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Generation of Impulses in Cutaneous Receptors

المؤلف:  Kim E. Barrett, Susan M. Barman, Heddwen L. Brooks, Jason X.-J. Yuan

المصدر:  Ganongs Review of Medical Physiology

الجزء والصفحة:  25th E, P162-163

2026-10-08

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The way that sensory receptors generate action potentials in the nerves that innervate them varies based on the complexity of the sense organ. In the skin, the Pacinian corpuscle has been studied in some detail. The myelin sheath of the sensory nerve begins inside the corpuscle (Figure 1). The first node of Ranvier is also located inside; the second is usually near the point at which the nerve fiber leaves the corpuscle.

Fig1. Demonstration that the generator potential in a Pacinian corpuscle originates in the unmyelinated nerve terminal. The electrical responses to pressures (black arrow) of 1, 2×, 3×, and 4× are shown. The strongest stimulus produced an action potential in the sensory nerve, originating in the center of the corpuscle. (Reproduced with permission from Waxman SG: Clinical Neuroanatomy, 26th ed. New York, NY: McGraw-Hill; 2010.)

GENERATOR POTENTIALS

When a small amount of pressure is applied to the Pacinian corpuscle, a nonpropagated depolarizing potential resembling an excitatory postsynaptic potential (EPSP) is recorded. This is called the generator potential or receptor potential (Figure 1). As the pressure is increased, the magnitude of the receptor potential is increased. The receptor therefore converts mechanical energy into an electrical response, the magnitude of which is proportional to the intensity of the stimulus. Thus, the responses are described as graded potentials rather than all-or-none as is the case for an action potential. When the magnitude of the generator potential reaches about 10 mV, an action potential is produced at the first node of Ranvier. The nerve then repolarizes. If the generator potential is great enough, the neuron fires again as soon as it repolarizes, and it continues to fire as long as the generator potential is large enough to bring the membrane potential of the node to the firing level. Thus, the node converts the graded response of the receptor into action potentials, the frequency of which is proportional to the magnitude of the applied stimulus.