Sense different type of pain from threshold potentials and all-or-none principle

1. Suppose a sensory neuron leads from a pain receptor in the finger to the spinal cord. A pin can be pressed against the skin without eliciting a response from the pain receptor; therefore an impulse is not generated in the sensory neuron. This is because the size of the stimulus is not sufficient to cause the neuron to reach the threshold potential. However, if the pin is lightly jabbed into the finger, the pain receptor may be stimulated and an action potential generated in the sensory neuron leading to the spinal cord. In other words, a threshold potential stimulus is applied and an action potential is generated in the neuron. If the pin is rammed into the finger, that one pain receptor responds and an action potential is generated in the sensory neuron. However, the strength of the action potential in that one neuron would be exactly the same. A neuron cannot send a mild or a strong response; it can respond or not respond (all or-none response). In the last scenario, a person may sense a greater level of pain, but that is due to more pain receptors being stimulated, thus generating action potentials in more neurons.

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