Many actions are controlled by autonomic nerves, except some, like breathing, can be interfered by the conscious, while others, like the beating of the heart, cannot. In fact, for breathing, the conscious decision can override the autonomic nerves such as holding your breath until a certain point. It’s like an admin user vs a guest user. But how does such privilege system work in terms of neurons? How does the control alternate between the conscious and the autonomic system?
“You are now manually beating your heart”. Nope, that doesn’t work no matter how hard you try it (except for Buddha monks I suppose), so does this mean there are no physical neuron connections between the conscious and the heart?
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TLDR: bodily functions aren‘t linked directly to the brain to reserve the brains capacity for your conciousness. Bodily functions sre outsourced to other parts of your nervous system, which your brain has no direct access to. Blinking and breathing are two exceptions.
First of all, from an evolutionary standpoint it makes sense that you can control your breathing and blinking both conciously and subconciously. You don‘t want to waste your brains capacity on something so mundane, but there may be times where you don‘t want to breath regularly (think of diving for example).
Generally speaking the brain has direct control of skeletal muscles. On the other hand the autonomic nervous system (ANS) has control of internal organs, smooth muscles and glands.
Skeletal muscles are those connected to the skeleton, such as the biceps. Basically all the muscles you need to move around. Smooth muscles are those are wrapped around other organs. For example the blood vessels can widen and shrink because of smooth muscles.
Breathing and blinking are the two functions that are controlled by both brain and ANS. Both work with skeletal muscles, hence your brain controls them. At the same time the ANS controls them since they are both functions you need to constantly do; conciously blinking and breathing all the time would be a waste of the brains capacity. Fun fact, other animals such as dolphins do conciously breath all the time.
Other bodily functions you just have no control over. They aren’t directly connected to the brain. They are only connected to the ANS, which controls them. The ANS in turn is connected to the brain, but only for stimulation and not control. For example panicking is a concious thing but it influences the ANS, which in turn regulates bodily functions to match the panic.
Your heart is a bit special. You cannot control your heartrate because it‘s not even controlled by the ANS. There is no nerve going to the heart that repeatedly sends a signal for every beat. The heart has its own pacemaker to control beating. The ANS can only stimulate it to beat faster or slower but it cannot override the heartbeat, nor can your brain. Also hormones can influence the heart, but that‘s even more complex.
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