Heart rate Regulation of heart rate Vasomotor center – cardiac center Motor (efferent) nerve fibers to heart Factors affecting vasomotor center Applied

1. HEART RATE
Pandian M
Dept of Physiology
D. Y. Patil Medical College, KOP

2. Objectives
•Heart rate
•Regulation of heart rate
•Vasomotor center – cardiac center
•Motor (efferent) nerve fibers to heart
•Factors affecting vasomotor center
•Applied

3. NORMAL HEART RATE
• Normal heart rate is 70 to 72/minute.
• It ranges between 60 and 80 per minute

4. VASOMOTOR CENTER – CARDIAC CENTER
• Vasomotor center is the nervous center that regulates the
heart rate
• It is the same center in brain, which regulates the blood
pressure.
• It is also called the cardiac center.
• Vasomotor center is bilaterally situated in the reticular
formation of medulla oblongata and lower part of pons.

5. Areas of Vasomotor Center
Vasomotor center is formed by three areas:
1. Vasoconstrictor area or Accelerator center
2. Vasodilator area or Inhibitory center
3. Sensory area.

6. VASOCONSTRICTOR AREA –
CARDIOACCELERATOR CENTER
Situation:-
•In reticular formation of medulla in floor of IV ventricle
and it forms the lateral portion of vasomotor center.
•It is otherwise known as pressor area or cardioaccelerator
center.

7. Function
•Vasoconstrictor area increases the HR by sending
accelerator impulses to heart, through sympathetic
nerves.
•It also causes constriction of blood vessels.
•Stimulation of this center in animals increases the HR and
•its removal or destruction decreases the heart rate.
Control Vasoconstrictor area is under the control of
hypothalamus and cerebral cortex.

8. VASODILATOR AREA –
CARDIOINHIBITORY CENTER
Situation;-
•In the reticular formation of medulla oblongata in
the floor of IV ventricle.
•It forms the medial portion of vasomotor center.
•It is also called depressor area or
cardioinhibitory center

9. •Function
•Vasodilator area decreases the HR by sending
inhibitory impulses to heart through vagus nerve.
•It also causes dilatation of blood vessels.
•When this area is removed or destroyed, heart rate
increases.

10. Control
•Vasodilator area is under the control of cerebral
cortex and hypothalamus.
•It is also controlled by the impulses from
baroreceptors, chemoreceptors and other
sensory impulses via afferent nerves.

11. SENSORY AREA
Situation
• Sensory area is in the posterior part of vasomotor center,
• which lies in nucleus of tractus solitarius in medulla and pons.
Function
• Sensory area receives sensory impulse via glossopharyngeal
nerve and vagus nerve from periphery, particularly, from the
baroreceptors.
• In turn, this area controls the vasoconstrictor and vasodilator
areas.

12. MOTOR (EFFERENT) NERVE FIBERS TO HEART
• Heart receives efferent nerves from both the divisions
of autonomic nervous system.
• Parasympathetic fibers arise from the medulla
oblongata and pass through vagus nerve.
• Sympathetic fibers arise from upper thoracic (T1 to
T4) segments of spinal cord

13. PARASYMPATHETIC NERVE FIBERS
•Parasympathetic nerve fibers are the
cardioinhibitory nerve fibers.
•These nerve fibers reach the heart through the
cardiac branch of vagus nerve.

14. Origin
• Parasympathetic nerve fibers supplying heart arise
from the dorsal nucleus of vagus.
• medulla oblongata and is in close contact with
vasodilator area.

15. Distribution
• Preganglionic parasympathetic nerve fibers from dorsal
nucleus of vagus reach the heart
• by passing through the main trunk of vagus and
cardiac branch of vagus.
• After reaching the heart, preganglionic fibers terminate
on postganglionic neurons.
• Postganglionic fibers from these neurons innervate
heart muscle.

16. • Most of the fibers from right vagus terminate in
sinoatrial (SA) node.
• Remaining fibers supply the atrial muscles and
atrioventricular (AV) node.
• Most of the fibers from left vagus supply AV node and
some fibers supply the atrial muscle and SA node.
• Ventricles do not receive the vagus nerve supply.

17. REGULATION OF HEART RATE

18. Function
•Vagus nerve is cardioinhibitory in function and
carries
•inhibitory impulses from vasodilator area to the
heart.

19. SYMPATHETIC NERVE FIBERS
Sympathetic nerve fibers supplying the heart have
cardioacceleratory function.
Origin
• Preganglionic fibers of the sympathetic nerves to heart arise
from lateral gray horns of the first 4 thoracic (T1 to T4)
segments of the spinal cord.
• These segments of the spinal cord receive fibers from
vasoconstrictor area of vasomotor center.

