L31 Neck and Pharyngeal arches

• Neck and pharyngeal arches

  The most distinctive feature in development of the head and neck
• Pharyngeal arches

  Appear in the 4th and 5th weeks of development
• Although development of pharyngeal arches, clefts, and pouches resembles formation of gills in fishes and amphibians, in the human embryo, real gills are never formed
• Each Pharyngeal arch

  • Consists of a core of mesenchyme, covered externally by ectoderm and internally by endoderm
  • Mesenchyme from paraxial and lateral plate mesoderm, ectoderm from neural crest, and ectodermal placodes, endoderm from pharyngeal gut

  
• Pharyngeal clefts

  Bars of mesenchymal tissue separated externally by deep clefts

  
• Pharyngeal pouches

  Outpocketings that separate the pharyngeal clefts internally
• Pharyngeal Arch Components

  • A pharyngeal arch artery
  • A cartilaginous rod that forms the skeleton of the arch
  • A muscular component that differentiates into muscles in the head and neck
  • Sensory and motor nerves that supply the mucosa and muscles derived from the arch
• Pharyngeal arch derivatives

  • Arch 1 (Mandibular): Nerve V, Muscles of mastication, mylohyoid, anterior belly of digastric, tensor palatine, tensor tympani
  • Arch 2 (Hyoid): Nerve VII, Facial expression muscles, posterior belly of digastric, stylohyoid, stapedius
  • Arch 3: Nerve IX, Stylopharyngeus
  • Arch 4-6: Nerve X, Cricothyroid, levator palatine, constrictors of pharynx, intrinsic muscles of larynx

  
• Pharyngeal pouch derivatives

  • Pouch 1: Tympanic cavity, auditory tube
  • Pouch 2: Tonsillar fossa, palatine tonsil
  • Pouch 3: Inferior parathyroid gland, thymus
  • Pouch 4: Superior parathyroid gland

  
• Pharyngeal cleft derivatives

  • Cleft 1: External acoustic meatus, tympanic membrane
  • Cleft 2: Cervical sinus, sinus of His
  • Cleft 3: Foramen cecum of tongue
• Sternocleidomastoid

  Named because it originates at the manubrium of the sternum and the clavicle, and has an insertion at the mastoid process of the temporal bone

  
• Omohyoid

  Named because Greek "omos" meaning shoulder (one of its attachments) and "hyoid" (other attachment - the hyoid bone)
• Hyoid bone

  A horseshoe-shaped bone situated in the anterior midline of the neck between the chin and the thyroid cartilage, derived from the Greek word hyoeides meaning "shaped like the letter upsilon"

  
• Anterior Triangles of Neck

  Bounded by the anterior border of the sternocleidomastoid muscle laterally, the inferior border of the mandible superiorly, and the midline of the neck medially

  
• Subdivisions of Anterior Triangle

  • Submandibular/digastric triangle
  • Muscular triangle
  • Carotid triangle
  • Submental triangle
• Submandibular/digastric triangle

  -superiorly by the inferior border of the mandible

  -inferiorly by the anterior and posterior bellies of the digastric muscle

  
• Contents of digastric/submandibular triangle

  • Submandibular gland
  • Submandibular lymph nodes
  • Facial vein
  • Facial artery
  • Mylohyoid vessels and nerve
  • Part of hypoglossal nerve
  • Lower part of parotid gland
  • External carotid artery
  • Carotid sheath containing ICA, IJV and vagus nerve

  
• Muscular triangle

  -anteriorly by the anterior median line of the neck (from hyoid bone to jugular notch)

  -postero-superiorly by the superior belly of the omohyoid muscle

  -postero-inferiorly by the anterior border of the sternocleidomastoid muscle
• Contents of muscular triangle

  • Thyroid gland
  • Larynx
  • Trachea
  • Oesophagus

  
• Carotid triangle

  -antero-superiorly by the stylohyoid muscle

  -posterior belly of the digastric

  -antero-inferiorly by the superior belly of the omohyoid muscle

  -posteriorly by the anterior border of the sternocleidomastoid muscle

  
• Contents of carotid triangle

  • Common carotid artery and branches (ICA and ECA)
  • Internal jugular vein and branches
  • Spinal part of accessory nerve
  • Hypoglossal nerve
  • Vagus nerve
  • Cervical part of sympathetic trunk
• Submental triangle

  Bounded inferiorly by the body of the hyoid, laterally by the right and left anterior bellies of the digastric muscles, and with an apex at the mandibular symphysis

  
• Contents of submental triangle

  • Submental lymph nodes
  • Small veins that unite to form the anterior jugular vein
• Posterior triangle

  Bounded anteriorly by the posterior border of the sternocleidomastoid, posteriorly by the anterior border of the trapezius, and inferiorly by the middle third of the clavicle
• Subdivisions of Posterior Triangle

  • Occipital triangle
  • Omoclavicular/supraclavicular triangle
• Contents of Occipital Triangle

  • Occipital artery
  • Spinal accessory nerve
  • 3rd and 4th cervical nerves
  • Dorsal scapular nerve
  • Four cutaneous nerves of the cervical plexus
  • Upper trunk of brachial plexus
• Contents of Omoclavicular/Supraclavicular Triangle

  • 3rd part of subclavian artery
  • Subclavian vein
  • External jugular vein
  • Trunks of brachial plexus
• Carotid pulse

  Palpable pulse in the carotid artery
• Jugular venous pulse/pressure (JVP)

  Visible pulse in the right internal jugular vein in the lower neck, used to assess atrial filling and venous pressures
• Central Venous Access

  Placing a large-bore catheter into the subclavian or internal jugular veins, requires care to avoid complications
• Tracheostomy


  Surgical procedure to create an opening in the trachea
• Fascia of the neck

  Structures in the neck are surrounded by a layer of subcutaneous tissue (superficial fascia) and compartmentalized by layers of deep cervical fascia, which determine the direction of infection spread
• Jugular venous pressure

  Used to assess atrial filling and elevated or diminished venous pressures
• Conditions suggested by elevated jugular venous pressure

  • Congestive or right-sided heart failure
  • Tricuspid valve regurgitation
  • Pericardial tamponade
  • Several other abnormalities
• Central venous access

  When one wishes to place a large-bore catheter into subclavian or internal jugular veins
• Introducing a central venous catheter

  • Care must be exercised as extensive bleeding and/or puncture of the apex of the pleural sac may occur
  • Ultrasonography is often used to help guide the catheter to the appropriate site
• Fascia of the neck

  Surrounded by a layer of subcutaneous tissue (superficial fascia)<|>Compartmentalized by layers of deep cervical fascia<|>The fascial planes determine the direction in which an infection in the neck may spread

  
• Superficial cervical fascia

  Layer of fatty connective tissue lying between the dermis of the skin and the investing layer of deep cervical fascia<|>Contains cutaneous nerves, blood and lymphatic vessels, superficial lymph nodes and variable amounts of fat<|>Anterolaterally it contains the platysma
• Platysma

  -A broad, thin sheet of muscle in the subcutaneous tissue of the neck

  -The anterior borders of the two muscles decussate over the chin and blend with the facial muscles

  -Depresses the mandible
• Deep cervical fascia

  Arranged in 3 layers: investing layer, pretracheal layer, prevertebral layer