Neural mechanisms of heart Neural mechanisms of heart regulationregulation

Effects of nn. vagiEffects of nn. vagi

Effects of nn. vagus on Effects of nn. vagus on the heart activity. the heart activity. Parasympathetic Parasympathetic stimulation causes stimulation causes decrease in heart rate decrease in heart rate and contractility, and contractility, causing blood flow to causing blood flow to decrease. decrease.

It is known as negative It is known as negative inotropic, dromotropic, inotropic, dromotropic, bathmotropic and bathmotropic and chronotropic effect. chronotropic effect.

Sympathetic effectsSympathetic effects

Sympathetic nerves from Th1-5 Sympathetic nerves from Th1-5 control activity of the heart and control activity of the heart and large vessels. First neuron lays in large vessels. First neuron lays in lateral horns of spinal cord. lateral horns of spinal cord. Second neuron locates in Second neuron locates in sympathetic ganglions. sympathetic ganglions. Sympathetic nerve system gives Sympathetic nerve system gives to the heart vasoconstrictor and to the heart vasoconstrictor and vasodilator fibers. Vasoconstrictor vasodilator fibers. Vasoconstrictor impulses are transmitted through impulses are transmitted through alfa-adrenoreceptors, which are alfa-adrenoreceptors, which are most spread in major coronary most spread in major coronary vessels. Transmission impulses vessels. Transmission impulses through beta-adrenergic through beta-adrenergic receptors lead to dilation of small receptors lead to dilation of small coronary vessels. coronary vessels.

Sympathetic influence produces Sympathetic influence produces positive inotropic, chronotropic, positive inotropic, chronotropic, dromotropic, bathmotropic dromotropic, bathmotropic effects, which is increase of effects, which is increase of strength, rate of heartbeat and strength, rate of heartbeat and stimulating excitability and stimulating excitability and conductibility also.conductibility also.

Control of heart activity by Control of heart activity by vasomotor centervasomotor center

Lateral portion of vasomotor center transmit Lateral portion of vasomotor center transmit excitatory signals through sympathetic fibers excitatory signals through sympathetic fibers to heart to increase its rate and contractility. to heart to increase its rate and contractility.

Medial portion of vasomotor center transmit Medial portion of vasomotor center transmit inhibitory signals through parasympathetic inhibitory signals through parasympathetic vagal fibers to heart to decrease its rate and vagal fibers to heart to decrease its rate and contractility. Neurons, which give impulses contractility. Neurons, which give impulses to the heart, have constant level of activity to the heart, have constant level of activity even at rest, which is characterized as even at rest, which is characterized as nervous tone. nervous tone.

Location of receptors in the Location of receptors in the heartheart

Heart muscle contains, both Heart muscle contains, both chemical and stretch receptors chemical and stretch receptors in coronary vessels, all heart in coronary vessels, all heart cameras and pericardium. cameras and pericardium. Stretch receptors are irritated by Stretch receptors are irritated by changing blood pressure in heart changing blood pressure in heart cameras and vessels. cameras and vessels.

Chemo sensitive cells, which are Chemo sensitive cells, which are stimulated by decrease O2, stimulated by decrease O2, increase of CO2, H+ and increase of CO2, H+ and biological active substances biological active substances also, are called as also, are called as chemoreceptors. chemoreceptors.

Reflexes from atriaReflexes from atria When atria pressure increase due to increasing blood When atria pressure increase due to increasing blood

volume, atria stretched. Signals pass to afferent volume, atria stretched. Signals pass to afferent arterioles in kidneys to cause vasodilatation and arterioles in kidneys to cause vasodilatation and glomerullar capillary pressure, thereby increasing glomerullar capillary pressure, thereby increasing glomerullar filtration. Signals also pass to hypothalamus glomerullar filtration. Signals also pass to hypothalamus to decrease antidiuretic hormone secretion and so fluid to decrease antidiuretic hormone secretion and so fluid reabsorbtion. It causes decreasing both blood volume reabsorbtion. It causes decreasing both blood volume and arterial pressure to normal.and arterial pressure to normal.

Other reflex reaction is known as atria and pulmonary Other reflex reaction is known as atria and pulmonary artery reflex. When atria pressure increase due to artery reflex. When atria pressure increase due to increasing blood volume, atria stretched. Low-pressure increasing blood volume, atria stretched. Low-pressure receptors, similar to baroreceptors, in atria and receptors, similar to baroreceptors, in atria and pulmonary arteries stretched and stimulated. Signals pulmonary arteries stretched and stimulated. Signals pass to vasomotor center and inhibit vasculomotor pass to vasomotor center and inhibit vasculomotor area. Arterial pressure decreases to normal.area. Arterial pressure decreases to normal.

