Lecture: 6 Head and neck Dr. Omar Riadh
18-10-2017
Vagus nerve:-
It is cranial nerve number ten, it is the longest cranial nerve arises from the brain and runs through the neck, thorax and abdomen. It arises from medulla oblongata dorsal to the olive in a line with glossopharyngeal and accessory nerve, these three nerve leave the skull through jugular foramen.The vagus nerve has two ganglia:1- superior ganglia within the jugular foramen and it is spherical in shape, 2- Inferior ganglia which is fusiform in shape and the vagus forms this ganglia after it leaves the jugular foramen.
Communications of vagus nerve with other nerves:-
With cranial part of accessory above the inferior vagal ganglia.
At the Inferior vagal ganglia also the vagus communicates with hypoglossal nerve and with a loop between 1st and 2nd cervical nerve.
Also the vagus nerve has communications with glossopharyngeal nerve and superior cervical sympathetic ganglia.
The nerve descends in the carotid sheath posterior to internal jugular vein and common carotid artery, in the left side it runs between left common carotid and left subclavian arteries then it crosses the arch of aorta where it gives the left recurrent laryngeal nerve which runs upward in a groove between trachea and esophagus.
In the right side the vagus nerve runs over the right subclavian artery and here it gives the right recurrent laryngeal nerve which loops around the subclavian artery and ascends to the larynx.
Components of the vagus nerve:-
General visceral efferent:- motor innervations to voluntary muscles of larynx, pharynx and palate (except tensor veli palatini).Special visceral efferent:- to involuntary muscles and glands of heart, esophagus, stomach, trachea, bronchi, intestine and other abdominal viscera.
General visceral afferent:- visceral sensation.
Special visceral afferent:- taste fibers from epiglottis and palate.
General somatic afferent:- cutaneous from external ear, external acoustic meatus and dura mater of posterior cranial fossa.
Branches of vagus nerve:-
Meningeal branch:- to the dura mater of posterior cranial fossa which return through the jugular foramen.
Auricular branch:- which distributes to external meatus and tympanic membrane.
Pharyngeal branch:- to the pharyngeal plexus which is formed on the constrictor muscles by branches from vagus, glossopharyngeal and superior cervical sympathetic ganglia, the plexus supplies the muscles of the pharynx and soft palate except stylopharyngeus and tensor veli palatine muscle. It gives nerve to the carotid body.
Superior laryngeal branch:- which runs downward and medial ward to the larynx medial to both external and internal carotid arteries. It divides into:- a- internal laryngeal nerve which passes with the superior laryngeal artery through the thyrohyoid membrane, this nerve supplies the larynx by sensation from upper part down to the vocal cord. b- external laryngeal nerve which runs downward with superior thyroid artery supplying cricothyroid and inferior constrictor muscle.
Cervical cardiac branch:- usually two upper and lower on each side which runs to cardiac plexus.
Recurrent laryngeal nerve:- supplies all the muscles of larynx except cricothyroid and also supplies sensation to the larynx below the vocal cord.
Hypoglossal nerve (12th cranial nerve):-
It is a motor nerve to the tongue arises from medulla oblongata between pyramid and olive, it leaves the skull through hypoglossal canal medial to internal carotid artery and internal jugular vein. It then descends between internal carotid artery and internal jugular vein till it reaches the lower border of posterior belly of digastric muscle where it turns forwards and medially loops around occipital artery and crosses the external and internal carotid arteries and the loop of lingual artery, then it passes forward and upward on the hyoglossus muscle deep to digastric, stylohyoid and posterior margin of mylohyoid it ends by curving upward towards the tip of tongue.
In the upper part of its course, the hypoglossal nerve joined by small branch from C1 and sometimes C2 this branch later leaves the hypoglossal nerve as descending branch, nerve to thyrohyoid and nerve to geniohyoid muscle.
Branches of hypoglossal nerve:-
Meningeal branch:- supplies the meninges of posterior cranial fossa.
Descending branch:- which forms the superior root of ansa cervicalis and supplies the infrahyoid muscles.
Nerve to thyrohyoid:- composed of C1 supplies thyrohyoid muscle.
