Overview
This lecture explains the crossed-extensor reflex, its function, mechanism, and how it works alongside the withdrawal reflex for coordinated limb movement.
Crossed-Extensor Reflex Overview
- The crossed-extensor reflex occurs when a painful stimulus causes one limb to withdraw while the opposite limb extends.
- This reflex helps maintain balance and posture during sudden limb withdrawal.
Mechanism of the Reflex
- When a painful stimulus (like stepping on a tack) activates sensory neurons, the signal enters the spinal cord.
- Interneurons in the spinal cord process the information and activate motor neurons on both sides of the body.
- On the same side as the stimulus, flexor muscles contract to pull the limb away (withdrawal reflex).
- On the opposite side, extensor muscles contract to support body weight (crossed extension).
Functional Importance
- The crossed-extensor reflex prevents falling or loss of balance during sudden, involuntary limb withdrawal.
- It is an automatic, polysynaptic (involving several neurons) reflex.
Key Terms & Definitions
- Crossed-Extensor Reflex — A spinal reflex that causes extension of the opposite limb when the other limb withdraws from a painful stimulus.
- Withdrawal Reflex — An involuntary response pulling a body part away from a painful stimulus.
- Flexor Muscle — Muscle that contracts to bend a limb.
- Extensor Muscle — Muscle that contracts to straighten or extend a limb.
- Polysynaptic Reflex — A reflex pathway involving multiple synapses and interneurons.
Action Items / Next Steps
- Review diagrams of the crossed-extensor and withdrawal reflex circuits.
- Read assigned textbook sections on spinal reflexes and their functional roles.