sensory receptor

Meaning: A sensory receptor is a specialized cell or nerve ending that detects a stimulus and converts that energy into a change in membrane potential, which can trigger action potentials. This conversion is sensory transduction, the first step of sensation. Each receptor type is tuned to one kind of stimulus: photoreceptors (rods and cones) respond to light, mechanoreceptors (including hair cells of the inner ear) to pressure, vibration, or stretch, thermoreceptors to temperature, nociceptors to damaging stimuli, and chemoreceptors to molecules in taste and smell.

On the MCAT: Questions ask you to match a receptor to its stimulus, or to follow the path from receptor to sensory neuron to the brain. Expect sensory adaptation too: when a stimulus is constant, receptors respond less, so you notice changes more than steady input. Rods work in dim light, while cones give color vision and sharp detail.

Common confusion: Students treat the receptor as the place where a sensation is experienced. The receptor only transduces the stimulus into neural signals; perception happens when the brain interprets them. This is why an unusual stimulus to a visual pathway, such as pressure on a closed eye, can still produce a sensation of light.