Development of Pharyngeal Arches Flashcards
Describe when and how the pharyngeal arches appear?
Occurs as the cranial neuropore closes, they appear as tissue bulges separated by clefts. They can also be known as branchial arches. They consist of 3 embryo layers (mesoderm core, ectoderm and endoderm)
What is the stomodeum?
Depression between the developing brain and pericardium in an embryo. Precursor for mouth and anterior lobe of pituitary lobe.
What forms the upper maxillary prominence and lower mandibular prominence?
The 1st pharyngeal arch. In between these is where the stomodeum.
What are somatomeres?
Ill defined segments of paraxial mesoderm in the head region rostral to somites.
What are ectodermal placodes?
Focal thickenings of cranial ectoderm which give rise to sensory ganglia/neurons.
What is does each pharyngeal arch contain?
- Muscle (branchial muscles),
- Cartilage element,
- Artery and,
- Cranial nerve
Where does the majority of the anterior skull develop originate from?
Neural crest cells
Where does the majority of the posterior skull originate from?
Paraxial mesoderm
Name the muscles derived from the first arch “mandibular arch”
- Muscles of mastication,
- Anterior belly of digastric,
- Mylohyoid,
- Tensor tympani,
- Tensor veli palatini. (muscles are also innervated by the nerve of the first asrch)
What are the skeletal derivatives of the first arch? (mandibular arch)
- Maxilla,
- Zygomatic bone,
- Mandible,
- Malleus,
- Incus,
- Meckel’s cartilage (later dissapears)
What is the nerve derived from the 1st pharyngeal arch?
- Trigeminal nerve
So it will supply the skin of the face and the 3rd division will supply the muscles of mastication and others
What artery does the 1st pharyngeal artery form?
Maxillary artery which is the terminal branch of the external carotid artery.
What muscles are derived from the second pharyngeal arch (hyoid arch)
- Muscles of facial expression,
- Stylohyoid,
- Stapedius,
- Posterior belly of digastric
(all will therefore be innervated by the nerve derived from the second pharyngeal arch)
What are the skeletal derivatives of the 2nd pharyngeal arch?
- Stapes,
- Styloid process and stylohyoid ligament,
- Lesser horn of hyoid and upper part of body of hyoid.
What nerve is derived from the second pharyngeal arch?
The CN VII nerve, the facial nerve
What artery is the 2nd pharyngeal associated with?
Hyoid and stapedial arteries
What are the muscles and skeletal (bones) that originate from the 3rd pharyngeal arch
Muscle - Stylopharyngeus,
Skeletal - Greater horn of hyoid and lower part of body of hyoid.
What is the nerve and artery associated with the 3rd pharyngeal arch
Nerve - Glossopharyngeal nerve (IX)
Artery - common carotid arteries and proximal internal carotid.
What are the muscles derived from the 4th pharyngeal arch?
All muscles of the pharynx except stylopharngeus.
All muscles of the palate except tensor veli palatini.
- Cricothyroid.
What are the skeletal derivates of the 4th arch?
Epiglottis, laryngeal cartilages, thyroid, cuneiform, corniculate and arytenoids.
What is the nerve that is derived from the 4th pharyngeal arch
The vagus, more specifically the superior laryngeal branch of the vagus.
What are the arteries associated with the 4th arch?
The 4th left arch gives off the aortic arch. The 4th right gives off the right subclavian artery
What are the muscular and skeletal derivates of the 6th pharyngeal arch?
All of the muscles of the larynx and the cricoid cartilage
What are the nerves and arterial derivates of the 6th pharyngeal arch
Recurrent laryngeal nerve (branch of vagus).
It gives rise to the pulmonary arteries and the ductus arteriosus (which is present on the left)
What does the paraxial mesoderm form?
(it forms pharyngeal arches 1-3) then, All voluntary muscles, arteries, neurocranium, meninges and dorsal skin. (it forms pharyngeal arches 1-3)
What does the lateral plate mesoderm
Forms pharyngeal arches 4-6. Also the laryngeal cartilages, regional connective tissue.
What does the neural crest tissue forms?
- Pharyngeal arch skeleton, viscerocranium, glandular connective tissue, parts of neurocranium, teeth as well as interacting with ectodermal placodes
What are the pharyngeal clefts and pouches?
The clefts are external and are derived from ectoderm where as the pouches are internal and are derived from endoderm
What is derived from the different pharyngeal pouches?
- Pouch 1 forms primitive tympanic cavity.
- Pouch 2 forms palatine tonsils/tonsillar fissure.
3 - Parathyroid (inferior) and thymus (will migrate down the neck),
4 - Parathyroid gland (superior) and ultimobranchial body (will form parafollicular cells of thyroid)
What is derived from the different pharyngeal clefts?
Cleft 1 - Dorsal part gives rise to external auditory meaturs and external part of tympanic membrane. Deepest part gives rise to the tympanic membrane (ear drum).
2nd cleft over grows 3rd and 4th arch. The 2nd, 3rd and 4th arch lose contact with exterior and forms cervical sinus. Which will usually disappear.
What are branchial cleft anomalies?
Most common congenital disease of the neck. Causes cervical fistula/sinus in children and can form a cervical cyst in adults. It will appear anterior to the sternocleidomastoid however you must presume it is a cancerous lump until proven otherwise.
What is carried from rhombomeres by neural crest cells and to which arch do these go to?
Neural crest cells carry expressions of homeodomain genes. Pharyngeal arch one is delivered the OTX2 gene.
Pharyngeal arch 2 is delivered the HOXA2 gene and,
The 3rd, 4th and 6th pharyngeal arch are delivered the HOXA3, HOXB3 and HOXD3.
The neural crest cells then respond to local patterns of endoderm signals
What is tracher collins syndrome?
First/second arch syndrome which ocurs when there is failure of formation of apoptosis of neural crest cells into 1st or 2nd pharyngeal arch. It causes abnormal eye shape, micrognathia (small lower jaw), Conductive hearing loss, underdeveloped zygoma and malformed ears
What is Di George Syndrome?
Genetic defect that is caused by 22q11 deletion. It causes 3rd and 4th arches fail to develop and causes thymus and parathyroid defects. Causes following symptoms (CATCH-22); cardiac abdnormality, abnormal faces, thymic aplasia, cleft palate, hypocalcaemia.
What can occur with inadequate/excess sonic hedgehog function?
Inadequate - narrowing and fusion so can case cyclopia if severe or a single median incisor if mild.
Excessive - widening structures or duplication so can cause diprosopus.
What are craniosynostosis syndromes?
Examples - apert and crouzon syndromes.
They can be caused by mutations in FGF receptors. This can cause premature fusion of bones of the skull. Can occur spontaneously with increased paternal age.
