Cardiac sympathetic nerve stimulation enhances cardiac activity

The left cardiac sympathetic nerve mainly controls the atrioventricular junction and ventricular myocardium, and mainly causes myocardial contractility to increase during excitement; The right cardiac sympathetic nerve mainly innervates the sinoatrial node, which mainly causes the heart rate to increase during excitement.

Positive inotropy: increased myocardial contractility Positive chronotropic effect: increased heart rate Positive conduction effect: increased conduction velocity

Blocker: β1 receptor blocker metoprolol

Cardiac vagus nerve excitation inhibits cardiac activity

Blocker: M receptor antagonist apinitor

Negative inotropy: reduced myocardial contractility Negative chronotropic effect: slowing of heart rate Negative transconduction effect: conduction velocity slows down

The automatic rhythm of the sinoatrial node when any innervation is removed is about 100 beats/min, but the resting heart rate of a normal person is about 70 beats/min. This is because the latter is dominant between cardiac sympathetic tone and cardiovagal tone at rest. .

Vasoconstrictor nerves are all sympathetic nerve fibers, so they are called sympathetic vasoconstrictor nerve fibers.

The transmitter released by its postganglionic fiber terminals is norepinephrine. There are two types of adrenergic receptors on vascular smooth muscle, α and β2

Norepinephrine binds to α-receptors to cause vascular smooth muscle contraction, and binds to β2-receptors to cause vascular smooth muscle relaxation. Norepinephrine binds to α-receptors more strongly than β2-receptors. Therefore, the main effect of sympathetic vasoconstrictor nerve fibers when excited is to constrict blood vessels.

Transfer from slow to urgent: Sympathetic vasoconstrictor nerves are most densely distributed in skin blood vessels, followed by skeletal muscles and internal organs, and the smallest ones are coronary blood vessels and cerebral blood vessels. The blood supply to the heart and brain is guaranteed to a certain extent.

1) Sympathetic vasodilatory nerve fibers

2) Parasympathetic vasodilatory nerve fibers

Involved in regulating organ blood volume

3) Vasodilator fibers in the posterior root of the spinal cord: This reaction that is completed only through the peripheral part of the axon is called an axonal reflex, but it does not conform to the concept of an axon.

The intersection point in the curve where the mean arterial pressure and the intra-sinus pressure are equal is the closed-loop operating point of the reflex. Normal people are about 100mmHg at rest, which means that the intra-sinus pressure and the mean arterial pressure have reached equilibrium at this level through this reflection. This point is Set point of the bucking reflex.

In patients with chronic hypertension or experimental hypertensive animals, the baroreceptor reflex function curve can be shifted to the upper right, causing the set point to rise. This small amount becomes the resetting of the baroreflex reflex, indicating that the blood pressure level is higher than normal. Keep blood pressure relatively stable

The baroreceptor reflex is a typical negative feedback regulation. Its physiological significance is mainly to quickly adjust arterial blood pressure in a short period of time, maintain the relative stability of arterial blood pressure, and prevent excessive fluctuations in arterial blood pressure.