 SAN
sets heart rate at about 120 beats
per minute
 Nerves act as
brake and accelerator
 Vagus nerve
slows heart rate
 Sympathetic nerve
speeds up heart rate
2
 The
intrinsic impulses of the SAN set the
heart beat
 These timings can be altered through the
neural control & hormones.
 Central to the regulation of heart rate is the
Cardiac Control Centre in the medulla- made
up of 2 components.
Autonomic Nervous System
Parasympathetic
SLOWER
Sympathetic
FASTER
Via Vegus Nerve
adrenaline/noradrenaline
Acetylcholine
 These both act on the SA node to change HR
 Think
of a cyclist going down hill.
 Speed of the bike is like the speed of your
heart
 Brakes- vagus nerve
 Pedals- sympathetic nerve
 To reduce the speed you use the brakes
 To speed up you pedal faster
 To go fast downhill you take the
brakes off completely (vegus nerve) and
pedal faster (sympathetic nerve)
Exercise - blood CO2 levels rise
Medulla
Detected by chemoreceptors
Decreased vagus
impulses to SAN - lets
heart beat faster
Increased sympathetic
impulses to SAN - lets
heart beat even faster
5
Medulla
Stop exercise – blood pressure falls
Detected by baroreceptors
Increased vagus
impulses to SAN - lets
heart beat slower
Decreased sympathetic
impulses to SAN - allows
heart rate to slow
6
Sympathetic system
Parasympathetic system
 A.Controlled
by medulla/cardiac centre
 B. Sympathetic pathway increases heart rate
 C. By release of adrenaline/noradrenaline
 D. Increase stroke volume/ejection fraction
 E. Parasympathetic decreases HR
 F. By vagus nerve
 G. Production of Acetylcholine
 H. (Both) act on sino atrial node/SAN
 Increase
in C02
 Causes increase in blood acidity, decrease in
pH.
 Detected by Chemorecepetors
 Sends impulse to medulla – Cardiac control
centre
 Decreases Vegus simulation
 Increase sympathetic pulses
 Heart rate increases!
*Breathing rate= respiratory control centre
 The
CCC receives information from lots of
different sources in the body.
 Mechanoreceptors & Proprioceptors
-Extent of movement taking place in the muscles.
In movement =
in HR.
 Chemoreceptors
-Detect changes in pH.
 Baroreceptors
-stretch receptor based in arteries and vena cava.
Detect increases in blood flow and pressure
 CCC
responds to information from these
sensory receptors during exercise.
 Stimulate the SA Node via sympathetic
nerve.
 This causes heart rate and stroke volume to
increase.
 Once exercise stops- stimulation of
sympathetic nerve decreases and allows
parasympathetic vagus nerve to take over
and slow heart rate down.
 Adrenaline
and noradrenaline are released
during times of stress- ‘butterflies’
 Prepares body for impending exercise by
increasing heart rate and strength of
ventricular contraction.
 Mimicking the action of the sympathetic
system
 Anticipatory
Rise
 Action
of another hormone Acetylcholine
released by Parasympathetic system that
slow the heart rate down
Neural Factors;
Proprioceptors & mechanoreceptors in muscles
relay info to the brain that amount of
movement has increased and muscles will
need more blood.
Chemoreceptors in aorta and carotid arteries
detect changes in composition of the bloodC02
Baroreceptors respond to changes in blood
pressure
Hormonal factors;
Release of adrenaline and noradrenaline
increase heart rate and strength of
contraction
Release of Acetylcholine following exercise to
reduce the heart rate
Intrinsic factors
Increase in temperature- blood flows better
less viscous
 Describe
how the parasympathetic and
sympathetic nervous pathways control
heart rate during a game.
 Explain
how levels of CO2 in blood cause
heart rate to increase
 How
does the cardiac control centre
regulate heart rate?
 Stroke
Volume- blood ejected per beat
Not all blood in ventricle is ejected..
 Ejection Fraction- amount of blood that
leaves the ventricle
 Cardiac Output – amount of blood pumped
out of a ventricle per minute
 Heart rate x stroke volume
 5 litres resting male
 Explain
the terms stroke volume and cardiac
output and the relationship between them
(3 marks)
 Amount
of blood ejected form the ventricle
per beat
 Amount of blood ejected from the ventricle
per minute
 Relationship- SV x HR = Cardiac output
 Subject
A
heart rate= 80bpm; stroke volume =90mls
 Subject
Bheart rate=110bpm; stroke volume = 100mls
 Subject
Cheart rate160bpm; stroke volume=120mls
 When
1)
2)
we exercise this will change...
More blood enters the ventricle during
diastole (venous return) as it is flowing
faster round the body
Walls of the ventricle stretch and contract
more forcibly.
Starlings law of the
heart
The greater the venous return,
the greater the strength of
contraction.
How does stroke
volume increase
during exercise?
Increased
venous return
Greater diastolic filling
Cardiac muscle stretched
Greater strength/ force of
contraction
Increased ejection fraction
 Increased
exercising heart rate and increased
stroke volume have a huge impact on Cardiac
Output
 Heart rate 200bpm
 Stroke volumes 180mls
 36 litres per minute
 Increase in Cardiac Output (Q) is to supply
working muscles with oxygen
What are the effects of
exercise on the heart?

heart rate increases

stroke volume increases

due to Starlings Law

cardiac output increase

because cardiac output= SV x HR