Describe the receptive field concept in the somatosensory system and give an example involving mechanoreceptors.

• A. A receptive field is defined as any area of skin that can be stimulated without altering firing of the neuron.
• B. A receptive field is the region where a stimulus causes the neuron to increase firing; all mechanoreceptors have the same field size.
• C. Receptive fields do not vary in size among mechanoreceptors.
• D. A receptive field is the skin region where a stimulus alters neuronal firing; small-field receptors (Merkel, Meissner) provide high acuity (fingertips), while large-field receptors (Pacinian) detect coarse touch and vibration.

Answer: (D)

The receptive field is the patch of skin where stimulation changes the firing of a specific somatosensory neuron. Receptive-field sizes vary among mechanoreceptors. Small-field receptors like Merkel discs and Meissner corpuscles have tiny, localized fields, concentrated in the fingertips, which lets you feel textures and edges with high spatial precision. Large-field receptors such as Pacinian corpuscles cover broad skin areas and are sensitive to high-frequency vibration and coarse touch, so the exact point of contact is less precisely localized. For example, a light touch on the fingertip activates the small-field Merkel/Meissner neurons and yields precise location and texture information, while a vibrating stimulus on a larger area of skin engages Pacinian receptors over a wide field, giving a sensation of vibration without sharp localization.