Reflex reactions from Reflex reactions from receptors of pericardium, receptors of pericardium,

endocardium and coronary endocardium and coronary vesselsvessels

Reflex reactions from receptors of Reflex reactions from receptors of pericardium, endocardium and coronary pericardium, endocardium and coronary vessels lead to stimulation n. vagus. It vessels lead to stimulation n. vagus. It leads to parasympathetic stimulation of leads to parasympathetic stimulation of the heart.the heart.

Parasympathetic stimulation causes Parasympathetic stimulation causes decrease in heart rate and contractility, decrease in heart rate and contractility, causing blood flow to decrease. It is known causing blood flow to decrease. It is known as negative inotropic, dromotropic, as negative inotropic, dromotropic, bathmotropic and chronotropic effect. bathmotropic and chronotropic effect.

Baroreceptor reflexesBaroreceptor reflexes Increasing arterial pressure stretched and Increasing arterial pressure stretched and

stimulated baroreceptors in carotid sinus and stimulated baroreceptors in carotid sinus and aortic arc. Signals pass through glossopharyngeal aortic arc. Signals pass through glossopharyngeal and vagal nerve to tractus solitarius in medulla. and vagal nerve to tractus solitarius in medulla. Secondary signals from tractus solitarius inhibit Secondary signals from tractus solitarius inhibit vasoconstrictor center and excite vagal center. vasoconstrictor center and excite vagal center.

Peripheral vasodilatation and decrease both heart Peripheral vasodilatation and decrease both heart rate and contractility occur. Arterial pressure rate and contractility occur. Arterial pressure decreases to normal. When arterial pressure decreases to normal. When arterial pressure decreases, whole process occurs, causing decreases, whole process occurs, causing opposite result.opposite result.

Irritation of visceroreceptorsIrritation of visceroreceptors

Irritation of visceroreceptors results in Irritation of visceroreceptors results in stimulation of vagal nuclei, which cause stimulation of vagal nuclei, which cause decreasing blood pressure and heartbeat. decreasing blood pressure and heartbeat. Parasympathetic stimulation causes Parasympathetic stimulation causes decrease in heart rate and contractility, decrease in heart rate and contractility, causing blood flow to decrease. It is known causing blood flow to decrease. It is known as negative inotropic, dromotropic, as negative inotropic, dromotropic, bathmotropic and chronotropic effect. bathmotropic and chronotropic effect.

This mechanism is important for doctor in This mechanism is important for doctor in performing diagnostic procedures, when performing diagnostic procedures, when probes from apparatuses are attached into probes from apparatuses are attached into visceral organs. This may cause excessive visceral organs. This may cause excessive irritation of visceral receptors.irritation of visceral receptors.

Mechanisms of heart auto Mechanisms of heart auto regulationregulation

Greater rate of metabolism or less blood flow Greater rate of metabolism or less blood flow causes decreasing O2 supply and other nutrients. causes decreasing O2 supply and other nutrients. Therefore rate of formation vasodilator substances Therefore rate of formation vasodilator substances (CO2, lactic acid, adenosine, histamine, K+ and H+) (CO2, lactic acid, adenosine, histamine, K+ and H+) rises. When decreasing both blood flow and oxygen rises. When decreasing both blood flow and oxygen supply smooth muscle in precapillary sphincter supply smooth muscle in precapillary sphincter dilate, and blood flow increases. dilate, and blood flow increases.

Moderate increasing temperature increases Moderate increasing temperature increases contractile strength of heart. Prolonged increase of contractile strength of heart. Prolonged increase of temperature exhausts metabolic system of heart temperature exhausts metabolic system of heart and causes cardiac weakness. Anoxia increases and causes cardiac weakness. Anoxia increases heart rate. Moderate increase CO2 stimulates heart heart rate. Moderate increase CO2 stimulates heart rate. Greater increase CO2 decreases heart rate.rate. Greater increase CO2 decreases heart rate.

Atria and pulmonary artery Atria and pulmonary artery reflexreflex

When arterial pressure increases due to When arterial pressure increases due to increasing blood volume, atria stretched. increasing blood volume, atria stretched. Low-pressure receptors, similar to Low-pressure receptors, similar to baroreceptors, in atria and pulmonary baroreceptors, in atria and pulmonary arteries stretched and stimulated. Signals arteries stretched and stimulated. Signals pass to vasomotor center and inhibit pass to vasomotor center and inhibit vasculomotor area. Arterial pressure vasculomotor area. Arterial pressure decreases to normal. decreases to normal.

