Common carotid artery

The common carotid artery is a major blood vessel that supplies oxygenated blood to the head and neck. It is one of the largest arteries in the body and is crucial in maintaining circulation to the brain and facial structures. There are two common carotid arteries one on the left and one on the right side of the body.

Location

The left common carotid artery originates directly from the aortic arch, while the right common carotid artery arises from the brachiocephalic trunk. Both arteries ascend along the neck, traveling within the carotid sheath, alongside the internal jugular vein and the vagus nerve. The common carotid artery runs vertically on either side of the trachea and divides into the internal and external carotid arteries at the level of the fourth cervical vertebra, near the upper border of the thyroid cartilage (around the level of the Adam’s apple). This bifurcation supplies blood to different regions of the head and neck.

Structure and Anatomy

Origin

The common carotid artery exists as a paired structure, with a right and left artery that differ slightly in their origins:

• Right Common Carotid Artery: Arises from the brachiocephalic trunk, which is a branch of the aortic arch. The right common carotid artery originates at the level of the sternoclavicular joint and ascends vertically in the neck.
• Left Common Carotid Artery: Arises directly from the aortic arch, making it longer than the right. The left common carotid artery originates in the thoracic region and ascends through the superior mediastinum into the neck.

Course

Both the right and left common carotid arteries ascend within the neck inside a fibrous structure known as the carotid sheath. The carotid sheath contains three key structures: the common carotid artery (medially), the internal jugular vein (laterally), and the vagus nerve (posteriorly and between the artery and vein).

The common carotid arteries run vertically along the lateral aspect of the trachea and esophagus. As they ascend through the neck, they are located deep to the sternocleidomastoid muscle. Along this path, the artery is relatively superficial and can be palpated at various points, such as along the lower neck.

Bifurcation

The common carotid artery travels upward until it reaches the level of the superior border of the thyroid cartilage, near the fourth cervical vertebra (C4). At this point, it bifurcates into two terminal branches:

• Internal Carotid Artery: This branch continues its path upward, entering the skull through the carotid canal to supply the brain and certain regions of the face and scalp.
• External Carotid Artery: This branch remains more superficial, supplying the face, neck, scalp, and external parts of the head through its branches.

Branches

The common carotid artery itself does not give off any branches before it bifurcates. However, after the bifurcation, the internal and external carotid arteries each give rise to multiple branches that supply various regions of the head and neck:

• External Carotid Artery: Gives off several branches including the superior thyroid artery, lingual artery, facial artery, occipital artery, and superficial temporal artery, among others, to supply the face, scalp, and neck.
• Internal Carotid Artery: Primarily supplies blood to the brain, eyes, and parts of the forehead, with branches such as the ophthalmic artery.

Carotid Sinus and Carotid Body

At the point of bifurcation, a notable anatomical feature of the common carotid artery is the carotid sinus, a dilation in the wall of the internal carotid artery. The carotid sinus contains baroreceptors, which monitor blood pressure. Nearby is the carotid body, a small cluster of chemoreceptors that sense changes in the levels of oxygen, carbon dioxide, and pH in the blood.

Surrounding Structures

The common carotid artery is surrounded by several important anatomical structures as it ascends through the neck:

• Medially: It lies adjacent to the trachea and esophagus.
• Laterally: It is flanked by the internal jugular vein, which drains blood from the brain and face, and the vagus nerve, which supplies parasympathetic innervation to the thorax and abdomen.
• Anteriorly: The artery is covered by the sternocleidomastoid muscle and various layers of fascia, making it relatively superficial in some regions, especially in the lower neck.
• Posteriorly: The artery is bordered by the cervical vertebrae and muscles of the vertebral column.

Relations with Neighboring Nerves

As the common carotid artery travels within the carotid sheath, it is closely associated with the vagus nerve, which lies between and posterior to the artery and internal jugular vein. The artery also lies near the sympathetic trunk, which provides sympathetic innervation to the head and neck.

Termination

The common carotid artery terminates at the level of the thyroid cartilage, where it bifurcates into the internal and external carotid arteries. This bifurcation marks the end of the common carotid artery’s course and the beginning of more specialized vascular supply to the brain (via the internal carotid artery) and the face and neck (via the external carotid artery).

Differences Between Left and Right Common Carotid Artery

Due to their different points of origin, the left common carotid artery is longer and has a slightly different course than the right common carotid artery. The left artery passes through the superior mediastinum before reaching the neck, while the right common carotid artery originates more directly from the brachiocephalic trunk and ascends within the neck.

Function

Primary Source of Oxygenated Blood to the Head and Neck

The common carotid artery is the main vessel responsible for delivering oxygenated blood to the head and neck. Its bifurcation into the internal and external carotid arteries ensures that various parts of the brain, face, neck, and scalp receive an adequate blood supply. By transporting oxygen and nutrients, the common carotid artery maintains the function of vital organs and tissues, including the brain, which requires a continuous and large supply of blood to function effectively.

Blood Supply to the Brain via the Internal Carotid Artery

One of the major functions of the common carotid artery is to ensure blood supply to the brain through its internal carotid branch. Once the common carotid artery bifurcates, the internal carotid artery continues to ascend and enters the cranial cavity through the carotid canal. This artery is crucial for supplying blood to the anterior and middle parts of the brain, including areas responsible for cognition, motor function, and sensory processing. Without the common carotid artery’s contribution, the brain would lack sufficient blood flow, leading to ischemia and dysfunction.

