Pharyngeal arches😊

Pharyngeal arches

  • Future neck
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Pharyngeal Arches (5)

  • primarily derived from
      • Origin
      Derivatives
      Cranial neural crest cells
      for skeletal and connective tissues
      Paraxial mesoderm
      for musculature and vasculature
      Endodermal derivative.
      Pharyngeal Pouches (4)
      Ectodermal derivative
      Pharyngeal Clefts (4)

Pharyngeal Membrane (4)

  • Formed by pharyngeal cleft + pharyngeal pouch + intervening mesoderm.
  • Derivative of all 3 germ layers.
  • First: Forms tympanic membrane.
  • Second, third, fourth: Regresses.
  • Note
    • Tympanic Membrane is derived from all 3 germ layers
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Cartilages

Arch
Cartilages
I
• Malleus (1)
• Incus (2)
• Meckel cartilage (3)
• Anterior ligament of malleus
• Sphenomandibular ligament
• Mandible
• Maxilla

Meckel’s cartilage doesn't form mandible
• because skull bones are membranous in ossification
• doesn't require hyaline cartilage
II

• Reichert's cartilage
• Stapes
• Styloid process
• Stylohyoid ligament
• Lesser horn of hyoid bone

Mnemonic: S4 Second → Reichert's cartilage
III
• Greater horn & body of hyoid bone
IV
• All the cartilages of the larynx
• except cricoid and base of arytenoid

↳ Not epiglottis. Epiglottis is derived from hypobranchial eminence of 4th arch
VI
Cricoid and base of arytenoid

Nerves and Muscles

Pharyngeal Arch
Nerve
5 7 9 10
Artery
Muscle
1
Mandibular Nerve

muscles for chewing and some palate muscles.
• Maxillary A
• Muscles of Mastication
• Tensor Veli Palatini
• Tensor Tympani
• Ant Belly of Digastric
• Mylohyoid
2
Facial Nerve

facial expression muscles and some ear/throat muscles.
• Stapedial A
• Hyoid A
• Muscles of facial expression
• Stapedius
• Post. Belly of Digastric
• Stylohyoid
3
Glossopharyngeal Nerve
• CCA, ICA
• 3 letters
• Stylopharyngeus
4
SLN
• Arch of Aorta
• Right Subclavian Artery
• Muscles of Pharynx
↳ (except stylopharyngeus)
↳ (except cricopharyngeus)
• Muscles of Palate
↳ (except TVP)
• Cricothyroid (larynx)
• Palatoglossus (tongue)
6
RLN
• Pulmonary Artery
• Ductus Arteriosis
• All muscles of larynx
↳ (except cricothyroid)
• Cricopharyngeus (pharynx)
”Mneumonic:
  • 1st → tension (Tensor Veli Palatini, Tensor Tympani) adich amy (Ant Belly of Digastric, Mylohyoid) chavakkunn → maxilla, mandible
  • 2nd → chirikkunn → facial N, muscles of facial expression
    • → face lum hyoid (hyoid A) lum stapler (stapedial A) adichu
  • 3 → Theettan → Glossy (GP N) Stylish (Stylopharyngeal) Caring (Carotid)
  • 3rd → GP CP →
    • → GP → GlossoPharyngeal
    • → C → carotid
    • → P → pharyngeus → stylopharyngeus
  • Ms palate, pharynx → SLN → 4
  • Ms larynx → RLN → 6
      • Anterior and post belly of digastric
      Anterior and post belly of digastric

Development of Larynx

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  • Supraglottis: From 4th Arch.
  • Subglottis and glottis: From 6th Arch.
    • Supraglottis: Above vocal cords.
    • Glottis: At vocal cord level and 1 cm below.
    • Subglottis: From 1 cm below vocal cords to lower cricoid border.
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Development of Epiglottis

  • Derived from hypobranchial eminence of floor of 4th arch.
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High Yield Points

  • All muscles of larynx derived from 6th arch.
    • Supplied by RLN
    • Except: Cricothyroid (4th arch → ELN of SLN)
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  • All muscles of pharynx derived from 4th arch.
    • Supplied by SLN
    • Except: Stylopharyngeus (3rd arch → Glossopharyngeal nerve)
    • Except: Cricopharyngeus (6th arch → RLN)
      • ↳ Cause for Killian dehiscence
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  • All muscles of palate derived from 4th arch.
    • Except: Tensor palatini (1st arch)
  • Middle ear muscles:
    • Tensor tympani: 1st arch.
    • Stapedius: 2nd arch.
  • Digastric muscles:
    • Anterior belly: 1st arch.
    • Posterior belly: 2nd arch.
  • All muscles of tongue
    • Derived from myotome of occipital somites (Paraxial mesoderm)
    • Supplied by the hypoglossal nerve
    • Exception: Palatoglossus (from 4th pharyngeal arch) → SLN (Vagus N)
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Derivatives of cleft and pouches

Ectodermal cleft
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1st
• External acoustic meatus
• Outer layer of the tympanic membrane
2nd, 3rd, and 4th
• Obliterate
• The 2nd arch overlaps the clefts.

Persistence of cervical sinus
↳ Branchial cyst/fistula (Swelling along SCM)
Endodermal Pouches
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1st
• Middle ear cavity
• Auditory (Eustachian) tube
• Inner layer of tympanic membrane
2nd
Epithelium of palatine tonsils
↳ including Crypta Magna
3rd
• Thymus
• Inferior parathyroid gland
• Mnemonic: Thymus third

After formation
• Thymus migrates down
↳ carries parathyroid along during migration
4th
Superior parathyroid gland
Branchial cyst/fistula
Branchial cyst/fistula
  • Ultimobranchial body → become Parafollicular C Cells
    • Derived from NCC (controversy)
    • Applied: Medullary Ca Thyroid

DiGeorge Syndrome:

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  • 22q11 deletion syndrome
  • TBX 1 gene defect
  • 3rd > 4th pouch
    • fails to develop thymus and inferior parathyroid gland.
  • No T lymphocytes
  • No PTH → No Ca
  • Leads to hypocalcemia and thymic hypoplasia → T cell dysfunction
  • CATCH 22 TB
    • Cardiac problems (TOF)
    • Abnormal faces
    • Thymus aplasia/hypoplasia (T-cell problems)
    • Cleft lip/palate
    • Hypocalcemia (No parathyroid)
  • Chromosome 22q11.2 Deletion syndrome/ Di-George Syndrome /
    Velocardiofacial syndrome (VCFS)
    • 30% of these cases may develop schizophrenia.
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