The Tongue And Its Muscular Depressant

The tongue is a muscular organ situated in the oral cavity, and its main functions include tasting, chewing, swallowing, speaking, and clearing the oral cavity. The muscles of the tongue can be divided by where they attach (internally or externally) or by the direction that the muscle fibres run. The tongue's muscles consist primarily of two groups: extrinsic and intrinsic. The extrinsic muscles include the genioglossus, hyoglossus, styloglossus, and palatoglossus. The genioglossus muscle, which is fan-shaped and comprises the bulk of the tongue's body, is the major muscle responsible for protruding or sticking out the tongue. Bilateral contraction of this muscle also depresses the central part of the tongue.

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Genioglossus muscle: a fan-shaped muscle that makes up the bulk of the tongue

The genioglossus muscle is a fan-shaped muscle that forms the majority of the tongue's body. It is one of the paired extrinsic muscles of the tongue, with the other extrinsic muscles being the hyoglossus, styloglossus, and palatoglossus. The genioglossus muscle is thick and arises from the superior mental spine of the mandible, inserting onto the hyoid bone and the bottom of the tongue. The muscle has a broader insertion, with its inferior fibres attaching to the hyoid bone and its superior fibres attaching along the entire length of the tongue's dorsum.

The genioglossus muscle plays a crucial role in tongue movement and protrusion. When contracted bilaterally, the genioglossus muscle depresses and protrudes the tongue, while unilateral contraction deviates the tongue to the contralateral side. This muscle is innervated by the hypoglossal nerve (cranial nerve XII), which is responsible for innervating both the intrinsic and extrinsic muscles of the tongue. The hypoglossal nerve can be tested by asking a patient to stick out their tongue, with damage resulting in deviation to the affected side.

The genioglossus muscle also has a significant impact on the upper airway. Its contraction stabilises and enlarges the portion of the upper airway that is most susceptible to collapse. Conversely, relaxation of the genioglossus muscle during REM sleep can contribute to obstructive sleep apnea. By pulling the mandible forward, the airway space can be maximised, preventing the tongue from obstructing the airway during anaesthesia.

The genioglossus muscle has a close relationship with the base of the skull (occipital bone) and the hyoid bone from an embryological perspective. It receives its blood supply indirectly from the external carotid artery. Additionally, the muscle is electrically involved in generating maximal sniff nasal inspiratory and nasal expiratory pressures. The genioglossus muscle also contributes to the ability to express phonemes and play wind instruments effectively by allowing better use of the vocal cords.

The canine genioglossus muscle has been categorised into horizontal and oblique compartments. It is susceptible to the negative effects of pathologies in the oral cavity and systemic diseases, such as constant hypoxia during sleep, which can alter muscle metabolism and lead to functional muscle weakness.

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Hyoglossus muscle: a quadrangular muscle that makes up the floor of the oral cavity

The hyoglossus muscle is one of the four extrinsic muscles of the tongue, along with the genioglossus, styloglossus, and palatoglossus. It is a thin, quadrangular muscle that makes up the floor of the oral cavity. The hyoglossus muscle originates along the entire length of the hyoid bone and inserts into the side of the tongue. The muscle fibres from the hyoid bone travel upwards and slightly forward, crossing each other along with the fibres of the styloglossus.

The hyoglossus muscle is located laterally towards the genioglossus muscles and is considered the key muscle of the suprahyoid region. It serves as a vital landmark for neighbouring structures, making it very important to surgeons. The muscle is innervated by the hypoglossal nerve (cranial nerve XII), which traverses the lower portion of the muscle from behind forwards. The lingual nerve, on the other hand, crosses the upper portion of the muscle from behind forwards.

The hyoglossus muscle acts to depress and retract the tongue. It receives its blood supply mainly from the lingual artery, with additional supply from the facial artery. The lingual artery is the third branch of the external carotid artery, which provides the main blood supply to the tongue.

The hyoglossus muscle is one of the tongue's intrinsic muscles, which originate and attach to other structures within the tongue. These muscles affect the tongue's shape and size and play a role in speech, eating, and swallowing. The hyoglossus, in particular, is essential in depressing and retracting the tongue, working alongside the styloglossus to perform these functions.

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Styloglossus muscle: a thin, stripe-shaped muscle that originates from the styloid process of the temporal bone

The styloglossus muscle is a thin, stripe-shaped muscle that plays a crucial role in tongue movement and articulation. It is one of the extrinsic muscles of the tongue, originating from the styloid process of the temporal bone, a slender, pointed projection located just below the ear. This muscle then inserts into the side of the tongue, contributing to tongue retraction and elevation.

