Anatomy & Physiology: The Unity of Form and Function, 7th Edition

Published by McGraw-Hill Education
ISBN 10: 0073403717
ISBN 13: 978-0-07340-371-7

Chapter 13 - Section 13.3 - Somatic Reflexes - Before You Go On - Page 502: 14

Answer

The crossed extension reflex is a neurological response that accompanies the withdrawal reflex when there is a need for maintaining balance and ensuring coordinated movement in response to a noxious or painful stimulus. These two reflexes work together to protect the body and allow for an effective response to a potentially harmful situation. Here's why the crossed extension reflex must accompany a withdrawal reflex of the leg: 1. **Withdrawal Reflex (Flexor Reflex):** The withdrawal reflex is responsible for quickly removing a limb or body part from a painful or harmful stimulus. For example, if you step on a sharp object, the withdrawal reflex will cause your leg to flex and pull away from the source of pain. This reflex protects the limb from further injury. 2. **Role of the Crossed Extension Reflex:** While the withdrawal reflex is essential for protecting the limb directly involved in the noxious stimulus, it may create an imbalance in the body's posture and stability. When one leg suddenly flexes to withdraw from a painful stimulus, it can shift the body's weight onto the other leg. 3. **Maintaining Balance:** To prevent falling and maintain balance, the crossed extension reflex comes into play. This reflex, as the name suggests, involves the extension of the contralateral (opposite) leg. In other words, while one leg flexes and withdraws, the other leg extends to support the body's weight. 4. **Coordination of Movement:** The crossed extension reflex ensures that you remain stable and can adapt to the sudden movement initiated by the withdrawal reflex. It helps you distribute your body weight and maintain your posture while withdrawing the injured limb. 5. **Functional Example:** Imagine stepping on a sharp object with your right foot. The withdrawal reflex causes your right leg to flex and pull away, preventing further injury to that leg. At the same time, the crossed extension reflex causes your left leg to extend, helping to support your body's weight and maintain balance so that you don't fall over. In summary, the crossed extension reflex is a complementary response to the withdrawal reflex. It helps prevent loss of balance and maintains posture by extending the opposite limb to support the body's weight during the withdrawal of the affected limb. This coordinated action is crucial for preventing injury and ensuring that the body responds effectively to potentially harmful stimuli.

Work Step by Step

The crossed extension reflex is a neurological response that accompanies the withdrawal reflex when there is a need for maintaining balance and ensuring coordinated movement in response to a noxious or painful stimulus. These two reflexes work together to protect the body and allow for an effective response to a potentially harmful situation. Here's why the crossed extension reflex must accompany a withdrawal reflex of the leg: 1. **Withdrawal Reflex (Flexor Reflex):** The withdrawal reflex is responsible for quickly removing a limb or body part from a painful or harmful stimulus. For example, if you step on a sharp object, the withdrawal reflex will cause your leg to flex and pull away from the source of pain. This reflex protects the limb from further injury. 2. **Role of the Crossed Extension Reflex:** While the withdrawal reflex is essential for protecting the limb directly involved in the noxious stimulus, it may create an imbalance in the body's posture and stability. When one leg suddenly flexes to withdraw from a painful stimulus, it can shift the body's weight onto the other leg. 3. **Maintaining Balance:** To prevent falling and maintain balance, the crossed extension reflex comes into play. This reflex, as the name suggests, involves the extension of the contralateral (opposite) leg. In other words, while one leg flexes and withdraws, the other leg extends to support the body's weight. 4. **Coordination of Movement:** The crossed extension reflex ensures that you remain stable and can adapt to the sudden movement initiated by the withdrawal reflex. It helps you distribute your body weight and maintain your posture while withdrawing the injured limb. 5. **Functional Example:** Imagine stepping on a sharp object with your right foot. The withdrawal reflex causes your right leg to flex and pull away, preventing further injury to that leg. At the same time, the crossed extension reflex causes your left leg to extend, helping to support your body's weight and maintain balance so that you don't fall over. In summary, the crossed extension reflex is a complementary response to the withdrawal reflex. It helps prevent loss of balance and maintains posture by extending the opposite limb to support the body's weight during the withdrawal of the affected limb. This coordinated action is crucial for preventing injury and ensuring that the body responds effectively to potentially harmful stimuli.
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