Excessive stretching of lung tissue causes Excessive stretching of lung tissue causes excitation of n. vagus. It leads to excitation of n. vagus. It leads to parasympathetic stimulation of the heart. parasympathetic stimulation of the heart. Parasympathetic stimulation causes Parasympathetic stimulation causes decrease in heart rate and contractility, decrease in heart rate and contractility, causing blood flow to decrease.causing blood flow to decrease.

Basal tone of vesselsBasal tone of vessels

When arterial pressure suddenly increases local When arterial pressure suddenly increases local blood flow tends to increase. It leads to sudden blood flow tends to increase. It leads to sudden stretch of arterioles cause smooth muscles in their stretch of arterioles cause smooth muscles in their wall to contract. Than local blood flow decreases to wall to contract. Than local blood flow decreases to normal level. Vessel walls are capable to prolonged normal level. Vessel walls are capable to prolonged tonic contraction without tiredness even at rest. Such tonic contraction without tiredness even at rest. Such a condition is supported by spontaneous myogenic a condition is supported by spontaneous myogenic activity of smooth muscles and efferent impulsation activity of smooth muscles and efferent impulsation from autonomic nerve centers, which control arterial from autonomic nerve centers, which control arterial pressure. pressure.

Partialy contraction of blood vessels caused by Partialy contraction of blood vessels caused by continual slow firing of vasoconstrictor area is called continual slow firing of vasoconstrictor area is called vasculomotor tone. Due to regulatory nerve and vasculomotor tone. Due to regulatory nerve and humoral influences this basal tone changes humoral influences this basal tone changes according to functional needs of curtain organ.according to functional needs of curtain organ.

Afferent linkAfferent link

Nerve receptors, which are capable Nerve receptors, which are capable react to changing blood pressure, lays react to changing blood pressure, lays in heart cameras, aorta arc, bifurcation in heart cameras, aorta arc, bifurcation of large vessels as carotid sinus and of large vessels as carotid sinus and other parts of vascular system. other parts of vascular system.

Irritation of these mechanical Irritation of these mechanical receptors produce nerve impulses, receptors produce nerve impulses, which pass to higher nerve centers for which pass to higher nerve centers for processing sensory information from processing sensory information from visceral organs.visceral organs.

Central linkCentral link Vasoconstrictor area of vasculomotor center is Vasoconstrictor area of vasculomotor center is

located bilaterally in dorsolateral portion of reticular located bilaterally in dorsolateral portion of reticular substance in upper medulla oblongata and lower substance in upper medulla oblongata and lower pons. Its neurons secrete norepinephrine, excite pons. Its neurons secrete norepinephrine, excite vasoconstrictor nerves and increase blood pressure. vasoconstrictor nerves and increase blood pressure. It transmits also excitatory signals through It transmits also excitatory signals through sympathetic fibers to heart to increase its rate and sympathetic fibers to heart to increase its rate and contractility. contractility.

Vasodilator area is located bilaterally in Vasodilator area is located bilaterally in ventromedial of reticular substance in upper ventromedial of reticular substance in upper medulla oblongata and lower pons. Its neurons medulla oblongata and lower pons. Its neurons inhibit dorsolateral portion and decrease blood inhibit dorsolateral portion and decrease blood pressure. It transmits also inhibitory signals through pressure. It transmits also inhibitory signals through parasympathetic vagal fibers to heart to decrease parasympathetic vagal fibers to heart to decrease its rate and contractility.its rate and contractility.

Posterolateral portions of hypothalamus cause Posterolateral portions of hypothalamus cause excitation of vasomotor center. Anterior part of excitation of vasomotor center. Anterior part of hypothalamus can cause mild inhibition of one. hypothalamus can cause mild inhibition of one. Motor cortex excites vasomotor center. Anterior Motor cortex excites vasomotor center. Anterior temporal lobe, orbital areas of frontal cortex, temporal lobe, orbital areas of frontal cortex, cingulated gyrus, amygdale, septum and cingulated gyrus, amygdale, septum and hippocampus can also control vasomotor center.hippocampus can also control vasomotor center.

