Chapter+05

Place your questions and answers for Chapter 5 here.

A: Amphioxus has gill arches and it also shares a nerve cord and notochord. these features have been modified by humans by our notochord being split up. this suggest that humans are more evolved than amphioxus because we have a more advanced notochord allowing us to grow bigger and stronger than organisms without a broken up notochord.(T. McDaniel)
 * Q: In this chapter, human embryos are compared to shark embryos with respect to their gill arches. What other organism is talked about in this chapter with gill arches? What other feature does this organism share with vertebras and what are some of the modifications to this structure that humans posses? What does this similarity suggest about evolution and how might have this trend been beneficial? (J. Speelman)**

A: Despite //Amphioxus'// lack of a backbone, it has a nerve cord along its back and a rod that runs the length of its body, which is parallel to the nerve cord. This nerve cord and rod, called the notochord, can be found in human embryos before it turns into the disks that are between our vertebrae. The notochord provides support for the body of //Amphioxus,// this support is advantageous because it allows more movement and flexibility than an exoskeleton, which is the support for many other invertebrate. It also allows for a structure that muscles can attach to, which other invertebrates lack. (J. terHorst)
 * Q: How is the //Amphioxus// similar to vertebrates even though it has no backbone? Why would these characteristics be beneficial to this organism, or how do these things give it an advantage over other invertebrates without these special characteristics? (A. Nolan)**

A: Structures called gill arches in embryos eventually developed in our facial and throat regions. They are structurally similar, as we both have four, and both species gill arches. Both human's and sharks gill arches more or less carry the instructions to form the same areas of the head. For instance, the first gill arch in both humans and sharks will form the jaw region of the head. The difference in development like sharks retaining its gills after birth and humans developing ears help the best suit each organism to its environment. (C.Nikolai). A: The structures in developing fetuses that help trace the origins of our face, throat, larynx, and ears can be identified as arches, of which there are four. These arches contain cells that will form bone tissue, muscle tissue, or blood vessels. Similarly, shark’s gill slits also assist in the formation of the head, but correspond to different structures, like their jaws and unique gills. The arches in humans are beneficial because they allow our body to develop segmentally and in a specialized fashion, ultimately and effectively resulting in our ability to swallow and hear. This is relatively similar is sharks, yet they benefit from more intense jaw development and the ability to use and move their gills. The arches and slit structures in each organism promotes the development of structures in the head region that increases their survival, but they are unique to each organism and their environments and needs. (M. Blanchard)
 * Q: What are the structures in a developing fetus called that help trace the origins of our face, throat, larynx, and ears? How are these structures in human fetuses similar to the gill slits in sharks and how are their differences beneficial to each organism? (T. Gebhart)**


 * Throughout Chapter 5, Shubin discusses some of the structures and developmental patterns shared by chordates, such as the development of gills arches, and the way cranial nerves are 'assigned' and develop. Another example of these 'carried over' features is the structure of the eyes. Do a little research on the development of eyes. Using Shubin's comparison with an refurbished building, explain some of the 'obtuse' or unintuitive designs of the eye (M. Purdon).**

A: Shubin said that the building he owned in Chicago was full of chaotic wires, pipes, and cables. Nobody in their right mind would have designed the building to be like this originally. However, he says you have to understand its history in order to understand its complexity. This is the same for the nerve pathways of the brain. These pathways cross over each other and branch off all throughout the brain in order to process certain information. This analogy works so well because in order to understand the complexity of nerve pathways within the brain, you first have to understand the history and how they developed to their current state. You have to know why certain nerves were needed in certain places in order to understand their complex pathways. The whole theme of the book is to understand the evolution of mammals from fish. In order to properly do this, you need to understand why certain aspects such as arms, legs, lungs, and fingers were needed in order to completely understand the complexity of mammals. This goes hand in hand with the message of the building analogy. (L. Bentley)
 * Q: In this chapter, Shubin creates an analogy of a 100 year old building that he owned in Chicago for Research and the nerve pathways of the brain. Why does this analogy work so well, taking into account what he said specifically about the history of the house? How does this play into the over all theme of evolution(C. King)**

A: Both the trigeminal and the facial nerve send branches to the muscle in the ears, because the trigeminal was created in the first arch. This means that it supplied all the structure in the first arch which include the ears. The facial nerve sends branches to the ears because it was created in the secind arch, and the ear muscles are also second arch derivatives. This has to do with evolution because the body has evolved to almost have a back up system when it comes to the ears, because it has evolved to develope in archs. A comparison for this kind of thing in my life would be two different teachers teaching me the same thing. The way they go about getting the information to me would be different, but the content is going to the same place. (E. Bach)
 * Q: In this chapter, Shubin emphasizes the complexity of the head and the cranial nerves. Why do both the trigeminal and facial nerve send branches to muscles in the ears? And what does this have to do with evolution? Finally, Shubin compares the complexity of cranial nerves to the inner wiring of an extremely old building, what in your life would be another good comparison to these nerves? (E. Olson)**

