Here are your notes on the Internal Carotid Artery of Human Neck!
It arises from the bifurcation of the common carotid, at the level of the upper border of thyroid cartilage opposite the disc between C3 and C4 vertebrae. At its commencement the artery dilates to form the carotid sinus which acts as baro- receptor.
Each artery passes straight upward through the neck within the carotid sheath, enters the skull through the carotid canal in the petrous part of temporal bone, and ends in the middle cranial fossa by dividing into the anterior and middle cerebral arteries. The entire course of the internal carotid artery may be subdivided into four parts – cervical, petrous, cavernous and cerebral.
The cervical part of internal carotid undergoes a straight course upto the base of the skull, does not provide any branch in the neck and is surrounded by a plexus of sympathetic nerves from the superior cervical ganglion of the sympathetic trunk. Its relationship with the external carotid artery is already discussed.
(a) In the lower part, crossed by the hypoglossal nerve, lingual and facial veins, posterior belly of the digastric and stylohyoid muscles, occipital and posterior auricular arteries;
(b) In the upper part, overlapped by the parotid gland with external carotid artery, styloid process and the muscles attached to it, glossopharyngeal and pharyngeal branch of vagus nerves.
(a) Transverse processes of upper three cervical vertebrae, prevertebral muscles covered by the prevertebral fascia, and the superior cervical ganglion of sympathetic trunk;
(b) Close to the base of the skull, internal jugular vein lies behind the internal carotid artery separated by the last four cranial nerves.
Medially, the wall of the pharynx, ascending pharyngeal artery and superior laryngeal nerve;
Laterally, internal jugular vein and vagus nerve.
The internal carotid traverses the petrous part of temporal bone in a carotid canal, in which it at first passes upward along the anterior wall of tympanic cavity and cochlea of internal ear, and then curves forward and medially below the auditory tube and trigeminal ganglion. The artery enters the cranial cavity through the apex of petrous temporal in the posterior wall of the foramen lacerum.
From the foramen lacerum the artery ascends to a point medial to the lingula of the sphenoid bone and enters the cavernous sinus. In the sinus the vessel passes forward and lodges in a ‘f’ shaped sulcus by the side of sella turcica. Here it occupies the floor and medial wall of the sinus outside the endothelial lining of the venous blood, is surrounded by sympathetic nerve plexus and is related to the abducent nerve immediately infero-lateral to the artery. Further laterally the artery is related to the oculomotor, trochlear, ophthalmic and maxillary nerves within the lateral wall of the sinus.
The internal carotid next ascends, and pierces the dural roof of the sinus between the anterior and middle clinoid processes.
The artery turns backward in the subarachnoid space along the roof of cavernous sinus, and lies below the optic nerve.
Finally the artery turns upward by the side of the optic chiasma and reaches the anterior perforated substance at the medial end of lateral sulcus, where it divides into the anterior and middle cerebral arteries. (Intracranial course and distribution are further described in the arterial supply of the brain in part-IV of author’s book on Neuro-anatomy).
It is thus evident that the internal carotid describes a U-shaped bend, convex forward, while passing through and above the cavernous sinus. Such a loop is known as the carotid siphon which perhaps damps down the pulsation of the artery and maintains a regular flow of blood to the brain.
From the petrous part
1. Carotico-tympanic branches.
2. Branches to pterygoid canal.
From the cavernous part
3. Inferior hypophysial arteries.
4. Meningeal branch.
From the cerebral part
5. Superior hypophysial arteries
6. Ophthalmic artery.
7. Posterior communicating artery.
8. Anterior choroid artery.
9. Anterior cerebral artery.