nervous and hormonal regulation of heartbeat Heart rate refers to the number of times the heart beats per minute and is directly related to workload being placed on the heart The normal heart rate of resting adult human- 60-100 Bradycardia- slow heart rate (below 60 bpm) Tachycardia- fast heart rate (above 100 bpm) Irregular pattern in heart beating is termed as Arrhythmia

1. Roll no- 1811854
Class- Bsc bioscience 6th semester
Section – D
Submitted to- Dr Surabhi Bajpai

2. Introduction
 Heart rate refers to the number of times the
heart beats per minute and is directly related
to workload being placed on the heart
 The normal heart rate of resting adult
human- 60-100
 Bradycardia- slow heart rate (below 60
bpm)
 Tachycardia- fast heart rate (above 100
bpm)
 Irregular pattern in heart beating is termed
as Arrhythmia

3. Regulation of heart rate
Intrinsic regulation Extrinsic regulation
Neural regulation
Parasympathetic
nervous system
Sympathetic
nervous system
Hormonal
regulation
Epinephrine/
Adrenaline
Norepinephrine/
Noradrenaline

4. Heart physiology: conduction of
heart beat
• Heart has intrinsic system composed of cardiac
muscle fibers called autorhythmic fibers which are
self excitable.
• Autorhytmic fibers- initiate action potential
• Have unstable resting potential called resting
potential
• Use calcium influx instead of sodium for rising
phase of action potential.
• Function of autorhythmic fibers-
• Act as pacemaker(setting rhythm of electrical
excitation that causes heart beat )
• Form cardiac conduction system

6. Conduction system
• small flattened mass of neuromuscular tissue
• Located near opening of superior vena cava in right atrium
• They don’t have a stable resting potential
• They repeatedly depolarize to threshold spontaneously. The spontaneous
depolarization is a pacemaker potential When the pacemaker potential
reaches threshold, it triggers an action potential
• It sets pace for heart hence called heart’s pacemaker
• SA node directly connected to atrial muscle to transmit impulse
Sino-
atrial
node
• Small mass of neuromuscular tissue
• located near atrioventricular valves
Atrioventricular
node
• Specialized fibers originating from AV node
• Divides into right and left branches at upper septum
• At ventricular myocardium they break into purkinje fibers
AV bundle
/bundle of
his

7. Sequence of excitation
 At regular interval, SA node generate impulse sending wave of
contraction throughout atria via gap junctions in the
intercalated discs of atrial muscle fibers
 It ultimately stimulate AV node through internodal pathway
present in posterior wall of septum of right atrium.
 At AV node impulse is delayed 0.1s letting atria complete
contraction before ventricular contraction begins
 From AV node impulse travel to AV bundle conducting action
potential from atria to ventricle
 The action potential enters left and right branches of AV bundle
which carries impulse toward apex of heart
 Finally, purkinje fibers conduct action potential from apex of
myocardium to upward remainder of ventricular myocarium.
 This wave sweeps upward pumping blood in pulmonary artery
and aorta

8. Sequence of excitation
Sino-atrial node
Atrioventricular node
Bundle of his/ atrioventricular
bundle
Left and right bundle branches
Purkinje fibers

9. Heart excitation related to ECG
 As muscle in SAN contract, it produces an electrical impulse which sweep through
all muscles in atria making them contract. This wave show in ECG as P wave.
Hence, it shows electrical activity before atrial systole
 From there impulse reaches AVN which delays impulse before it transfer
downward which is not recorded by ECG
 Impulse moving along AV bundle and purkinje fibers arrives at ventricle apex and
moves upward through ventricle wall. This is shown by QRS wave of ECG. After
which ventricle contract
 The ventricle then contract indicated in T wave
 Then SAN contract again and whole sequence is repeated

10. Extrinsic regulation of heart rate

11. Neural regulation
 Carried out by autonomic
nervous system(ANS)
 Nervous system regulation of
heart originates at cardio-
vascular center in the
medulla oblangata
 It receives input from variety
of sensory receptor and from
higher brain centers like
limbic system and cerebral
cortex
 It then direct appropriate
output by increasing or
decreasing the frequency of
nerve impulse in both
sympathetic and
parasympathetic nerve

12. Innervation to heart
Efferent nerve supply to
heart is from both
sympathetic and
parasympathetic nerves
Parasympathetic nerve
supplying the heart comes
from vagus nerve. The vagal
axon terminate SA node, AV
node and atrial myocardium.
Sympathetic cardiac
accelerator nerve comes from
lateral horn cells of T1-T5
(thoracic) segments of spinal
cord extend out to the SA
node, AV node, and most
portions of the myocardium.

