Head and Neck Embryology Flashcards
RECAP- what happens after the sperm fertilises the egg?
Zygote divides to form blastocyst
RECAP- the blastocyst flattens. What does this form?
Bilateral disc which then develops into three layers = trilaminar disc
RECAP- name the three layers of the trilaminar disc.
Ectoderm
Mesoderm
Endoderm
RECAP- name the space above the ectoderm/.
Amniotic cavity
RECAP- name the space below the endoderm.
Yolk sac
RECAP- the notochord forms in the trilaminar disc. This is the axis for many developments. However, the notochord does not fully extend from the very top of trilaminar disc to the very bottom.
What happens in these sections?
No mesoderm so ectoderm and endoderm fuse.
There are two areas with no mesoderm and these form the mouth and the anus.
RECAP- describe the development of the neural tube.
Notochord releases chemicals which causing thickening of ectoderm epithelium. This forms neural crests.
The ends of the neural crests come together and closes, forming the neural tuber which then sinks down away from the ectoderm.
->if you don’[t understand this, watch the Part 1 of Head and Neck Embryology, goes over a recap of what we know so far and might be useful before exam!
RECAP- what forms from the neural tube?
Brain and spinal cord
RECAP- in the process of neural tube formation, what else is produced?
Neural crest cells which migrate and give rise to many different structures.
RECAP- what comes from the paraxial mesoderm?
Somites
What do somites go onto develop?
Axial skeleton
Muscles
RECAP- how many somites are formed in human embryos?
33
RECAP- what does the ectoderm develop into?
Skin
->think, the ectoderm goes around everything
RECAP- what does the mesoderm develop into?
Muscle, connective tissue
RECAP- what does the endoderm develop into?
Gut tube
RECAP- where does the respiratory tract develop from?
Foregut regions
What are the pharyngeal/brachial arches?
Series of arches which develop around the future mouth and pharynx.
When in the process of embryological development do the pharyngeal/branchial arches develop?
Late week 4- week 6
How many branchial arches develop?
5
->six start to develop but no.5 disappears leaving us with 1,2,3,4,6
What makes up the branchial arches?
Ectoderm- makes outside
Mesoderm- bulky middle section + neural crest cells
Endoderm- lines inside of arch
Which structures develop in the mesoderm of the branchial arches?
Blood vessels
Nerves
Skeletal elements
(think about what arises from mesoderm in general)
What else can the ectoderm form in the branchial arches as well as forming the outer layer?
Forms clefts between the arches
These clefts can develop into structure like the tongue
What else can the endoderm form in the branchial arches as well as forming the inner layer?
Forms pouches between the arches
Cranial nerves form from the branchial arches.
Which nerve develops from the first branchial arch?
IMPORTANT TO REMEMBER, COMMON EXAM QUESTION
Mandibular branch of Trigeminal nerve (CN V3).
Cranial nerves form from the branchial arches.
Which nerve develops from the second branchial arch?
IMPORTANT TO REMEMBER, COMMON EXAM QUESTION
Facial nerve (CN VII)
Cranial nerves form from the branchial arches.
Which nerve develops from the third branchial arch?
IMPORTANT TO REMEMBER, COMMON EXAM QUESTION
Glossopharyngeal nerve (CN IX).
Cranial nerves form from the branchial arches.
Which nerve develops from the fourth branchial arch?
IMPORTANT TO REMEMBER, COMMON EXAM QUESTION
Superior laryngeal branch of the Vagus nerve (CN X)
Cranial nerves form from the branchial arches.
Which nerve develops from the sixth branchial arch?
IMPORTANT TO REMEMBER, COMMON EXAM QUESTION
Recurrent laryngeal branch of the Vagus nerve (CN X)
Which nerve innervates all the muscles of face expression of the face?
Facial nerve (CN VII)
Therefore, which branchial arch does nerve supplying the face come from?
Second branchial arch
What is the anterior belly of the digastric muscle innervated by?
Mandibular branch of trigeminal nerve
What is the posterior belly of the digastric muscle innervated by?
Facial nerve
Which nerve innervates the muscles of mastication (chewing)?
Which branchial arch will this be developed from?
Submandibular branch of trigeminal nerve (CN V3).
