The hypoglossal nerve is the twelfth cranial nerve that innervates all the muscles of the tongue except one. Damage to this nerve can cause unilateral paralysis of the tongue, causing it to curve towards the affected side when protruded. Causes of hypoglossal nerve palsy include strokes, brain tumors, multiple sclerosis, and infections. Affected individuals may have difficulty swallowing and speaking due to misarticulation of several sounds. Treatment involves speech therapy and tongue exercises.

1. HYPOGLOSSAL NERVEPALSY

2. Hypoglossal nerveThe hypoglossal nerve is the twelfth cranial nerve (XII), leading to the tongue. The nerve arises from the hypoglossal nucleus and emerges from the medulla oblongata in the preolivary sulcus separating the olive and the pyramid. It then passes through the hypoglossal canal.

3. It supplies motor fibres to all of the muscles of the tongue, except the palatoglossus muscle, which is innervated by the vagus nerve (cranial nerve X) or, according to some classifications, by fibers from the glossopharyngeal nerve (cranial nerve IX) that "hitchhike" within the vagus.The hypoglossal nerve is derived from the basal plate of the embryonic medulla oblongata.

6. Testing the hypoglossal nerveTo test the function of the nerve, a person is asked to poke out his/her tongue. If there is a loss of function on one side (unilateral paralysis), the tongue will point toward the affected side.The strength of the tongue can be tested by getting the person to poke the inside of his/her cheek, and feeling how strongly he/she can push a finger pushed against the cheek - a more elegant way of testing than directly touching the tongue.

7. The tongue can also be looked at for signs of lower motor neuron disease, such as fasciculation and atrophy.Paralysis/paresis of one side of the tongue results in ipsilateral curvature of the tongue (apex toward the impaired side of the mouth); i.e., the tongue will move toward the affected side.Cranial Nerve XII is innervated by the contralateral cortex, so a purely upper motor neuron lesion will cause the tongue to deviate away from the cortical lesion.

8. CAUSESThe causes may be central or peripheral and include cerebrovascular accidents, brain stem tumours, multiple sclerosis, syringomyelia, and infectious poly neutritis.Injury to this nerve causes dysarthria and dysphagia.

9. CHARACTERISTICS In peripheral lesion there is deviation of the tongue towards the affected side, during protrusion. When in tongue rest on the floor of the mouth, a mild deviation towards the unaffected side may be observed.In central lesion, involvement is often bilateral. The patient cannot protrude the tongue, and attempt movement of tongue posteriorly is defective and un co-ordination. The tongue is also small and firm.

10. These individuals will also have problem in swallowing. There is no control over tongue that results in swallowing problems

12. SPEECH CHARACTERISTICSThe abnormality of tongue will lead to misarticulation.The individuals will have problem in producing /t/, /d/,/t∫/,/l/,/n/,/i/,/j/,/k/ and /g/.Due to dysarthria these individuals may have distorted vowel and word flow without pausesSeverity ranges from occasional articulation difficulties to verbal speech that is completely unintelligible.

13. MANAGMENTSpeech therapy should be givenExercise for the treatment of dysarthria may help to improve tongue co-ordination and strength. Treatment of hypoglossal nerve injuries due to penetrating wounds is surgical and the nerve tend to recover quite well