Crossed extensor reflex

Definition

The crossed extensor reflex is a protective spinal reflex that involves the withdrawal of a limb from a painful stimulus while simultaneously activating the extensor muscles of the opposite limb to maintain balance and stability. This reflex is crucial for postural control, allowing the body to quickly respond to threats and maintain equilibrium by redistributing weight across the limbs during sudden movements.

5 Must Know Facts For Your Next Test

1. The crossed extensor reflex is a polysynaptic reflex, meaning it involves multiple synapses in the spinal cord, allowing for coordinated responses between limbs.
2. This reflex helps maintain balance by activating the extensors of the opposite leg when one leg withdraws from a painful stimulus, ensuring stability during withdrawal.
3. The crossed extensor reflex is initiated by nociceptors that detect painful stimuli, transmitting signals to interneurons in the spinal cord that coordinate the response.
4. This reflex is critical in situations like stepping on a sharp object; while one foot pulls away, the other foot extends to support body weight and prevent falling.
5. The efficiency of the crossed extensor reflex can be influenced by factors such as fatigue, injury, and neurological conditions, impacting overall postural control.

Review Questions

• How does the crossed extensor reflex contribute to maintaining postural control when a person encounters a painful stimulus?
  • The crossed extensor reflex contributes to postural control by ensuring that when one limb withdraws from a painful stimulus, the opposite limb extends to provide stability and support. This coordinated response prevents falls and allows for quick adjustment in body posture. By activating motor neurons in the opposite limb, this reflex ensures balance is maintained even in response to sudden pain.
• Discuss the role of interneurons in facilitating the crossed extensor reflex and how they interact with motor neurons.
  • Interneurons play a crucial role in facilitating the crossed extensor reflex by processing sensory input from nociceptors and coordinating responses between flexor and extensor motor neurons. When a painful stimulus is detected, sensory neurons activate excitatory interneurons that stimulate motor neurons for flexor muscles to withdraw from pain, while simultaneously activating inhibitory interneurons that inhibit flexor muscles on the opposite side. This complex interaction allows for a smooth and effective reflex response.
• Evaluate how abnormalities in the crossed extensor reflex could affect an individual's ability to maintain balance during dynamic movements.
  • Abnormalities in the crossed extensor reflex can significantly impair an individual's ability to maintain balance during dynamic movements by disrupting the coordination between limbs. If the response is delayed or inadequate, it could lead to instability when one limb is withdrawn from a painful stimulus, increasing the risk of falls or injury. Such impairments may arise from neurological disorders or injuries affecting motor neuron pathways, highlighting the importance of this reflex in maintaining overall postural stability.

Related terms

withdrawal reflex: A reflex action that occurs when a body part is pulled away from a painful stimulus, involving the flexor muscles of the affected limb.

spinal cord: The cylindrical structure that runs through the vertebral column and serves as the main pathway for transmitting signals between the brain and the rest of the body, including reflex actions.

motor neurons: Nerve cells that transmit signals from the spinal cord to muscles, initiating movement and reflex actions.