Heart Rate Regulation: Nervous System Control

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Questions and Answers

What two centers in the medulla oblongata regulate heart rate?

VCC (connected with the sympathetic nervous system) and CIC (connected with the vagus nerve, i.e., parasympathetic nervous system)

List three categories of afferent impulses that the VCC and CIC receive.

From higher brain centers/supraspinal centers, from the circulatory system, from outside the circulatory system.

How does the cerebral cortex influence heart rate and provide two examples?

The cerebral cortex influences heart rate through voluntary control, emotions, and conditioned reflexes. Examples: yoga, startling reflex, or seeing an examiner.

Explain how the hypothalamus affects heart rate during emotional responses.

<p>The hypothalamus, along with the limbic system and cerebral cortex, impacts heart rate through emotional responses. It stimulates either the sympathetic or parasympathetic system based on the type of emotion.</p> Signup and view all the answers

Describe how lung inflation affects the Bainbridge reflex and overall heart rate during inspiration.

<p>During inspiration of the lung, intrathoracic pressure decreases, which subsequently increases venous return and right atrial pressure leading to an increased heart rate.</p> Signup and view all the answers

Explain the Bainbridge reflex and its significance.

<p>Increased blood volume leads to increased venous return, stimulation of stretch receptors in the right atrium, stimulation of VCC, and inhibition of CIC, resulting in increased heart rate which prevents the stagnation of blood in the veins.</p> Signup and view all the answers

Describe the Mc Dowel's reflex and its significance.

<p>A decrease in venous return or right atrial pressure leads to increased heart rate and vasoconstriction of arterioles to help raise arterial blood pressure (ABP) and maintain circulation to vital organs.</p> Signup and view all the answers

Describe Mary's reflex (Mary's law).

<p>Heart rate is inversely proportional to arterial blood pressure. If arterial blood pressure increases, heart rate decreases, and vice versa.</p> Signup and view all the answers

How does a decrease in arterial blood pressure affect the baroreceptors and subsequent heart rate?

<p>A decrease in arterial blood pressure reduces inhibitory impulses from the baroreceptors, leading to increased heart rate and vasoconstriction.</p> Signup and view all the answers

What is the Carotid Sinus Syndrome and treatment?

<p>Abnormal hypersensitivity of to the carotid sinus to mild pressure from outside. It is treated by avoiding pressure on the carotid sinus area, giving anticholinergic drugs e.g. atropine or denervation of carotid sinus.</p> Signup and view all the answers

Describe the Coronary chemoreflex (Bezold-Jarisch reflex).

<p>Injection of serotonin and veratridine into coronary arteries supplying the left ventricle leads to stimulation of ventricular chemoreceptors, resulting in changes in heart rate and blood pressure that lead to hypotension and bradycardia.</p> Signup and view all the answers

How does distension of the left ventricle lead to the Ventricular (coronary) stretch reflex?

<p>Distension of the left ventricle stimulates baroreceptors near coronary vessels, which then discharge impulses in afferent vagal fibers. This leads to stimulation of CIC and VDC causing bradycardia and hypotension.</p> Signup and view all the answers

Describe the Pulmonary stretch reflex.

<p>Lung inflation during inspiration causes a rise in heart rate. Stimulation of stretch receptors in bronchial walls and alveoli stimulates VCC which increases heart rate.</p> Signup and view all the answers

Explain what happens in the Pulmonary chemoreflex.

<p>Pulmonary congestion or embolization/injection of serotonin leads to stimulation of pulmonary chemoreceptors, discharge of impulses in afferent vagal fibers and then stimulation of CIC &amp; VDC. It may result in hypotension, bradycardia and apnea followed by rapid breathing.</p> Signup and view all the answers

Describe the muscle-related reflex (Alam Smirk reflex) and its impact on heart rate.

<p>Contraction of voluntary muscles stimulates proprioceptors which causes an increase in heart rate</p> Signup and view all the answers

How does the Oculo-cardiac reflex help in medical procedures?

