What Is the Carotid Sinus?

The carotid sinus is located at the beginning of the internal carotid artery. Here the blood vessel wall is slightly thin and the lumen is slightly enlarged, so it is called carotid sinus. With the exception of ruminants, almost all mammals have carotid sinuses. Its functional anatomy is characterized by a well-developed sinus wall and adventitia, containing a large amount of collagen fibers, sparse smooth muscles, and more elastic fibers. Deep in the adventitia of the sinus wall is a baroreceptive nerve terminal device, which is a carotid sinus baroreceptor; on the ventral side of the sinus cavity, there is a chemoreceptor nerve terminal device, which is a carotid chemoreceptor.

The carotid sinus is located at the beginning of the internal carotid artery. Here the blood vessel wall is slightly thin and the lumen is slightly enlarged, so it is called carotid sinus. With the exception of ruminants, almost all mammals have carotid sinuses. Its functional anatomy is characterized by a well-developed sinus wall and adventitia, containing a large amount of collagen fibers, sparse smooth muscles, and more elastic fibers. Deep in the adventitia of the sinus wall is a baroreceptive nerve terminal device, which is a carotid sinus baroreceptor; on the ventral side of the sinus cavity, there is a chemoreceptor nerve terminal device, which is a carotid chemoreceptor.

Chinese name

Carotid sinus

Foreign name

internal carotid sinus

lie in

At the upper edge of flat thyroid cartilage

Aka

Baroreceptor

Carotid Sinus Histology and Embryology:

Carotid sinus is an enlarged part of the common carotid artery branch and the internal end of the internal carotid artery. It is found in all mammals except ruminants. Physiological research confirms that this part is the main baroreceptor, which is sensitive to changes in blood pressure. Its sensory nerve comes from the carotid sinus nerve branched from the glossopharyngeal nerve. In addition, the aortic arch and common carotid artery also have baroreceptors, and the aortic arch also plays an important role.

Light microscopy studies have shown that the medial wall of the carotid sinus vessel wall is thin, with more elastic membranes and fewer smooth muscles. The outer membrane is also thin. When myelinated nerve fibers enter the junction of the adventitia and the media, the myelin sheath is lost, forming a rich branch. These branches form nerve endings of varying sizes and are distributed in the inner adventitia. These nerve endings may feel the stimulation of blood vessel wall expansion when the blood pressure rises, and the afferent brain reflexes the visceral blood vessels to dilate, slowing the heart rate and lowering blood pressure. [1]

Electron microscopy studies show that the nerve fiber branches significantly expand in the adventitia, forming two types of nerve endings of different sizes: small ends: 600-2000 nm in diameter, containing many mitochondria, located at the junction of the adventitia and adventitia and media, which are located at Between elastic fibers and smooth muscles; large tip: 5,000-8000 nm in size, also containing more mitochondria, mainly distributed in the adventitia. In addition, mitochondrial-enlarged portions may be formed in the middle or end of the axon, and may have sensory functions. The nerve endings are surrounded by special cells that are branched, probably belonging to nerve membrane cells. Some scholars believe that cells and the surrounding nerve endings together form a functional unit. But the relationship between these ultrastructures and functions is unknown.

Carotid Sinus Anatomy:

1. Carotid sinus:

The structure and function of the carotid sinus is completely different from that of the carotid body. The carotid sinus is at the base of the internal carotid artery or at the common carotid bifurcation, where the arterial wall becomes thinner, with less muscle in the wall and increased elastic tissue. Its internal nerves come from the sensory nerve endings of the glossopharyngeal nerve. In order to transmit the impulse of blood pressure to the vasomotor center of the medullary medulla, blood pressure and heart rhythm are adjusted. Stimulating nerve endings in the carotid sinus can lead to slower heartbeat and lower blood pressure.

Baroreceptors throughout the body are not limited to the carotid sinus. The right subclavian artery and the aortic arch also have similar functions. Therefore, removing one or both carotid sinus sensory nerves has no effect on blood pressure.

What is significant is that it is particularly sensitive to stress, even a small amount of stress can cause slow heartbeat, lower blood pressure, and even loss of consciousness. For cervical lymphadenectomy, when the carotid sinus is treated, the anesthesiologist may notice a sudden and significant drop in blood pressure, accompanied by a slowed pulse. If the anesthesiologist discovers this situation, 1 to 2 ml of 1% lidocaine can be injected into the adventitia at the bifurcation of the common carotid artery, which can immediately relieve this phenomenon.

Most or all of the nerves that innervate the carotid body and carotid sinus come from the glossopharyngeal nerve, which declines through the connective tissue between the internal and external carotid arteries or along the internal jugular vein. This nerve is connected to the superior cervical ganglia of the vagus nerve. When dealing with carotid bifurcation, lidocaine should be injected between the internal carotid artery and the external carotid artery, or in the adventitia of the internal carotid artery, in order to avoid stimulating the carotid sinus and slowing heartbeat and blood pressure.

2. Internal carotid artery:

The internal carotid artery is one of the terminal branches of the common carotid artery and is mainly distributed in the brain and optics. In the carotid triangle, from the common carotid artery above the plane of the upper edge of the thyroid cartilage. He first resided in the posterolateral side of the external carotid artery, then turned upward through the posterior deep side of the biceps to the posteromedial side, along the side of the pharynx to the base of the skull, and penetrated the carotid artery into the skull. The internal carotid artery is divided into two parts: intracranial and extracranial. The external part of the skull is the neck, accompanied by the internal jugular vein and vagus nerve, and the posterior part of the three is the cervical sympathetic trunk. The internal carotid artery is separated from the external carotid artery by the styloid muscle and styloid muscle. The internal carotid artery is not branched. A few have also been reported ascending the pharyngeal artery (4%) and the occipital artery (1%).

3. External carotid artery:

The external carotid artery is one of the terminal branches of the common carotid artery. The upper edge of the flat thyroid cartilage originates from the common carotid artery. It is divided into the maxillary artery and the superficial temporal artery at the anterior medial side of the internal carotid artery, then turns to the anterolateral side and rises to the lower jaw joint. The external carotid artery is superficial in the carotid triangle, where external carotid surgery can be performed. In addition to the two terminal branches, the external carotid artery is sent forward along the way with three branches of the superior thyroid artery, lingual artery, and facial artery; three branches of the sternocleidomastoid muscle artery, occipital artery, and posterior auricular artery are issued backward; Issue the ascending pharyngeal artery. They are distributed in head and neck organs other than the brain and eyes.