Head and Neck Embryology Flashcards
What does the neck develop from?
Branchial/pharyngeal arches
What does the face develop from?
5 mesenchymal processes/prominences
What is mesenchyme?
Embyonic connective tissue, has the same properties as conective tissue and develops into bone, cartilage, blood vessels etc
What does the skull develop from?
Mesenchyme in the head region of the developing embryo
Give a recap of the origin of embryology?
1) Ball of cells (blastula)
2) Flattened plate of cells is formed (bilaminar germ disc)
3) Trilaminar germ disc is formed which has amniotic cavity dorsally and yolk sac ventrally
4) Notochord formation leads to axis formation in embryo (ie embryo now has a right and left side)
What are the 2 areas of the early embryo where there is no mesoderm?
Sites of future mouth and anus
Explain the development of the neural tube and neural crest cells?
1) Some of ectoderm in midline folds down to form neural tube
2) Some cells at the crest of neural tube separate to form the neurla crest which migrate and give rise to a variety of structures
3) Neural crest cells in the head and neck region mix with the mesoderm
What does the neural tube go onto form?
Brain and spinal cord
What are somites derived from?
Paraxial mesoderm
What do somites form?
Structures like the axial skeleton and muscles
How many somites are there?
Around 33
What do somites in the future head region help with?
Cranial skeleton development
What are the series of arches called that develop around the future mouth and pharynx?
Pharyngeal/branchial arches
What is the precurser of the mouth?
Stomatodeum
What role does the pharyngeal/branchial arches have?
Supports primitive embryo
Develops into the face and neck
What forms the pharynx?
Developing foregut from the mouth to respiratory diverticulum
How many branchial arches develop?
5 (6 arches start to develop but number 5 disapears)
What are the 5 branchial arches?
1, 2, 3, 4, 6 (5 disapears)
What embryonic tissue makes up the branchial arches?
Ectoderm lines the outside (also forms clefts between arches)
Mesoderm in the middle (forms cartilage and muscle)
Endoderm on the inside (also forms mooches between arches)
What innervates each branchial arch?
A different cranial nerve
What cranial nerve innerates the 1st branchial arch?
Mandibular branch of trigeminal
What cranial nerve innervates the 2nd branchial arch?
Facial nerve
What cranial nerve innervates the 3rd branchial arch?
Glossopharyngeal nerve
What cranial nerve innervates the 4th branchial arch?
Superior laryngeal branch of vagus nerve
What cranial nerve innervates the 6th branchial arch?
Recurrent laryngeal branch of vagus nerve
What are all of the muscles of the face innervated by (expect the diagastric muscle)?
Facial nerve (CN VII)
What are the 2 components of the digastric muscle?
Anterior belly
Posterior belly
What is the anterior belly of the digastric muscle innervated by?
Mandibular division of trigeminal nerve (V3)
What is the posterior belly of the digastric muscle innervated by?
Facial nerve
When muscles migrate what do they take with them?
Nerves
Where is the first branchial arch?
Midline of mandible along the mandible region of the ear
Where is the 2nd branchial arch?
Parralel to the first, from the upper part of hyoid bone to styloid process
What are some important structures that develop from the branchial arches?
Tongue
Thyroid gland
Parathyroid glands
Part of the pituitary gland
How many processes/prominences does the face develop from?
5
What are the processes called that the face develops from?
One frontonasal process (from mesenchymal superior to future mouth)
Two maxillary processes (form maxillary part of 1st arch mesoderm)
Two mandibular processes (also 1st arch mesoderm)
What happens to allow the processes that form the face to eventually form the nasal pit then nostril?
1) Mandibular processes fuse in midline
2) Ectodermal thickening (nasal placode) pushes inwards to form nasal pit and then nostril
3) Medial nasal process further grows downwards and laterally to form process called the philtrum
Explain the development of the palate?
1) Medial nasal process grows downwards and forms philtrum, forming primary palate
2) From maxillary processes two palatine shelves grow inwards
3) The palatine shelves meet in the midline to form the secondary palate
4) Now the oral cavity and nasal cavity are seperate
What congenital conditions can occur when development of the palate does not happen correctly?
Cleft lip and palate
What is A?
What is B?
What is C?
What is D?
What is E?
What forms the primary palate?
Medial nasal process growing downwards to form philtrum
What forms the secondary palate?
Palatine shelves meeting in the midline
What is the thickened ectoderm that forms the nasal pit called?
Nasal placode, pushes inwards to form the nasal pit and then nostril
What is the skull vault?
Space in the skull occupied by the brain
What kind of bones make up the cranial vault?
Flat bones
What kind of ossification forms the bones at the base of the skull?
Endochondrial ossification
What kind of ossification forms the bones of the cranial vault?
Membranous ossification
What kind of bones forms the base of the skull?
Irregular bones
What is the viscerocranium?
Skeleton of the face
What does the viscerocranium form from?
Partly form branchial arches, and party from sensory (special sense) capsules
Explain the skull vault development?
Mesenchyme derived from mesoderm that lie above the surface of developing brain ossify directly (membranous ossification)
What is the mesenchyme that forms the skull vault derived from?
Mesoderm that lies about the surface of developing brain
When is the skull vault fully formed?
Not at birth, anteiror fontanelle closes 1.5 years after birth
Why can the skull vault become deformed during passage through the birth canal?
Sutures between them are soft
What is a fontanelle?
Soft sutures between cranial bones on an infant
How many fontanelles are there on an infant?
6, they are of clinical importance
What is a congenital problem of skull vault development?
Craniosynostosis
What is craniosynostosis?
Suture close to early causing brain growth issues
Explain the development of the base of the skull?
1) Mesenchyme around notochord is derived predominantly from neural crest cells
2) Preform in cartilage first
Later they ossify
What are sensory capsules derived from?
Mesoderm of smoites in the head and neck region
What do sensory capsules go onto form?
Bones around the sense organs (nose, ears and eyes)
Explain the development of sensory capsules to bones?
1) Preform in cartilage
2) Ossify to form bones around sense organs
From what bones do sensory capsules form from?
Partly base of skull, parly viscerocranium
What is an example of a 1st branchial arch abnormality?
Treacher Collins Syndrome
