Heart rate by Pandian M, Tutor, Dept of Physiology, DYPMCKOP,MH. This ppt for 1 MBBS, BPTH, Nursing and BDS. with SLOs

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 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? Because the heart pumps blood, it is essential to maintain normal blood pressure. Blood contains oxygen, which all tissues must receive continuously. 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 .

28. 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

32. 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.

33. 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 .

34. 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.

35. 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.

36. 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.

37. 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)

38. 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:

39. Factor causing variation in heart rate

40. 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 Ca 2+ alter HR and contractility Heart rate

41. 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

42. 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 .

43. 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

44. 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.

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

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

47. 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

48. 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, T he nervous system ensures that the heart will be able to meet these demands in different situations .

49. 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

50. THANK YOU . . .