On page 164, Neil Shubin talks about the movement of rocks in the inner ear. What would happen if a human did not have enough rocks to stimulate hair cells? Talk about the evolutionary significance of these rocks and what benefits they provide for bipedal organisms.
Yekaterina Khavkhalyuk (kittykatx93x@yahoo.com)
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ReplyDeleteOur inner ear is a very cool organ. It has a sac of gel called a utricle in the tubes that make up the snail-shape. The lining of the utricle is filled with cells that are the end of neurons. These cells project tiny hair-like things into the utricle. As we move our head, the gel in the utricle moves around according to external forces like gravity and our own acceleration. As the gel shifts, the tiny hairs get stimulated in different ways. The hairs send signals to the brain, which interprets the different signals as a feeling of orientation or acceleration. Embedded in the membrane of the utricle are tiny rocks of calcium carbonate. These rocks accentuate the movement of the gel, and our orientation is more specific. The rocks themselves don't stimulate our hairs, they merely amplify the system. They can actually make us dizzy. If one of the rocks gets loose (like in a head injury) and falls into the ear canal, it triggers cells there and makes our brain feel like our head is moving faster than it really is. This is what the feeling of vertigo really is. (http://www.npr.org/templates/story/story.php?storyId=103463398) So if we were to have no rocks, it's not that we would lose our sense of orientation, it would just feel muted, similar to the way your sense of smell is affected when you have a cold, or how your sense of hearing is affected after getting off of a plane.
ReplyDeleteJeremy Solomon
imabum14@gmail.com
Like Jeremy explained, the inner ear is composed of tubes and some gel-filled sacs. Shubin explained that the inner ear serves many functions, including hearing, telling us which way our head is tilted, and how fast our head is accelerating or stopping (Shubin 164). Jeremy already effectively explained the gel and the hair-like projections it sends from the specialized cells, so in direct response to the question regarding what would happen if a human did not have enough rocks, the answer is, we would not be able to balance. Dizziness is due to loose rocks/crystals in the ear. “The tiny rocks serve an important purpose: They stimulate nerve cells when we move our heads — and send signals to our brain that guide our sense of up and down” (http://www.npr.org/templates/story/story.php?storyId=103463398), therefore, with too few rocks, our nerve cells wouldn’t be effectively stimulated, and those hair-like projection signals wouldn’t be sent to our brain, and we would not balance. Too many rocks, however, like Jeremy explained, or the rocks becoming loose are causes of vertigo.
ReplyDeleteBipedalism is when an organism moves by means of its two legs. Bipedalism requires adjustments to the inner ear, since bipedal animals must be able to balance on two legs. Balance comes from the rocks in the ear (as I have just explained), and clearly it takes more to balance on two legs than it would be to balance on four; therefore, the inner ear (the rocks) is what has changed in evolutionary history to allow for this balance. Before rocks became useful in balance, in evolutionary history, it can be seen that fish (our predecessors) used other mechanisms to know where they were going in equilibrium. Some fish have a “mechanism that allows them to sense the current and the motion of the water around them” (Shubin 169). At this point in time, fish did not have true legs that they walked on, instead they swam around. Down the evolutionary timeline, after limbs began to develop, like that of Tiktaalik’s, balance on four legs seemed equally important and the inner ear had to morph into something that was able to control balance. Those organisms with rocks that helped them balance had the selective advantage because they were able to walk around; without it, life would seem nearly impossible. Because of this, they lived and were able to reproduce. It proved to be a selective advantage, and as a part of natural selection, the organisms with rocks within their inner ears structured in a way that helped them balance were carried down the evolutionary timeline and are currently present on all organisms with limbs that they walk on. Bipedal animals, specifically, need rocks to balance, so, with that same process, all bipedal organisms had to have rocks to survive and reproduce.
-Michelle Layvant, michellel94@hotmail.com
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ReplyDeleteThe ear is a complex structure, as Michelle and Jeremy pointed out. Its role consists of many aspects outside of simply hearing. This includes maintaining balance, determining our head tilt, and recording head movement (Shubin, 164). The structure and function must first be understood, however, to clear up the complexity that is the inner ear. The inner ear could be viewed as a “maze” of fluid-filled tubes that are found through the temporal bone of the skull. The fluid-filled tubes that are called the “bony labyrinth” are filled with a fluid called perilymph, which is simply extracellular fluid. Within the bony labyrinth are delicate cellular tubes or the “membranous labyrinth” that holds the hearing cells, “the hair cells of the organ Corti” (Campbell, 1093). The front portion of the inner ear is the “snail-shaped cochlea” functioning in hearing; the rear part is the semicircular canals maintains balance, and the vestibule that interconnects the first two contain utricle and saccule sense organs responsible for balance (“The Ear: Auditory and Vestibular Systems”, Partners in Assistive Technology Training and Services). Shubin states that different parts of the ear function generally in the same way (Shubin, 164). He further explains this by discussing a sort of flow chart that the ear processes. The gel within the ear moves causing the hairs on the ends of the nerve cells to bend, sending electrical impulses to the brain to be recorded as a sound, position, or acceleration (Shubin 165). The “rocks” in question are tiny rock-like structures at the top of the membrane of that accentuates the movement of the gel in the ear, “increasing sensitivity of the system” (Shubin, 166). The utricle and saccule, sensory organs, contain rows of hair cells embedded in a jelly-like layer that contains the rock-like structures in question. These structures pull in the opposite direction when the body moves forwards or backwards to create friction against the hairs beneath them (“Rocks in Your Head”, Other Sensory Receptors). This allows an increase in sensitivity to allow the body to understand how the body is moving. If there was a deficiency in these rock crystals, there would be a decrease in sensitivity in movement, and therefore a deficiency in balance, as Michelle had pointed out earlier.
ReplyDeleteJust as Michelle had explained, fish can determine which way water is flowing around them by deforming a sac similar to the structure of our inner ear that causes hair-like projections to bend and send impulses for understanding. The inner ear that has most likely evolved from this sac that came with the evolution of the terrestrial bipedal body. As the complexity of the structure of species increased, their minor functions had to adapt as well. As organisms became bipedal, our species became “taller” or moved farther way from the ground. Therefore, balance became a more crucial aspect to our functioning ability. These rocks allowed for an increased sensitivity as opposed to simply having hair-like projections. This added weight caused these hair-like projections to bend farther. Therefore, it’s an added benefit to increasing sensitivity and overall improving the balance of our bipedal structure as humans. This balance, as Michelle had explained, brought about a selective advantage because it improved the ability of humans to move. Having sensitive movement allows bipedal organisms to be able to move from location to location at a quicker, more efficient rate, and also to be able to protect themselves in the case of running away from a predator. These rock-like structures, as nominal as they may seem, improve the transmission of electrical impulses that allow organisms like humans to comprehend the movement of their bodies.
Sonia Doshi (soniadoshi7@gmail.com)