On page 190, Shubin discusses our relation to fish and tadpoles by talking about hiccups. He brings up the similarities between our respiratory system and the respiratory system of fish. He says that the brain stem-controlled breathing apparatus was taken from fish, and evolved into what we (as mammals) have right now (191).
Why do you think the arrangement works so well for humans and fish; that is, why would the nervous system usage of the brain stem as the “central pattern generator” be so successful? Unfortunately, the transition between fish respiration and mammal respiration was a difficult one; the air has to travel a lot farther in us mammals. What are the differences between mammals and fish when it comes to respiration? How exactly does the brain stem control our breathing? How could mammals perhaps adapt to the difficulties we inherited from the fish respiratory system?
Eugene Bulkin (doubleaw002@gmail.com)
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ReplyDeleteNetworks of neurons that regulate breathing, called breathing control centers, are located in the brainstem, particularly the medulla oblongata and the pons (Campbell, 922). During inhalation, “sensors that detect stretching of the lung tissue send nerve impulses to the control circuits in the medulla”, which regulates how deep a mammal can inhale (Campbell, 922). As we learned in the Respiration Unit, breathing is not controlled by the brainstem, rather the receptors in the brainstem sense how much carbonic acid (carbon dioxide dissolved in water) is in the blood.
ReplyDeleteThe breathing apparatus in aquatic and terrestrial chordates are extremely similar, which may provide evidence of an evolutionary relationship. A feature in both aquatic and terrestrial chrodates that suggests a significant evolutionary relationship is hiccupping. Scientists believe that “the hiccup is an evolutionary remnant of earlier [aquatic respiration in which animals] gulp air and water via a rather simple motor reflex akin to mammalian hiccuping” (Strauss, 2003). Also, Neurons located in the brainstem of fish are responsible for the genesis of the respiratory rhythm, much like in humans. The position of these neurons is slightly different from the centers of respiratory genesis in mammals but they are located in the same brain compartment (Russell). I would agree with Shubin's idea that the brain stem-controlled breathing apparatus shows that fish and mammals share ancestral origins.
http://onlinelibrary.wiley.com/doi/10.1002/bies.10224/abstract
http://www.springerlink.com/content/j1q45g379420w127/
Troy Glickstern
cleverstar8@comcast.net
As Troy said, the breathing apparatus’s of fish and humans are very similar. Because of this, an evolutionary relationship can be seen. Also, Troy was correct in saying that the neurons in the brainstem of fish are responsible for the respiratory rhythm.
ReplyDeleteAlthough the air has a farther distance to travel, the same basic concepts of diffusion through capillaries to re-oxygenate blood still occurs. The increase in distance is taken care of by Boyle’s law as an increase in volume of the chest cavity causes the air to go and fill the lungs (Campbell Chapter 42). Thus, there is no work done to bring air into the lungs. Thus, an increased distance is not a disadvantage. A disadvantage would be that our body is very large and needs a large amount of oxygen to handle everyday work. Thus, we must constantly inhale and exhale in order to replenish our cells. However, that also isn’t necessarily a disadvantage because this is something we must do to live. It is just an add-on to living. The change from fish to humans had little disadvantages as we were able to change in a way that allowed us to supply our body with sufficient resources necessary to life.
However, a recent experiment (in 2005) was performed by a scientist from Yale University and University of Charlottesville. From the experiment, the 2 scientists concluded that nerve cells were located on the ventral area of the brainstem. The location on the ventral side is an advantage because the neurons are within close proximity to the ventral surface of the brain. The close proximity allows for the neurons to sense changes in pH in the cerebrospinal fluid. Thus, neurons, along the ventral side of the brain stem control breathing as a part of the autonomic nervous system.
Sources:
http://www.sciencedaily.com/releases/2005/05/050512203033.htm
Campbell (Chapter 42)
Shreeraj Patel
shreeraj.patel1@gmail.com