Pharyngeal arches Flashcards
- What are pharyngeal arches and when do they form?
Answer:
Pharyngeal arches are paired embryonic structures that form in Week 4-5 and give rise to bones, muscles, nerves, and glands in the face and neck.
- What are the three main components of the pharyngeal apparatus?
Answer:
Pharyngeal Arches – Contain mesoderm, neural crest cells, nerves, and blood vessels.
Pharyngeal Clefts (Grooves) – External indentations lined by ectoderm.
Pharyngeal Pouches – Internal indentations lined by endoderm.
- What types of cells contribute to the formation of pharyngeal arches?
Answer:
Neural crest cells → Bones, cartilage, connective tissue.
Mesoderm → Muscles, blood vessels.
Ectoderm → Outer lining, cranial nerves.
Endoderm → Inner lining, glandular structures.
- What does the 1st pharyngeal arch develop into?
Answer:
✅ Bones: Maxilla, Mandible, Malleus, Incus
✅ Muscles: Chewing muscles (Masseter, Temporalis)
✅ Nerve: Trigeminal nerve (CN V)
✅ Other: Anterior 2/3 of the tongue
What structures come from the 2nd pharyngeal arch?
Answer:
✅ Bones: Stapes, Styloid process, part of Hyoid bone
✅ Muscles: Facial expression muscles
✅ Nerve: Facial nerve (CN VII)
What are the key derivatives of the 3rd pharyngeal arch?
Answer:
✅ Bones: Lower hyoid bone
✅ Muscle: Stylopharyngeus muscle
✅ Nerve: Glossopharyngeal nerve (CN IX)
✅ Other: Contributes to common & internal carotid arteries
- What structures do the 4th and 6th pharyngeal arches form?
Answer:
✅ Cartilage: Thyroid & Cricoid Cartilages
✅ Muscles: Pharyngeal & Laryngeal muscles
✅ Nerve: Vagus nerve (CN X)
What does the 1st pharyngeal pouch develop into?
Answer:
The Eustachian tube and the middle ear cavity.
What are the derivatives of the 3rd and 4th pharyngeal pouches?
Answer:
✅ 3rd Pouch → Thymus & Inferior Parathyroid Glands
✅ 4th Pouch → Superior Parathyroid Glands & Thyroid
How does the tongue develop from pharyngeal arches?
Answer:
✅ 1st arch → Anterior 2/3 of the tongue (Trigeminal nerve, CN V).
✅ 3rd & 4th arches → Posterior 1/3 of the tongue (Glossopharyngeal & Vagus nerves, CN IX & X).
What happens if pharyngeal clefts fail to close properly?
Answer:
Failure of closure can lead to branchial cleft cysts, which appear along the anterior border of the sternocleidomastoid (SCM) muscle.
What is the significance of neural crest cells in pharyngeal arch development?
Answer:
Neural crest cells migrate into the arches and form most bones, cartilage, and connective tissue of the face and neck.
Which syndromes result from defective pharyngeal arch development?
Answer:
Treacher Collins Syndrome – Defects in 1st arch neural crest migration → affects jaw, zygomatic bone, ear development.
DiGeorge Syndrome – Failure of 3rd & 4th pouches, leading to absent thymus & parathyroid glands.
What structures develop from pharyngeal clefts?
Answer:
✅ 1st cleft → External auditory meatus & tympanic membrane
✅ Other clefts disappear (if not, they form branchial cysts).
What structures form from the pharyngeal pouches?
Answer:
✅ 1st Pouch → Middle ear cavity & Eustachian tube
✅ 2nd Pouch → Palatine tonsils
✅ 3rd Pouch → Inferior parathyroid glands & Thymus
✅ 4th Pouch → Superior parathyroid glands
How do pharyngeal arches contribute to cardiovascular development?
Answer:
Each arch has a blood vessel, which later forms major arteries:
✅ 3rd Arch → Internal Carotid Arteries
✅ 4th Arch → Aortic Arch & Right Subclavian Artery
✅ 6th Arch → Pulmonary Arteries & Ductus Arteriosus
How do cranial nerves correspond to the pharyngeal arches?
Answer:
✅ 1st Arch → Trigeminal Nerve (CN V)
✅ 2nd Arch → Facial Nerve (CN VII)
✅ 3rd Arch → Glossopharyngeal Nerve (CN IX)
✅ 4th & 6th Arches → Vagus Nerve (CN X)
What are placodes, and how do they relate to pharyngeal development?
Answer:
Placodes are thickenings of ectoderm that give rise to sensory ganglia of cranial nerves (e.g., trigeminal, facial, vagal).
What structures do the facial and trigeminal nerves innervate?
Answer:
✅ Trigeminal Nerve (CN V) → Muscles of mastication (chewing)
✅ Facial Nerve (CN VII) → Muscles of facial expression
What is the relationship between pharyngeal arch development and thyroid formation?
Answer:
The thyroid gland develops from the 3rd & 4th pharyngeal pouches and migrates downward to its final position in the neck.