A: The slits seal over and form the four arches that would have been gills in fish. The arches are caused by the slits sealing over, so the instructions for the slits to be closed would be evidenced in the DNA for the arch formation, pre-embryo. However, in some human cases, the arches are not formed because the slits fail to close, leaving a pouch or a cyst as a remnant. (T. Russell)
 * Q. This chapter discusses in depth the four arches that embryos develop relatively early on. How do these arches change as an embryo develops into an adult? Is there any clear evidence of arches without looking first at an embryo? What are some examples of mutations that can be caused by an issue in one of the arches? (C. Sanders)**

A: They divide to produced the stapes bone. This bone supports the upper and lower jaw in sharks, to help it chew its food. It also helps the shark rotate its upper jaw. This bone is also found n the middle ear of humans. This bone is unique to humans, because humans use the stapes bone to hear and swallow. (H. Schwarz) A: The second gill arch divide to produce the stapes, a tiny throat bone, and the majority of muscles which are used to control facial expressions., while in a shark it splits up into two bones, one similar to our hyoid which controls the lower jaw and an upper support jaw bone. What is used as the hyoid in the human body allows humans to swallow and hear, while in sharks it allows them to chew. Another bone that is related between humans and sharks is the stapes: our middle ear bone which doubles as shars upper jaw bone, the stapes. It's function is similar to that of the hyoid in that is allows us both to eat. (I. Perler)
 * Q: Throughout this chapter, Shubin focuses on the four arches of development. More specifically, in both humans and sharks, there is a similarity found in the second gill arch. What do the second gill arch cells divide to produce that can be comparable to both humans and sharks? In humans, why is this** **specific bone unique? (O. Heltman)**

A: Plates, blocks, and rods. Plates protect the brain simply by covering it, forming much of the cranium. Blocks hold the brain up, and have many arteries and nerves within them. Rods don't play much of a role in protecting the brain, but are used to help us chew, swallow, and hear. It is essential for humans to have extra layers of protection because the brain is the most important organ in the body, and needs much protection because any damage to the brain can have profound effects on the person. (N. Sarkar)
 * Q: In this chapter, Shubin goes into some debth about cranial anatomy. He describes the head being broken into three fundemental parts, what are the three parts that he is talking about? Explain how these three parts play a role in protecting the brain, as well as why it is so important for it to have extra layers of protection. (E. Bach)**

A: The notochord in the //Amphioxus// is necessary because it is its support system. Without the notochord the //Amiphoxus// would pretty much be a blob. Humans no longer have this structure because we have replace it with a spine making us vertebrates and giving us the ability to walk to feet (bipedal) and able to support much more weight. If humans still had notochords we would be much smaller because the notochord is not as strong as the spine, we would most likely not be bipedal because the notochord would not be able to support all our weight on just two feet. (C. Hurst)
 * Q: Shubin describes a jelly-filled rod running the length of the body of //Amphioxus// called the notochord. Why is this structure necessary for this species, and why do we humans no longer have this structure as a main support system? -- What would happen if we did? (L.Bercz)**

A: Because the nerves with very simple functions take very simple paths throughout the body, but the cranial nerves take more complex paths throughout the body. It doesn't affect their function or slow down the signals because it is programmed to do this and reach the certain parts of the brain. It looks like its a mess but when you break it down its really not. Yes there is a way that this is actually more advantageous for an organism because it allows it to be more complex and take on more tasks. ( A. Schmidt)
 * Q: In this chapter, Shubin describes the vessels and nerves of the human head as a clump of "tangled fishing lines". He goes on to describe how many of them have very simple functions and carry out many seemingly simple tasks throughout the body. If this is true, why are the vessels and nerves in such a mess, and how does this not affect their function or slow down the signals? Is there a way that this is actually more advantageous for an organism? (M. McKinney)**

A: The major muscle used to frown is called the depressor anguli oris while it takes 43 muscles total to frown but only 17 muscles total to smile. (R.Heis)
 * Q: What muscle does Shubin describe as a major muscle used in frowning ("it moves the corners of our mouth down")? That aside, about how many muscles total does it take for somebody to frown (bonus points if you can name the amount to smile as well)? (N. Braun)**