A 7-year-old boy presents with his mother to the emergency department for evaluation of a burn, which he sustained 25 minutes ago after spilling hot soup onto his arm. Past medical history is noncontributory, and he takes no medications. Vital signs are within normal limits, and physical examination reveals a teary child with an irregular three-inch patch of red skin on the right forearm that is starting to blister.
Which of the following types of sensory nerves mediate the ability to sense the temperature of the soup?
A) Free nerve endings
Free nerve endings are responsible for sensation of pain and temperature. They are present in all tissues except cartilage and the lenses of the eyes. They are broken into two groups: A-delta fibers (fast and myelinated) and C fibers (slow and unmyelinated).
Answer choice B: Meissner corpuscles, is incorrect. Meissner corpuscles are large myelinated nerves responsible for the sensations of dynamic/fine touch, low frequency vibration, and skin indentation. They are most numerous in hairless skin.
Answer choice C: Merkel discs, is incorrect. Merkel discs are large myelinated nerves responsible for the sensations of pressure and deep static touch. They are most numerous in the fingertips.
Answer choice D: Pacinian corpuscles, is incorrect. Pacinian corpuscles are large myelinated nerves responsible for the sensations of pressure and high frequency vibration. They are found in deep skin layers, ligaments, and joints.
Answer choice E: Ruffini corpuscles, is incorrect. Ruffini corpuscles are large myelinated nerves responsible for the sensation of stretch. They are most numerous in the fingertips and joints.
Key Learning Point
Specialized nerves mediate different sensations, though some may have overlapping roles. Free nerve endings primarily sense pain and temperature; Meissner corpuscles sense fine touch; Merkel discs sense deep touch; Pacinian corpuscles sense pressure; and Ruffini corpuscles sense stretch.
