Sorry to bring this back on the table, but in the other thread I had said that the RLN probably had a reason/function for it's passage down under the aorta. I just read today what the textbook 'Gray's anatomy' had to say about it:
quote:As the recurrent nerve hooks around the subclavian artery or aorta, it gives off several cardiac filaments to the deep part of the cardiac plexus. As it ascends in the neck it gives off branches, more numerous on the left than on the right side, to the mucous membrane and muscular coat of the esophagus; branches to the mucous membrane and muscular fibers of the trachea; and some pharyngeal filaments to the Constrictor pharyngis inferior.
But there is no reason for the nerves fibers which communicate with the larynx to be so routed. You would further need a good reason why all the nerve fibers should be bundled together as the recurrent nerve.
If the shortest rail connection between Ottawa and Montreal was via Vancouver, one could hardly justify that design decision by pointing out that some people do in fact want to get off the train at Vancouver.
So it seems that it does in fact have a role in supplying parts of the heart, windpipe muscles, mucuous membranes and the esophagus.
No it doesn't. The Vagus nerve, of which the Laryngeal nerve is a part does. The Laryngeal nerve, as the name suggests, only goes to the larynx, it doesn't connect to anything else.
Can a discussion be continued based on this new information ?
It isn't exactly new, we know what the different nerve endings of the Vagus nerve connect to, and it does nothing to the argument that the Laryngeal nerve doesn't have to take that route from a design standpoint.
Watch this video of the dissection of a giraffe again, the nerve that goes down is the Vagus nerve (listen to the woman doing the dissecting, she esplains this), which "splits" at the bottom and the Laryngeal nerve is the nerve that runs right back up again. Why would it do this? It could just "split" right at the top, have the rest of the Vagus nerve go down, and have the Laryngeal nerve connect to the larynx. At least, from a design point.
No it doesn't. The Vagus nerve, of which the Laryngeal nerve is a part does. The Laryngeal nerve, as the name suggests, only goes to the larynx, it doesn't connect to anything else.
While the page deals with the vagus nerve generally, it also discusses its various branches of communication severally. And slevesque's quote is specifically about the recurrent branch of the vagus nerve, it says that right there in the quote.
While the page deals with the vagus nerve generally, it also discusses its various branches of communication severally. And slevesque's quote is specifically about the recurrent branch of the vagus nerve, it says that right there in the quote.
Yes, but isn't this supposed to be about the Laryngeal nerve? that doesn't have to be recurrent, does it? Like I said, it could "split" from the rest of the Vagus nerves at the top, and let the rest continue downward.
Or am I missing something here?
Get your sackcloth and ashes.
Gladly, I just don't seem to see where I went wrong.
The laryngeal nerve is the name for a bundle of nerve fibers, some of which terminate at the larynx and some of which don't get that far. It doesn't just designate the ones that terminate at the larynx.
You're using "laryngeal nerve" to mean the nerve fibers which do terminate at the larynx, but that's not what it means in medical terminology --- it includes those that are part of that whole bundle of nerves but which (for example) terminate at the cardiac plexus. Which slevesque's quote and link should have made clear. That was your mistake.
Slevesque's mistake is to treat the existence of this bundle of nerves (the recurrent laryngeal nerve) as though its existence was somehow inevitable, rather than just being a term we've adopted to describe the facts as we've found them. Under that assumption there is a good reason why the recurrent laryngeal nerve should go round by the heart --- it needs to connect with the cardiac plexus. But then of course the specific nerve fibers which connect to the larynx don't need to be part of the recurrent pharyngeal nerve.
The laryngeal nerve is the name for a bundle of nerve fibers, some of which terminate at the larynx and some of which don't get that far. It doesn't just designate the ones that terminate at the larynx.
You're using "laryngeal nerve" to mean the nerve fibers which do terminate at the larynx, but that's not what it means in medical terminology --- it includes those that are part of that whole bundle of nerves but which (for example) terminate at the cardiac plexus. Which slevesque's quote and link should have made clear. That was your mistake.
Aha.
Slevesque's mistake is to treat the existence of this bundle of nerves (the recurrent laryngeal nerve) as though its existence was somehow inevitable, rather than just being a term we've adopted to describe the facts as we've found them. Under that assumption there is a good reason why the recurrent laryngeal nerve should go round by the heart --- it needs to connect with the cardiac plexus. But then of course the specific nerve fibers which connect to the larynx don't need to be part of the recurrent pharyngeal nerve.
Does that straighten things out? (So to speak.)
It does, and I see where I went wrong. So, for that, I appologize. I do think however that the main point remains. The nerves that connect to the larynx do not need to go all the way down the neck.
These excerpts were copied from an ICR website written by Jerry Bergman
The RLN design is due to developmental constraints. Human-designed devices, such as radios and computers, do not need to function until their assembly is complete. By contrast, living organisms must function to a high degree in order to thrive during every developmental stage from a single-cell zygote to adult. The embryo as a whole must be a fully functioning system in its specific environment during every second of its entire development. For this reason, adult anatomy can be understood only in the light of development.
