Acetylcholine: Can it be used as a NT for the SNS to increase cardiac output?

[To be MD]

EK 1001 has the following question following a passage about Starling's Laws (about Cardiac Output):

While deriving his 3rd law, Starling needed to increase the cardiac heart rate and may have used which of the following mechanisms to do so?

I. Acetylcholine
II. Norepinephrine
III. Epinephrine
_______________________________



The answer to the question says just II & III because "the SNS increases heart rate through Norep & Ep, and Acetylcholine is a PNS neurotransmitter--the PNS decreases heart rate."

Is it not true, though, that the Sympathetic Nervous system also uses ACh and, in this scenario, does so to activate the Adrenal Medulla's synthesis of Epinephrine which would also, eventually, increase cardiac heart rate?

---

Members don't see this ad.

 

[torontopharm]

EK 1001 has the following question following a passage about Starling's Laws (about Cardiac Output):

While deriving his 3rd law, Starling needed to increase the cardiac heart rate and may have used which of the following mechanisms to do so?

I. Acetylcholine
II. Norepinephrine
III. Epinephrine

Is it not true, though, that the Sympathetic Nervous system also uses ACh and, in this scenario, does so to activate the Adrenal Medulla's synthesis of Epinephrine which would also, eventually, increase cardiac heart rate?

Sympathetic fire off ACh at the preganglionic neuron, and Norepi/Epi at the postganglionic neuron. Since whatever being released at the postganglionic neuron affects the target organ (effector), that's what we concentrate on for these questions.
Parasympathetic fire off ACh at the preganglionic neuron, and ACh at the postganglionic neuron.

 

[To be MD]

Sympathetic fire off ACh at the preganglionic neuron, and Norepi/Epi at the postganglionic neuron. Since whatever being released at the postganglionic neuron affects the target organ (effector), that's what we concentrate on for these questions.
Parasympathetic fire off ACh at the preganglionic neuron, and ACh at the postganglionic neuron.

Is this a representative MCAT question, you think? Because I don't see the reasoning as being wrong... ACh is used to make the adrenal glands pump out Epi which would increase heart rate

 

[aldol16]

Try to focus less on the minutiae and more on the overall big picture. That's what the MCAT is about. For these types of questions, also focus on primary, proximal drivers of effects. One could say that a random signaling molecule at a distant point in the pathway could exert some effect on heart rate as well, but you primarily want to focus on the ones that directly cause the effect. The MCAT will also be very unambiguous.

 

[torontopharm]

Is this a representative MCAT question, you think? Because I don't see the reasoning as being wrong... ACh is used to make the adrenal glands pump out Epi which would increase heart rate

Technically, you're right. But you see, ACh isn't directly acting on the effector (the heart) in the sympathetic system. In the sympathetic system, ACh directly acts on the adrenal medulla as you said, not the heart.
I think you're overthinking this a bit. Just know the general idea for the MCAT. While we're at this, also know how ACh always exerts excitatory effects on skeletal muscles at the somatic motor branch of PNS. I do think this makes a good MCAT question! They won't try to screw you by being ambiguous.

 

[Necr0sis713]

I don't know why this hasn't been mentioned.

AcH SLOWS the heartrate via the parasympathetic nervous system. It acts on muscarinic AcH receptors (as opposed to nicotinic).
Epinephrine acts with B-adrenergic receptors to speed heart rate.

Please look into this, because it's high yield.

Muscarinic Ach= inhibitory (usually)
Nicotinic Ach= stimulatory, or simply skeletal muscle.

 

[Astra]

Another way to think about this is the following:

You increase acetylcholine concentrations in the body.
What happens?
BOTH sympathetic and parasympathetic nervous systems are affected.
What is the net result?

Nothing. The parasympathetic nervous system would decrease heart rate the same amount the sympathetic would increase it.

If you increase epinephrine and norepinephrine, only affects the sympathetic nervous system and this causes a NET INCREASE