Nerve to geniohyoid:- composed of C1 fibers is giving off on the side of tongue.
Muscular branches:- to styloglossus, hyoglossus, genioglossus and intrinsic muscles of the tongue.
Cervical sympathetic ganglia:-
It is an upward continuation of the thoracic sympathetic trunk, it lies behind the carotid sheath in the prevertebral muscles. It has three ganglia (superior, middle and inferior), the superior cervical ganglia represents the fusion of upper four cervical nerves, the middle cervical ganglia represents the 5th and 6th cervical nerves and the inferior cervical ganglia represents the 7th and 8th cervical nerves.
Superior cervical ganglia:- lies opposite to the transverse process of atlas, it gives the following branches:-
Internal carotid nerve distributes with internal carotid artery.
External carotid nerve distributes with external carotid artery.
Communicantes with glossopharyngeal, vagus and hypoglossal nerve.
Grey rami communicantes to the upper four cervical nerves.
Pharyngeal branch to pharyngeal plexus.
Superior cervical cardiac branch to the cardiac plexus.
Middle cervical ganglia:- smallest and sometimes absent lies at the level of cricoid cartilage at the bent of inferior thyroid artery. branches:-
Grey rami communicantes to 5th and 6th cervical nerve.
Thyroid branch to thyroid gland along the inferior thyroid artery.
Middle cervical cardiac branch.
Inferior cervical ganglia:- mostly fused with the 1st and sometimes the 2nd thoracic ganglia formed what is called cervicothoracic or stellate ganglia, it lies anterior to the transverse process of 7th cervical vertebra and posteromedial to vertebral artery. the sympathetic trunk between the middle and inferior ganglia divides into two branches, a large one passes under subclavian artery and small one passes anterior to subclavian artery curving around the artery and join the large branch forming the ansa subclavia which supplies sympathetic to subclavian artery.
Branches:-
Grey rami communicantes ti 7th and 8th cervical nerve.
Branch to vertebral and subclavian artery.
Inferior cervical cardiac nerve
Thyroid gland:-
It is an important gland which control the metabolism of the body, it presents in front of neck and covered by pretracheal fascia and connects to the larynx by ligament so it is moves with swallowing. The gland composed of two lobes connected by isthmus, the lobes extend from the oblique line of thyroid cartilage to the 6th tracheal ring and the isthmus covers tracheal rings 2nd, 3rd and 4th.The glands has it is own capsule and embedded in its posterior surface two pairs of parathyroid gland. The gland covered anteriorly by infrahyoid muscles (sternohyoid, sternothyroid and superior belly of omohyoid), posterolateral to it is the carotid sheath and its contents, while medial it is in relation with the thyroid and cricoid cartilage above and below it is related to esophagus, trachea and in between is the recurrent laryngeal nerve.
Blood supply of thyroid gland:-
Arterial supply:-
Superior thyroid artery:- branch of external carotid artery, when reaches the apex of the gland it is divided into anterior and posterior branches, the anterior branch anastomose with corresponding branch of the other side, while the posterior branch anastomose with the inferior thyroid artery.
Inferior thyroid artery:- arises from thyrocervical trunk of subclavian artery ascends upward to the lower border of cricoid cartilage where it bent medially and downward, at the bent it gives ascending cervical artery and gives branch to the larynx called inferior laryngeal artery which runs with recurrent laryngeal nerve. In the thyroid it anastomose with the posterior branch of superior thyroid artery and give special branch to parathyroid gland.
Thyroidea ima artery:- variable if presents it may be arises from arch of aorta or brachiocephalic trunk , it ascends on trachea and distributes to the isthmus.
Venous drainage of thyroid gland:-
By three pairs of veins two superior, two middle and two inferior, the superior and middle drain to internal jugular vein while the inferior thyroid vein drains to brachiocephalic vein.
Nerve supply of thyroid gland:-
nerve passes to the gland through inferior thyroid artery which carries sympathetic from middle cervical sympathetic ganglia.
Lymphatic drainage of thyroid gland:-
To superior deep cervical lymph nodes, pretracheal and paratracheal lymph nodes.