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Practice Set 4 P.2 #13 & Channels Question
Keira_6444
#1 Posted : Friday, June 18, 2021 8:08:29 PM
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Hi for #13 in passage 3, the question asks "in healthy individuals, heart rate is controlled by..." and the answer says "Ach release by the PSNS" which I agree with. However wouldn't option D "Epinephrine/NE release from the SNS" also be true? Because doesn't the SNS increases HR and the PSNS decrease HR?

Also, would you be able to clarify the difference between ligand-gated and voltage-gated channels and where they function in the axon and axon terminal? I am getting a little confused with the terms and which ion (K+ or Na+) is used for which one?

Thanks!
INSTR_Shinthujah_131
#2 Posted : Monday, June 21, 2021 7:11:35 PM
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Hi Keira,

1) Acetylcholine and Epinephrine do regulate our heart rate as necessary, however, this questions speaks to how our SA node has parasympathetic innervation on a day to day basis in order to maintain our resting HR around 60-80 bpm. Our intrinsic HR is actually quite high so we have a constant vagal tone (vagus nerve innervation, acetylcholine) to reduce it to our working resting HR.

2) Ligand-gated channels require ligand binding (via neurotransmitters for example) to open channels whereas voltage-gated channels require a change in voltage (specific to the channel) to open and close it. VG-channels are typically found throughout the axon and LG-channels are found in the dendrites/axon terminal.

Hope this helps!
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