Embryology Flashcards
what side of the trilaminar disc is the amniotic cavity on?
the dorsal side, the side of the ectoderm
what side of the trilaminar disc is the yolk sac on?
the ventral side, side of the endoderm
what forms at the two areas of the trilaminar disc where there is no mesoderm and the ectoderm and the endoderm are connected?
the mouth and anus
what leads to the axis formation in the embryo?
the notochord formation
describe the formation of the neural tube
the notochord sends out signals to the ectoderm causing it to thicken, this forms the neural plate in the midline. this plate sinks downwards so there are crests on either sides (like two hills and a valley). these two sides join up in the midline forming the neural tube
what do some of the cells in the crest of the neural fold do?
they proliferate rapidly and separate to form the neural crest cells and migrate to form a variety of structures.
in the head and neck region what do the neural crest cells mix with?
the mesoderm
what are somites derived from?
the paraxial mesoderm
what sort of structures do somites form?
axial skeleton bones and muscle
how many somites develop in human embryos?
around 33
what are the pharyngeal/brachial arches?
a series of arches which develop around the future mouth and pharynx
what supports the primitive pharynx?
the pharyngeal/brachial arches
how many brachial arches develop in humans?
5
what brachial arch disappears resulting in five brachial arches being present in development?
number 5
what lines the outside of the brachial arches?
ectoderm
what forms the clefts between the brachial arches?
the ectoderm
what is in the middle of the brachial arches?
the mesoderm and the neural crest cells
what does the mesoderm in the brachial arches go onto form?
cartilage and muscle
what is on the inside of the brachial arches?
endoderm
what forms the pouches between the arches?
endoderm
what is in the mesoderm in the brachial arches?
> skeletal element
artery
nerve
what is the nerve of the 1st brachial arch?
mandibular branch of the trigeminal nerve
what is the nerve of the 2nd brachial arch?
facial nerve
what is the nerve of the 3rd brachial arch?
glossopharyngeal nerve
what is the nerve of the 4th brachial arch?
superior laryngeal branch of the vagus
what is the nerve of the 5th brachial arch?
HA!THERE IS NO 5TH BRACHIAL ARCH
what is the nerve of the 6th brachial arch?
recurrent laryngeal branch of the vagus
from what brachial arch are the muscles of the face derived from?
the 2nd brachial branch (as they are all innervated by the VII cranial nerve, the facial nerve)
from what brachial arch is the digastric muscle derived from?
Anterior: 1st arch (innervated by mandibular division of the trigeminal nerve V3)
Posterior: 2nd arch (innervated by the facial nerve)
what is the only muscle derived from the third brachial arch?
stylopharyngeal muscle
why by knowing the nerve supply to a muscle can you work out which arch it came from?
as the muscle migrates it takes the nerve with it so you can work out which arch it came from
what begins to form around the future pharynx from the brachial arches?
skeletal elements
what other important structures develop from the branchial arches?
> tongue
thyroid gland
parathyroid gland
part of the pituitary gland
from what 5 processes does the face develop?
> one frontonasal process
two maxillary processes
two mandibular processes
what forms the two maxillary processes and 2 mandibular processes that go onto form the face?
maxillary part of 1st branchial arch mesoderm
where do the two mandibular processes fuse in the development of the face?
in the midline
describe the formation of the nasal pits
there is ectodermal thickening which pushes inwards or invaginates to form the nasal pits/nostrils
how is the philtrum developed?
after the formation of the nasal pits the medial nasal process grows downward and laterally to form a process, the philtrum (bit under the nose and above the mouth)
describe the development of the palate
> medial nasal process grows downwards to form the philtrum and primary palate.
two palatine shelves grow inwards from the maxillary processes.
the palatine shelves meet in the midline to form the secondary palate.
this separates the oral and nasal cavity
why are some children born with cleft palates?
the maxillary process has not fused with the philtrum
what sort of ossification forms the flat bones of the skull?
membranous ossification
what type of ossification forms the irregular bones of the skull?
endochondral ossification
from what is the skeleton of the face formed?
partly the branchial arches and partly from sensory capsules
describe the formation of the skull vault
the mesenchyme derived from mesoderm that lies directly above the surface of developing brain ossifies directly
why is the skull vault not fully formed at birth?
to allow deformation during the passage through the birth canal
when does the anterior fontanelle close?
at 1.5 years
what is craniosynostosis?
when sutures form earlier than they should resulting in a variety of clinical presentations and abnormal brain and skull development
describe the formation of the base of the skull
mesenchyme around the notochord is derived from neural crest cells. this then preforms in cartilage then later ossifies
what are sensory capsules derived from?
mesoderm of somites in head and neck region
what do sensory capsules form?
partly the base of the skull and partly the viscerocranium
