Earlier this evening I repaired a cassette tape. The repair was simple enough – the leader had broken, but enough of it was left over so that when I opened up the cassette and attached the remaining piece to the reel I’m not already into the brown magnetic portion of the tape every time I press ‘play’, but it led me to thinking about cassette tapes, CDs, mp3s, etc. The benefits of technology, etc. Because although I’ve repaired several tapes, I’ve never yet had to repair a CD. Not that I’d know how, aside from the polishers that I’ve seen for sale. And to repair an mp3? Forget it.
There is a connection here to the difficulty that the medical community presently has with death, though for the moment I forget what it is (I placed the newspaper article down on the computer before I left earlier, since I saw the connection, but now that I’ve returned to the keyboard the thought has flown). And by problem with death, I don’t mean delaying death; I mean deciding when to declare it.
100 years ago, when you were dead, you were dead. No pulse? That’s it; send for the grave-diggers. But then we began to parse death. What do we do with someone who continues to have a pulse, but is irresponsive to all stimuli? Is this person alive? Technology advanced, and things only got messier. Heart-lung machines enable the body, and sometimes the mind to survive periods of death. Heart transplants involved patients living without hearts in their bodies at all, albeit only for the period between when their own heart was removed and the donor heart installed. CPR confused matters as well, as did defibrillation, with their abilities to return a nonbeating heart to proper order.
At the same time, we plunged further into the brain, developing EEGs and debating over the meaning of “brain death”. Some of you will remember the Terri Schiavo case of 2005, which revolved on this issue, among others, but another focus of this discussion is organ donation. Organ viability rapidly declines after perfusion ceases, or even decreases below normal levels. Thus, it is in the best interest of the patient receiving the organs to declare the death of the donor earlier, rather than later. Of course, it is arguably in the best interest of the donor to declare death later, rather than earlier. The same declaration of death must be used for both contexts.
I am here reminded of sub-subatomic particles. The presence of electrons, neutrons, and protons seems obvious to anyone looking at atomic structure, but what about quarks, mesons, etc? Did these only come into being once we shattered our protons and neutrons, much as the shards of a mirror only come into being once the mirror is shattered?
Well, it's late, and I'm tired. I don't know how coherent this is, but I'm off to bed.
Source: Nano, Stephanie. “Doctors Examine When to Declare Organ Donors Dead”. p8B, The Journal News, 14 August 2008
EDIT: in an earlier version of this article it was incorrectly stated that for organ recipients, best practice was to declare the death of the donor later rather than earlier. This is incorrect: organ viability decreases as blood flow decreases, thus donated organs are healthier if harvested earlier. Some spelling errors were also made.
Showing posts with label neurology. Show all posts
Showing posts with label neurology. Show all posts
Saturday, August 16, 2008
Thursday, March 6, 2008
Delegation of authority: the brain and the spinal cord
We tend to think of our brain as being the processing center of our body, making all decisions and directing all activity. The truth is that, while the brain does direct the actions of our body, it delegates a lot of control to the spinal cord.
The most obvious example of this is our reflexes. When you touch a hot stove, you reflexively withdraw your hand; the pain signal travels to your spinal cord and directly triggers the nerve circuit that activates the muscles in your arm, so by the time your brain is aware of what is happening, your hand has already been safely removed from danger. This is good, because it reduces the amount of time that our hand is on the stove, and so reduces the amount of damage we sustain.
Similar to this is the stretch reflex. When we receive something into our hands, we mentally estimate how much the object will weigh. We then activate enough of the cells in each muscle to exactly balance that estimated weight, and usually we're pretty close. Our hand might fall or rise slightly as we fine tune the amount of force we use to hold the object, but the movement is minor and smooth. If our estimate is far off, however, there is a more violent reaction. If we underestimate the weight, the object falls, and pulls our hand down with it, and we quickly exert more force to prevent the object from slipping out of our hands. This reflex, whether it is the fine adjustments of the first scenario or the gross adjustments of the second, are also regulated at the spinal cord.
Walking is a more complex example. As we learn to walk, much of the processing and regulation is done by the brain. Once we're adept walkers, however, the task is handed off to the spinal cord, with the brain only providing general directions. More specifically, the brain determines the direction and speed, and the spinal cord takes care of moving the feet.
