Question

Match the sensory characteristic with how it is coded by the nervous system. Sensory modality Location of the stimulus Intensity of the stimulus Duration of stimulus A. Which sensory neurons are activated B. Receptive fields C. Frequency of action potentials D. Duration of action potential train (i.e., continued firing of action potentials in sensory neurons) E. Size of action potential F. Duration of a single action potential

Answer 1

(C)

Physiologically, action potential frequencies of up to 200-300 per second (Hz) are routinely observed. Higher frequencies are also observed, but the maximum frequency is ultimately limited by the absolute refractory period.

(D)

Sodium-based action potentials usually last for under one millisecond, but calcium-based action potentials may last for 100 milliseconds or longer.

(E)

There are no big or small action potentials in one nerve cell - all action potentials are the same size. Therefore, the neuron either does not reach the threshold or a full action potential is fired - this is the "ALL OR NONE" principle. Action potentials are caused when different ions cross the neuron membrane.

(F)

In muscle cells, a typical action potential lasts about a fifth of a second. In some other types of cells, and also in plants, an action potential may last three seconds or more.