20. Course and Distribution
• Preganglionic fibers reach the superior, middle and
• inferior cervical sympathetic ganglia situated in the
sympathetic chain.
• Inferior cervical sympathetic ganglion fuses with first
thoracic sympathetic ganglion, forming stellate
ganglion.
• From these ganglia, the postganglionic fibers arise.

21. Function
•Sympathetic nerves are cardioaccelerators in
function
•and carry cardioaccelerator impulses from
vasoconstrictor area to the heart.

22. SENSORY (AFFERENT) NERVE
FIBERS FROM HEART
• Afferent (sensory) nerve fibers from the heart pass
through inferior cervical sympathetic nerve.
• These nerve fibers carry sensations of stretch and pain
from the heart to brain via spinal cord.

23. Autonomic nerve impulses alter the activities of the S-A and A-V nodes

24. The autonomic nervous system has two divisions:
• Sympathetic and parasympathetic:-
• Sympathetic impulses from the accelerator center along sympathetic
nerves increase heart rate and
• force of contraction during exercise and stressful situations (the
neurotransmitter is norepinephrine).
• Parasympathetic impulses from the inhibitory center along the vagus
nerves decrease the heart rate (the neurotransmitter is acetylcholine).
• At rest these impulses slow down the depolarization of the SA node to
what we consider a normal resting rate,
• they also slow the rate after exercise is over.

25. Our next question might be: What information is received by the
medulla to initiate changes?
1. Because the heart pumps blood, it is essential to maintain
normal blood pressure.
2. Blood contains oxygen, which all tissues must receive
continuously.
3. Therefore, changes in blood pressure and oxygen level of
the blood are stimuli for changes in heart rate

26. Reflex arc like action on Heart

27. • Pressoreceptors and chemoreceptors are located in the carotid arteries and
aortic arch.
• Pressoreceptors in the carotid sinuses and aortic sinus detect changes in
blood pressure.
• Chemoreceptors in the carotid bodies and aortic body detect changes in
the oxygen content of the blood.
• The sensory nerves for the carotid receptors are the glossopharyngeal (9th
cranial) nerves;
• the sensory nerves for the aortic arch receptors are the vagus (10th cranial)
nerves.
• If we now put all of these facts together in a specific example, you will see
that the regulation of heart rate is a reflex, and the nerve impulses follow a
reflex arc.

29. Reflex Arc
• A reflex arc is the pathway that nerve impulses travel when a
reflex is elicited, and there are five essential parts:
1. Receptors—detect a change (the stimulus) and generate
impulses.
2. Sensory neurons—transmit impulses from receptors to the
CNS.
3. Central nervous system—contains one or more synapses
(interneurons may be part of the pathway).
4. Motor neurons—transmit impulses from the CNS to the
effector.
5. Effector—performs its characteristic action.

30. Reflex arc like action on Heart

31. • A person who stands up suddenly from a lying position may feel light-
headed or dizzy for a few moments,
• because blood pressure to the brain has decreased abruptly.
• The drop in blood pressure is detected by pressoreceptors in the carotid
sinuses—notice that they are “on the way” to the brain, a very strategic
location.
• The drop in blood pressure causes fewer impulses to be generated by the
pressoreceptors.
• These impulses travel along the hering’s nerve branch of
glossopharyngeal nerves to the medulla, and the decrease in the frequency
of impulses stimulates the accelerator center.
Reflex arc like action on Heart

33. • The accelerator center generates impulses that are carried by
sympathetic nerves to the SA node, AV node, and ventricular
myocardium.
• As heart rate and force increase, blood pressure to the brain is
raised to normal, and the sensation of light-headedness passes.
• When blood pressure to the brain is restored to normal, the heart
receives more parasympathetic impulses from the inhibitory
center along the vagus nerves to the SA node and AV node.
• These parasympathetic impulses slow the heart rate to a normal
resting pace.

34. • The heart will also be the effector in a reflex stimulated by a decrease in the
oxygen content of the blood.
• The aortic receptors ({chemoreceptor}carotid bodies and aortic body ) are
strategically located so as to detect such an important change as soon as
blood leaves the heart.
• The reflex arc in this situation would be
(1) aortic chemoreceptors,
(2) vagus nerves (sensory),
(3) accelerator center in the medulla,
(4) sympathetic nerves, and
(5) the heart muscle, which will increase its rate and force of
contraction to circulate more oxygen to correct the hypoxemia.

