In any sensory system (sound, light, chemical), the lower limit of detection is often determined by the "background' noise level" of the sensory system. One could think of this as signals that are generated by the sensory system in the absence of any physical or chemical stimulus.

Which of the following represents this background noise level of sensory inputs to the nervous system?


(a)the largest graded potential that will not produce an action potential
(b)the smallest amount of neurotransmitter that will cause a detectable change in the post-synaptic membrane potential
(c)randomly generated action potentials on a sensory neuron
(d)the smallest action potential that can be produced