In the case of a spinal break that causes someone to become paralyzed, why would organs and other bodily functions un-affected if the cause is a separation of the brain’s ability to communicate with the body? Does the brain not also subconsciously control breathing, heart beat, etc?
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So, if you get a spine break too high up, you will stop breathing. The nerve that controls the lungs separates from the spinal cord a lot sooner than the rest of the nerves though, meaning it’s possible – if the break is low enough – to have your arms paralyzed but still breathe.
Your heart is neat in that it can actually control itself! Your brain doesn’t need to tell your heart to beat, the heart sends itself its own triggers to keep beating. You can see this effect when someone gets heart surgery, and the removed heart keeps beating outside of the body.
I’m not sure about many others. This is all just superficial knowledge from a Lifeguarding class years ago.
**Edit:** As u/Med_vs_Pretty_Huge pointed out, the nerve doesn’t control your lungs, but rather your diapraghm, which is the muscle that makes you breathe.
The heart and lungs are innervated (that is: receive nerve signals) from nerves that actually begin above the spine, including the vagus nerve and the glossopharyngeal nerve.
This means that even spinal chord damage done high on the spine is unlikely to stop the heart and lungs.
But it can still make things harder – the muscles around the heart and lungs receive innervation from normal spinal nerves. Thus the diaphragm can be paralysed, making anything but the most shallow breathing very hard and the contractility of the heart can be reduced, again leading to shallow beats, even if the heart rate is normal.
But as you’ve noticed, other organs don’t completely shut down, even after a very high spinal injury.
This is because of the autonomic nervous system.
In essence, most of your organs have their own set of nerves that they use to send signals back and forth and which act independently from thought or signal from the brain.
With this in mind, the kidneys will keep filtering blood, the intestines will continue peristalsis and so on at a sort of baseline level.
What will change is any time that baseline level isn’t enough as well as any point that normally needs somatic (conscious) control.
For example, if you eat a big meal and your stomach stretches, normally it sends a message to the brain saying “get the intestines ready, this is a big one”. But without the spinal cord, this message gets lost and so it can lead to distension (uncomfortable swelling of the intestine) and blockage, so many paraplegics find they need to eat smaller meals and avoid certain foods.
Similar, the bladder can’t send a message saying “I’m full, we need to urinate”, so paraplegics may find themselves urinating unexpectedly or developing distension and UTIs if the bladder doesn’t void itself – sometimes leading to a need for 24/7 catheterization.
Even with the autonomic nervous system doing it’s best, we are often surprised at the number of functions that diminish or stop entirely when the spinal cord is disrupted – it is not a fun injury.
A lot of the organ functions are regulated through the endocrine or hormone system. Your brain will release chemicals that make it to your thyroid and the thyroid will then release chemicals into the blood and those chemicals will then act on the organs triggering further chemical reactions. The endocrine can typically skip the spinal stimulation altogether albeit some may travel down the spinal area or through the spinal fluid, as long as they enter the blood stream they’ll make it to the organ. Sometimes hormones can go straight from the brain to the organ. Typically the hormones are made in super long strands and cut up into pieces and delivered to multiple organs at once. Since the lungs and heart work directly with the muscles they are more susceptible to nerve damage. Some bodily functions are regulated from the top of the spine and into the medulla or bottom of the brain so these functions would still be regulated as normal with a mid or lower spine injury.
Well, if it does happen, we don’t tend to call them “paralysed”. We tend to say “they died from a broken neck”. People don’t often get effective treatment for that, or at least not fast enough to survive it and be declared as paralysed XD
That said, it can happen. The catch is that the nerves for your organs tend to split off from the spinal chord fairly early in comparison to your arms/legs.
If we brake your spine at the hips, your arms will be fine because the nerves in your arms split off from the spine before that.
If we break your spine by the shoulders, your lungs will probably be fine because the nerve controlling them doesn’t reach that point. (In fact, I’m pretty sure in the lung & heart’s case, they’re connected to the vagus nerve, meaning they avoid the spinal column entirely.)
The other catch is that some of these essential organs can do fine on their own without the brain. They can have small, autonomic nervous systems of their own that can send signals back and forth to themselves. Your heart for example can continue to keep rhythm even if its connection to the brain is severed.
Think about it like this
Your spine has a lot of nerves in it. Its effectively a giant stick with strings coming out of it at different points that tell different parts of your body what to do
The higher you go, the more important the bodypart. The lower you go, the less important the body part
Something like control of the lower limbs can be lost and you can still maybe survive to have kids. This is true maybe even for upper limbs, although less so
However, if you became unable to breathe, then ho boy you’re probably not going to survive
For this reason, over the course of hundreds of thousands of years, the human body basically sorted the spine so that the most expendable functions were at the lower portion of the spine – where we are most likely to sustain damage
Of course, there are a lot of exceptions, like the heart, which can pump itself. Hopefully this cleared things up!
Other answers have talked about the heart and lungs, so I won’t repeat that, but there are other bodily functions that don’t rely on nerves from the brain.
For example, many organs communicate via hormones (e.g. adrenaline, ghrelin, and a million others)
Another striking one is that the digestive system effectively has [its own brain](https://gut.bmj.com/content/47/suppl_4/iv15), which is pretty mind blowing!
Not all organs function directly from nerves coming from the spinal cord.
Breathing does have some nerves from the spinal cord, but the nerves involved come from very high up in the spine, so you would need damage high up to stop breathing.
Other organs do have nerves going to them that don’t go through the spine. The vagus nerve is one of these and is a major component of the autonomic nervous system and has an impact of how the organs work.
There are also other ways the organs work that don’t involve nerves at all. Hormones (chemicals secreted by one organ into the blood to have an effect of other part of the body) is one way. For example insulin. When we eat and digest food, the sugar goes into our blood. To be able to come out of the blood into tissues that need it, our pancreas makes and releases insulin. Insulin is like a key that opens a door to allow the sugar into other cells. Because the pancreas senses blood sugar levels directly from the blood, it is unaffected by spinal cord damage and continues to make insulin.
You then have other organs that function without nerves and with limited hormone input. The kidneys for example are effectively just filters. In very simple terms they sieve out waste products and some water to help get rid of them. This happens automatically. There is then some hormone control over how much or little it does this (eg if we are dehydrated we need to keep as much water as we can, so a hormone is produced to get the kidney to reduce the amount of urine produced).
Hope this helps
the human body wants first and foremost to live. I know that sounds silly but major adaptations through evolution were made with that goal in mind. If an injury would shut down a vital organ and leave the legs working we wouldn’t know because they would be dead.
wouldn’t it be an unconscious process, as opposed to subconscious – i don’t believe organs are controlled in any conscious way.
Hi I’m c5 complete. It was explained to me that the brain is not involved in certain operations like breathing at my level. C3 and above would require a ventilator. Also spinal injuries are very unique to the person eg complete or incomplete damage to the cord. My breathing is not normal though. No core function to help. Blood pressure is low by standard and hard to raise the same for heart rate. If I go balls out on the skierg probably get up to 120 bpm. At my level I also don’t sweat so very hard to regulate temperature in the heat. My level also suffers with autonomic dysleflexia. This means any pain below the level of injury would present its self with sweating rising blood pressure and pounding headache left untreated could cause a stroke. Anything below c7 don’t have this though
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