Biological Systems MCAT Practice Exam

What type of reflex involves reciprocal inhibition?

1. Monosynaptic reflexes

2. Polysynaptic reflexes

3. Supraspinal reflexes

4. Conditioned reflexes

The correct answer is: Polysynaptic reflexes

Reciprocal inhibition is a key mechanism that occurs in polysynaptic reflexes. In these reflexes, when a sensory neuron is activated by a stimulus, it not only stimulates a motor neuron to trigger the desired response but also activates an inhibitory interneuron. This interneuron inhibits the motor neuron that would provide an opposing action. For instance, during the withdrawal reflex, if you touch something painful, the sensory neuron conveys that signal to the spinal cord. The spinal cord processes that signal, activating motor neurons that cause the arm to pull away while simultaneously activating interneurons that inhibit the opposing muscles, ensuring that the response is smooth and effective without unnecessary action from the antagonist muscles. This mechanism is vital for coordinated movement and allows for rapid responses to harmful stimuli. In contrast, monosynaptic reflexes, such as the knee-jerk reflex, involve a direct connection between one sensory neuron and one motor neuron without the involvement of interneurons. Supraspinal reflexes involve pathways that ascend to the brain and may not always incorporate reciprocal inhibition in the same way. Conditioned reflexes are learned responses and differ fundamentally in their mechanism from reflexes that exhibit reciprocal inhibition. Thus, polysynaptic reflexes effectively illustrate the concept of reciprocal inhibition,