<p>Pressure over the eyeball causes stimulation of optic nerve and then CIC which causes an increased vagal discharge to the heart, resulting in a reflex decrease in heart rate. This maneuver can be used to terminate attacks of paroxysmal atrial tachycardia.</p> Signup and view all the answers

Describe the physical regulation of heart rate in the body.

<p>Increase in body temperature (during exercise or fever) leads to an increase in heart rate due to direct stimulation of the SAN as well as VCC.</p> Signup and view all the answers

How does hypothermia impact the physical regulation of HR?

<p>HR decreases by 10 beats / min for each 1°C in body temperature due to an effect opposite that of fever.</p> Signup and view all the answers

How does mild to moderate hypoxia affect heart rate and through what mechanism?

<p>Mild to moderate hypoxia leads to an increase in heart rate due to stimulation of VCC reflexly, direct stimulation of SA node, and, direct inhibition of CIC.</p> Signup and view all the answers

Explain the effect of severe hypoxia on heart rate.

<p>Severe hypoxia decreases heart rate and then leads to cardiac arrest due to paralysis of the cardiovascular centers and inhibition of SA node activity.</p> Signup and view all the answers

How does a moderate increase in carbon dioxide (CO2) and H+ affect heart rate?

<p>Initially, you have an initial decrease in heart rate due to weak inhibition of SA node. After the initial decrease of heart rate an increased heart rate occurs due to inhibition of CIC and stimulation of VCC.</p> Signup and view all the answers

Explain how severe hypercapnia or acidemia affects heart rate.

<p>Severe hypercapnia or acidemia decreases heart rate.</p> Signup and view all the answers

How do small and large doses of adrenaline affect heart rate, and what laws govern these effects?

<p>Small doses of adrenaline increase heart rate due to direct stimulation of the SAN. Large doses also increase ABP and decrease HR governed by Mary's Law.</p> Signup and view all the answers

What is the effect of noradrenaline on heart rate and what law governs it?

<p>Noradrenaline affects heart rate by causing vasoconstriction (V.C) leading to a increase in ABP and then a decrease in HR governed by Mary's law.</p> Signup and view all the answers

Describe the general mechanisms by which thyroxine influences heart rate.

<p>Heart rate increases due to direct stimulation of the SAN. It also leads to increased sensitivity of the SAN to the circulating adrenaline as well as general metabolism of the body and body temperature.</p> Signup and view all the answers

Name two types of chemicals that increase heart rate and give an example of each.

<p>Sympathomimetic drugs (e.g., ephedrine and amphetamine) and Parasympatholytic drugs (e.g., atropine).</p> Signup and view all the answers

What are three specific chemicals and mechanisms which decrease heart rate?

<p>Parasympathomimetic drugs (e.g. acetylcholine and pilocarpine), Bile salts (direct inhibition of SAN and stimulation of CIC) and Morphine (stimulates CIC).</p> Signup and view all the answers

Based on the scenario, what are the expected changes in the employee's body at the time of the incident?

<p>I would anticipate an increase in heart rate, increase in blood pressure, increase in respiratory rate, diversion of blood to skeletal muscles. Pupils would likely dilate.</p> Signup and view all the answers

Based on the scenario, what is the most likely reading/change in heart rate observed for the employee?

<p>Heart rate is expected to increase.</p> Signup and view all the answers

Explain how the Bainbridge reflex is initiated and what its overall effect is on the heart.

<p>It starts with increased blood volume → increased venous return → stimulation of stretch receptors in the right atrium. This then stimulates the VCC and inhibits the CIC, ultimately increasing the heart rate.</p> Signup and view all the answers

Explain how the Bainbridge reflex promotes circulation.

<p>The increased HR pumps the excess VR to the arterial side and prevents stagnation of blood in veins.</p> Signup and view all the answers

What are the consequences of an increased heart rate when venous return (VR) is decreased?

