Reflejo

Reflejo is a Spanish noun that has two primary senses: the physical phenomenon of light bouncing off a surface and a biological, automatic response to a stimulus. The term can also be used in a broader, figurative sense to denote a reflection or imitation of something.

In optics, a reflection occurs when light rays strike the boundary between two media and bounce back into the original medium. The law of reflection states that the angle of incidence equals the angle of reflection with respect to the normal to the surface. Reflections can be specular, produced by smooth, mirror-like surfaces that form clear images, or diffuse, produced by rough surfaces that scatter light in many directions. Mirrors, polished metals, and bodies of water are common sources of specular reflection, and reflections are fundamental to devices such as cameras, telescopes, and optical sensors.

In physiology, a reflex is an involuntary and nearly instantaneous movement in response to a stimulus. It is mediated by a reflex arc, which typically involves a receptor, a sensory neuron, sometimes an interneuron in the spinal cord or brainstem, a motor neuron, and an effector such as a muscle or gland. Reflexes serve protective and regulatory roles, helping to maintain posture and respond to sudden changes. Common examples include the knee-jerk reflex and the blinking reflex.

Figuratively, reflejo can describe how a person, situation, or work mirrors a larger reality or truth, as in phrases that speak of a “reflejo de la realidad.” Etymology traces to Latin reflexus, from reflectere, meaning to bend back.

See also: pupillary reflex, tendon reflex.