Download 3 Control of heart rate

Review: The Cardiac Cycle
1. Label the diagram of the heart in as
much detail as you can.
2. Annotate the next three diagrams to
show the different stages of the
cardiac cycle.
What structure?
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The cardiac cycle
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Myogenic stimulation of the heart
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Today we are covering from the
specification:
How is the nervous system organized?
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Control of Heart Rate
Autonomic
Sympathetic
Positive stimulation
(speed up activity)
Uses the
neurotransmitter
noradrenaline.
Parasympathetic
Inhibitory
(slows down activity)
Uses the
neurotransmitter
acetylcholine.
Control of heart rate
Heart rate is controlled by the part of the brain called
cardioregulatory centre in the medulla oblongata
Has two centres:
1.Acceleratory centre - Increases heart rate (linked to
the sinoatrial node by the sympathetic nervous system)
2.Inhibitory centre - Decreases heart rate (linked to the
sinoatrial node by the parasympathetic nervous system)
The centre that is stimulated depends on:
•Chemical changes in the blood
•Pressure changes in the blood
Control by chemoreceptors
Found in the walls of the carotid artery and
aorta (in the carotid and aortic bodies).
Sensitive to
changes in the pH
of the blood that
result from
changes in carbon
dioxide
concentration (in
solution CO2 forms
carbonic acid.)
When the blood has a higher than normal
concentration of CO2, pH decreases.
Chemoreceptors in the wall of the carotid arteries and
the aorta detect this.
Frequency of nervous impulses to the cardioregulatory
centre increases.
Frequency of impulses from accelerator centre via
sympathetic NS to the SAN is increased.
Heart rate increases.
Heart rate increases.
The increased blood flow that this causes leads to more
CO2 being removed in the lungs so CO2 levels return to
normal.
Chemoreceptors are no longer stimulated, so send fewer
impulses to the cardioregulatory centre.
Fewer impulses are sent from the accelerator centre to the
SAN so heart rate decreases back to normal.
Control by pressure receptors
Pressure receptors (baroreceptors) occur within
the walls of the carotid arteries and the aorta.
http://www.youtube.com/watch?v=G2nLL_O_U7w
When a blood pressure is higher than normal:
1) Nervous impulses are transmitted to the
cardioinhibitory centre.
2) Impulses are sent via the parasympathetic
nervous system to the SAN, decreasing heart
rate.
Control by pressure receptors
When a blood pressure is lower than normal:
1) Nervous impulses are transmitted to the
cardioacceleratory centre.
2) Impulses are sent via the sympathetic nervous
system to the SAN, increasing heart rate.
N.B. This system relies on the different neurotransmitters
released at the SAN by the two systems.
Brain
Cardioaccelerator
centre
Cardioinhibitory centre
Medulla oblongata
Spinal cord
Carotid body
Sympathetic nerve
Carotid arteries
Aortic body
Parasympathetic nerve
SAN
AVN
Right atrium
Right ventricle
Aorta
Left atrium
Bundle of His
Left ventricle
Try the questions on p142-143.