Tongue
Anatomy and Physiology of the Tongue
The tongue is a muscular organ in the mouth that is crucial for various functions, including taste, speech, and mastication. It is covered with a mucous membrane and contains numerous papillae, which house the taste buds. The tongue is anchored to the floor of the mouth by a fold of mucous membrane called the frenulum.
Structure
The tongue is divided into two main parts: the anterior two-thirds, known as the oral part, and the posterior one-third, known as the pharyngeal part. The oral part is highly mobile and is involved in manipulating food and forming speech sounds. The pharyngeal part is less mobile and plays a role in swallowing.
The tongue is composed of intrinsic and extrinsic muscles. The intrinsic muscles, which are not attached to any bone, allow the tongue to change its shape. These include the superior longitudinal, inferior longitudinal, transverse, and vertical muscles. The extrinsic muscles, which are attached to bones, allow the tongue to change its position. These include the genioglossus, hyoglossus, styloglossus, and palatoglossus muscles.
Blood Supply and Innervation
The tongue receives its blood supply from the lingual artery, a branch of the external carotid artery. Venous drainage is primarily through the lingual veins, which drain into the internal jugular vein.
The tongue's sensory innervation is complex. The anterior two-thirds are innervated by the lingual nerve (a branch of the mandibular nerve) for general sensation and by the chorda tympani (a branch of the facial nerve) for taste. The posterior one-third is innervated by the glossopharyngeal nerve for both general sensation and taste. Motor innervation to the tongue muscles is provided by the hypoglossal nerve, except for the palatoglossus muscle, which is innervated by the vagus nerve.
Functions of the Tongue
The tongue performs several critical functions, including taste, speech, and swallowing.
Taste
Taste is one of the primary functions of the tongue. The taste buds, located on the papillae, are responsible for detecting different tastes: sweet, salty, sour, bitter, and umami. The taste buds are connected to sensory neurons that send signals to the brain, where the perception of taste is processed.
Speech
The tongue is essential for articulating sounds and forming words. It works in conjunction with the lips, teeth, and palate to produce a wide range of speech sounds. The precise movements of the tongue are crucial for the clarity and intelligibility of speech.
Swallowing
Swallowing, or deglutition, is a complex process that involves the tongue pushing food to the back of the mouth and into the pharynx. The tongue's movements are coordinated with those of the soft palate, pharynx, and esophagus to ensure that food is directed into the digestive tract and not the respiratory tract.
Clinical Significance
The tongue can be affected by various medical conditions, which can impact its function and overall health.
Infections
Infections of the tongue can be caused by bacteria, viruses, or fungi. Common infections include oral thrush, caused by the fungus Candida albicans, and herpes simplex virus infections, which can cause painful sores on the tongue.
Tumors
Tumors of the tongue can be benign or malignant. Squamous cell carcinoma is the most common type of malignant tumor affecting the tongue. Early detection and treatment are crucial for improving outcomes.
Disorders of Taste
Disorders of taste, or dysgeusia, can result from various factors, including infections, medications, and systemic diseases. Loss of taste, or ageusia, can significantly impact quality of life and nutrition.
Trauma
Trauma to the tongue can result from accidents, burns, or biting. Severe trauma may require medical intervention to repair damage and restore function.
Evolutionary Perspective
The tongue has evolved to perform various functions that are crucial for survival. In different species, the tongue has adapted to meet specific needs. For example, in reptiles, the tongue is often used for sensory purposes, while in mammals, it plays a significant role in feeding and communication.