relaxes. This crossed - extensor reflex allows us to rapidly withdraw from a painful stimulus (like stepping on a tack) without losing our balance. 27
158) Researchers have developed a "bionic arm." This technology is possible primarily because of two facts of amputation. First, the motor cortex still sends out control signals even if certain voluntary muscles are no longer there to innervate. Second, when doctors amputate a limb, they do not remove all the nerves that once carried signals to the muscles in that limb. If those nerve endings can be redirected to a working muscle group, and the person thinks "grab the handle and turn," then the brain will send out corresponding signals to the nerves and communicate with the new limb. Based on your knowledge of voluntary motor tasks, explain how this technology is possible. Answer: There are four main steps involved in the successful execution of a voluntary motor control of a muscle. First, there must be intention or in this case the thought of "grab the handle and turn." Then, a program of motor commands must be generated in the primary motor cortex which sends information to be "executed" by afferent motor tracts (primarily the pyramidal and rubrospinal tracts). Finally, feedback must be sent back to the CNS, this time no doubt by some electrode in the "bionic arm" to ensure the original program is being followed. This "bionic arm" must work very similarly to the example given in the textbook where mission controllers program a trajectory but a computer on board the spacecraft can always make adjustments to the program based on feedback. This means the cerebellum must also be involved in controlling the bionic arm keeping track of its position and movements. 28
159) Liz is a seventy - year - old woman who is both a wife and a mother. She is moderately obese (BMI 32), and has smoked a half a pack to a pack of cigarettes a day since she was 16 years old. Liz awakes one morning with weakness on her right side. She is confused, sees double, and has slurred speech. She stumbles and has an awkward gait trying to get to the restroom, where she collapses. Her husband calls 911 and Liz is transported to the hospital. Upon physical examination, Liz is found to have partial paralysis (hemiparesis) on her right side and diminished sensitivity to a pin prick on her arm and right side of her face. She has difficulty answering questions, speaking only a few words which are slurred and grammatically incorrect. Her ability to respond to verbal commands, whether spoken or written, is not impaired. In addition, her blood pressure is high (148/and a serum lipid profile that was ordered when she first arrived at the hospital has come back with a high LDL and total cholesterol level. Based on this case answer the following questions: a) What is a stroke?
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