This crossed extensor reflex allows us to rapidly

relaxes. This crossed - extensor reflex
allows us to rapidly withdraw from a painful stimulus (like stepping on a tack) without losing our
balance.
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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.
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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?