carotid sinus vs aortic arch

[3dee]

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If a pt has high BP, both the carotid sinus and aortic arch are stimulated, right?

For the carotid sinus, is CN9 the afferent and CN10 the efferent?

and for the aortic arch it's just CN10?

First aid isnt too clear on this. Clarification would be awesome!

thanks

 

[loveoforganic]

Looks right to me. I'm not sure how much of a role the arch actually plays in BP regulation, but in theory it does respond to pressure increases

 

[Phloston]

Side note:

One of the highest yield details I've come across so far is that the central chemoreceptors are in the 4th ventricle and only respond to CSF H+. In other words, they don't respond to CO2 directly; they respond to CO2 indirectly via the H+ it produces through dissolution. I also underlined CSF because the protons must pass from the blood, through the BBB and into the CSF before being sensed. H+ is not sensed from the blood.

Also, if CNIX firing increases from the carotid due to increased BP, increased efferent vagal stimulation decreases HR and BP, leading to a compensatory DECREASE in vagal firing from the aortic arch.

 

[JackShephard MD]

If a pt has high BP, both the carotid sinus and aortic arch are stimulated, right?

For the carotid sinus, is CN9 the afferent and CN10 the efferent?

and for the aortic arch it's just CN10?

First aid isnt too clear on this. Clarification would be awesome!

thanks

For the carotid sinus, it responds mostly to decreases in BP (although increases also) the afferent nerve is IX and it is sent to the vasomotor center in the brainstem (cardiovascular control center in the medulla). In the case of decreased BP, decreased parasympathetic activity to the heart would be sent (increasing HR).

The aortic arch has X as its afferent and will send its information to the same place. It only responds to increases in BP (BRS physio - as mentioned above, although I did take a look in Lily Cardiology, it doesn't go out of the way to explain this). Increases in BP for either baroreceptor would lead to increased parasympathetic tone.

 

[loveoforganic]

Side note:

One of the highest yield details I've come across so far is that the central chemoreceptors are in the 4th ventricle and only respond to CSF H+. In other words, they don't respond to CO2 directly; they respond to CO2 indirectly via the H+ it produces through dissolution. I also underlined CSF because the protons must pass from the blood, through the BBB and into the CSF before being sensed. H+ is not sensed from the blood.

Just to give a mechanism beyond fact memorization - this is due to the BBB. Passage of charged compounds is going to be restricted while nonpolar/tiny CO2 can freely diffuse. This is also why there's a short lag period in ventilatory response to pH changes

 

[Phloston]

For the carotid sinus, it responds mostly to decreases in BP (although increases also) the afferent nerve is IX and it is sent to the vasomotor center in the brainstem (cardiovascular control center in the medulla). In the case of decreased BP, decreased parasympathetic activity to the heart would be sent (increasing HR).

The aortic arch has X as it's afferent and will send it's information to the same place. It only responds to increases in BP (BRS physio - as mentioned above, although I did take a look in Lily Cardiology, it doesn't go out of the way to explain this). Increases in BP for either baroreceptor would lead to increased parasympathetic tone.

I've always heard that the solitary nucleus of the medulla is the relay center. Is this what you mean by "vasomotor center?"

 

[Phloston]

Just to give a mechanism beyond fact memorization - this is due to the BBB. Passage of charged compounds is going to be restricted while nonpolar/tiny CO2 can freely diffuse. This is also why there's a short lag period in ventilatory response to pH changes

I'm on 4 hours of sleep and had just posted in the cardiovascular thread, so when I saw your comment, I was like, "why in the world is he talking about bundle branch blocks?" Wow.

 

[JackShephard MD]

I've always heard that the solitary nucleus of the medulla is the relay center. Is this what you mean by "vasomotor center?"

You're correct, the caudal portion of the nucleus solitarius is the cardiorespiratory center that is the initial relay, but eventually it relays to the vasomotor center (rostral ventrolateral medulla), here's Costanza physio:

the vasomotor center receives information about blood pressure from baroreceptors in the carotid sinus and compares this information to a blood pressure set point. If corrections are necessary, the vasomotor center orchestrates changes in output of both the sympathetic and the parasympathetic innervation of the heart and blood vessels to bring about the necessary change in blood pressure.

It's analogous to a respiratory center (i.e. not the actual afferent nucleus always).