 Dear students, in this topic we shall discuss the process of sensory transduction in detail. The sensory receptor cells convert the physical or chemical energy of the stimulus into the electrical signals that is nerve impulse. This conversion is called sensory transduction. Dear students, the sensory transduction takes place in four steps. The first step is the detection of stimulus. Second step is amplification of the stimulus. Third step is the encoding of signal. And fourth step is the transmission of signal. First, we shall discuss the detection of stimulus, which is the initial event in all sensory transduction systems. As we have already discussed that only the stimuli that have a threshold level of energy are detectable. What is this threshold? Threshold is defined as the smallest amount of energy that can produce a response in the sensory cells 50% of the time. Meaning as a minimum level, which sometimes is detected or sometimes is not detected, 50% times if it is detected, then that level is the threshold level. The second step of sensory transduction is the amplification of stimulus. Weaker stimuli are amplified in the sensory system. This amplification occurs within the receptor cells. Amplification involves a cascade of chemical reactions, meaning a series of chemical reactions, as a result of which signals are amplified. This is called cascade of chemical reactions. As a result, signal is amplified by many orders of magnitude. When we say many orders of magnitude, then this means double or triple is not possible. In fact, it levels to 10 raised to the power of 4, 5, 6 normally amplification occurs at this level. After amplification, the signal is encoded. This encoding of signal is an intracervular process in which physical or chemical energy is converted into electrical energy. As a result, the ionic grunts are produced and these ionic grunts have encoded in them all the characteristics and attributes of original stimulus in electrical form. After encoding, a last step, transmission of stimulus. The encoded signal is transmitted to the nervous system by either action potentials or by electronic conduction. Dear students, a single receptor can encode information of only one quality of a stimulus. It cannot report all qualities of the stimulus. For example, a single photoreceptor can report the intensity of the light, but it cannot report its color. To report all the qualities of a stimulus, the receptors are arranged in sensory organs. Sensory organ has a variety of receptor cells for a single type of stimulus. Each receptor responds differentially to different qualities of the stimulus. For example, some photoreceptors receive a red light stimulus. Some other cells receive a blue light stimulus. In this way, all the photoreceptors receive all the light characters. As a result, an integrated information is sent to the brain in which all the qualities of the stimulus are included. In this way, we can say that the receptors which are grouped in sensory organs convey significantly more information about the stimulus.