SunsetDriver
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I'm currently revising control of heart rate and using 2 different textbooks- my CGP book and OCR textbook. However, I am slightly confused.

Im trying to understand what happens when there is high O2 levels in the blood: the CGP book states that:

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However my OCR Textbook states:

Name:  controlling heart rate.PNG
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I wanted to confirm that is it the frequency of nerve impulses that are sent to the medulla decrease the frequency of impulses that reach the SAN via the sympathetic system? (and hence more impulses are sent through the parasympathetic system) Or is it impulses being sent along the parasympathetic neurones that causes them to secrete acetylcholine which decreases the heart rate?
Last edited by SunsetDriver; 1 year ago
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acromo123
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It's a lot more trickier than it. IT's essentially the impulses from the medulla that do the job.
What your textbooks don't say is that the medulla sends impulses along both parasymp and symp. Essentially when heart rate needs to be increased, more impulses are sent to this "vasomotor" centre from the medulla which is responsible for sending MORE impulses to the SAN via the symp nerves, but at the same time, the medulla also sends impulses to another part (forgot the name) that sends less impulses to the SAN via the Parasym nerves. Essentially what it does is it increases the symp and decreases the parasym.
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SunsetDriver
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(Original post by acromo123)
It's a lot more trickier than it. IT's essentially the impulses from the medulla that do the job.
What your textbooks don't say is that the medulla sends impulses along both parasymp and symp. Essentially when heart rate needs to be increased, more impulses are sent to this "vasomotor" centre from the medulla which is responsible for sending MORE impulses to the SAN via the symp nerves, but at the same time, the medulla also sends impulses to another part (forgot the name) that sends less impulses to the SAN via the Parasym nerves. Essentially what it does is it increases the symp and decreases the parasym.
Ok, but for a-level knowledge, which info is more reliable
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acromo123
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(Original post by SunsetDriver)
Ok, but for a-level knowledge, which info is more reliable
for alevel, just understand that if HR needs to be increased, medulla sends MORE impulses THROUGH SYMP fibres to the SAN (noradrenaline secreted by them which binds to SAN receptors,), apposite for if HR needs to be reduced (and ACh instead)
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SunsetDriver
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(Original post by acromo123)
for alevel, just understand that if HR needs to be increased, medulla sends MORE impulses THROUGH SYMP fibres to the SAN (noradrenaline secreted by them which binds to SAN receptors,), apposite for if HR needs to be reduced (and ACh instead)
thanks so would u say the info on controlling heart rate in the ocr textbook isn't the best?
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