
middle third of face
upper jaw
most of the lip and sides of the nose
wht do the paired mandibular prominences form
lower third of the face - lower jaw and lip
what is the first evidence of nose formation and how does the nose form
appearance of 2 ectodermal thickenings which are the nasal placdes wither side of the midline on the ventrolateral aspect of the frontonasal prominence
the nasal placodes invaginate and form deep pits the nasal pits with the entrance of each pit being the future nostril
what is a placodeo
an area of ectoderm that starts to thicken and differentiate itself from its surrounding tissue to give rise to sensory structures
oronasal membrane
a thin sheet of cells between the stomadaeum and deepening nasal pits which disappears and the oral and nasal cavities become one continous space
how does the palate develop
medial nasal prominences merge in the midline separating the nostrils form the mouth
this forms the philtrum of upper lip and a small midlne component of palate
a palatal shelf grows from each maxillary prominence towards the midline
they fuse with each other and with the primary palate
fusion creates the secondary palate and separates the nasal cavity from oral cavityv
why do clefts develop
failure of fusion betwen tructures of the developing face
how does a clefy lip arise
failure of the fusion of the medial nasal prominence and maxilllary prominence
how does a cleft palate arise
failure of fusion of the palatal shelves - hard palate - to meet in the midline
aetiology of clefts
both genetic and environmental fatcors
why does fetal alcohol syndrome present with low set ears
alcohol arrests the ascent of ears
at innervates the anterior 2/3 of the tngue
general sensation from trigeminal
taste from facial
posterior 1/3 of tongue innervation
general sensation and taste from glossopharyngeal
where does the thyroids develop fro
thyroid diverticulum whihc originates from the foramen caecum therefore tongue
from which pharyngeal arch are the maxilary and mandibular prominences formed
first
what happens to the pharyngeal grooves or clefts in the devloping embryo
all are obliterted except 1 because the secon pharyngeal acrh grows caudally covering all the other pharygeal arches and tehir grooves
this creates a small space called the cervical sinus which eventually fuses closed as the grooves disappear
outline how a branchial cyst develops
incomplets fusion of the second pharyngeal arch iver the other arches/ grooves allows persistence of the cervical sinus
an open channel for communication between the sinus and the external environment may persist this gives rise to a branchial sinus
what predisposes a branchial cyst
infection
minor trauma
this causes the cyst to swell making it become apparent
how do branchial cysts present
smooth non tender soft masses along the anterior border of teh SCM