<p>A decrease in venous return or right atrial pressure, such as in hemorrhage, leads to increased HR and vasoconstriction. This increases arterial blood pressure (ABP).</p> Signup and view all the answers

Explain how the reflexes that are stimulated maintain circulation to the vital organs during a sudden hemorrhage?

<p>Increased HR and VC help to raise ABP and maintain circulation to the vital organs.</p> Signup and view all the answers

Define Mary's reflex, also known as

<p>Mary's Law. It states that the heart rate is inversely proportional to the arterial blood pressure provided other factors affecting HR remain constant.</p> Signup and view all the answers

Briefly outline the steps involved in the vascular response to elevated blood pressure (BP) as mediated by baroreceptors in Mary's reflex.

<p>Elevated BP triggers baroreceptors, sending afferent impulses via the sinus and aortic nerves to stimulate the CIC and inhibit the VCC. This leads to vasodilation and a drop in BP.</p> Signup and view all the answers

How does lung inflation during ventilation influence the central nervous system and heart rate?

<p>Lung inflation stimulates stretch receptors, sending signals via the vagus nerve to stimulate the VCC which increases cardiac output (HR).</p> Signup and view all the answers

If a patient is experiencing a low heart rate due to activation of the oculocardiac reflex, what area is being stimulated and what nerve is being affected?

<p>Pressure over the eye stimulates the optic nerve and thus the the CIC.</p> Signup and view all the answers

How can the oculocardiac reflex mechanism improve treatment outcomes in various medical situations?

<p>The oculocardiac reflex's ability to induce bradycardia can be utilized during particular procedures or arrhythmias to reduce heart rate and improve stability.</p> Signup and view all the answers

Explain direct and indirect mechanism of hypoxia on heart rate regulation.

<p>Hypoxia leads to stimulation of VCC reflexly to increase cardiac output. It also leads to direct stimulation of SA node to increase HR pacemaker cells. Severe hypoxia on the other hand leads to inhibition of cardiovascular centers.</p> Signup and view all the answers

Discuss the factors of hormone regulation on heart rate regulation.

<p>A small dose of adrenaline increases the heart rate by stimulating SA nodes, whereas noradrenaline acts by increasing vasoconstriction, thyroxin helps in increase sensitivity of SA nodes to blood hormones.</p> Signup and view all the answers

What are the two centers in the medulla oblongata that regulate heart rate, and which nervous system is each connected to?

<p>The two centers are the VCC (connected to the sympathetic nervous system) and the CIC (connected to the parasympathetic nervous system via the vagus nerve).</p> Signup and view all the answers

Describe how the Bainbridge reflex influences heart rate. Include which receptors are stimulated and the subsequent effect on the SA node.

<p>The Bainbridge reflex increases heart rate in response to increased venous return. Stretch receptors in the right atrium are stimulated, leading to increased activity of the SA node.</p> Signup and view all the answers

Explain how the body's response to mild or moderate hypoxia affects heart rate and the mechanisms involved. Then describe the effects of severe hypoxia on heart rate.

<p>Mild to moderate hypoxia increases heart rate through stimulation of VCC by peripheral chemoreceptors and direct stimulation of the SA node. Severe hypoxia, however, decreases heart rate and can lead to cardiac arrest due to paralysis of cardiovascular centers.</p> Signup and view all the answers

How does the oculo-cardiac reflex work, and under what conditions might it be intentionally used in a clinical setting?

<p>Pressure on the eyeball stimulates the optic nerve, leading to increased vagal discharge and activation of the CIC, resulting in a decreased heart rate. This maneuver can be used to terminate paroxysmal atrial tachycardia.</p> Signup and view all the answers

Explain how changes in body temperature regulate heart rate, specifying the rate of change per degree Celsius and the mechanisms involved.

