Final answer:
Simple reflexes are the most rapid reflexes because peripheral nerves synapse directly into the spinal cord
Step-by-step explanation:
These reflexes are controlled by a single synapse between a sensory neuron and a motor neuron in the spinal cord. For example, the knee reflex is a simple reflex that is tested by a doctor during a physical exam. When the sensory neuron detects a stretch in the knee, it activates the motor neuron to contract the quadriceps muscle and extend the leg.
Reflexes are so fast because they don't require the involvement of the brain. The sensory information is processed at the level of the spinal cord, which allows for a quick response. The spinal cord contains interneurons that transmit information to the brain to convey what happened after the reflex occurred.
So therefore simple reflexes are the most rapid because they involve local synaptic connections in the spinal cord. The sensory information is processed in the spinal cord, allowing for a quick response without the involvement of the brain.