Blood Supply to the Face, Neck, and Scalp via the External Carotid Artery

The external carotid artery, another branch from the bifurcation of the common carotid artery, is primarily responsible for vascularizing the face, neck, scalp, and upper portions of the thyroid. The external carotid artery gives rise to several important branches, such as:

• Facial Artery: Supplies the muscles and skin of the face, particularly in the cheek, lips, and nose.
• Lingual Artery: Supplies the tongue and the floor of the mouth.
• Occipital and Posterior Auricular Arteries: These branches nourish the scalp and areas behind the ear. Through these branches, the common carotid artery supports the health and function of facial muscles, glands, and skin, playing a vital role in facial expressions, speech, swallowing, and sensory perception.

Regulation of Blood Pressure via the Carotid Sinus

The carotid sinus, a slight dilation located at the bifurcation of the common carotid artery, contains specialized baroreceptors. These receptors monitor changes in blood pressure and send signals to the brain via the glossopharyngeal nerve (cranial nerve IX). When blood pressure rises, the carotid sinus receptors help mediate responses that lower blood pressure, such as slowing the heart rate and dilating blood vessels. The function of the carotid sinus is critical for maintaining stable blood pressure and protecting the brain from damage caused by hypertension or hypotension.

Regulation of Blood Gases via the Carotid Body

Located near the carotid sinus is the carotid body, a small cluster of chemoreceptors that monitor the levels of oxygen, carbon dioxide, and pH in the blood. The carotid body responds to changes in blood chemistry by sending signals to the respiratory centers of the brain to adjust the breathing rate. For example, if oxygen levels are low, the carotid body signals the brain to increase the respiratory rate, ensuring that more oxygen enters the bloodstream. The carotid body plays an essential role in maintaining proper oxygenation of the brain and other tissues.

Ensuring Adequate Collateral Circulation

Through its internal and external branches, the common carotid artery contributes to a robust network of collateral circulation in the head and neck. This system of anastomoses (connections between blood vessels) ensures that if one part of the vascular system is compromised—such as in cases of arterial blockage—blood can still be delivered to critical areas through alternative routes. For example, the external carotid artery’s branches can provide some collateral supply to parts of the face and neck if the internal carotid artery is obstructed. This redundancy is crucial for preventing ischemic damage and maintaining tissue health.

Supporting Key Head and Neck Functions

By supplying the facial muscles, glands, skin, and connective tissues, the common carotid artery indirectly supports vital functions like speech, facial expression, chewing, and swallowing. The facial artery’s branches nourish the muscles involved in these processes, ensuring they receive sufficient blood to operate efficiently. The artery also plays a role in the vascularization of the thyroid gland (via the superior thyroid artery), which is important for regulating metabolism and growth.

Nutrient Delivery and Waste Removal

Like all arteries, the common carotid artery serves a critical role in delivering oxygen, glucose, and other nutrients to the tissues of the head and neck. In turn, it also aids in the removal of carbon dioxide and metabolic waste products from these tissues by ensuring a healthy and continuous blood flow. This function is essential for maintaining cellular health and preventing tissue damage due to hypoxia (lack of oxygen).

Thermoregulation of the Face and Neck

The extensive network of blood vessels originating from the external carotid artery, including the occipital, superficial temporal, and facial arteries, helps regulate body temperature in the face and neck. Blood flow through these vessels increases in hot environments to dissipate heat and cool the body. In cold conditions, blood flow decreases to conserve heat. This thermoregulation is important for maintaining the body’s internal temperature and protecting sensitive tissues in the face and scalp from extreme temperature changes.

Clinical Significance

The common carotid artery is of great clinical importance due to its role in supplying blood to the brain, head, and neck. It is a key artery involved in various medical conditions and procedures.

Carotid Artery Disease

Atherosclerosis, or the buildup of plaque in the common carotid artery, can lead to narrowing (stenosis) and reduce blood flow to the brain, increasing the risk of strokes and transient ischemic attacks (TIAs). Carotid artery disease is commonly diagnosed through imaging techniques like Doppler ultrasound, and severe cases may require carotid endarterectomy (surgical removal of plaque) or carotid stenting to restore normal blood flow.

Carotid Pulse Examination

The common carotid artery is easily accessible and its pulse can be palpated in the neck. Clinicians often assess the carotid pulse to gauge the strength and regularity of the heartbeat and to check for vascular conditions such as atherosclerosis or blockages.

Carotid Sinus Hypersensitivity

The carotid sinus, located at the bifurcation of the common carotid artery, contains baroreceptors that regulate blood pressure. In some individuals, pressure on the carotid sinus (such as from tight collars or neck manipulation) can cause a sudden drop in blood pressure, leading to fainting (syncope). This condition, called carotid sinus hypersensitivity, is clinically relevant in older adults and requires careful management.

Emergency Access for Vascular Surgery

The common carotid artery is often used as an access point in vascular surgeries and procedures involving the head and neck, such as carotid endarterectomy or placement of arterial lines during critical care. Its superficial location makes it an important site for surgical interventions aimed at restoring or maintaining blood flow to the brain.