<p>An increase in body temperature increases heart rate by 10 beats/min per 1°C due to direct stimulation of the SAN and stimulation of VCC by the heat regulating center in the hypothalamus. Conversely, a decrease in body temperature decreases heart rate.</p> Signup and view all the answers

With reference to blood hormone regulation of heart rate, compare and contrast the effects of small and large doses of adrenaline on heart rate and blood pressure.

<p>A small dose of adrenaline increases heart rate through direct stimulation of the SAN. A large dose of adrenaline increases blood pressure (ABP) and may increase heart rate.</p> Signup and view all the answers

Explain Mary's Law and describe the mechanism by which changes in arterial blood pressure affect heart rate according to this law.

<p>Mary's Law states that heart rate is inversely proportional to arterial blood pressure. A decrease in blood pressure reduces inhibitory impulses from the baroreceptors, leading to increased heart rate and vasoconstriction.</p> Signup and view all the answers

Describe the coronary chemoreflex and how injecting serotonin or veratridine into the coronary arteries impacts ventricular function.

<p>Injection of serotonin or veratridine stimulates ventricular chemoreceptors, leading to impulses that travel via afferent vagal fibers, stimulating CIC &amp; VDC. This results in hypotension, bradycardia, and apnea followed by rapid breathing.</p> Signup and view all the answers

What is Carotid Sinus Syndrome, and how is it related to abnormal hypersensitivity, and what are the steps taken to avoid it?

<p>Carotid Sinus Syndrome is an abnormal hypersensitivity of the carotid sinus to external mild pressure. It is avoided by avoiding pressure on the carotid sinus area or denervation of the Carotid Sinus.</p> Signup and view all the answers

Describe the pulmonary chemoreflex and how its stimulus impacts VDC and CIC.

<p>The pulmonary chemoreflex is stimulated by pulmonary congestion or embolization of Serotonin causes the discharge of impulses in afferent vagal fibers. This stimulatation causes stimulation of CIC and VDC results with hypertension, bradycardia and followed by apnea.</p> Signup and view all the answers

Flashcards

Rate of impulse

Heart rate is determined by this, discharged from the SA node.

Regulation centers

The heart rate is regulated by two of these, present in the medulla oblongata.

Vasoconstrictor center (VCC)

This nervous center is connected with the sympathetic nervous system.

Cardiac Inhibitory Center (CIC)

This nervous center is connected with the vagus nerve, a parasympathetic nerve.

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Cerebral cortex

Part of the brain that affects heart rate; includes frontal lobe, orbital cortex motor and premotor areas.

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Conditioned reflexes

In these conditions, seeing, hearing or smelling objects can lead to a change in heart rate.

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Voluntary control

Yoga players can increase or decrease their heart rate.

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Emotions

It leads to increased heart rate; sudden unexpected shocking news may stop the heart

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Hypothalamus

Part of the brain that controls emotional reactions.

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Inspiration

During this respiratory phase, heart rate will increase.

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Lung inflation

During inspiration this happens; stimulates stretch receptors, causing impulses via afferent vagus nerve excitation of VCC.

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Irradiation

During inspiration, this is inhibited and the vasomotor center is stimulated.

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Bainbridge reflex

Located on the venous side (Rt. side of the heart); increased blood volume that increases heart rate

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Mc Dowel's reflex

Located on the venous side (Rt. side of the heart); decreased VR or drop of right atrial pressure leads to increased HR and V.C of arterioles.

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Mary's reflex (Mary's law)

The heart rate is inversely proportional to the arterial blood pressure provided that other factors affecting heart rate remain constant.

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Carotid Sinus syndrome

Abnormal hypersensitivity of this structure, causes bradycardia and vasodilatation.

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Coronary chemoreflex

Injection of this causes bradycardia and apnea followed by rapid breathing.

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Trigger zones

Irritation of the larynx, epigastrium, pericardium and testis severly affects

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Oculo-cardiac reflex

Pressure over this can cause stimulation of the vagus nerve; used to treat paroxysmal atrial tachycardia.