Therefore, the muscles of mastication are developed from the first branchial arch.
The glossopharyngeal nerve innervates a single muscle. Name it and tell me the branchial arch it developed from.
Stylopharyngeus muscle.
This muscle must have developed from the third branchial arch :)
->this makes sense to me when I am writing this but if you need a recap, go over part 2 of the lecture, so well explained!!
The superior and recurrent laryngeal nerves (both branches of Vagus nerve) supply the muscles of the vocal cord.
Where will these muscles have developed from?
Branchial arches 4&6
Skeletal elements also develop from the branchial arches.
Which bones would form from the first branchial arch?
Mandible, malleus and incus.
Skeletal elements also develop from the branchial arches.
Which bones would form from the second branchial arch?
Upper hyoid bone
Stapes
Stylohyoid ligament
Styloid process
Skeletal elements also develop from the branchial arches.
Which bones would form from the third branchial arch?
Lower part of hyoid bone
Skeletal elements also develop from the branchial arches.
Which bones would form from the fourth branchial arch?
Thyroid cartilages
Skeletal elements also develop from the branchial arches.
Which bones would form from the sixth branchial arch?
Lower thyroid cartilage
Cricoid cartilage
The clefts and pouches which are formed by the endoderm and ectoderm give rise to structures. Name them.
Tongue
Thyroid gland
Parathyroid gland
Part of pituitary gland
The face develops from five processes/prominences. Please name them.
1 frontonasal process
2 maxillary processes
2 mandibulae processes
Where do the two maxillary processes develop from?
Maxillary part of first branchial arch
Where do the two mandibular processes develop from?
First branchial arch
Where does the frontonasal process develop from?
The mesenchyme superior to the future mouth
What happens to the 2 mandibular processes?
They fuse together in the midline
There is ectodermal thickening in the frontonasal process. What does this form?
Nasal placode
What happens to the nasal placode?
Invaginates to form nostrils
The invagination of the nasal placode divides the frontonasal process into two parts. Name them.
Lateral nasal process
Medial nasal process
What separates the nasal opening from the mouth?
Philtrum
What do the lateral nasal processes form?
Lateral parts of nose
What do the medial nasal processes form?
Bridge and pointy bit of nose
What do the maxillary processes form?
Join and form upper lip
What do the mandibular processes form?
Lower lip
What needs to develop in order to separate the nasal and mouth cavities?
Palate
Describe the formation of the primary palate.
Medial nasal process grows downwards and forms the philtrum which forms the primary palate.
What happens to the maxillary processes in the development of the palate?
Two primary palatine shelves grow inwards
How is the secondary palate formed?
Palatine shelves meet in the midline to form secondary palate which separates the nasal and oral cavities.
Which congenital issue may arise if the maxillary processes do not fully fuse with the philtrum?
Cleft lip (harelip)
Apart from cosmetic reasons, why would you want to make a diagnosis of cleft lip?
No separation between oral and nasal cavities meaning food and drink may be aspirated in the baby
Name the three regions of the skull.
Cranial vault
Base of skull
Viscerocranium
Which type of bones make up the cranial vault of the skull?
Flat bones
Which type of bones make up the base of the skull?
Irregular bones
How are the cranial vault bones formed?
Formed by membranous ossification calvaria as are membranous bones.
How are the base bones of the skull formed?
Endochondral ossification
What does the viscerocranium do?
Forms capsules around sensory special sense organs e.g. eyes
Describe the bones of the cranial vault of the skull at birth.
Not fully formed
Soft sutures between them
Deformation during birth may occur
At what age does the anterior fontanelle close?
Approx. 1.5yrs
What is meant by a fontanelle?
Softer spots on an infant’s head where the bone has not fully fused together
What happens if the fontanelles fuse too quickly?
Does not provide space for facial skeleton and brain to grow, leading to deformities.
Name some deformities seen when the fontanelles fuse too quickly.
Craniosynostosis
What can happen in craniosynostosis.
Abnormal face shape
Sometimes mental retardation
How do the base bones of the skull get formed?
Initially cartilage which then becomes ossified in the process of endochondral ossification
Where do the sensory capsules for the sensory organs develop from?
The mesoderm of somites
