Cranial Nerve 10 – Vagus Nerve

@   SVE、GVE、SVA、GVA、GSA

@   Nuclei Related with the Vagus Nerve

1.     Middle part of the nucleus ambiguus Þ 含Branchio-motor (SVE) neurons，支配咽部的收縮肌、喉部的組成肌、食道的骨骼肌，其發出的投射纖維與Cranial part of spinal accessory nerve聯合形成Inferior (recurrent) laryngeal nerve。亦含有GVE neurons，形成Cardiac plexus去支配心臟。

2.     Dorsal motor nucleus Þ 是最大的副交感神經核，含GVE neurons。Dorsal motor nucleus Þ Vagus nerve (Preganglionic fibers) Þ Pulmonary plexus、Auerbach (= Myenteric) plexus、Meissner (= Submucosal) plexus。

3.     Nodosal ganglion (小結神經節) = Inferior vagal ganglion

(1)  含有味覺的Primary sensory (SVA) neurons，可傳遞散佈在會厭處味蕾的Gustatory sense (Taste)。Taste buds Þ Pharyngeal branch of the vagus nerve Þ Cell bodies in the nodosal ganglion Þ Solitary tract Þ Gustatory nucleus (位於Rostral part of the nucleus of the solitary tract)。

(2)  含有內臟感覺的Primary sensory (GVA) neurons，可傳遞Pharynx、Larynx、Trachea、Esophagus、Carotid body、Thoracic and abdominal viscera的感覺。Cell bodies in the nodosal ganglion Þ Solitary tract Þ Nucleus of the solitary tract。

4.     Jugular ganglion (頸靜脈神經節) = Superior vagal ganglion Þ 含有一般感覺的Primary sensory (GSA) neurons，可傳遞Cutaneous sensory impulses from areas back of the ear and posterior wall of the external acoustic meatus。Auricular branch of the vagus nerve Þ Jugular ganglion Þ Dorsomedial part of the spinal trigeminal tract Þ Spinal trigeminal nucleus。

@   Unilateral Lesion of the Vagus Nerve

1.     Ipsilateral paralysis of the soft palate, pharynx, and larynx, which results in hoarseness (嗄聲), dyspnea (呼吸困難), and dysphagia (吞嚥困難).

2.     Anesthesia of the pharynx and larynx results in an ipsilateral loss of the cough reflex.

3.     Destruction of visceral motor fibers results in an ipsilateral loss of the carotid sinus reflex.

4.     A deviation of the uvula to the contralateral side of the lesion.

※ Corticonuclear fibers projecting to nucleus ambiguous motor neurons are generally bilateral. However, the motor neurons that innervate muscular parts of the soft palate and uvula receive mainly contralateral input. Consequently, a lesion of corticonuclear fibers may produce a weakness in the affected muscles and result in failure of the soft palate to elevate on the contralateral side and in deviation of uvula toward the side of the lesion on phonation.

@   Bilateral Lesions of the Vagus Nerve

1.     They as a rule are fatal unless immediate precautions are instituted to prevent asphyxia (窒息) resulting from complete laryngeal paralysis.

2.     Paralysis and atonia of esophagus and stomach induce pain and vomiting with the hazards of aspiration.

3.     Bilateral lesions most frequently are due to pathology within the medulla.

@   Vagus Nerve in the PNS

1.     Meningeal nerve Þ 為Sensory fibers，支配Dura mater in part of the posterior cranial fossa。

2.     Auricular nerve Þ 為Sensory fibers，支配外聽道背部及下部皮膚、下半部鼓膜。因此刺激此區或此區疼痛，會轉移至喉部而引發咳嗽，或轉移胃區而引發Nausea。

3.     To carotid body

4.     Pharyngeal nerve Þ 組成Pharyngeal plexus，支配Pharynx與Soft palate的骨骼肌。亦含有SVA fibers與GVA fibers。 (Uvulae m.、Levator veli palatini m.、Palatoglossus m.、Palatopharyngeus m.、Superior, middle and inferior pharyngeal constrictor muscles、Salpingopharyngeus m.)

5.     Superior laryngeal nerve Þ 在Middle pharyngeal constrictor muscle處分枝為：

(1)  External laryngeal nerve Þ 位在Superior thyroid artery的深部，支配Cricothyroid muscle與部份的Inferior pharyngeal constrictor muscle。

(2)  Internal laryngeal nerve Þ 穿過Thyroid membrane，感覺枝去支配Mucous membrane of the larynx as far inferior as the vocal cords、 Membrane on the posterior surface of the epiglottis、Valleculae between the epiglottis and the larynx，為引起Cough reflex的主要成份，是一條保命神經。運動枝則可能去支配Part of the transverse arytenoid muscle。

6.     Cardiac nerves

7.     Inferior (recurrent) laryngeal nerve Þ 左右兩側的起始點不同，右邊起自Subclavian artery之下並繞過此動脈，左邊的Recurrent laryngeal nerve則繞過Aortic arch與Ligamentum arteriosum，二者上行於氣管與食道之間，伴隨著Inferior laryngeal branch of the inferior thyroid artery，由甲狀軟骨下角與環狀軟骨交接處穿入喉部，去支配All the muscles of the larynx except the cricothyroid m. (and possibly the transverse arytenoid m.)、Mucous membrane from the vocal cords down。切斷兩側喉返神經會造成Suffocate (窒息而死)，因為All control of the vocal cords is lost, and the cricothyroid and transverse arytenoid muscles tend to bring the vocal cords closer together。 (Posterior cricoarytenoid m.、Lateral cricoarytenoid m.、Transverse arytenoid m.、Oblique arytenoid m. 、Vocalis m.、Aryepiglottic m.、Thyroarytenoid m.、Thyroepiglottic m.)