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10 beats/min

Increase in body temperature increases heart rate by this amount per degree Celsius.

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Direct stimulation

This results in an increase in heart rate as they directly stimulate the SA node.

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Oxygen

Mild or moderate lack of this stimulates both the VCC reflexly and the SA node directly, increasing heart rate.

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Hypoxia

Stimulation of VCC

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VCC reflexly

Mild or moderate stimulates the peripheral chemoreceptors.

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Severe hypoxia

This slows heart rate or causes heart to stop, due to paralysis of cardiovascular centers and inhibition of SA node.

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Moderate increase in CO2 and H

Stimulation of the peripheral & central chemoreceptors

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Adrenaline

These hormones act by directly stimulating the SA node, increasing heart rate

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Noradrenaline

Small or large dose decreases V.C - -generalized

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Thyroxin

Hormone that directly stimulates SA node, increasing heart rate

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Sympathomimetic drugs

These are drugs that increase HR

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Parasympathomimetic drugs

These are drugs that decreases HR

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Study Notes

Regulation of Heart Rate Overview

  • Heart rate depends on the rate of impluse discharge from SA node
  • Nervous, physical, and chemical factors all regulate heart rate

Nervous Regulation

  • Two centers in the medulla oblongata regulate heart rate
  • The VasoConstrictor Center (VCC) connects with the sympathetic nervous system
  • The Cardio Inhibitory Center (CIC) connects with the vagus nerve, part of the parasympathetic nervous system
  • Impulses get received by the VCC and CIC

Afferent Impulses from Higher Centers

  • Cerebral cortex
  • Frontal lobe, orbital cortex, motor, and premotor areas have an affect
  • Conditioned reflexes, like seeing an examiner, affect heart rate
  • Emotions such as fear, anger, and anxiety increase heart rate
  • Surprising news may stop the heart due to the startling reflex
  • Hypothalamus
  • Controls emotional reactions in conjunction with the limbic system and cerebral cortex.
  • Most emotions, like fear and anger, stimulate the sympathetic activity through posterior hypothalamic nuclei, increasing HR
  • Severe emotions stimulate parasympathetic activity via anterior hypothalamic nuclei, affecting HR.
  • Respiratory center
  • Inspiration increases HR, expiration decreases HR, known as respiratory sinus arrhythmia
  • Lung inflation stimulates stretch receptors, exciting VCC via the vagus nerve
  • Impulses irradiate from the inspiratory center, inhibiting CIC and stimulating the vasomotor center
  • The Bainbridge reflex decreases intrathoracic pressure during inspiration, which increases VR and right atrial pressure, increasing HR
  • Expiration has the opposite effects, decreasing HR

Afferent Impulses from the Circulatory System

  • Bainbridge reflex on the venous side (right side of heart)
  • Increased blood volume and venous return (VR) raises right atrial pressure
  • It stimulates stretch receptors that signal VCC to increase HR via sympathetic fibers, while inhibiting CIC.
  • Significance: prevents blood stagnation by pumping excess VR to arterial side
  • Mc Dowel's reflex on the venous side (right side of heart)
  • Decreased VR or right atrial pressure, as in hemorrhage, causes HR and V.C of arterioles
  • Significance: increased HR and VC raises ABP and aids circulation to vital organs during hemorrhage
  • Mary's reflex (Mary's law) on the arterial side
  • HR is inversely proportional to arterial blood pressure if other factors remain constant: Increased ABP causes decreased HR
  • Increased ABP excites baroreceptors, sending impulses through the sinus and aortic nerves, increasing CIC and decreasing VCC, causing vasodilation
  • Decreased arterial blood pressure in hemorrhage reduces inhibitory impulses, leading to increased HR and vasoconstriction
  • Carotid sinus syndrome due to arterial issues
  • Abnormal carotid sinus hypersensitivity to external pressure
  • Mild pressure on the carotid sinus (during shaving, tight collars) causes bradycardia, vasodilation, decreased COP/ABP, brain ischemia and syncope
  • Treated by pressure avoidance on the carotid sinus and anticholinergic drugs like atropine or carotid sinus denervation
  • Coronary chemoreflex (Bezold-Jarisch reflex)
  • Serotonin and veratridine injected into coronary arteries that supply the left ventricle stimulate ventricular chemoreceptors
  • This leads to afferent vagal fibers stimulating CIC and VDC causing hypotension, bradycardia, and apnea which is followed by rapid breathing

