The carotid arteries are a pair of major blood vessels located on either side of the neck. Their function is to transport oxygen-rich blood from the heart to the brain and head. Because the brain has a constant and significant demand for oxygen and nutrients, these arteries are among the most important in the human body. Understanding their location and the distinct roles of their branches is fundamental to grasping several common and serious health issues.
The Anatomy: Locating the Carotid Arteries
The two Common Carotid Arteries (CCAs) begin in the chest, originating from different sources. The right CCA branches off the brachiocephalic trunk, while the left CCA arises directly from the aortic arch. Both vessels then ascend vertically through the neck, encased within the carotid sheath, traveling lateral to the trachea and esophagus.
Each Common Carotid Artery travels up the neck until it reaches the superior border of the thyroid cartilage, often corresponding to the fourth cervical vertebra (C4). At this point, the CCA undergoes a division, known as the bifurcation. It splits into two branches: the Internal Carotid Artery (ICA) and the External Carotid Artery (ECA).
The External Carotid Artery (ECA) remains closer to the skin’s surface and supplies structures outside the skull. Its branches distribute blood to the face, scalp, tongue, and most neck structures, including muscles and skin. In contrast, the Internal Carotid Artery (ICA) takes a deeper, more direct path and does not give off any branches in the neck. The ICA enters the base of the skull through a canal in the temporal bone to reach its destination: the brain.
Essential Function: Supplying the Head and Brain
The purpose of the carotid arteries is to maintain a continuous, high-volume supply of oxygenated blood and nutrients to the head, particularly the brain. The brain is highly sensitive to interruptions in blood flow, as its cells begin to die after only a few minutes without oxygen. The carotid system works with the vertebral arteries to ensure constant circulation.
The Internal Carotid Artery (ICA) is the primary conduit for the brain’s circulation. It supplies the anterior two-thirds of the cerebral hemispheres, including areas responsible for functions like thought, language, and movement. Once inside the skull, the ICA branches to form several major arteries, such as the anterior and middle cerebral arteries. These distribute blood across the majority of the brain’s surface. The ICA also supplies the eyes.
The External Carotid Artery (ECA) manages the blood supply for all non-brain structures of the head. The ECA delivers blood to the muscles of the face, the scalp, and the jaw. This division ensures that the brain’s needs are met by the ICA’s dedicated pathway, while the remaining external tissues are supplied by the ECA.
Health and Practical Relevance
The accessible location of the carotid arteries makes them a common site for checking a pulse. The carotid pulse can be felt by gently placing the index and middle fingers in the groove on the side of the neck, between the windpipe and the large muscle. It is important to apply only light pressure and never to press on both carotid arteries simultaneously. Doing so can severely restrict blood flow to the brain and potentially cause dizziness or fainting.
The health of the carotid arteries is directly linked to cardiovascular well-being, most notably through Carotid Artery Disease (CAD). This disease is caused by atherosclerosis, where fatty deposits and cholesterol, known as plaque, build up inside the artery walls. The accumulation of this plaque narrows the artery, a condition known as stenosis, which impedes the normal flow of blood.
The primary danger of Carotid Artery Disease is the increased risk of an ischemic stroke. An ischemic stroke occurs when blood flow to the brain is blocked. This blockage happens if the plaque buildup in the carotid artery becomes severe enough to cut off blood flow. More commonly, a small piece of plaque breaks off, travels up the bloodstream, and lodges in a smaller artery within the brain. This immediately cuts off the oxygen supply and causes brain cells to die. Risk factors for plaque buildup include high blood pressure, high cholesterol, diabetes, and smoking.