Nervous Regulation of Cardiovascular Activities Qiang XIA (夏强), PhD Department of Physiology...

Nervous Regulation of Cardiovascular

Activities

Qiang XIA (夏强 ), PhDDepartment of Physiology

Room C518, Block C, Research Building, School of MedicineTel: 88208252

Email: xiaqiang@zju.edu.cn

Innervation of the heart

• Cardiac sympathetic nerve• Cardiac vagus nerve

1. 起源 origin

2. 节前纤维 preganglionic fiber

3. 外周神经节 ganglion

4. 节后纤维 postganglionic fiber

5. 支配 distribution

6. 递质 neurotransmitter

Cardiac sympathetic actions

• Positive chronotropic effect正性变时作用• Positive dromotropic effect正性变传导作用• Positive inotropic effect正性变力作用

Cardiac mechanisms of norepinephrine

Mechanisms of norepinephrine

—increase Na+ & Ca2+ permeability

• If , phase 4 spontaneous depolarization,

autorhythmicity

• Ca2+ influx , phase 0 amplitude & velocity ,

conductivity

• Ca2+ influx , Ca2+ release , [Ca2+ ]i , contractility

（ CICR ）

Asymmetrical innervation of sympathetic nerve

Cardiac parasympathetic actions

• Negative chronotropic effect负性变时作用• Negative dromotropic effect负性变传导作用• Negative inotropic effect负性变力作用

Cardiac mechanisms of acetylcholine

Mechanisms of acetylcholine

—increase K+ & decrease Ca2+ permeability

• K+ outward , |MRP| , phase 4 spontaneous

depolarization , autorhythmicity

• Inhibition of Ca2+ channel, phase 0 amplitude &

velocity , conductivity

• Ca2+ influx , [Ca2+ ]i , contractility

Cardiac effect of parasympathetic stimulation

Vagal Maneuvers

• Valsalva maneuver

– A maneuver in which a person tries to exhale forcibly with a closed glottis (the windpipe) so that no air exits through the mouth or nose as, for example, in strenuous coughing, straining during a bowel movement, or lifting a heavy weight. The Valsalva maneuver impedes the return of venous blood to the heart.

– Named for Antonio Maria Valsalva, a renowned Italian anatomist, pathologist, physician, and surgeon (1666-1723) who first described the maneuver.

Physiological response in Valsalva maneuver

• The normal physiological response consists of 4 phases

Physiological response in Valsalva maneuver

• The normal physiological response consists of 4 phases– Initial pressure rise: On application of expiratory force, pressure rises inside the chest forcing

blood out of the pulmonary circulation into the left atrium. This causes a mild rise in stroke volume.

– Reduced venous return and compensation: Return of systemic blood to the heart is impeded by the pressure inside the chest. The output of the heart is reduced and stroke volume falls. This occurs from 5 to about 14 seconds in the illustration. The fall in stroke volume reflexively causes blood vessels to constrict with some rise in pressure (15 to 20 seconds). This compensation can be quite marked with pressure returning to near or even above normal, but the cardiac output and blood flow to the body remains low. During this time the pulse rate increases.

– Pressure release: The pressure on the chest is released, allowing the pulmonary vessels and the aorta to re-expand causing a further initial slight fall in stroke volume (20 to 23 seconds) due to decreased left ventricular return and increased aortic volume, respectively. Venous blood can once more enter the chest and the heart, cardiac output begins to increase.

– Return of cardiac output: Blood return to the heart is enhanced by the effect of entry of blood which had been dammed back, causing a rapid increase in cardiac output (24 seconds on). The stroke volume usually rises above normal before returning to a normal level. With return of blood pressure, the pulse rate returns towards normal.

Interaction of sympathetic and parasympathetic nerves

Predominance of autonomic nerves

Tonus紧张• Cardiac vagal tone心迷走紧张• Cardiac sympathetic tone心交感紧张

Innervation of the blood vessels

• Vasoconstrictor nerve缩血管神经– Sympathetic vasoconstrictor nerve交感缩血管神经

• Vasodilator nerve舒血管神经– Sympathetic vasodilator nerve交感舒血管神经– Parasympathetic vasodilator nerve副交感舒血管神经

– Dorsal root vasodilator nerve脊髓背根舒血管神经

Cardiovascular Center

A collection of functionally similar neurons that

help to regulate HR, SV, and blood vessel tone

Vasomotor center

Located bilaterally mainly in the reticular substance of the medulla and of the lower third of the pons

– Vasoconstrictor area– Vasodilator area– Cardioinhibitor area – dorsal nuclei of the

vagus nerves and ambiguous nucleus

– Sensory area – tractus solitarius

Vasomotor center

– Reticular substance

of the pons

– Mesencephalon

– Diencephalon

– Hypothalamus

– Cerebral cortex

– Cerebellum

Higher cardiovascular centers

Baroreceptor Reflexes

• Arterial baroreceptors– Carotid sinus receptor– Aortic arch receptor

• Afferent nerves (Buffer nerves)

• Cardiovascular center: medulla• Efferent nerves: cardiac sympathetic nerve,

sympathetic constrictor nerve, vagus nerve• Effector: heart & blood vessels

Baroreceptor neurons function as sensors in the homeostatic maintenance of MAP by constantly monitoring pressure in the aortic arch and carotid sinuses.

Characteristics of baroreceptors:

Sensitive to stretching of the vessel walls

Proportional firing rate to increased

stretching

Responding to pressures ranging from 60-

180 mmHg

Receptors within the aortic arch are less

sensitive than the carotid sinus receptors

The action potential frequency in baroreceptor neurons is represented here as being directly proportional to MAP.

Baroreceptor neurons deliver MAP information to the medulla oblongata’s cardiovascular control center (CVCC);the CVCC determines autonomic output to the heart.

i.e., MAP is above

homeostatic set point

i.e., reduce cardiac output

Reflex pathway

Click here to play theBaroreceptor Reflex Control

of Blood PressureFlash Animation

Typical carotid sinus reflex

Maintaining relatively

constant arterial

pressure, reducing the

variation in arterial

pressure

Physiological Significance

Other Cardiovascular Reflexes

Click here to play theChemoreceptor Reflex Control

of Blood PressureFlash Animation

Cardiovascular Responses to Exercise

When exercise begins, mechanosensory input from working limbs combines with descending pathways from the motor cortex to activate the cardiovascular control center in the medulla oblongata.

The center responds with sympathetic discharge that increases cardiac output and causes vasoconstriction in many peripheral arterioles.

Cardiac output increases during exercise

Peripheral blood flow redistributes to muscle during exercise

Blood pressure rises slightly

during exercise

VO2 max (also maximal oxygen consumption, maximal oxygen uptake or aerobic capacity) is the maximum capacity of an individual's body to transport and utilize oxygen during incremental exercise, which reflects the physical fitness of the individual.

Baroreceptor reflex adjusts to exercise

• During exercise, blood pressure increases without activating homeostatic compensation of baroreceptor reflex

• Why?– Signal from the motor cortex during exercise

reset the arterial baroreceptor threshold to a higher pressure

The End.