A reflex arc typically involves which arrangement of neurons?

• A. Brain-centered loop
• B. Sensory only to brain
• C. A direct connection between a sensory neuron and a motor neuron
• D. Only motor neurons without sensory input

Answer: (C)

A reflex arc is built for speed, using a simple neural path that bypasses higher brain processing. The typical arrangement is a direct connection between a sensory neuron and a motor neuron, forming a monosynaptic pathway. When the sensory receptor is stimulated, it sends a signal straight to the spinal cord where it synapses directly onto a motor neuron, which then activates the muscle to produce the reflex. This setup minimizes delay so the response is very fast. Some reflexes do involve interneurons and longer, polysynaptic routes, but the most common and fastest arrangement is the direct sensory-to-motor connection. The other options would either require brain processing, involve signals only to the brain without a direct effector response, or have no sensory input to trigger the reflex.