Afferents from the Lungs

  • Pulmonary stretch reflex
  • Rise in HR occurs because lung inflation during inspiration stimulates stretch receptors in the bronchial wall and alveoli
  • VCC is stimulated
  • Pulmonary chemoreflex
  • Pulmonary congestion or embolization, or injection of serotonin, leads to stimulation of pulmonary chemoreceptors
  • Afferent vagal fibers discharge impulses
  • stimulation of CIC & VDC occurs leading to hypotension, bradycardia, and apnea followed by rapid breathing

Afferent Impulses from Other Body Parts

  • Alam Smirk reflex
  • Voluntary muscle contraction stimulates proprioceptors in muscles and joints
  • Results in VCC stimulation leading to increased HR
  • Skin and viscera
  • Mild to moderate skin pain stimulates the hypothalamus, increasing VCC activity and consequently HR
  • Severe pain from skin (burns) or viscera stimulates CIC, increasing HR
  • Trigger zones
  • Stimulation of sensitive areas (larynx, epigastrium, pericardium, testis) stimulates parasympathetic fibers
  • Severe inhibition in HR, even stopping the heart
  • Oculo-cardiac reflex
  • Eyeball pressure stimulates the optic nerve, which stimulates CIC
  • Increased vagal discharge to the heart results in a reflex decrease in HR
  • Used to stop paroxysmal atrial tachycardia by terminating attacks

Physical Regulation of Heart Rate

  • Rise in body temperature
  • HR inreases by 10 beats/min for each 1°C
  • Direct stimulation of SA node and stimulation of VCC through the heat-regulating center in the hypothalamus
  • Drop in body temperature:
  • HR decreases by 10 beats/min for each 1°C

Chemical Regulation of Heart Rate

  • Mild/moderate hypoxia
  • Increases HR by VCC stimulation through peripheral chemoreceptors in carotid and aortic bodies and direct stimulation of SA node pacemaker cells and direct inhibition of CIC
  • Severe hypoxia
  • Decreases HR and may stop the heart completely due to paralysis of the cardiovascular centers
  • Moderate increases of CO2 and H
  • Initial increase in HR occurs
  • Is followed by an increase in HR because it stimulates VCC
  • This is caused by weak inhibition of SA node activity and stimulation of VCC
  • The excitation originates from peripheral and central chemoreceptors
  • Severe hypercapnia or acidemia decreases HR
  • Effect is like severe hypoxia
  • Blood hormones regulate heart rate
  • Small adrenaline doses increase HR by directly stimulating SAN
  • Large adrenaline doses Increase rise of ABP
  • Noradrenaline in small or large doses causes generalized V.C.
  • Thyroxin increases HR by directly stimulating SAN, increasing SAN sensitivity to adrenaline, and increasing general metabolism and body temperature

Other chemicals impacting heart rate

  • Increases HR
  • Sympathomimetic drugs (ephedrine, amphetamine)
  • Parasympatholytic drugs (atropine): inhibit vagal effects
  • Histamine causes marked V.D.
  • Decreases HR
  • Parasympathomimetic drugs(acetylcholine, pilocarpine)
  • Bile salts: cause direct SAN inhibition and CIC stimulation
  • Morphine and Toxins canstimulate CIC

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