ing heart rate of about 60-70 bpm is below the intrinsic rate of Title effect on
ID: 3516635 • Letter: I
Question
ing heart rate of about 60-70 bpm is below the intrinsic rate of Title effect on the force of lbre parasympathetic activity to the heart than SA node. Parasympathetic stimulation of the SA node 16, textbook). Today we will see how resting and exercising have an effect on the astonomic nervous system, in turn, influencing the heart rate. ile sympathetic stimulation causes the cells to reach threshold at a faster rate (see Fie 14 causes the pacemaker cells to take longer to reach 1. After viewing Figure 14-16 in the text, how long does it take for an SA node cell (autohythmic cell) to go from-60 mV to the threshold of -40 mV without any neural stimulation? a) 0.1 sec b) 0.3 sec c) 0.8 sec When acetylcholine is released onto the SA node, what is the outcome? a) The SA node cells (autorhythmic cells) reach-40mV quicker. b) The SA node cells (autorhythmic cells) take longer to reach -40 mv. onto the SA node, what is the outcome? a) The SA node cells (autorhythmic cells) reach -40mV quicker. b) The SA node cells (autorhythmic cells) take longer to reach-40 mV. 3. When norepinephrine or epinephrine is released 4. During intensive exercise, which nervous system and neurotransmitter gains control of the autorhythmic cells? c) sympathetic, ACh a) parasympathetic; ACh b) parasympathetic; norepinephrine d) sympathetic; norepinephrine uith erercise there will also be changes in the ECG too.Explanation / Answer
1) I couldn't find the figure attached. However since normal heart rate is 72 beats per minute- the SA node must stimulate the heart musculature 72 times in 60 seconds which implies every 0.8 seconds a new action potential must have been generated. Therefore, option c- 0.8 seconds is correct.
2) Acetylcholine has parasympathetic effects on heart. Thus on release of acetyl choline in SA node, the SA node takes longer to reach threshold. Option b is correct.
3) Both norepinephrine and epinephrine have sympathatic effects on SA node and thus the release of these causes SA node to reach threshold quicker. Option a is correct.
4) During exercise or emotional excitement or any other phenomenon ehich causes heart rate to rise, sympathatic system is activated and thus norepinephrine neurotransmitter comes into action. Option d is correct here.
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