1. Although the origin of the
heartbeat comes from within the
heart (the SAN), it is necessary
for the heart rate
to be modified to meet the
different demands of the body
This modification is controlled by:
2.Nervous system
3.Hormonal system

2. 1. Nervous System controlling Heart Rate
‘fight or flight’ responses ‘relaxing’ responses
Sympathetic nerves release Parasympathetic nerves release
Neurotransmitter molecules Neurotransmitter molecules
to INCREASE heart rate to DECREASE heart rate

3. The medulla oblongata contains the
cardiovascular centre

4. 1. Nervous System controlling Heart Rate
Two nerves link the cardiovascular
centre in the medulla oblongata of
brain with the SA node of the heart
1. Accelerator nerve
2. Vagus nerve
(sympathetic NS).
(parasympathetic NS).
When stimulated, When stimulated, releases
releases neurotransmitter at the SA node to
neurotransmitter DECREASE heart rate
at the SA node to
INCREASE heart rate
Numerous sympathetic
nerves also link to
the walls of the
two ventricles where they
increase the force of
contraction of these
chambers

5. 1. Nervous System controlling Heart Rate
The heart rate is therefore determined
by the balance between sympathetic
and parasympathetic nerve activity
The cardiovascular centre receives
input from 4 main receptor groups,
these inputs are processed and the
sympathetic/ parasympathetic NS is
recruited accordingly.

6. Receptor groups that send inputs to
the cardiovascular centre
1. Pressure receptors in heart
2. Chemoreceptors in heart (detects
CO2 and O2 levels via changes in pH)
3. Thermoreceptors in muscles
4. Stretch receptors in muscles

7. Controlling
Heart rate

8. How does the nervous system
control heart rate during exercise?
1. During exercise oxygen is used up more rapidly, this
decrease in O2 concentration and increase in CO2
chemoreceptors
concentration is detected by …………………… in the
Heart
…………. The body responds by dilating veins.
2. This causes more blood to be returned to the heart and
therefore the heart is stretched more and the pressure
in the heart increases.
Stretch receptors and
3. This is detected by …………………
Heart
pressure receptors in the …………….
……………………
4. The cardiovascular centre processes this
information and responds by making the heart beat
and faster With greater strength

9. How does the nervous system
control heart rate during exercise?
1. During exercise oxygen is used up more rapidly, this
decrease in O2 concentration and increase in CO2
concentration is detected by …………………… in the
…………. The body responds by dilating veins.
2. This causes more blood to be returned to the heart and
therefore the heart is stretched more and the pressure
in the heart increases.
3. This is detected by ………………… and
…………………… in the …………….
4. The ..................................... processes this information
and responds by making the heart beat,...........
and ....................................

10. One heart beat = 0.8s

12. 1. Nervous System controlling Heart Rate
When do you think:
c) the Sympathetic NS is most dominant?
d) the Parasympathetic NS is most
dominant?

13. 1. Nervous System controlling Heart Rate
When do you think:
• the Sympathetic NS is most dominant?
Stress and excitement
• the Parasympathetic NS is most
dominant? Rest and sleep

14. 2. Hormonal System controlling Heart Rate
• The hormone adrenaline is secreted
from the adrenal glands.
• Adrenalin increases heart rate by
• increasing the frequency of impulses
released from the SAN,
• increasing the force of contraction
Therefore CO will…….