Tongue Anatomy I

The tongue:
- Which is located in the oral cavity and oropharynx is a mass of muscle that is almost completely covered by a thick mucous membrane.
The primary function of the tongue:
- Is taste sensation:
  - But it also assists with:
    - Mastication
    - Deglutition
    - Articulation
    - Oral cleansing
The complex innervation of this multifunctional organ is provided by:
- Five cranial nerves.
The embryologic origins of the tongue:
- First appear at 4 weeks’ gestation.
- The first branchial arch is responsible for the development of the tongue derivatives:
  - It gives rise to two lateral lingual swellings and one median swelling (known as the tuberculum impar):
    - The two lateral lingual swellings grow over the tuberculum impar and merge:
      - Forming the anterior two thirds of the tongue.
- Portions of the second, third, and fourth branchial arches:
  - Give rise to the base of the tongue.
- The intrinsic musculature of the tongue derives from occipital somites which give rise to myoblasts.
Macroscopically from anterior to posterior:
- The tongue has three surfaces:
  - Tip
  - Body
  - The base
  - The tip of the tongue is:
    - The highly mobile, pointed, anterior portion of the tongue.
  - Behind to the tip lies the body of the tongue:
    - Which has a dorsal (superior) and a ventral (inferior) surfaces.
  - The median sulcus of the tongue:
    - Separates the body into left and right halves.
  - The terminal sulcus is a V-shaped furrow:
    - That separates the body of the tongue from the base of the tongue:
      - At the tip of this sulcus is the foramen cecum:
        
        A remnant of the proximal thyroglossal duct.
  - The base of tongue contains:
    - The lingual tonsils:
  - The inferior most portion of Waldeyer’s ring.
  - The body of the tongue derives its characteristic surface appearance:
    - From the presence of lingual papillae:
      - Which are projections of lamina propria covered with epithelium.
      - Four different types of lingual papillae exist:
        
        Circumvallate (vallate):
        
        The circumvallate papillae are flat, prominent papillae that are surrounded by troughs.
        
        There are approximately eight to 12 circumvallate papillae:
        
        Located directly anterior to the terminal sulcus.
        
        The ducts of the lingual glands of von Ebner:
        
        Secrete lingual lipase into the surrounding troughs to begin the process of lipolysis.
        
        Foliate:
        
        They are located on the lateral surface of the tongue:
        
        They are small folds of mucosa.
        
        Filiform:
        
        The filiform papillae are thin and long.
        
        They are the most abundant papillae in the tongue.
        
        They are located:
        
        Along the entire dorsum of the tongue.
        
        They are not involved in taste sensation.
        
        Fungiform:
        
        Are the mushroom shaped papillae.
        
        They are scattered most densely along the tip and lateral surfaces of the tongue.
        
        The human tongue has roughly:
        
        200 to 300 fungiform papillae.
      - Each circumvallate, foliate, and fungiform papilla:
        
        Contains taste buds (250, 1000, and 1600 taste buds, respectively):
        
        Innervated by multiple nerve fibers.
        
        All taste buds can perceive the five different taste qualities:
        
        Salt
        
        Sweet
        
        Bitter
        
        Acid
        
        Umami
        
        The taste bud consists of a:
        
        Taste receptor, basal cell, and edge cell.
        
        When a taste molecule binds to a taste receptor:
        
        The receptor cell depolarizes, causing an influx of Ca++:
        
        Which results in the release of an unidentified neurotransmitter
        
        Following the depolarization:
        
        The afferent neural pathway depends on the location of the taste bud that was stimulated:
        
        In the anterior two thirds of the tongue:
        
        The chorda tympani branch of the facial nerve (cranial nerve VII) is stimulated
        
        The lingual-tonsillar branch of the glossopharyngeal nerve (cranial nerve IX) relays taste information from the posterior third of the tongue
The tongue has four intrinsic and four extrinsic muscles:
- The muscles on each side of the tongue are separated by a fibrous lingual septum
- The extrinsic muscles are so named because they:
  - Originate outside the tongue and insert within it
- The intrinsic muscles are within the substance of the organ and do not insert on bone
- Though the muscles do not act in isolation:
  - Intrinsic muscles generally:
    - Alter the shape of the tongue
  - Whereas extrinsic muscles alter its position:
    - The extrinsic muscles of the tongue are:
      - Genioglossus
      - Hyoglossus
      - Styloglossus
      - Palatoglossus
    - The hypoglossal nerve provides the motor innervation to all muscles of the tongue except the palatoglossus:
      - Which is supplied by the pharyngeal plexus
    - The arterial supply to the tongue and floor of the mouth is derived from the:
      - Dorsal lingual, sublingual, and deep lingual branches of the lingual artery
    - The venous drainage of the tongue is into the lingual veins, which drain into the:
      - Facial and retromandibular veins:
        
        Which join to form the common facial vein