Carotid sinus

Anatomy and Topography

The carotid sinus is located in the neck, in the area of the carotid bifurcation (bifurcatio carotidis), where the common carotid artery divides into the internal (a. carotis interna) and external (a. carotis externa) carotid arteries. Above this dilation, the internal carotid artery enters the carotid canal (canalis caroticus) of the temporal bone.

• Skeletotopy: the bifurcation and sinus project at the level of the upper border of the thyroid cartilage (cartilago thyroidea), which corresponds to the C4 cervical vertebra.
• Carotid neurovascular bundle (vagina carotica): the trachea and esophagus are located medially, the internal jugular vein (v. jugularis interna) laterally, and the vagus nerve runs between them posteriorly.
• Adjacent structures: on the posterior or medial surface of the bifurcation, near the sinus, lies the carotid body (glomus caroticum) — a small body connected to the arterial wall by connective tissue.

What receptors does it contain?

The following types of receptors are present in the carotid sinus area:

• Baroreceptors — sensitive to pressure changes.
• Osmoreceptors — respond to changes in plasma osmolarity.
• Volume receptors — respond to changes in circulating fluid volume and vascular stretch.

Function and regulation mechanism

Normally, blood pressure fluctuations are regulated through changes in depressor impulses:

1. When blood pressure increases, impulses from baroreceptors increase.
2. Depressor impulses travel to the vasomotor center of the medulla oblongata.
3. The balance between the excitatory influences of the brain and inhibitory afferentation from baroreceptors maintains blood pressure at a normal level. When blood pressure decreases, impulses decrease.

Innervation

The carotid sinus has a robust periadventitial nerve plexus. Its innervation involves:

• Hering's depressor nerve, or the sinus branch, whose fibers enter the brain as part of the glossopharyngeal nerve (n. glossopharyngeus, cranial nerve IX).
• Branches of the vagus nerve (n. vagus, cranial nerve X).
• Fibers of the sympathetic trunk.

Clinical significance

• Reflex reactions: irritation of the carotid sinus leads to reflex bradycardia.
• Pathology of blood pressure regulation: if stress persists, the load on the baroreceptors of the sinocarotid zone increases, central regulation is disrupted, and the sympathoadrenal system is activated, causing an additional rise in blood pressure due to increased levels of catecholamines in the blood.
• Surgery and imaging: the bifurcation of the common carotid artery at the C4 level serves as a landmark for punctures and surgeries on the carotid arteries. Anatomical landmarks of the common, external, and internal carotid arteries and the carotid sinus are visualized using contrast-enhanced MR angiography.

Class and exam questions

What else to study on this topic

• Common carotid artery (a. carotis communis)
• Internal carotid artery (a. carotis interna)
• Carotid body (glomus caroticum)
• Glossopharyngeal nerve (n. glossopharyngeus)
• Vagus nerve (n. vagus)

Other topics in the "Anatomical Structures" section

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