Biology Forums - Study Force

Explain frequency/intensity coding and localization in the ear. (simplified)

All receptors, by definition, must transduce the energy from a stimulus (such as a sound wave) into an electrical signal before that information can be sent to the central nervous system. Our perception of a stimulated receptor (such as the hair cells found within the cochlea) is based upon the sensory pathway activated and the region of the brain where those pathways terminate. Thus, activation of an auditory neuron will result in the perception of sound independent of how that neuron was activated.

The specific pathway that transmits information is referred to as labeled lines, with each sensory receptor having its own unique labeled line. Stimulus intensity is coded for in two ways:

• Action potential frequency (frequency coding) and
• The number of receptors activated (population coding).

As stimulus intensity increases, the magnitude of the graded potential will increase, resulting in more frequent action potentials (increased frequency). Alternatively, a stronger stimulus could activate more receptors. The number of receptors activated depends upon the size and density of each receptorʹs receptive field. Slowly adapting receptors work best for coding intensity while rapidly adapting receptors are better for coding change (not magnitude of change). The location of a stimulus is coded by location of their receptive field. The precision with which we can perceive location is called acuity. Acuity for a particular stimulus will depend upon a receptive fieldʹs size, number of receptors, the extent of overlap, and its lateral inhibition. These can vary considerably between receptive fields throughout the body.

Lateral inhibition describes a situation where input from a strongly stimulated receptor will inhibit the afferent pathway transmitting information from nearby receptors.