Final answer:
The crossed-extensor reflex is a crucial reflex action that demonstrates double reciprocal innervation, ensuring coordinated movement during reflex actions. It incorporates collateral branches from sensory axons to activate and inhibit specific muscles, thus allowing for withdrawal on one side and compensatory counterbalancing actions on the other. This complex interaction is integral to maintaining balance and stability in response to sudden stimuli.
Step-by-step explanation:
The crossed-extensor reflex is an important reflex that helps maintain balance while performing a withdrawal reflex. This reflex involves a double reciprocal innervation, which means that while one muscle group is activated, the opposing muscle group is inhibited to allow for coordinated movement. For instance, if a person steps on a tack with one foot, not only will there be a withdrawal reflex causing the muscles responsible for lifting the foot (dorsiflexion) to contract, but there will also be a contraction of the extensor muscles of the opposite leg to maintain balance.
In the context of a withdrawal reflex, such as pulling away from a painful stimulus like a hot stove, collateral branches of the sensory axon play a crucial role. One branch activates the motor neurons to contract the biceps brachii, and another collateral inhibits the motor neurons controlling the triceps brachii, ensuring a rapid withdrawal. Simultaneously, there's activation on the contralateral side in response to the same sensory input, involving yet another collateral which causes contraction of the extensor muscles. This complex action is facilitated by interneurons in the spinal cord that process sensory input, and the resulting motor output leads to a coordinated, counterbalancing action across both sides of the body.
Another example is the stretch reflex, which serves a similar homeostatic function for muscle length control. For example, the patellar tendon reflex, commonly tested with a rubber mallet during a physical exam, is a type of stretch reflex that helps maintain posture and balance by ensuring that our muscles respond properly to external forces.