Carotid sinus aortic arch baroreflex

The neck mainly plays the role of connecting the human head and torso, but the bones of the neck are very fragile and cannot play this supporting role very well. Therefore, the muscles of the neck are also abnormally developed to help the bones provide support. However, the skin on the neck is extremely fragile. If it is stimulated by external force or infected by bacteria, it can easily cause abnormal symptoms in the carotid artery. So what happens when a patient has a carotid sinus-aortic arch baroreflex?

When arterial blood pressure rises, it can cause a pressure-sensitive reflex, the reflex effect of which is to slow down the heart rate, reduce peripheral vascular resistance, and drop blood pressure.

1. Arterial baroreceptors The sensing device of the pressure-sensitive reflex is the sensory nerve endings located under the adventitia of the carotid sinus and aortic arch blood vessels, called arterial baroreceptors. Arterial baroreceptors do not directly sense changes in blood pressure, but rather the degree of mechanical stretch of the blood vessel wall. When arterial blood pressure rises, the arterial wall is stretched to a greater extent, and the nerve impulses released by the pressure receptors increase. Within a certain range, the frequency of incoming impulses to the baroreceptors is proportional to the degree of dilation of the arterial wall.

2. Afferent nerves and central connections The afferent nerve fibers of the carotid sinus pressure receptors constitute the carotid nerve. The sinus nerve joins the glossopharyngeal nerve, enters the medulla oblongata, and forms synaptic connections with neurons in the nucleus tractus solitarius. Afferent nerve fibers from the aortic arch baroreceptors travel along the vagus nerve trunk, then enter the medulla oblongata and reach the nucleus tractus solitarius. The aortic pressure receptor afferent fibers of the rabbit's aortic arch form a bundle and run along with the vagus nerve, which is called the aortic nerve.

3. Reflex effect When arterial blood pressure rises, the number of impulses afferent to the pressure receptors increases, which, through the central mechanism, increases cardiac vagal tension and decreases cardiac sympathetic tension and sympathetic vasoconstrictor tension. The effect is a slowing of the heart rate, a reduction in cardiac output, and a decrease in peripheral resistance, so the arterial blood pressure drops. On the contrary, when arterial blood pressure decreases, the impulses transmitted to the pressure receptors decrease, which weakens the vagal tone and strengthens the sympathetic tone, thereby increasing the heart rate, cardiac output, peripheral resistance, and blood pressure.

4. Reflex process : arterial blood pressure ↑ → carotid sinus pressure receptors → sinus nerve → glossopharyngeal nerve → medullary solitary nucleus → cardiac vagus nerve strengthening, cardiac sympathetic nerve weakening, sympathetic vasoconstriction weakening → heart rate ↓, cardiac output ↓, peripheral vascular resistance ↓, arterial blood pressure ↓

Arterial blood pressure↑→aortic arch baroreceptors→vagus nerve→medullar nucleus solitarius→cardiac vagus nerve strengthening, cardiac sympathetic nerve weakening, sympathetic vasoconstriction weakening→heart rate↓, cardiac output↓, peripheral vascular resistance↓, arterial blood pressure↓

5. The physiological significance of the baroreceptor reflex The baroreceptor reflex is a negative feedback regulation, and its physiological significance lies in maintaining the relative constancy of arterial blood pressure.

This reflex plays an important role in the rapid regulation of arterial blood pressure when there are sudden changes in cardiac output, peripheral resistance, blood volume, etc., so that arterial blood pressure does not fluctuate excessively. Therefore, in physiology, the afferent nerves of arterial pressure receptors are called buffer nerves. The baroreflex does not play an important role in the long-term regulation of arterial blood pressure. In patients with chronic hypertension or animals with experimental hypertension, the operating range of the baroreceptor reflex changes, that is, it works at a blood pressure level higher than normal, so the arterial blood pressure is maintained at a relatively high level.