TONGUE DEVELOPMENT

• M.B KEDIA DENTAL COLLEGE• Presenter: Nakul Bista

‘If there is goodness in your heart, it will come to your tongue’.

Development of Tongue• The three l ingual buds result f rom the

prol i ferat ion of mesenchyme in ventromedia l parts of the first pair of pharyngeal arches

• The dista l tongue buds rapid ly increase in s ize, merge with each other, and overgrow the median tongue bud

• The merged dista l tongue buds form the anter ior two-th i rds (ora l part) of the tongue

Development of Tongue

• Fusion of the distal tongue buds is indicated by a middle groove, the median sulcus of the tongue and internally by the fibrous lingual septum

• Median tongue bud forms no recognizable part of the adult tongue

Formation of Posterior third of Tongue

• It is indicated by two elevations that develop caudal to the foramen cecum

• Copula: Forms by fusion of the ventromedial part of the second pair of pharyngeal arches

• The hypopharyngeal eminence: Develops caudal to the copula from mesenchyme in the ventromedial parts of the third and fourth pairs of arches

Formation of Posterior third of Tongue

• As the tongue develops the copula is gradually overgrown by the hypopharyngeal eminence and disappear

• As a result, the pharyngeal part of the tongue develops from the rostral part of the hypopharyngeal eminence

• The line of fusion of the anterior and posterior parts of the tongue is roughly indicated by a V-shaped groove called terminal sulcus

Formation of Posterior third of Tongue

• Pharyngeal mesenchyme forms the connective tissue and vasculature of the tongue

• Most of the tongue muscles are derived from myoblasts that migrate from the occipital myotomes

• The hypoglossal nerve (CN Ⅻ) accompanies the myoblast during their migration and innervates the tongue muscles as they develop

• The entire tongue is within the mouth at birth, its posterior third descends into the oropharynx by 4 years of age

Papillae and Taste Buds

• Lingual papillae appear towards the end of the eighth week

• The vallate and foliate papillae appear first, close to the terminal branches of the glossopharyngeal nerve (CN Ⅸ)

• The fungiform papillae appear later near termination of chorda tympani branch of the facial nerve

Papillae and Taste Buds• The most common lingual papillae, known as filiform

papillae because of their threadlike shape, develop during early fetal period (10-11 weeks)

• They contain afferent nerve endings sensitive to touch

• Taste buds develop during 11-13 weeks

• Most taste buds form on the dorsal surface of the tongue

Papillae and Taste Buds

• Fetal responses in the face can be induced by bitter tasting substances at 26-28 weeks, indicating that the reflex pathways between taste buds and facial muscles are established by this age

Nerve Supply of the Tongue

• The development of tongue explains its nerve supply

• The sensory supply to the mucosa of almost the entire anterior two-thirds of the tongue is from the lingual branch of the mandibular division of the trigeminal nerve

• This nerve is the nerve of first pharyngeal arch and this arch forms the median and distal tongue buds

Nerve Supply of the Tongue

• Facial nerve is the nerve of second pharyngeal arch

• Its chorda tympani branch supplies the taste buds in the anterior two-thirds of the tongue except the vallate papillae

• The facial nerve does not supply any of the tongue mucosa, except for taste buds in the oral part of the tongue

Nerve Supply of the Tongue

• The vallate papillae in the oral part of the tongue are innervated by glossopharyngeal nerve (CN Ⅸ) of the third pharyngeal arch

• This is due to the reason that mucosa of posterior two third of the tongue is pulled slightly anteriorly as the tongue develops

• The posterior third of the tongue is innervated mainly by the glossopharyngeal nerve, which is a nerve of third pharyngeal arch

Nerve Supply of the Tongue

• The superior laryngeal branch of the vagus nerve (CN Ⅹ) of the fourth arch supplies small area of the tongue anterior to the epiglottis

• All muscles of the tongue are supplied by the hypoglossal nerve (CN Ⅻ), except for palatoglossus, which is supplied from pharyngeal plexus by fibers arising from the vagus nerve

Clinical Notes Lacerations of the tongue Tongue-Tie

(ankyloglossia) (due to large frenulum)

Lesion of the hypoglossal nerve– The protruded tongue

deviates toward the side of the lesion

– Tongue is atrophied & wrinkled