My mind runs through things way too much, and one of the topics I’ve been thinking about today while working on the farm is re-attaching severed heads. Medical science has already learned how to re-attach arms, legs, and penises with success (even, I assume, re-attaching motor and sensory nerves). Also, cryogenic technology enables bodies to survive transplants of vital organs (I’ve heard too that severed limbs stand a better chance of re-attachment if kept cold). It also occurred to me that brain damage and brain death was forestalled for unlikely lengths of time by cold in more than one case (IIRC) of drowning in extremely cold water.
(DISCLAIMER: I admit I am ignorant, let’s just get that out of the way. One monkey wrench in the works here is that nerve tissue, such as the spinal cord, can’t be easily re-attached, right? Just thought of that.)
Given these facts (and I’m sorry there are no cites, slap me or something), I have been wondering how close medicine is to being able to save decapitation victims? Have there been any attempts, or successful re-attachment of partially severed necks? It seems that with cryogenics and microsurgery, someone should be able to come up with a way to re-attach a severed head. Any thoughts?
Being as you only have minutes before the brain begins to die from anoxia, I don’t see it being possible in any practical sense, even if the technical challenges can be overcome. In the field, the victim would be dead before the paramedics even got there.
Except in the most unlikely circumstances (head bitten off by giant clam while scuba diving in freezing waters), head reattachment surgery is unlikely ever to come up in the emergency room, largely because brain death will have occurred long before the victim ever shows up in the ER. Not to mention that most accidental decapitations are unlikely to be made with surgical precision, so the various components are not likely to be in mint condition.
You might broaden your query to how likely it is to have a full body transplant in cases where a victim is brain dead and another person is dying and requires a new body. Surprisingly enough, doing a search on head transplant indicates that some [reasonable but controversial progress has been made.](http://news.bbc.co.uk/1/hi/health/1263758.stm)
Did you ever see the episode of Futurama where Fry had his head transplanted onto Amy's shoulder? Not so far from the mark, as it turns out.
I learned in training that we do not have the technology to reattach nearves at all. If a bullet wound goes through your phrenic nerve, that’s it. There’s no way to sew the nerve back together. Good thing we have two of those.
When learning about heart transplants I was told that the nerves are not reconnected. Because of this, there is no innervation to a transplanted heart. It’s rate is controlled by hormones only and not neurotransmitters.
Am I way off here? Can we sew nerves back together and fix ripped nerves?
I doubt if there is even any investigation in this area. My guess is that the other trauma in a decapitation is so great that the loss of a head is almost a side issue.
Erm, for one thing neurotransmitters are hormones. Perhaps the ones most immediately important to control of cardiac function are certain catecholamines and acetylcholine. It’s true that an unenervated heart can keep pumping just fine, as it’s got its own network of “pacemaker” cells and a system of conductance that allows it to maintain a life-sustaining rate of contraction autonomously. Anyone with the right kind of spinal cord injury provides a good example of this.
In the case of heart transplants, I don’t know, but it is quite possible to stitch nerves together, and they can heal well enough after severing and religation to restore function. Some nerves simply heal on their own. As long as it’s not the central nervous system, that is. Break your back, or (urk), sever your head, and you’ve got a cut that won’t heal. But it seems to me, theoretically, at least, that it ought to be possible to hook up a donor heart to a recipients vagus nerve, for instance, so long as some portion of the donor vagus nerve is carried over with the heart and survives. Again, I have no idea if this is done in practice, but in principle, it shouldn’t be impossible.
loopydude, while some chemicals can act as both hormones and neurotransmitters, I believe it incorrect to claim "for one thing neurotransmitters are hormones. Hormones are systemic. Neurotransmitters are local - effecting just their particular neural junction.
Am I incorrect? Is this just symantics? This is just how I learned it.
This is specifically what I was told could not be done. And because the vagus nerve is not around to tell the heart to slow down (through neurotransmitters), the heart relies on hormones produced to tell it the body no longer requires a greater output and faster heart rate. This process works, but not as well as it would with the parasympathetic vagus nerve around doing its job.
Again, I could be off… if I am, I’d like someone to convince me. It shouldn’t be too hard.
Actually, now that I think about it, an injury to the spinal cord should not necessarily affect the vagus nerve, as it originates in the brainstem and runs down the neck next to, but not within, the spine.
