Internal Carotid Artery

Course

The internal carotid artery arises as a terminal branch of the common carotid artery within the carotid triangle of the neck. Its origin is approximately at the level of the superior border of the thyroid cartilage (C4).

The artery ascends within the carotid sheath, lying anterior to the transverse processes of the C3–C1 vertebrae. It then enters the cranial cavity via the carotid canal, which passes through the petrous part of the temporal bone.

Within the carotid canal, the internal carotid artery is accompanied by the internal carotid nerve – a branch of the superior cervical ganglion carrying sympathetic fibres. These fibres form the internal carotid plexus around the artery.

After entering the cranial cavity, the internal carotid artery passes through the cavernous sinus. On exiting, it gives rise to the ophthalmic artery, which passes through the optic canal to supply the eye, forehead and nose.

Just inferior to the anterior clinoid processes of the sphenoid bone, the artery makes a sharp 180-degree turn. It then terminates by dividing into the anterior cerebral artery and middle cerebral artery, which contribute to the circle of Willis.

By TeachMeSeries Ltd (2026)

Fig 1
Cervical course of the internal carotid artery.

Carotid Sinus

The carotid sinus is a dilatation of the proximal internal carotid artery (or distal common carotid artery) which contains baroreceptors innervated by the glossopharyngeal nerve (CN IX).

These receptors detect changes in blood pressure, with an increase in pressure resulting in reflex slowing of the heart rate and vasodilation.

Supply

The internal carotid artery supplies the brain, as well as the orbit and surrounding structures. This is achieved via several major branches (in addition to smaller unnamed branches).

The first major branch is the ophthalmic artery is the ophthalmic artery, which supplies the orbit and contributes to the forehead and nose:

• Forehead – supplied by the supraorbital and supratrochlear arteries
• Nose – supplied by the dorsal nasal and anterior ethmoidal arteries

The internal carotid artery also gives rise to branches that contribute to the circle of Willis – including the anterior cerebral artery, middle cerebral artery, and posterior communicating artery. These vessels supply the majority of the cerebral hemispheres, with the anterior cerebral artery supplying the medial surfaces and the middle cerebral artery supplying the lateral surfaces.

Lastly, the internal carotid artery also gives rise to the anterior choroidal artery, which supplies deeper structures of the brain.

By TeachMeSeries Ltd (2026)

Fig 2
Structure of the circle of Willis.