Exam Study Guide
Exam Study Guide BIO 152
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This 2 page Study Guide was uploaded by Samuel Croteau on Friday April 8, 2016. The Study Guide belongs to BIO 152 at Massachusetts College of Pharmacy & Health Sciences taught by Dr. Demasi in Fall 2016. Since its upload, it has received 36 views. For similar materials see Biology of the organism in Biology at Massachusetts College of Pharmacy & Health Sciences.
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Date Created: 04/08/16
16.Receptors for fine touch are typically located in the shallow layers of the skin, while receptors for stronger touch stimuli are typically located in deeper layers. Why might this be so? What happens to mechanical energy with depth of tissue? So, if fine touch receptors were located deep in the skin, would they ever get excited? What would happen if course receptors, for stronger stimuli, were located nearer the surface? Would they rarely be stimulated or constantly stimulated? The receptors for fine touch are closer to the surface because it they were lower in the skin, they would not be able to perceive the stimuli. Those for a stronger stimuli must be further down in the skin because if they were on the surface, even the smallest stimuli would stimulate and cause the receptors to sense the touch, or pressure. Pressure and touch and move the extracellular anchoring proteins which pull on the ion channel causing them to change and alter the movement of ions across the membrane, this changing the membrane potential of the cell and allowing the cells to transduce mechanical signals. If fine touch receptors were deep in the skin, they would never be excited, and if stronger touch receptors were in the upper layers of the skin, they would be constantly excited. Mechanical energy decreases with a greater depth of tissue. 17.Vertebrate organs of hearing and equilibrium contain hair cells with receptor proteins. Why are they called hair cells? Refer to bottom left page 278. Identify the labeled parts of a vertebrate. They are deemed hair cells because of the prominent cilia that extend from the apical end of each cell. A) Sterocilia B) Top Link C) Kinocillium Are the steroecilia true cilia comprised of core 9 + 2 Microtubules or microvilli comprised of microfilaments of actin? Do the hair cells of adult mammals have kinocilium? Therefore, do kinocilium or sterocilia play a critical role in mechanoreception? What are the proteinaceous fibers that connect each of the sterocilia and kinocilium? What are the nature of receptor proteins in the membrane – which type of mechanoreceptor are they – refer to two types you identified in question 13 (really 14). Be able to explain signal transduction in a vertebrate hair cell as illustrated in figure 7.20 The sterocilia are not true cilia comprised of core 9 +2 microtubules. They are actually microvilli that are composed of microfilaments of actin. The hair cells of adult mammalian ears lack kinocilium suggesting that it is not necessary for mechnoreception sterocilia play the critical role in mechanosensory transduction. The proteinaceous fibers that connect each of the sterocilia and kilocillium are called the tip link. They connect the top of each shorter sterocilia to the side of the adjacent taller one. They play an important role in sound transduction. Signal Transduction Figure 7.20: -‐ at rest, the hair cells are slightly depolarized, and release moderate amounts of neurotransmitter onto the primary afferent neuron. -‐ When a pressure signal causes the sterocilia to pivot toward the kinocillium, mechanically gated ion channels on the sterocilia to open, this allowing more K+ to enter the cell from the extracellular fluid which has a high concentration of K+ The resulting depolarization causes Ca2+ gated channels to open allowing Ca2+ to enter the cell. This influx causes an increased release of neurotransmitter to the primary afferent neuron increasing the frequency of action potentials. -‐ When a pressure signal causes stereocilia to pivot away from the kinocillium, the mechanically gated ion channels on the sterocilia close, hyperpolarizing the cell and closing the voltage gated Ca2+ channels. This results in the intercellular Ca2+ to decrease the release of neurotransmitter onto the primary afferent neuron reducing the frequency of action potentials. 18.Hair cells have prominent cilia on their apical surface. Why do these cilia increase the sensitivity of a hair cell to mechanical stimuli? Refer to page 278, third and fourth paragraphs on right hand column. Think about the way the cilia move and their extent of movement caused by a small amount of mechanical energy. Think about the way that cilia can move in either direction therefore their ability to detect direction of movement. When they are exposed to a vibration they pivot about their bases, where they become rigid and will not move. If they turn in the way of the kilocillium mechanosensetive ion channels open. Even a small amount of vibration can cause the sterocilia to move and change direction this then creating an action potential . 19.Describe the role of tip links in mechanosensory transduction. Refer to page 280, top left-‐hand column.
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