Mary Roach’s book <i>Stiff: the curious lives of human cadavers</i> covers this question and plenty more. I just finished reading it – it manages to be both funny and strangely heartwarming while educating us on the ways of corpses. Check it out!
No, the whole head is actually easier. No one at this point is talking about the science-fiction idea of transplanting someone’s brain into a new body that they can live in normally. What the OP raises is the idea of keeping someone’s head alive using a body as a life-support system. They would effectively be a quadraplegic, paralyzed from the neck down. But the nerve connections in the head would remain intact; at least they’d still be able to see, hear, feel from the neck up, and maybe even talk with some artificial assistance. By contrast, a brain transplant, if it could be done at all, would condemn the subject to total sensory deprivation. A hellish prospect.
Well, I’ve seen about 15 different definitions of “hormone”. At their most restrictive, they define chemical messengers secreted by specialized cells that are transported throughout the body by the bloodstream to other cells, affecting their function. I don’t like this definition. There’s lots more to fluids of the body than the bloodstream, and hormones can be transported through all of them. A better definition, IMO, is “A chemical messenger within the body that is secreted by one type of cell and acts on another type of cell.” A lot of the definitions for “hormone” seem to have and implicit or explicit requirement that the messenger act over some great distance. Well, how great does it need to be? It’s really arbitrary. So, I say, if it’s made by one type of cell, say a motor neuron, and acts on another cell, say a skeletal muscle cell, it’s a hormone. So, according to my preferred definition, acetylcholine, wich is secreted at neuronal terminals of the vagus nerve and acts on cells in the myocardium, is acting as a hormone. I guess it’s best to say neither one of us is wrong, but I hope I can convince you that most definitions of a hormone, especially ones that restrict transport to the blood circulatory system, are inadequate, and broader definitions are technically and conceptually more useful.
As for the heart transplant stuff: Again, I have no clue. It just seems to me that if peripheral neurons can be ligated and heal well enough to allow some level of functionality, why not those that ennervate the heart? However, this rule may not apply to, say elements of the parasympathetic nervous system. I really don’t know, and don’t know all that much about the nuts and bolts of heart transplants. I should, as I work in cardiovascular science, so I’m a tad embarassed. I’ll hit up some real cardiologists tomorrow for some answers!
Peering into the crystal ball, I assume the first head “transplant” would actually be more like a head and full spinal transplant, when it becomes possible. Which, with enough time and medical progress seems a definite possibility.
Major Problems Associated with such a procedure:
(1) Damage to Hard Tissue
(2) Damage to Soft Tissue
(3) Damage to Nervous System
(4) Stasis of Head and Body
(1) Damage to Hard Tissue: Spinal Vertebrae can be repaired, or at least a structural equivalent can be fabricated to support the head.
(2) Damage to Soft Tissue: The neck contains a number of major blood vessels, including the internal and external carotid arteries as well as the exterior jugular vein. But skin, muscle and blood vessels can be repaired.
(3) Damage to the Nervous System: This is by far the most difficult task here. The organization and complexity of the nerves running down the spinal column are beyond comparison. As of right now, we have only begun to understand the repair mechanism used in the periphery nervous system of damaged neurons using myelin debris to regrow and resynnapse. However, no such repair system has been identified in the Central Nervous system as of yet. Re-aligning the specific nerves with their correct counterparts would also be very difficult, since determining the origin and termination of nervous pathways, not to mention the pathway itself, is nearly impossible. Especially since most pathways rely on multiple synaptic connections be made. The depth of this part is far more than I have the space to go into here, leave it to say that it will be nearly impossible to generate a model for it, on top of which, as we all know, everyone is a little different.
(4) Stasis of Head and Body: This is also very difficult. Both the head and body must be maintained in such a way that either (a) homeostasis is maintained and all the cellular and tissue requirements are met - daunting in itself, or (b) cellular function and degradation can be stopped in such a way as to not damage the cells or their components. This hasn’t been found to be possible yet. Cryogenics doesn’t even appear to be able to do this, since the freezing process used causes ice crystals to form within the tissue, and these crystals will most likely damage the walls of the cells beyond repair. The freezing and re-thawing of single celled organisms may be possible, but due to the number and complexity (not to mention the variable constituencies of the cells/tissues) of the human head and body make this near impossible.
In other words: I wouldn’t hold my breath.
