1. The heart rate is regulated by the nervous system, specifically the vasomotor center located in the medulla oblongata. 2. The vasomotor center contains vasoconstrictor and vasodilator areas that regulate heart rate by sending sympathetic or parasympathetic signals via the spinal cord. The vasoconstrictor area increases heart rate while the vasodilator area decreases it. 3. Factors like emotions, exercise and respiration can trigger the vasomotor center to adjust heart rate through sympathetic or parasympathetic outflow as part of reflex responses mediated by baroreceptors and chemoreceptors.

1. REGULATION
OF HEART
RATE
GOVERDHAN.R

2. HEART
• Normal heart rate is
72/minute. It range
between 60 and 80 per
minutes.
• It is subjected for
variation during normal
physiological condition
such as exercise,
emotion , etc.

3. Regulation of heart rate:
▪ Heart rate is regulated by nervous mechanism.
▪ Nervous mechanism consists of three
components:
1.Vasomotor center.
2.Motor nerve fibers to the heart (efferent).
3.Sensory nerve fibers from the heart (afferent).
3

4. Vasomotor center:
▪ It is the nervous center that regulates the heart rate.
▪ It is situated in the reticular formation of medulla
oblongata and the lower part of the pons.
▪ It has three areas:
1. Vasoconstrictor area.
2. Vasodilator area.
3. Sensory area.
4

5. Vasomotor centers:
Vasomotor
center
Situation Function
Vasoconstrictor
area
Reticular formation of medulla in
the floor of the IV ventricle and
forms the lateral portion of
Vasomotor center
It increases the heart rate by
sending accelerator impulses to
heart through sympathetic
nerves
Vasodilator area Reticular formation of medulla in
the floor of the IV ventricle and
forms the medial portion of
Vasomotor center
It decreases the heart rate by
sending inhibitor impulses to the
heart through vagus nerve
Sensory area Posterior part of vasomotor
center, which lies in nucleus of
tractus solitaries in medulla
It controls the vasoconstrictor
and vasodilator area
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6. Motor (efferent) nerve fibers to heart
▪ Heart receives efferent nerves from both the
divisions of autonomic nervous system.
▪ Parasympathetic nerve fibers arise from the
medulla oblongata and pass through vagus.
▪ Sympathetic nerve fibers arise from upper
thoracic (T1-T4) segments of spinal cord.
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7. Nerve supply to heart:
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8. Brain and spinal cord:
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9. Parasympathetic nerve fibers:
▪ Origin: They arise from the dorsal nucleus of
vagus. The nucleus is situated in the IV ventricle
in medulla oblongata.
▪ Function: The vagus nerve fibers are
cardioinhibitory in function and carry inhibitory
impulses from vasodilator area to heart.
▪ Vagal tone: It is the continuous stream of
inhibitory impulses from vascodilatory area to
heart.HR is inversely proportional to vagal tone.
9

10. Parasympathetic nerve fibers(contd…)
Effects of stimulation of vagus nerve:
▪ Vagal escape:
▪ Stimulation of right vagus stops the heart beat due to inhibition of SA
node and atria.
▪ Because of this, when stoppage of heart beat is continued for some time, a
part of ventricular musculature becomes a pacemaker and starts producing
impulses.
▪ Heart block:
▪ Stimulation of left vagus inhibition of Av node. Because of this, some of
the impulses from SA node are not conducted to ventricles. This is called
the partial heart block.
▪ Stimulation with strong stimulus causes stoppage of ventricular
contraction, which causes Complete heart block
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11. Effect of vagal stimulation on frog heart
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12. Sympathetic nerve fibers:
▪ Origin: The preganglionic fibers of sympathetic
nerves to the heart arise from lateral grey horns
of the first four thoracic(T1-T4) segments of the
spinal cord.
▪ Function: The sympathetic nerves are
cardioaccelarators in function and carry
cardioaccelarator impulses from vasoconstrictor
area to the heart.
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13. Sensory Nerve fibers from heart:
▪ The afferent nerve fibers from the heart pass
through the inferior cervical sympathetic nerve.
▪ These nerve fibers carry sensations of stretch
and pain from the heart to the brain via spinal
cord.
13

14. Factors affecting vasomotor center:
1. Impulses from higher centers.
2. Impulse from respiratory centers.
3. Impulses from Baroreceptors-Mary’s Reflex
4. Impulses from Chemoreceptors
5. Impulses from Right atrium-Bainbridge reflex
14

15. 1. Impulses from the higher centers:
▪ Cerebral cortex: During emotional conditions, this area
sends inhibitory impulses to the vasodilator area. This
causes reduction in vagal tone leading to
cardioaccelaration.
▪ Hypothalamus: It influences heart rate via vasomotor
center. Stimulation of posterior and lateral hypothalamic
nuclei causes Tachycardia
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16. 2. Impulses from Respiratory centers:
▪ In forced breathing, HR increases during inspiration and
decreases during expiration and this variation is called
respiratory sinus arrhythmia.
▪ Sinus arrhythmia is due to alternation of vagal tone because
of impulses arising from respiratory center during
inspiration.
▪ These impulses inhibits the vasodilator area, result in
increase of heart rate.
▪ During expiration ,respiratory center stop sending impulses
to vasodilator center. Now, vagal tone increases, leading to
decrease in heart rate.
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17. Nerve supply to baroreceptors
and chemoreceptors
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18. 3.Impulses from baroreceptors - Mareys Reflex
▪ It is a cardionhibitory reflex that decreases heart
rate when blood pressure increases.
▪ Whenever the blood pressure increases the
aortic and carotid baroreceptors are stimulated.
▪ The stimulatory receptors are sent to nucleus of
tractus solitarius.
▪ Nucleus of tractus solitarius stimulates the
vasodilator area, which in turn increases the
vagal tone leading to decrease in heart rate.
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19. Marey reflex
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20. Marey’s Law:
▪ Pulse rate is inversely proportional to blood
pressure.
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21. 4. Impulses from chemoreceptors
▪ Chemoreceptors give response to change in chemical
constituents of blood, particularly oxygen, carbon
dioxide and hydrogen ion concentration.
▪ Peripheral chemoreceptors are situated in the carotid
body and aortic body, adjacent to baroreceptors.
Structure.
▪ Chemoreceptors in the carotid body are supplied by
Hering nerve. Chemoreceptors in the aortic body are
supplied by aortic nerve.
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22. 4. Impulses from chemoreceptors(contd…)
▪ Whenever there is hypoxia, hypercapnea and increased
hydrogen ions concentration in the blood, the
chemoreceptors are stimulated.
▪ Inhibitory impulses are sent to vasodilator area. Vagal
tone decreases and heart rate increases.
▪ The nerves supplying these receptors are called buffer
nerves.
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23. 5. Impulses from right atrium –
bainbridge reflex
▪ Bainbridge reflex is a cardioaccelerator
reflex that increases the heart rate when venous
return is increased.
▪ Since this reflex arises from right atrium, it is also
called right atrial reflex.
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24. Bainbridge
(cardioaccelerator) reflex
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