Lecture 1 - Development of the H&N Flashcards
What are the pharyngeal arches covered by?
Externally the arches are covered by ectoderm, internally by endoderm.
How many branchial arches are there?
Six branchial arches, but fifth is rudimentary and merges with the fourth
What are branchial arches separated by on the outside?
Branchial clefs
What are branchial arches separated by on the inside?
Branchial pouches
What are the largest branchial arches?
1st & 2nd
What is inside each branchial arch?
Artery
Vein
Cranial nerve
Mesenchyme (mesodermal/neural crest)
What are the three main parts of the brain?
o Prosencephalon – Forebrain
o Mesencephalon – Midbrain
o Rhombencephalon – Hindbrain
What are the three main roles of cranial nerves?
Somatic efferent
Special sensory
Nerves of the pharyngeal arches
- Somatic and visceral afferent from skin and mucous membranes
- Visceral motor
- Special visceral motor or branchial motor to striated muscles
What are the five cranial nerves of the pharyngeal arches?
Trigeminal nerve (1st) Facial nerve (2nd) Glossopharyngeal nerve (3rd) Vagus nerve (4th and 6th)
What arteries are derived from the first three branchial arches?
Common, external and internal carotid arteries and branches
What arteries are derived from the fourth branchial arch
Aortic arch
Part of right subclavian artery
What arteries are dervived from 6th branchial arch?
Pulmonary arteries
What happens to 1st and 2nd arch arteries?
They disappear
What happens to the third arch artery?
Becomes internal carotid
What happens to 4th arch artery?
Arch of aorta (L) and brachiocephalic (R)
What happens to 6th arch artery?
Becomes pulmonary artery
What muscles are derived from the first arch?
Innervated by?
Muscles of mastication Anterior belly of digastrics Mylohyoid Tensor tympani Tensor palatini
Mandibular branch of the trigeminal nerve
What muscles are derived from the 2nd branchial arch?
Innervated by?
Muscles of facial expression Posterior belly of digastrics Stylohyoid Stapedius Auricular
Facial nerve
What muscles are derived from the 3rd branchial arch?
Stylopharyngeus
Glossopharyngeal nerve
What muscles are derived from arches 4-6?
Striated muscle of upper oesophagus Cricothyroid Levator palatini Constrictors of the pharynx Intrinsic muscles of the larynx
Superior laryngeal branch of vagus
Recurrent laryngeal branch of vagus
What is the facial skeleton made from embryologically speaking, and what arch is it derived from?
The frontal nasal skeleton
1st pharyngeal arch
What are the muscles of mastication derived from?
1st pharyngeal arch
What are the muscles of facial expression derived from?
2nd pharyngeal arch
What skeletal elements are derived from 1st pharyngeal arch
Meckels cartilage
- Mandibular prominence
- Malleus and incus
What skeletal elements are derived from 2nd pharyngeal arch?
Rechert’s cartilage
- Stapes
- Styloid process
- Hyoid bone (less comu and upper body)
What skeletal elements are derivdd from 3rd arch?
Hyoid bone (greater cornu and lower body)
What skeletal elements are derived from 4th arch?
Hypobranchial eminence (becomes epiglottis)
What skeletal elements are derived from 4-6th branchial arch?
Cartilages of the larynx
What is found in 1st pharyngeal pouch?
Eustachian tube and middle ear cavity
What is found in 2nd pharyngeal pouch?
Crypts of palatine tonsil
What is found in 3rd pharyngeal pouch?
Dorsal part – Inferior Parathyroid
Ventral part – Thymus
What is found in 4th pharyngeal pouch?
Dorsal Part – Superior Parathyroid Ventral Part (ultimobranchial body) – Thyroid C cells
What does the middle ear develop from?
o Ossicles
Cartilage bar derivatives (Meckel’s/Reichert’s)
o Tympanic Cavity and Auditory Tube
1st Pharyngeal pouch derivatives
What happens to the pharyngeal clefts
The 1st cleft is the only one that remains, as the 2nd arch grows down to cover the others. However, there can be remnants.
How are branchial cysts formed?
If the cervical sinus is not obliterated, cysts or fistulae can occur. These can occur anywhere along the anterior border of sternocleidomastoid.
