What are simple (spinal) reflexes?

Simple reflexes, often referred to as spinal reflexes, are characterized by their operation through the spinal cord without the direct involvement of higher brain centers. These reflexes are typically automatic, rapid responses to specific stimuli. When a sensory neuron detects a stimulus, it transmits the signal directly to the spinal cord, where it synapses with a motor neuron. This results in an immediate response, such as pulling a hand away from a hot surface.

This direct pathway allows for quicker reactions than if the signal had to travel to the brain and back. For example, the knee-jerk reflex demonstrates this mechanism; when the patellar tendon is tapped, the leg kicks forward without the need for brain processing. The essential feature of simple reflexes is their reliance solely on the spinal cord, making them crucial for protective responses and basic motor functions.