Oral Biology: Comprehensive Study Notes on the Muscles of the Tongue

Classification of Tongue Musculature

  • The muscles of the tongue are fundamentally categorized into two primary groups based on their origin, insertion, and functional role within oral biology:

    • Intrinsic Muscles: These muscles are contained entirely within the structure of the tongue itself. Their primary function is to change the shape of the tongue during various activities.

    • Extrinsic Muscles: These muscles have their origin points outside the anatomical structure of the tongue (out-with the structure). Their primary function is to change the overall position of the tongue within the oral cavity.

Intrinsic Muscles: Anatomy and Path

  • All intrinsic muscles of the tongue are classified as voluntary muscles. They are responsible for the complex transformations in tongue shape required for speech and swallowing.

  • Superior Longitudinal Muscle:

    • Anatomical Path: This muscle runs backwards from the tip of the tongue, situated just below the dorsal surface (the top surface of the tongue).

  • Inferior Longitudinal Muscle:

    • Anatomical Path: This muscle also runs backwards from the tip of the tongue but is located closer to the ventral surface (the underside of the tongue).

  • Vertical Muscle:

    • Anatomical Path: These fibers run vertically from the dorsal surface of the tongue down to the inferior (ventral) surface.

  • Transverse Muscle:

    • Anatomical Path: This muscle consists of fibers that originate from the median septum (the central fibrous partition of the tongue). The fibers pass laterally (sideways) and are inserted into the lateral borders of the tongue.

Intrinsic Muscles: Physiological Actions

  • The contraction of intrinsic muscles facilitates specific shape changes:

    • Superior Longitudinal: Contraction of this muscle turns the tip of the tongue upwards.

    • Inferior Longitudinal: Contraction turns the tip of the tongue downwards.

    • Vertical: Contraction of these fibers flattens and broadens the tongue.

    • Transverse: Contraction of these fibers narrows and lengthens the tongue.

Extrinsic Muscles: Origin, Insertion, and Innervation

  • Extrinsic muscles are responsible for moving the tongue body. There are four major extrinsic muscles described:

  • Genioglossus:

    • Origin: Superior genial tubercle.

    • Insertion: Whole undersurface of the tongue.

    • Action: Pulls the tongue forward (protrusion).

    • Nerve Supply: Hypoglossal Nerve.

  • Hyoglossus:

    • Origin: Body of the hyoid bone.

    • Insertion: Side of the tongue.

    • Action: Depresses the tongue (pulls it downwards).

    • Nerve Supply: Hypoglossal Nerve.

  • Palatoglossus:

    • Origin: Aponeurosis of the soft palate.

    • Insertion: Side of the tongue.

    • Action: Elevates the tongue and seals off the mouth from the pharynx (essential during swallowing).

    • Nerve Supply: Accessory Nerve.

  • Styloglossus:

    • Origin: Tip of the styloid process.

    • Insertion: Side of the tongue.

    • Action: Draws the tongue up and back (retraction and elevation).

    • Nerve Supply: Hypoglossal Nerve.

General Physiological Functions of the Tongue

  • The tongue serves several vital biological and social functions:

    • Mastication: Aids in the process of chewing food and forming a bolus.

    • Speech: Essential for the articulation of sounds and language.

    • Taste: Houses the gustatory receptors for the perception of flavor.

    • Oral Hygiene: Aids in the mechanical cleansing of the mouth and teeth.

    • Sensory Function in Infants: Serves as a primary sensory organ for babies to explore their environment through touch and taste.

    • Expression: Plays a role in facial expressions and non-verbal communication.