35. • the hormone epinephrine is secreted by the adrenal medulla in
stressful situations.
• One of the many functions of epinephrine is to increase heart
rate and force of contraction.
• This will help supply more blood to tissues in need of more
oxygen.

36. The Cardiovascular Stress Response
• Get the heart to beat faster: ↑ SNS tone, ↓ PNS tone
• Norepinephrine (NE) and epinephrine (Epi) ↑ slow inflow of Na+ and
Ca++  increase rate of re-excitation in SA node.
• This ↑ Ca++ also increases contractility.
• SNS terminals also excite AV node and whole myocardium: enhances
contractility everywhere.

37. PNS
• Vagus nerve (via ACh) ↓ HR by ↓ slow inflow of Na+ and
Ca++ and by ↑ the subsequent outflow of potassium (K+).
• Acts at SA and AV nodes.
• May treat SNS-driven heart attack by gagging or massage of
carotid arteries  activate vagal reflexes  PNS counteracts
SNS.

38. Heart rate
Autonomic regulation (medullary
CV center): Receives input from
higher brain centers and variety of
sensory receptors
• Proprioceptors
• Chemoreceptors
• Baroreceptors
• Sympathetic output ↑HR and
contractility
• Parasympathetic impulses
↓ HR
• Little effect on contractility
(does not innervate
ventricular myocardium)

41. Atrial stretch receptors
• Atrial stretch receptors present in the walls of atria are
also called low-pressure receptors.
• Types of atrial stretch receptors. Atrial stretch receptor
have been studied in detail by Prof. A. S. Paintal (an
Indian scientist) in 1953.
• These can be divided into following types:

42. Factor causing variation in heart rate

43. • Several factors contribute to regulation of heart rate:
• Chemical regulation
• Cardiac activity depressed by
• Hypoxia
• Acidosis
• Alkalosis
• Hormones
• Catecholamine's and thyroid hormones increase HR and contractility
• Cations
• Alterations in balance of K+, Na+ and Ca2+ alter HR and contractility
Heart rate

44. • Several other factors contribute to regulation of heart rate:
• Age
• Gender
• Female HR higher
• Physical fitness
• Resting bradycardia
• Body temperature
• Increase causes SA node to discharge more rapidly
Heart rate

45. TACHYCARDIA
The term “tachycardia” means fast heart rate, Usually defined
in an adult person as faster than 100 beats/min.
Physiological Conditions when Tachycardia Occurs
1. Childhood
2. Exercise
3. Pregnancy
4. Emotional conditions such as anxiety.

47. Pathological Conditions when Tachycardia Occurs
1. Fever
2. Anemia
3. Hypoxia
4. Hyperthyroidism
5. Hypersecretion of catecholamine's
6. Cardiomyopathy
7. Diseases of heart valves

48. BRADYCARDIA
• The term “bradycardia” means a slow heart rate,
• Usually defined as fewer than 60 beats/min.
Physiological Conditions
when Bradycardia Occurs
1. Sleep
2. Athletes.
Pathological Conditions when
Bradycardia Occurs
1. Hypothermia
2. Hypothyroidism
3. Heart attack
4. Congenital heart disease
5. Degenerative process of aging
6. Obstructive jaundice
7. Increased intracranial pressure.

51. Drugs which Induce Bradycardia
1. Beta blockers
2. Channel blockers
3. Digitalis and other antiarrhythmic drugs.

52. Vasopressin
• Enhances water retention
• Causes vasoconstriction
• Secretion increased by aortic baroreceptors and
atrial sensors
http://www.cvphysiology.com/Blood%20Pressure/BP016.htm

54. Summary of long term BP control
• Cardiac output and BP depend on renal control
of extra-cellular fluid volume via:
• Pressure natriuresis, (increased renal filtration)
• Changes in:
• Vasopressin
• Aldosterone
• Atrial natiuretic peptide
All under the control of altered cardiovascular
receptor signaling

55. SUMMARY
• As you can see, the nervous system regulates the
functioning of the heart based on what the heart is
supposed to do.
• The pumping of the heart maintains normal blood
pressure and proper oxygenation of tissues,
• The nervous system ensures that the heart will be able
to meet these demands in different situations.

56. References
•Text book of Medical Physiology
• Guyton & Hall
•Human Physiology
• Vander
•Text book of Medical Physiology
• Indukurana, Sembu, LPR
•Principles of Anatomy and Physiology
• Totora
•Net source

57. THANK YOU . . .