Human Anatomy & Physiology (9th Edition)

Published by Pearson
ISBN 10: 0321743261
ISBN 13: 978-0-32174-326-8

Chapter 13 - The Peripheral Nervous System and Reflex Activity - Review Questions - Page 522: 22


Homeostasis is the condition in which the physical, physiological, and biochemical parameters of the body are within optimal ranges. However, external and internal environmental changes constantly threaten to disturb homeostatic conditions.The body has hormonal and neurological mechanisms to correct potentially dangerous deviations outside these optimal ranges. Reflexes are quicker than conscious CNS reactions, and CNS reactions are quicker than hormonal reactions. Spinal reflexes have many protective features but their most important feature is the rapidity with which they react (involuntarily) to restore normality to internal conditions: Spinal reflexes respond to abnormal conditions of pressure, temperature, pain, and stretch. The stretch reflex prevents muscles from being stretched too much with possible resultant tearing. The withdrawal reflex responds to pain from excessive heat, and protects against tissue injury. The crossed extensor reflex functions to limit wound injury, and to restore balance.

Work Step by Step

Spinal reflexes are of important medical diagnostic value: a. Flexor reflexes are of important survival value: They may be used as tests of peripheral nerve damage, of neurosyphilis infection, and of early onset of diabetes mellitus Abnormal flexor reflexes may also indicate corticospinal tract damage. b.The knee-jerk reflex can give an indication of the degree of sensitivity of the spinal cord.
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