Climbing or descending stairs is handled similarly, with one exception. Walking involves flat ground - whether we walk on the street or in our homes; the experience is the same. Stairs add a third dimension, and the amount we have to figure out how much to raise our foot for each step if we are to gracefully climb the stairs rather than trip and fall on them. Here, the brain steps in briefly - we look at the beginning of a staircase, using eye-foot coordination to safely land our feet on each of the first two steps, but if we're dealing with a regular staircase (i.e. each step is the same height and the same depth) our spine takes the height and depth information and plugs it into the general procedure for climbing stairs. At this point we focus our brain's attention, and our eyes, somewhere else until we reach the other end of the stairs, when our brain tunes in again to issue a "stop climbing stairs, start walking" order.
As with many phenomena, this is most obvious when something goes wrong. If you've ever tripped over an extra-high step in the middle of a staircase, or placed your foot down heavily on a step that wasn't as tall as those before it, you've experienced a case where the spinal column expected a step to be in one place, and directed your leg muscles to put your foot there - where the step turned out not to be. Your brain then steps in to clear up the confusion, and you're on you're way again.
Incidentally, this is a reason to be careful with home-made stair cases - the top and/or bottom steps are often of a different height than the rest of the staircase (building a set of stairs properly is more difficult than you might think).
And, no surprise, perhaps, this brings me back to driving once again. Much of driving is routine, and over time I expect that we hand off a lot of control to our spinal cord, and we turn our attention elsewhere. Unfortunately, the consequences of blithely missing a step, though occasionally severe, rarely approach the seriousness of blithely driving our car into an accident.
Inspired by: http://www.ethanhein.com/memebase/solving_problems/darwin_saves.html#saccade.
The most obvious example of this is our reflexes. When you touch a hot stove, you reflexively withdraw your hand; the pain signal travels to your spinal cord and directly triggers the nerve circuit that activates the muscles in your arm, so by the time your brain is aware of what is happening, your hand has already been safely removed from danger. This is good, because it reduces the amount of time that our hand is on the stove, and so reduces the amount of damage we sustain.
Similar to this is the stretch reflex. When we receive something into our hands, we mentally estimate how much the object will weigh. We then activate enough of the cells in each muscle to exactly balance that estimated weight, and usually we're pretty close. Our hand might fall or rise slightly as we fine tune the amount of force we use to hold the object, but the movement is minor and smooth. If our estimate is far off, however, there is a more violent reaction. If we underestimate the weight, the object falls, and pulls our hand down with it, and we quickly exert more force to prevent the object from slipping out of our hands. This reflex, whether it is the fine adjustments of the first scenario or the gross adjustments of the second, are also regulated at the spinal cord.
Walking is a more complex example. As we learn to walk, much of the processing and regulation is done by the brain. Once we're adept walkers, however, the task is handed off to the spinal cord, with the brain only providing general directions. More specifically, the brain determines the direction and speed, and the spinal cord takes care of moving the feet.
Climbing or descending stairs is handled similarly, with one exception. Walking involves flat ground - whether we walk on the street or in our homes; the experience is the same. Stairs add a third dimension, and the amount we have to figure out how much to raise our foot for each step if we are to gracefully climb the stairs rather than trip and fall on them. Here, the brain steps in briefly - we look at the beginning of a staircase, using eye-foot coordination to safely land our feet on each of the first two steps, but if we're dealing with a regular staircase (i.e. each step is the same height and the same depth) our spine takes the height and depth information and plugs it into the general procedure for climbing stairs. At this point we focus our brain's attention, and our eyes, somewhere else until we reach the other end of the stairs, when our brain tunes in again to issue a "stop climbing stairs, start walking" order.
As with many phenomena, this is most obvious when something goes wrong. If you've ever tripped over an extra-high step in the middle of a staircase, or placed your foot down heavily on a step that wasn't as tall as those before it, you've experienced a case where the spinal column expected a step to be in one place, and directed your leg muscles to put your foot there - where the step turned out not to be. Your brain then steps in to clear up the confusion, and you're on you're way again.
Incidentally, this is a reason to be careful with home-made stair cases - the top and/or bottom steps are often of a different height than the rest of the staircase (building a set of stairs properly is more difficult than you might think).
And, no surprise, perhaps, this brings me back to driving once again. Much of driving is routine, and over time I expect that we hand off a lot of control to our spinal cord, and we turn our attention elsewhere. Unfortunately, the consequences of blithely missing a step, though occasionally severe, rarely approach the seriousness of blithely driving our car into an accident.
Inspired by: http://www.ethanhein.com/memebase/solving_problems/darwin_saves.html#saccade.
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