10. Development Flashcards
What proportion of the total length of the embryo do the head and neck make up at week 4?
1/2.
What are the pharyngeal arches?
A sequence of ridges that form in the lateral walls of the embryonic pharynx bulging into the lumen of the pharynx and to the outside as the future face and neck regions.
What covers the pharyngeal arches internally and externally?
Internally - endoderm.
Externally - ectoderm.
What are the branchial arches separated by on the outside of the head?
Branchial clefts/grooves.
What are the branchial arches separated by on the inside
Branchial pouches.
What does the branchial membrane separate?
The branchial grooves and pouches that meet end-on.
What is the cervical sinus?
The space created by a flap of tissue from the second arch that grows down to cover the third to sixth arches and grooves.
What is in each branchial arch?
An artery, a vein, a cranial nerve, and some mesenchyme.
What forms the brain?
The anterior end of the neural tube.
What are the sections of the brain in the three vesicle stage?
Prosencephalon - forebrain.
Mesencephalon - midbrain.
Rhombencephalon - hindbrain.
How are cranial nerves classified?
On the basis of function and their embryonic origin: somatic efferent, special sensory, nerves of the pharyngeal arches.
What are the four cranial nerves of the pharyngeal arches?
CN V (trigeminal), CN VII (facial), CN IX (glossopharyngeal), CN X (vagus).
Which arch is the trigeminal nerve from?
1st.
What are the functions of the trigeminal nerve?
Principle sensory nerve of the head - skin of the face, lining of the mouth and nose.
Motor to muscles of mastication and mandibular process.
Which arch is the facial nerve from?
2nd.
What are the functions of the facial nerve?
Motor to muscles of facial expression and muscles derived from 2nd pharyngeal arch.
Sensory - taste buds on anterior 2/3 of tongue.
Which arch is the glossopharyngeal nerve from?
3rd.
What are the functions of the glossopharyngeal nerve?
Motor - stylopharyngeus.
Sensory - general and special sensory to posterior 1/3 tongue.
Which arches is the vagus nerve from?
4th and 6th.
What are the functions of the vagus nerve?
4th arch branch is superior laryngeal nerve - cricothyroid and constrictors of the pharynx.
6th arch branch is recurrent laryngeal nerve - intrinsic muscles of the larynx.
What are the arteries from each branchial arch?
1st, 2nd, and 3rd - common, external, and internal carotid arteries and branches.
4th - aortic arch, part of right subclavian artery.
6th - pulmonary arteries.
What does the facial skeleton derive from?
Frontonasal prominence, 1st pharyngeal arch.
What do the muscles of mastication derive from?
1st pharyngeal arch.
What do the muscles of facial expression derive from?
2nd pharyngeal arch.
What are the cartilages that develop from pharyngeal arches?
1st - Meckel's cartilage. 2nd - Reichert's cartilage. 3rd - Hyoid bone. 4th - Hypobranchial eminence (-> epiglottis). 4th and 6th - cartilages of the larynx.
What is Meckel’s cartilage a template for?
Mandible by membranous ossification.
What do the pharyngeal pouches become?
1st -> eustachian tube and middle ear cavity.
2nd -> crypts of palatine tonsil.
3rd: dorsal part -> inferior parathyroid, ventral part -> thymus.
4th: dorsal part -> superior parathyroid, ventral part -> thyroid C cells.
What makes up the middle ear and what are they derived from?
Ossicles from cartilage bar derivatives, tympanic cavity and auditory tube from 1st pharyngeal pouch.
What is the fate of the pharyngeal clefts?
The 1st cleft remains but the 2nd one grows down to cover all the other so they go.
What is a possible result of failure to be obliterated of the cervical sinus?
Cysts of fistulae anywhere along the anterior border of the sternocleidomastoid.
What is the first evidence of facial development?
Appearance of a depression in the ectoderm on the ventral aspect of the head - the stomadaeum (site of the future mouth).
What are the five folds that form around the stomadaeum to form the face?
Frontonasal prominence, two maxillary prominences, and two mandibular prominences.
Where is the frontonasal prominence and what does it go on to form?
Superior in the midline. Forms the forehead, bridge of nose, upper eyelids, philtrum.
Where are the maxillary prominences and what do they go on to form?
Lateral, derived from 1st pharyngeal arch. Forms middle third of face, upper jaw, most of the lip, sides of the nose.
Where are the mandibular prominences and what do they go on to form?
Inferolateral, derived from 1st pharyngeal arch. Forms lower thirds of face, lower jaw, lip.
What do the facial prominences consist of?
Mesenchyme with a covering of ectoderm.