Branchial arches



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BRANCHIAL ARCHES



  • The human head and neck structures are derived from discrete evolutionary precursors (ancient gill apparatus)

  • 5 pairs of arches form on either side of the pharyngeal foregut

  • Begins on Day 22 (week 3)

  • Layers

  1. outer ectoderm

  2. inner endoderm

  3. mesenchyme core derived from lateral plate mesoderm with contributions from adjacent somites/somitomeres and neural crest

  • Each arch separated by

    1. ectodermally lined cleft

    2. mesodermal pharyngeal membrane

    3. endodermal pharyngeal pouch

  1. Arch 5 never forms in humans or promptly regresses

  2. Only first cleft forms a definitive structure - Clefts 2-4 are obliterated

  • Constituents

  1. cartilaginous support

  2. aortic arch artery

  3. cranial nerve

Branchial Arch 1


Artery:

Maxillary artery
Skeletal:

From maxillary cartilage

  1. sphenoid

  2. incus

From mandibular cartilage (Meckel’s)

  1. malleus

  2. sphenomandibular ligament

From direct ossification of dermal mesenchyme

  1. maxilla

  2. zygoma

  3. squamous portion of temporal bone

  4. mandible


Muscles (from cranial somitomere 4)

  1. temporalis

  2. masseter

  3. lateral pterygoid

  4. medial pterygoid

  5. mylohyoid

  6. anterior belly digastric

  7. tensor tympani

  8. tensor palate


Cranial Nerve

  1. Maxillary and mandibular divisions of trigeminal nerve


Pouch

  1. Tubotympanic recess – tympanic cavity and Eustachian tube

  2. Anterior 2/3rd tongue


1st Branchial cyst

    • Located inferior or ventral to external acoustic meatus

    • May drain thru a cervical aural fistula which usually opens into the EAM

Branchial Arch 2



Artery:

Stapedial artery
Skeletal – Reichert’s cartilage

  1. Stapes

  2. Styloid process

  3. Hyoid bone – lesser horn and superior rim of body

  4. Stylohyoid ligament



Muscles (from cranial somitomere 6)

  1. Muscles of facial expression

  2. Posterior belly digastric

  3. Fronto-occipitalis

  4. Stylohyoid

  5. Stapedius


Cranial Nerve

  1. Facial nerve

Cleft

    1. External acoustic meatus


Pouch

  1. Palatine tonsils

  2. Copula tongue (overgrown)


2nd Branchial cyst

    • Located just ventral to the ventral border of sternomastoid

    • May have external and/or internal fistula

    • Internal fistula travels through carotid bifurcation to open into palatine tonsils

Branchial Arch 3



Artery:

Common carotid artery
Skeletal

  1. Hyoid – greater horn and inferior rim of body



Muscles (from cranial somitomere 7)

  1. stylopharyngeus


Cranial Nerve

  1. Glossopharngeal nerve


Pouch

  1. thymus gland

  2. inferior parathyroid glands

Branchial Arch 4



Artery:

Arch Aorta
Skeletal

  1. Laryngeal cartilages



Muscles (from occipital somites 2-4)

  1. Pharyngeal constrictors

  2. Cricothyroid

  3. Levator veli palatini


Cranial Nerve

  1. Superior laryngeal branch of Vagus nerve


Pouch

  1. Superior parathyroid glands

Branchial Arch 6



Artery:

Ductus arteriosus
Skeletal

  1. Laryngeal cartilages



Muscles (from occipital somites 1-2)

  1. Intrinsic muscles larynx


Cranial Nerve

  1. recurrent laryngeal branch of Vagus nerve


Pouch

Ultimobranchial bodies



  • differentiate into C cells (parafollicular) of thyroid

  • produce calcitonin


Origins of craniofacial muscles


Mesodermal Origin

Muscles

Innervation

Somitomeres 1, 2

Superior, medial and ventral recti

CN III

Somitomere 3

Superior oblique

CN IV

Somitomere 4

Muscles of mastication

CN V

Somitomere 5

Lateral rectus

CN VI

Somitomere 6

2nd arch muscles

CN VII

Somitomere 7

Stylopharyngeus

CN IX

Somites 1, 2

Intrinsic laryngeals

CN X

Somites 2-5

Tongue muscles

CN XII



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