The styloglossus muscle is the shortest and smallest of the three styloid muscles, including the stylopharyngeus and stylohyoid muscles. It arises from the anterior and lateral surfaces of the styloid process, near its apex, and from the stylomandibular ligament. The muscle passes anterioinferiorly, descending anteriorly and dividing into longitudinal and oblique parts upon insertion.

The longitudinal part of the styloglossus muscle enters the tongue posterolaterally, blending with the inferior longitudinal lingual muscle fibres. Meanwhile, the oblique part overlaps and decussates with the hyoglossus muscle, which lies anterior to the longitudinalis inferior muscle. This complex arrangement of muscles allows for precise tongue movements during speech and swallowing.

The styloglossus muscle is innervated by the hypoglossal nerve (cranial nerve XII), which also innervates other extrinsic muscles of the tongue, such as the genioglossus. The genioglossus muscle, a fan-shaped muscle, is responsible for protruding or sticking out the tongue. It works in conjunction with the styloglossus muscle to facilitate tongue retraction and elevation, allowing for a wide range of tongue movements.

Understanding the anatomy of the styloglossus muscle and its attachment to the temporal bone is essential for studying tongue function during speech and food manipulation. Its contraction and relaxation play a vital role in processes such as swallowing, where it retracts the tongue to help push food down the throat, and in modifying tongue shape for articulating specific sounds during speech.

Palatoglossus muscle: a muscle of the soft palate, innervated by the vagus nerve

The tongue is made up of both intrinsic and extrinsic muscles. The genioglossus is a fan-shaped extrinsic muscle that comprises the bulk of the tongue's body. It is innervated by the hypoglossal nerve and is responsible for protruding or sticking out the tongue. The muscle is paired, with left and right portions that work together to depress the centre of the tongue at its back.

The palatoglossus muscle, also known as musculus palatoglossus, is one of the four extrinsic muscles of the tongue and the paired muscles of the soft palate. It arises from the palatine aponeurosis of the soft palate and inserts onto the side of the tongue. Some of its fibres extend over the dorsum of the tongue, while others pass into the substance of the tongue to intermingle with the transverse muscle of the tongue. The palatoglossus muscle functions to elevate the posterior portion of the tongue and draw the soft palate inferiorly, narrowing the diameter of the oropharyngeal isthmus. This action is essential during swallowing, as it propels food towards the oesophagus and prevents retrograde flow.

The palatoglossus muscle is innervated by the vagus nerve, specifically the pharyngeal branch of the cranial nerve X. It is the only muscle of the tongue not innervated by the hypoglossal nerve. The vagus nerve has three distinct branches: superior, middle, and inferior. The superior branch of the vagus nerve contributes to the innervation of the palatoglossus muscle, along with the glossopharyngeal nerve.

The vagus nerve also plays a role in the innervation of the genioglossus muscle, which is primarily controlled by the hypoglossal nerve. The vagus nerve's involvement helps the genioglossus muscle retract and dilate the upper airway.

Genioglossus and sleep: relaxation of the genioglossus is implicated in sleep apnea

The genioglossus is a fan-shaped extrinsic muscle that forms the bulk of the tongue's body. The name is derived from the Greek words "geneion" (chin) and "glossa" (tongue). It is innervated by the hypoglossal nerve (cranial nerve XII). The genioglossus muscle is responsible for protruding and depressing the tongue.

During sleep, the activity of the genioglossus muscle diminishes. In susceptible individuals, this loss of muscle activity can lead to obstructive sleep apnea (OSA), a common sleep-breathing disorder characterised by repeated partial or complete upper airway collapse during sleep. OSA is caused by a loss of upper airway dilator muscle tone during sleep and an inadequate compensatory response by these muscles, resulting in an anatomically compromised airway. The genioglossus is the main upper airway dilator muscle, and its relaxation, especially during REM sleep, is implicated in OSA.

OSA treatments targeting the genioglossus muscle have been developed to improve its function. Hypoglossal nerve electrical stimulation has shown significant improvements in objective and subjective measurements of OSA severity. However, its invasive nature limits its application. A recently introduced combination of drugs administered orally before bedtime has been found to reduce the apnea-hypopnea index (AHI) and improve the responsiveness of the genioglossus muscle.

The genioglossus muscle is also involved in other physiological functions, such as facilitating speech and eating. It is supplied blood by the external carotid artery and is negatively affected by pathologies of the oral cavity and systemic diseases. For example, constant hypoxia during sleep can alter muscle metabolism and lead to functional muscle weakness.

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