The tongue is a complex and agile organ, central to eating and speaking. Its structure allows for a wide range of motion, enabling it to manipulate food, articulate sounds, and clean the oral cavity. This versatility stems from its muscle architecture and precise neural control. The tongue’s anatomy and nervous system pathways explain how it accomplishes these intricate actions.
The Tongue’s Unique Muscular Structure
The tongue’s flexibility is due to its composition as a muscular hydrostat, a structure made almost entirely of muscle without skeletal support. This allows it to change its shape and position precisely. Its muscle fibers are organized into two main groups: intrinsic and extrinsic muscles. The two sides of the tongue are separated by a vertical fibrous tissue called the lingual septum, which serves as an anchor point for some muscles.
The intrinsic muscles are located entirely within the tongue and are responsible for altering its shape. This group includes four pairs of muscles:
- Superior longitudinal
- Inferior longitudinal
- Transverse
- Vertical muscles
The superior and inferior longitudinal muscles run along the tongue’s length; their contraction shortens the tongue and allows its tip to curl. The transverse and vertical muscles run across the width and height, working to make the tongue narrower, wider, or flatter.
The extrinsic muscles originate from bones in the skull and jaw and attach to the tongue, controlling its position within the mouth. The genioglossus muscle attaches to the mandible and is responsible for protruding the tongue and depressing its center. The styloglossus muscle originates from the temporal bone and retracts the tongue and elevates its sides, forming a trough for swallowing. The hyoglossus connects to the hyoid bone and pulls the tongue downward and backward.
Nerve Pathways Controlling the Tongue
Every movement of the tongue is directed by signals from the brain that travel along nerve pathways to activate the muscles. The primary nerve for motor control is the hypoglossal nerve (cranial nerve XII). It originates from the brainstem and innervates all extrinsic and intrinsic tongue muscles, except for the palatoglossus muscle.
Damage to the hypoglossal nerve visibly impacts tongue movement. When this nerve is impaired on one side, the tongue deviates toward the affected side upon protrusion. This occurs because the genioglossus muscle on the healthy side pushes its half of the tongue forward without opposition from the paralyzed side. This clinical sign is used to assess neurological function.
While the hypoglossal nerve manages motor functions, other cranial nerves transmit sensory information like taste and touch to the brain. The lingual nerve, a branch of the trigeminal nerve (cranial nerve V), carries general sensation for the anterior two-thirds of the tongue. Taste from this same region is handled by the chorda tympani, a branch of the facial nerve (cranial nerve VII). For the posterior one-third, the glossopharyngeal nerve (cranial nerve IX) supplies both general sensation and taste.
Coordinated Actions for Speech and Swallowing
The interplay between the tongue’s muscles and neural control is fundamental to speaking and swallowing. For speech, the tongue acts as a primary articulator, altering its shape and position to modify airflow from the lungs, which creates the sounds of consonants and vowels. For example, producing a ‘t’ or ‘d’ sound involves the tongue tip touching the alveolar ridge behind the upper teeth to block and release airflow.
Creating a ‘k’ or ‘g’ sound requires the back of the tongue to rise and contact the soft palate. Vowel sounds are produced by changing the tongue’s overall shape to alter the resonant space of the oral cavity without creating a significant obstruction. The speed and accuracy required for fluent speech highlight the coordination between the intrinsic muscles, which fine-tune the tongue’s shape, and the extrinsic muscles, which position it within the mouth.
During swallowing (deglutition), the tongue performs a sequence of movements. It first manipulates food during chewing, mixing it with saliva to form a soft mass called a bolus. The tongue then initiates swallowing by pressing the bolus against the hard palate. A wave-like motion propels the bolus toward the pharynx (throat), triggering the swallowing reflex. The styloglossus muscle aids this by elevating the sides of the tongue to form a central channel, guiding the food backward.
Disorders of Tongue Movement
Impairments to the tongue’s structure or neural control can cause difficulties with speech and eating. These disorders can be congenital or acquired later in life from injury or disease. A common congenital condition is ankyloglossia, or tongue-tie. This occurs when the lingual frenulum, the tissue connecting the underside of the tongue to the floor of the mouth, is short, thick, or tight, restricting its range of motion.
This restriction can interfere with an infant’s ability to breastfeed by preventing the tongue from extending and elevating to latch properly. In some cases, ankyloglossia may also affect speech articulation, making it difficult to produce sounds that require precise tongue placement. The condition is diagnosed and treated early if it causes functional problems.
Acquired disorders often result from neurological damage that disrupts brain signals. Dysarthria, characterized by slurred or slow speech due to muscle weakness, can occur after a stroke, brain injury, or from neurodegenerative diseases. Dysphagia (difficulty swallowing) can result from the same causes, impairing the tongue’s ability to control and propel food, which can lead to choking or aspiration.