A stimulus (a cut on the skin) acts on a receptor that then conveys this information to a sensory neuron. The stimulus is extraordinarily large (lots of pain and bleeding!). In order to communicate the intensity of the stimulus to the central nervous system, the sensory neuron will most likely

Question

A stimulus (a cut on the skin) acts on a receptor that then conveys this information to a sensory neuron.  The stimulus is extraordinarily large (lots of pain and bleeding!).  In order to communicate the intensity of the stimulus to the central nervous system, the sensory neuron will most likely

BlackTom AI · Accepted Answer

Neurons encode stimulus intensity primarily by changing the frequency of action potentials (rate coding) and by recruiting more sensory receptors (population coding). The action potential itself is an all-or-none event: once threshold is reached, the AP amplitude and shape are determined by ion channel kinetics and ionic gradients, not the strength of the stimulus.

Step-by-step reasoning:
1. A larger cut produces a larger receptor (generator) potential in the sensory ending. That receptor potential is an analog graded signal whose amplitude increases with stimulus intensity.
2. A larger receptor potential causes the sensory neuron membrane to reach threshold more often in a given time, producing more action potentials per unit time (higher firing rate). For example, a weak stimulus might elicit 5 Hz firing, whereas a very strong stimulus could raise firing to tens or hundreds of Hz, limited by the neuron's refractory period (absolute refractory ≈1 ms sets a theoretical max near 1000 Hz, but physiological rates are lower).
3. The action potential waveform (peak voltage, rising/falling phases) remains essentially the same for each spike because the peak is set by the sodium equilibrium potential (~+30 to +60 mV depending on conditions) and the ion channel kinetics. This is the all-or-none principle.
4. Additionally, very strong stimuli can recruit neighboring sensory fibers, increasing the total number of afferent spikes reaching the CNS (population coding), reinforcing the intensity signal.

Why the correct answer is correct:
- "Generate a greater number of APs in a given period of time" describes rate coding: stronger stimulus → larger receptor potential → increased firing frequency.

Why the other options are incorrect:
- Conduct at a faster speed: Conduction velocity depends on axon diameter and myelination, not instantaneous stimulus intensity.
- Depolarize or repolarize much more quickly: Ion channel kinetics set rise/fall times; stimulus magnitude affects frequency, not the fundamental time course of each AP.
- Trigger shouting of bad words: Behavioral response is irrelevant to the neuronal encoding mechanism asked.
- Produce an AP which peaks at value higher than +40 mV: AP peak is constrained by ion equilibrium potentials and does not scale with stimulus intensity.

Final confirmation: The correct answer is "generate a greater number of APs in a given period of time."

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