Head and Neck Embryology Flashcards
Where does the neck, face and skull develop from?
Neck = branchial/pharyngeal arches
Face = 5 mesenchymal processes/prominences
Skull: develops from the mesenchyme in the head region of developing embryo
Briefly run over somites again and how they relate to the head and neck
Somites are derived from the paraxial mesoderm and form structures like the axial skeleton and muscles
In human embryos around 33 somites develop
Somites in future head region of the embryo help in cranial skeleton development
Describe the neural tube and crest cells in terms of development of the head and neck
Some of the ectoderm in the midline folds down to form neural tube ->brain + spinal cord
Some cells at the crest of this neural fold separate to form the neural crest cells.
They migrate and give rise to a wide variety of structures.
The neural crest cells in the head and neck region mix with the mesoderm
What are the pharyngeal/ branchial arches?
Series of arches which develop around the future mouth (stomatodeum) and pharynx
Support the primitive pharynx.
Face and neck develop from them
How many pharyngeal arches form?
In humans 5 pharyngeal arches develop.
6 start to develop but arch 5 disappears so we are left with arches 1, 2, 3, 4, and 6
What embryological tissues make up the pharyngeal arches?
Ectoderm lines the outside (also forms clefts in between arches)
Mesoderm in the middle + neural crest cells (cartilage, muscles)
Endoderm on the inside (also forms pouches in between arches)
What are the nerves of the pharyngeal arches
1st arch = mandibular branch of trigeminal
2nd arch = facial nerve
3rd arch = glossopharyngeal nerve
4th arch = superior laryngeal branch of vagus
6th arch = recurrent laryngeal branch of vagus
What nerve is the muscles of the face innervated by and why does this give a clue as to where they develop from?
All the muscles of the face innervated by the VII cranial nerve (facial nerve)
Therefore all these muscles develop from the 2nd branchial arch
What nerve innervate the digastric muscle and therefore which pharyngeal arch do they develop from?
Anterior belly innervated by the mandibular division of the trigeminal nerve = 1st arch
Posterior belly innervated by the facial nerve = 2nd arch
How can you work out which pharyngeal arch muscles develop from?
Muscles migrate and take the nerve supply with them.
If you know the nerve supply you know the arch
Name other important structures developing from the branchial arches other than the muscles
Tongue
Thyroid gland
Parathyroid gland
Part of the pituitary gland
The face develops from which 5 processes?
One frontonasal process
-From mesenchyme superior to future mouth
Two maxillary processes
-From maxillary part of 1st pharyngeal arch mesoderm
Two mandibular processes
-Also 1st arch mesoderm
How do the processes at the head form the face?
The two mandibular processes fuse in the midline
Ectodermal thickening (nasal placode) pushes inwards or invaginates to form the nasal pit -> nostril
The medial nasal process further grows downwards and laterally, to form a process called the Philtrum
How does the palate develop?
Stage 1: Medial nasal process grows downwards and forms philitrum. This forms the primary palate
Stage 2: From the maxillary processes, two palatine shelves grow inwards
Stage 3: The palatine shelves meet in the midline to from the secondary palate
Now the oral cavity and nasal cavity are separate
What bones are contained in the cranial vault?
How are they formed?
Flat bones
Membranous bones -> formed by membranous ossification
What are the bones forming the base of the skull?
How are they formed?
Irregular bones
Bones formed by endochondrial ossification
What are the bones of the viscerocranium?
How are they formed?
Skeleton of the face
Partly from branchial arches and partly from sensory (special sense) capsules
Describe the formation of the skull vault
Mesenchyme derived from mesoderm that lies above the surface of developing brain ossify directly (membranous ossification)
The skull vault isn’t fully formed at birth
Sutures between them are soft (allowing deformation during passage through birth canal)
6 membrane covered fontanelle are of clinical significance
Describe the formation of the base of the skull
Mesenchyme around notochord is derived predominantly from neural crest cells
These preform in cartilage first
Later then ossify
What are the sensory capsules?
Derived from mesoderm of “somites” in head and neck region
These preform in cartilage and ossify to form bones around the sense organs (i.e. nose eye and ear)
They form partly base of skull, partly viscerocranium
