Why fingertips outfeel your back

Science · The Human Body · ages 20-21

Name ______________________ Date ____________

When a shirt rests steadily on the skin, which receptor response helps it become less noticeable?
- Slow adapters stop whenever pressure is steady
- All touch receptors keep firing at an unchanged rate
- Rapid adapters quieten under steady input
Which pairing gives common examples of free and encapsulated skin endings?
- Free: pressure only; encapsulated: nociception only
- Free: temperature and nociception; encapsulated: touch
- Free: nociception only; encapsulated: all skin touch
Cortical map area matches body part size.
Circle one: True False
Which listed structure contains circuits that can inhibit or amplify nociceptive transmission from body skin?
- In the skin's outer dead-cell layer
- In the spinal cord
- In the connective capsule around a touch ending
At the same small spacing, two contacts can feel separate on a fingertip but merge on the back. What helps explain this?
- Denser touch innervation and smaller receptive fields
- Larger receptive fields that collect both contacts together
- Equal receptor density but a larger fingertip skin surface
In the simplified dorsal-column pathway from body skin to somatosensory cortex, how many neurons form the main ascending chain, including the primary sensory neuron but excluding local interneurons?
Answer: ______________
Gentle, non-painful rubbing near a minor bump sometimes eases the ache. Which spinal mechanism could contribute?
- Touch recruits spinal inhibitory interneurons
- Touch directly blocks every peripheral nociceptor
- Touch repairs damaged tissue through spinal reflexes
A student says felt pain always equals injury size. What is wrong?
- Pain intensity is fixed by the number of damaged skin cells
- Inhibitory circuits change the injury without changing its signals
- Spinal circuits can change onward nociceptive transmission

Answer key

For grown-ups. Fold this page away before handing over the rest.

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Rapid adapters quieten under steady input · Rapid adapters respond to change and reduce their response when input stays steady. This contributes to reduced awareness; slow adapters and attention still matter.
Free: temperature and nociception; encapsulated: touch · Free endings include temperature and nociceptive receptors. Encapsulated endings include touch receptors, but Merkel endings show that touch does not require a capsule.
False · The cortical map is not a scale drawing of skin area. Hands have much more cortical representation relative to their skin area than the torso.
In the spinal cord · Spinal circuits can decrease or increase onward nociceptive transmission. This is one stage of processing that can affect pain perception.
Denser touch innervation and smaller receptive fields · Dense innervation and small receptive fields support fine spatial sampling. Nearby contacts can produce more distinct population activity on a fingertip than on the back.
3 · Count the primary sensory neuron, the medullary relay neuron and the thalamic neuron projecting to cortex. This main ascending chain contains three neurons.
Touch recruits spinal inhibitory interneurons · Non-painful touch can activate local inhibitory circuits that reduce onward nociceptive transmission. This may contribute to less pain; relief is not guaranteed.
Spinal circuits can change onward nociceptive transmission · Spinal inhibition or amplification can change nociceptive transmission. Further brain processing also affects pain, so felt pain is not a direct measure of injury size.