Head and Neck Embryology Flashcards
What does the neck form from?
Branchial/pharyngeal arches
What does the face form from?
5 mesenchymal processes / prominences
Where does the skull develop from?
Mesenchyme in the head region of developing embryo
What is mesenchyme?
Mesenchyme is embryonic connective tissue
What is the development of the blastula?
Forms bilaminar disk - forms trilaminar disk.
Trilaminar disk contains amniotic cavity dorsally (ectoderm) and yolk sak ventrally (endoderm side)
What leads to axis formation of the embryo?
Notochord formation
What does the neural tube form from?
Forms from the ectoderm in the midline - forms - brain and spinal cord
What does the neural crest form from?
Some cells at the crest of the neural fold separate to form the neural crest cells
(neural crest is seen here as the green)
What happens to 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.
The neural crest cells give rise to a wide variety of structures - migrate for example dorsal root ganglia, sympathetic chain and autonomic plexus
Where do somites arise from?
Paraxial mesoderm
What do somites form?
Form structures like the axial skeleton and the muscles
How many somites develop in humans?
33 in total
What are pharyngeal branches?
Series of arches which develop around the future mouth and pharynx.
They support the primitive pharynx
Face and neck develop from the
What embryolgical tissue makes up the branchial arches?
Ectoderm lines the outside and forms celfts between the arches
Mesoderm in the middle - cartilage nad muscle
Endoderm on the inside - forms pouches in between arches
What are the nerves of the branchial arches?
1st arch - mandibular branch of trigeminal
2nd - arch facial nerve
3rd - arch glossopharyngeal n.
4th - arch superior laryngeal branch of vagus
(no 5th arch)
6th - arch recurrent laryngeal branch of vagus
What are the muscles of the face innervated by?
Facial nerve
If the facial nerve supplies muscles of the face, which branchial arch did they arise from?
From the 2nd arch
What innervates the digastric muscle?
Anterior belly - mandibular division of the trigeminal nerve
Poesterior belly - facial nerve
What cartilages form from the 1st branchial arch?
Meckels cartilage
Maleus
Incus
What cartilages form from the 2nd branchial arch?
Stapes
Styloid process
Stylohyoid ligament
What cartilage forms from the third branchial arch?
Greater horn of the hyoid bone
What cartilage forms from the 4th branchial arch?
Thyroid cartilage
What cartilage forms from the 6th branchial arch?
Cricoid cartilage
What are pther important structures developing from the branchial arches?
- Tongue
- Thyroid gland
- Parathyroid gland
- Part of the pituitary gland
What are the 5 prominences that the face develops from?
The frontonasal process
Two maxillary processes
Two mandibular processes
Where does the frontonasal process come from?
From mesenchyme superior to future mouth
Where do themaxillary processes come from?
From maxillary part of first branchial arch mesenchyme
Where do the mandibular processes come from?
1st arch mesoderm
What is the activity of the 2 mandibular processes?
They fuse in the midline
How is the nasal pit formed?
Ectodermal thickening (nasal placode) pushes inwards to form the nasal pit
How is the philtrum formed?
The medial nasal process further grows downwards and laterally
Which colour in the picture represents the philtrum?
Green portion just below the nose
What are the stages of development of the palate?
Stage 1: Philtrum forms by downward growth of the medial nasal process. This is known as the primary palate.
Stage 2: 2 palantine shelves grow inwards from the maxillary processes
Stage 3: Palantine shelves meet in the midline to form the secondary plate
Oral and nasal cavity are now complete.
What are the three bony regions of the head?
Cranial vault
Base of the skull
Viscerocranium
What bones form the cranial vault and how are they formed?
Flat bones - formed by membranous ossification calvaria
What bones form the base of the skull and how are they formed?
Irregular bones - endochondral ossification
How are the bones of the viscerocranium formed?
Partly from branchial arches, and partly from sensory (special sense) capsules
Where does the mesenchyme aris from that is involve in skull vault ossification?
Mesenchyme is derived from the mesoderm and lies above the surface of developing brain - ossifies directly (membranous ossification)
Why are sutures soft in the skull vault?
Allows deformation during passage through birth canal
How many fontanelle are of clinical significance?
6
What are fontanelle?
A space between the bones of the skull in an infant or fetus, where ossification is not complete and the sutures not fully formed. The main one is between the frontal and parietal bones.
Where does the mesenchyme arise from that forms the base of the skull?
It is found around the notochord and is derived predominantly from neural crest cells
How are the bones of the base of the skull formed?
Preform in cartilage
Later they ossify
Where are sensory capsules formed?
Derived from mesoderm of somites in head and neck region
What do sensory capsules form?
Preform in cartilage and ossify to form bones around the sense organs
nose, eye and ear
They form partly base of skull, partly viscerocranium
