Final answer:
The hypoglossal nerve controls motor function of the tongue's intrinsic and extrinsic muscles, affecting swallowing and speech. Lesions to this nerve can impair tongue movement and placement, leading to difficulty with forming a bolus and controlling the larynx. A clinical exam can reveal the nerve's status by observing tongue protrusion.
Step-by-step explanation:
Motor Function of the Hypoglossal Nerve and Tongue Muscles
The hypoglossal nerve is the primary motor nerve responsible for tongue movement, innervating both intrinsic and extrinsic tongue muscles, save for the palatoglossus muscle which is controlled by the vagus nerve. Intrinsic muscles of the tongue handle the shape of the tongue, while extrinsic muscles adjust the tongue's position. Key extrinsic muscles include the genioglossus, which protrudes the tongue, and the geniohyoid, which helps pull the hyoid bone anteriorly. These muscles are crucial for forming a bolus of food and swallowing. A lesion of the hypoglossal nerve can result in difficulties with manipulating food in the mouth and decreased control over laryngeal elevation, essential for swallowing and speech.
During a neurological examination, assessing the ability to protrude the tongue helps ascertain the integrity of the hypoglossal nerve. Dysfunction may present as deviation of the tongue toward the affected side and can signal damage to the nerve itself or to nerve nuclei and nearby structures, such as those involved in cardiovascular, respiratory, and digestive control.