Tongue - Anatomy & Physiology

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Introduction

The tongue (lingua) occupies the ventral aspect of the oral cavity and oropharynx. Itis involved with grooming, lapping, prehension and manipultaing food in oral cavity. It is also involved in the deglutition reflex and vocalisation.

The tongue is capable of vigerous and precise movements due to the apex being free of attachments to the oral cavity.

Functional Anatomy

Skeletal muscle dorsally

Structural fat surrounded by cartilagenous sheath forming lyssa (canids only) ventrally

Attached root and body with a free apex

Frenulum (fold of mucosa) attaches the body of the tongue to the floor of the oral cavity

Root of tongue attached to hyoid bone

In the horse and dog the tongue is 'u' shaped, becoming broader towards the tip. The furrow in the centre of the canid tongue is called the median sulcus.

In the ox, sheep and pig the tongue if 'v' shaped with a pointed apex. The tonus linguae is a swelling across the tongue laterally which pushes food against the hard palate.

Muscles

Intrinsic Muscles

The dorsal and ventral longitudinal

Transverse and vertical bundles

Extrinsic Muscles

Styloglossus

   -Origin: Hyoid apparatus (stylohyoid)
   -Retracts and elevates tongue

Genioglossus

   -Origin: Incisive part of mandible
   -Protrudes and depressed tongue

Hyoglossus

   -Origin: Hyoid apparatus (basihyoid)
   -Retracts and depresses tongue

Geniohyoideus

   -Origin: Incisive part of mandible
   -Insertion: Body of hyoid
   -Lies below the tongue (not within it)
   -Draws the hyoid and therefore the tongue forward

Innervation

All muscles moving the tongue are innervated by the hypoglossal nerve (CN XII)

Rostral 2/3 of tongue is innervated by the lingual branch of trigeminal (CN V) which is sensory supplying temperature, touch and pain. The Chorda tympani of facial (CN VII) supplies the taste.

The caudal 1/3 of tongue is innervated by the glossopharyngeal (CN IX) providing motor function for taste.

Histology

Stratified squamous epithelium

Lingual glands

Mucosal covering tightly adheres to the contact surface

Degree of keratinisation depends on diet

Less keratinisation on ventral surface and sides of tongue

Covered by papillae (taste buds)for protection and taste

Papillae are specialised projections of the mucosa

Some papillae have taste buds others are mechanical to roughen surface of tongue

Types of Papillae

Conical

   -Not in horses
   -Caudal 1/3 of tongue
   -Point caudally
   -No taste buds
   -Thick epithelium

Foliate

   -8 to 12 papillae in group, one either side of tongue midline
   -Stratified squamous epithelium
   -Caudal 1/3 of tongue
   -Taste buds present

Vallate

   -3 to 6
   -Often secondary papillae in taste buds
   -Broad glands
   -Caudal 1/3 of tongue
   -Taste buds present

Fungiform

   -Red dots on tongue surface
   -Keratinised, stratified squamous epithelium
   -Blood vessels
   -Loss of heat via panting in dogs
   -Rostral 2/3 of tongue
   -Taste buds present

Filoform

   -Most numerous
   -Points caudally
   -No taste buds
   -Smallest
   -Thick epithelium
   -Very prominent in cat
   -Rostral 2/3 of tongue

Taste Buds

Also found on the soft palate and pharynx (but sparsely distributed)

Constant cell turnover

Flat, think cells

Taste hairs (microvilli) pointing though taste pore

Nerves transduce chemical signals into nervous signals

Species Differences

Dog has stretch receptors in the tongue

Dog uses the tongue to lose heat by panting

Ruminant tongue is heavily keratinised with long papillae for eating (protective surface)

Cat has long papillae for grooming so tongue is rough

Ox has lenticular papillae which are hard and horny due to heavy keratinisation

Most of the papillae in the pig are soft, long and directed caudally