Central linkCentral link Vasoconstrictor area of vasculomotor center is Vasoconstrictor area of vasculomotor center is

located bilaterally in dorsolateral portion of reticular located bilaterally in dorsolateral portion of reticular substance in upper medulla oblongata and lower substance in upper medulla oblongata and lower pons. Its neurons secrete norepinephrine, excite pons. Its neurons secrete norepinephrine, excite vasoconstrictor nerves and increase blood pressure. vasoconstrictor nerves and increase blood pressure. It transmits also excitatory signals through It transmits also excitatory signals through sympathetic fibers to heart to increase its rate and sympathetic fibers to heart to increase its rate and contractility. contractility.

Vasodilator area is located bilaterally in Vasodilator area is located bilaterally in ventromedial of reticular substance in upper ventromedial of reticular substance in upper medulla oblongata and lower pons. Its neurons medulla oblongata and lower pons. Its neurons inhibit dorsolateral portion and decrease blood inhibit dorsolateral portion and decrease blood pressure. It transmits also inhibitory signals through pressure. It transmits also inhibitory signals through parasympathetic vagal fibers to heart to decrease parasympathetic vagal fibers to heart to decrease its rate and contractility.its rate and contractility.

Posterolateral portions of hypothalamus cause Posterolateral portions of hypothalamus cause excitation of vasomotor center. Anterior part of excitation of vasomotor center. Anterior part of hypothalamus can cause mild inhibition of one. hypothalamus can cause mild inhibition of one. Motor cortex excites vasomotor center. Anterior Motor cortex excites vasomotor center. Anterior temporal lobe, orbital areas of frontal cortex, temporal lobe, orbital areas of frontal cortex, cingulated gyrus, amygdale, septum and cingulated gyrus, amygdale, septum and hippocampus can also control vasomotor center.hippocampus can also control vasomotor center.

Efferent linkEfferent link

Stimulation of sympathetic vasoconstrictor Stimulation of sympathetic vasoconstrictor fibers through alfa-adrenoreceptor causes fibers through alfa-adrenoreceptor causes constriction of blood vessels. Stimulation constriction of blood vessels. Stimulation of sympathetic vasodilator fibers through of sympathetic vasodilator fibers through beta-adrenoreceptors as in skeletal beta-adrenoreceptors as in skeletal muscles causes dilation of vessels. muscles causes dilation of vessels.

Parasympathetic nervous system has Parasympathetic nervous system has minor role and gives peripheral minor role and gives peripheral innervations for vessels of tong, salivatory innervations for vessels of tong, salivatory glands and sexual organs.glands and sexual organs.

Reflexes from proprio-, Reflexes from proprio-, termo- and interoreceptorstermo- and interoreceptors

Contraction of skeletal muscle during Contraction of skeletal muscle during exercise compress blood vessels, exercise compress blood vessels, translocate blood from peripheral vessels translocate blood from peripheral vessels into heart, increase cardiac output and into heart, increase cardiac output and increase arterial pressure. increase arterial pressure.

Stimulation of termoreceptors cause Stimulation of termoreceptors cause spreading impulses from somatic sensory spreading impulses from somatic sensory neurons to autonomic nerve centers and neurons to autonomic nerve centers and so leads to changing tissue blood supply. so leads to changing tissue blood supply. Irritation of visceroreceptors results in Irritation of visceroreceptors results in stimulation of vagal nuclei, which cause stimulation of vagal nuclei, which cause decreasing blood pressure and heartbeat.decreasing blood pressure and heartbeat.

Regulation of Regulation of blood flow in blood flow in

physical physical exercisesexercises

In physical exercises impulses In physical exercises impulses from pyramidal neurons of from pyramidal neurons of motor zone in cerebral cortex motor zone in cerebral cortex passes both to skeletal muscles passes both to skeletal muscles and vasomotor center. Than and vasomotor center. Than through sympathetic influences through sympathetic influences heart activity and heart activity and vasoconstriction are promoted. vasoconstriction are promoted. Adrenal glands also produce Adrenal glands also produce adrenalin and release it to the adrenalin and release it to the blood flow. blood flow.

Proprioreceptor activation Proprioreceptor activation spread impulses through spread impulses through interneurons to sympathetic interneurons to sympathetic nerve centers. So, contraction nerve centers. So, contraction of skeletal muscle during of skeletal muscle during exercise compress blood exercise compress blood vessels, translocate blood from vessels, translocate blood from peripheral vessels into heart, peripheral vessels into heart, increase cardiac output and increase cardiac output and increase arterial pressure.increase arterial pressure.

Cardiovascular Adjustments Cardiovascular Adjustments to Exerciseto Exercise

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