Developmental Variations
The human body begins as a sphere called a blastocyst and gradually becomes more elongated as it develops. Some structures, such as the carotid duct, are simply obliterated during development, and some are eliminated and replaced. Other structures, including the recurrent laryngeal nerve, move downward as development proceeds. The movement occurs because the neck's formation and the body's elongation during fetal development force the heart to descend from the cervical (neck) location down into the thoracic (chest) cavity.
As a result, various arteries and other structures must be elongated as organs are moved in a way that allows them to remain functional throughout this entire developmental phase. The right RLN is carried downward because it is looped under the arch that develops into the right subclavian artery, and thus moves down with it as development proceeds.
The left laryngeal nerve recurs around the ligamentum arteriosum (a small ligament attached to the top surface of the pulmonary trunk and the bottom surface of the aortic arch) on the left side of the aortic arch. It likewise moves down as the thoracic cavity lengthens. The body must operate as a living, functional unit during this time, requiring ligaments and internal connections to secure various related structures together while also allowing for body and organ movement. For the laryngeal nerve, the ligamentum arteriosum functions like a pulley that lifts a heavy load to allow movement.
As a result of the downward movement of the heart, "the course of the recurrent laryngeal nerves becomes different on the right and left sides." These nerves cannot either be obliterated or replaced because many of them must function during every fetal development stage. No organ could exist that is functionless during its development, an axiom that also applies to the nervous system. This movement appears designed to position the left RLN downward as the body elongates.
In addition, the laryngeal branch splits up into other branches before entering the larynx at different levels. These many RLN branches serve several other organs with both motor and sensory branches, including the upper esophagus, the trachea, the inferior pharynx, and the cricopharyngeus muscle, the lowest horizontal bandlike muscle of the throat just above the esophagus. The fact that the left RLN also gives off some fibers to the cardiac plexus is highly indicative of developmental constraints because the nerve must serve both the larynx (in the neck) and the heart (in the chest).
After looping around the aorta, the RLN travels back up to innervate the larynx. The superior and recurrent laryngeal nerves then innervate an area known as Galen's anastamosis.
It then migrates caudally as the embryo enlarges by differential growth of the head and thorax areas, taking the nerve with it. The diaphragm cannot have evolved step-wise, since a partial diaphragm results in an imperfect chest-abdomen separation. Even a small defect results in herniation of the gut contents into the chest--which either compresses the lungs or results in strangulation of the gut.
Without explaining the nerve structure's design system, function, and ultimate connections, alleging that the RLN is a poor design is a meaningless assertion.
Edited by ICDESIGN, : listed the source of information
You really should send him an email and tell him you'll charge him with plagiarism unless he takes that page down. He would be well advised to follow our Forum Guidelines as closely as EvC Members do:
Never include material not your own without attribution to the original source.
Of course, unlike evolution, a design hypothesis does not explain why the various bits of the body start off in the wrong places and then have to migrate to the right ones.
Also, like slevesque, you have taken the existence of the particular bundle of nerve fibers known as the RLN as a given. So you write: "In addition, the laryngeal branch splits up into other branches before entering the larynx at different levels. These many RLN branches serve several other organs with both motor and sensory branches" ... without asking why the particular nerve fibers that serve the larynx couldn't just have gone straight to the larynx.
These considerations would doubtless have occurred to you if you'd spent half a minute thinking about anatomy instead of spending five seconds stealing.
If you think you have a superior RLN design why don't you volunteer to have a surgeon go in and shorten yours so we can see how much better it works?
What makes you think that an invasive risk-laden surgical procedure is comparable to an in-situ system, albeit a questionably poor engineered system such as the RNL is?
We are comparing what could have been (had it been intelligently designed from first principles by a higher power) against what we have actually ended up with. You can't glibly compare what exists in nature against a surgical procedure to modify said design....partly because that involves ripping up a current system to alter it (and that isn't comparable with a design from first principles - look in any engineering text-book if you don't understand what I'm saying), and partly because any invasive surgical procedure involves both medical risk and trauma damage — which then doesn’t favour unbiased comparison of the subject in question in the first place.
The comparison you are setting up is infantile and larded over with emotion. Try to keep on the track of whether the system is an example of first-principle intelligent design rather than "well let's see you alter it in-situ to something better".
I'm not even sure what you evolutionists are complaining about with the RLN. Is there anyone out there who is having a problem because of the design of their RLN?
Your mission should be to show how the evolutionary model is a better explanation for the design of the human body. If all you can come to the table with is your sniveling about the RLN being 7inches too long... well it makes me feel like I came to the knife fight toting a 44 magnum.
Among many other sound design reasons (outlined in the link provided by Percy from which I used excerpts also), the reason due to developmental constraints is more than good enough to explain this intelligent design plan.
Instead of whining about being 7 inches too long you need to be showing how it is possible that evolution once again managed to produce another body function with the "appearance" of purpose. Where did the RLN originate from? How did it randomly end up connected to the larynx as well as the other organs it services. What is the probable path random mutation and natural selection took to end up with the end result we see in the current RLN system we now have?
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