13. NEURAL REGULATION OF HEART BEAT

14. Sympathetic nerve regulation
 Impulses in the cardiac accelerator nerves trigger the
release of norepinephrine, which binds to beta-1 (1)
receptors on cardiac muscle fibers.
 This interaction has two separate effects:
 SA (and AV) node fibers speeds the rate of spontaneous
depolarization making pacemakers fire impulses more
rapidly, increasing heart rate
 Contractile fibers in atria and ventricle-enhances calcium
entry through the voltage-gated slow calcium channels
increasing contractility resulting greater volume of blood is
ejected during systole this doesn’t decline with increased heart
rate due to increased contractility
 With maximal stimulation heart rate reach 200 beat/ min

15. Parasympathetic nerve
regulation
 Vagal axon release acetylcholine, which decreases heart rate
by slowing the rate of spontaneous depolarization in
autorhythmic fibers.
 There are only few vagal fibers innervating ventricular
muscle, changes in parasympathetic activity have little effect
on contractility of the ventricles
 With maximal stimulation by the parasympathetic division,
the heart can slow to 20 or 30 beats/min, or can even stop
momentarily.
 Parasympathetic stimulation predominates at rest at that
time heart rate is about 75 beats/min which is usually lower
than the autorhythmic rate of the SA node that is 100
beats/min
 There is shifting balance between parasympathetic and
sympathetic nerve, they work together to regulate heart rate

16. Receptor
• Monitors movement
• Monitoring the position of limbs and muscles
Proprioreceptor
• Stretch receptor
• Located in walls of carotid sinus located at beginning
of internal carotid artery and arch of aorta.
Baroreceptors
• Chemical receptor
• These receptor are carotid and aortic bodies
Chemoreceptor
• located in bifurcation of common carotid artery
(commencement of occipital artery
Carotid body
• Present in arch of aorta
Aortic bodies

17. Proprioreceptor mechanism
 They get stimulated during physical activity
especially in competitive situation
 As physical activity begins, they send nerve
impulses at an increased frequency to the
cardiovascular center causing quick rise in
heart rate
 There is anticipatory increase in heart rate
before physical activity begins because the
limbic system sends nerve impulses to the
cardiovascular center in the medulla

18. Baroreceptor mechanism
 They get stimulated when there is increase in blood
pressure. They respond better when blood flow in
above vessel is pulsatile
 Afferent impulse travel from
 Carotid sinus- via sinus nerve branch of glossopharyngeal
nerve
 Arch of aorta- via aortic nerve a branch of vagus
 This impulse will stimulate cardio-inhibitory center in
brainstem which will increase number of efferent
impulses along the vagus to heart which will decrease
the heart rate
 There is inverse relationship between blood pressure
and heart rate as stated by Marey’s law except in case
of exercise, anxiety where both blood pressure and
heart rate increases

19. Reflex pathway in baroreceptor
mechanism

20. Chemoreceptor mechanism
 They respond to chemical changes in blood
namely decrease in pO2 increase of pCO2 and
increase in hydrogen ion concentration
 Afferent impulse generated carried from
 Carotid body- via sinus nerve branch of
glossopharyngeal nerve
 Aortic body- via aortic nerve branch of vagus
 After this it is similar to baroreceptor
mechanism but instead of decrease it causes
increase in heart rate.

21. Hormonal regulation of heart
beat
• Release Epinephrine and norepinephrine that enhance the
heart’s pumping effectiveness
• Exercise, stress, and excitement cause the adrenal medullae to
release more hormones.
• These hormones affect cardiac muscle fibers increasing both
heart rate and contractility
Adrenal
medulla
• They enhance cardiac contractility and increase heart rate.
• As hyperthyroidism (excessive thyroid hormone) causes
tachycardia
Thyroid
gland
• Catecholamine Natriuretic peptides
• Endothelins Oxytocin
• Aldosterone Antidiuretic hormones
• Acetylcholine
Other
hormones

22. Effect of neurohormone
Heart
rate
Heart
rate

23. Cationic regulation of heart beat
 Ionic imbalances can decrease the pumping effectiveness of
the heart as ionic concentration difference across
membrane is required for conduction of impulse.
 Especially the relative concentrations of three cations-
potassium, calcium and sodium effect cardiac function
largely
 Elevated blood levels of potassium or sodium decrease
heart rate and contractility.
 Excess sodium blocks calcium inflow during cardiac action
potentials, thereby decreasing the force of contraction,
 Excess potassium blocks generation of action potentials.
 Moderate increase in interstitial calcium level speeds heart
rate and strengthens the heartbeat.

24. Importance of regulation of
heart beat
 cardiac output depends on both heart rate
and stroke volume. Adjustments in heart
rate are important in the short-term
control of cardiac output and blood
pressure.
 To create a homeostatic mechanism to
maintain adequate cardiac output by
increasing the heart rate and contractility.

25. Conclusion
 The basal heart rate is determined within the
heart by the pacemaker, it can be regulated
by external signal
 Nerve signal from brain can trigger rapid
changes
 Hormonal signal can trigger more sustained
changes
 Changes to blood pressure levels or
carbondioxide concentration(and thereby
blood pH) can also trigger changes in heart

26. Bibliography
 www.thesciencncenotes.com
 www.slideshare.net
 byjus.com
 Ib.bioninja.com.au
 Health.ucdavis.edu
 Slideplayer.com
 Cvphysiology.com
 www.biologydiscussion.com
 Books- principles of anaotomy and physiology 13th
edition tortora
 Hole’s essential of human anatomy and physiology