is the SA node controlled by the brain?

Question

my textbook says "the autonomic nervous system which includes the sympathetic and parasympathetic nerves in the brain stimulate the SAN".So that does mean the SA node needs signals signals from the brain to send impulses for the cardiac muscle to contract?Can it still contract on its own without the signals?My teacher said it is myogenic so does it mean it can contract without signals from the autonomic nervous system or does it needs signals to send impulses for the cardiac muscle to contract?if it can contract without the signals from the brain,then why are the parasympathetic and sympathetic connected to the SAN?What is its purpose if the SA node doesn't need impulses from the brain?also can the SA node function even if it wasn't connected to the parasympathetic and sympathetic nerves(autonomic nervous system)?

Answer 1

Your teacher is right - the heart does not need the brain to generate a heartbeat. In fact, if the SA node isn't' working the myocytes will contract on their own. The heart can be influence by the vagus nerve, which will slow it down, or by sympathetic stimulation, which will speed it up.



A completely denervated heart will still beat, and that is why heart transplants can be successful.

Answer 2

Pangolin is spot on. The SAN functions without the brain at a baseline. It can speed up with sympathetic input from the brain (sympathetic nerves) or slow down with input from the brain (via the vagus/10th cranial nerve). Actually, a normal SAN will have 'tonic' vagal input... this means that in a normal state, it actually wants to go off a lot more often than the always present vagal/parasympathetic input allows. At a resting heart rate, the parasympathetic/vagal input keeps it depolarizing at 60-100 beats per minute. When you exercise, the vagal input decreases so that it speeds up (it wants to speed up) and to get really high heart rates as in strenuous exercise, the sympathetic system increases the heart rate to those really high levels.

Answer 3

The heart has to have communication in order to adjust activity according to changing activity. If I remember correctly, the vagus (cranial nerves are outgrowths of the brain) and other contributors are innervative to the SA node but the heart is always ready to contract and does have myogenic contractile tendencies but is moderated by other factors.

Answer 4

Your medulla oblongata controls how fast your heart beats. Yes, the SA nodes produce electrical activity but your brain tells your heart how fast it needs to beat.