Development of Pharyngeal Arches

Question 1

Describe when and how the pharyngeal arches appear?

Answer 1

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)

Question 2

What is the stomodeum?

Answer 2

Depression between the developing brain and pericardium in an embryo. Precursor for mouth and anterior lobe of pituitary lobe.

Question 3

What forms the upper maxillary prominence and lower mandibular prominence?

Answer 3

The 1st pharyngeal arch. In between these is where the stomodeum.

Question 4

What are somatomeres?

Answer 4

Ill defined segments of paraxial mesoderm in the head region rostral to somites.

Question 5

What are ectodermal placodes?

Answer 5

Focal thickenings of cranial ectoderm which give rise to sensory ganglia/neurons.

Question 6

What is does each pharyngeal arch contain?

Answer 6

• Muscle (branchial muscles),
• Cartilage element,
• Artery and,
• Cranial nerve

Question 7

Where does the majority of the anterior skull develop originate from?

Answer 7

Neural crest cells

Question 8

Where does the majority of the posterior skull originate from?

Answer 8

Paraxial mesoderm

Question 9

Name the muscles derived from the first arch “mandibular arch”

Answer 9

• Muscles of mastication,
• Anterior belly of digastric,
• Mylohyoid,
• Tensor tympani,
• Tensor veli palatini. (muscles are also innervated by the nerve of the first asrch)

Question 10

What are the skeletal derivatives of the first arch? (mandibular arch)

Answer 10

• Maxilla,
• Zygomatic bone,
• Mandible,
• Malleus,
• Incus,
• Meckel’s cartilage (later dissapears)

Question 11

What is the nerve derived from the 1st pharyngeal arch?

Answer 11

• Trigeminal nerve

So it will supply the skin of the face and the 3rd division will supply the muscles of mastication and others

Question 12

What artery does the 1st pharyngeal artery form?

Answer 12

Maxillary artery which is the terminal branch of the external carotid artery.

Question 13

What muscles are derived from the second pharyngeal arch (hyoid arch)

Answer 13

• Muscles of facial expression,
• Stylohyoid,
• Stapedius,
• Posterior belly of digastric
  (all will therefore be innervated by the nerve derived from the second pharyngeal arch)

Question 14

What are the skeletal derivatives of the 2nd pharyngeal arch?

Answer 14

• Stapes,
• Styloid process and stylohyoid ligament,
• Lesser horn of hyoid and upper part of body of hyoid.

Question 15

What nerve is derived from the second pharyngeal arch?

Answer 15

The CN VII nerve, the facial nerve

Question 16

What artery is the 2nd pharyngeal associated with?

Answer 16

Hyoid and stapedial arteries

Question 17

What are the muscles and skeletal (bones) that originate from the 3rd pharyngeal arch

Answer 17

Muscle - Stylopharyngeus,

Skeletal - Greater horn of hyoid and lower part of body of hyoid.

Question 18

What is the nerve and artery associated with the 3rd pharyngeal arch

Answer 18

Nerve - Glossopharyngeal nerve (IX)

Artery - common carotid arteries and proximal internal carotid.

Question 19

What are the muscles derived from the 4th pharyngeal arch?

Answer 19

All muscles of the pharynx except stylopharngeus.
All muscles of the palate except tensor veli palatini.
- Cricothyroid.

Question 20

What are the skeletal derivates of the 4th arch?

Answer 20

Epiglottis, laryngeal cartilages, thyroid, cuneiform, corniculate and arytenoids.

Question 21

What is the nerve that is derived from the 4th pharyngeal arch

Answer 21

The vagus, more specifically the superior laryngeal branch of the vagus.

Question 22

What are the arteries associated with the 4th arch?

Answer 22

The 4th left arch gives off the aortic arch. The 4th right gives off the right subclavian artery

Question 23

What are the muscular and skeletal derivates of the 6th pharyngeal arch?

Answer 23

All of the muscles of the larynx and the cricoid cartilage

Question 24

What are the nerves and arterial derivates of the 6th pharyngeal arch

Answer 24

Recurrent laryngeal nerve (branch of vagus).

It gives rise to the pulmonary arteries and the ductus arteriosus (which is present on the left)

Question 25

What does the paraxial mesoderm form?

Answer 25

(it forms pharyngeal arches 1-3) then, All voluntary muscles, arteries, neurocranium, meninges and dorsal skin. (it forms pharyngeal arches 1-3)

Question 26

What does the lateral plate mesoderm

Answer 26

Forms pharyngeal arches 4-6. Also the laryngeal cartilages, regional connective tissue.

Question 27

What does the neural crest tissue forms?

Answer 27

• Pharyngeal arch skeleton, viscerocranium, glandular connective tissue, parts of neurocranium, teeth as well as interacting with ectodermal placodes

Question 28

What are the pharyngeal clefts and pouches?

Answer 28

The clefts are external and are derived from ectoderm where as the pouches are internal and are derived from endoderm

Question 29

What is derived from the different pharyngeal pouches?

Answer 29

• 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)

Question 30

What is derived from the different pharyngeal clefts?

Answer 30

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.

Question 31

What are branchial cleft anomalies?

Answer 31

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.

Question 32

What is carried from rhombomeres by neural crest cells and to which arch do these go to?

Answer 32

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

Question 33

What is tracher collins syndrome?

Answer 33

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

Question 34

What is Di George Syndrome?

Answer 34

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.

Question 35

What can occur with inadequate/excess sonic hedgehog function?

Answer 35

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.

Question 36

What are craniosynostosis syndromes?

Answer 36

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.