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# 30.1 The Stimulation of Sensory Cells Triggers a Specific Perception in the Brain Why do we get a sudden sweat when we’ve just eaten a pizza topped with pepperonis? We expect taste and smell stimuli from food. The chemicals in tomatoes, cheese, and spices cause stimulation of taste and smell sen...

# 30.1 The Stimulation of Sensory Cells Triggers a Specific Perception in the Brain Why do we get a sudden sweat when we’ve just eaten a pizza topped with pepperonis? We expect taste and smell stimuli from food. The chemicals in tomatoes, cheese, and spices cause stimulation of taste and smell sensory cells. Another ingredient in pepperonis, capsaicin, stimulates a heat-sensing receptor cell type. Whether heat or taste is perceived, sensory cells convey stimuli in the same way as shown in Figure 1: Cells perceive sensory stimuli and transmit this to the brain, which processes the signals as an action potential. **How the Brain Processes Information:** The type of perception felt depends on the pathway the action potential takes to the brain. For instance, light stimuli stimulate light-sensitive cells in the eyes, generating signals which travel along the optic nerve to the brain where signals are processed as light. A "false stimulus" in the eye, like a blow, can still elicit an action potential that the brain interprets as light, which is an unusual but possible occurrence. Capsaicin from the pepperonis, for example, can activate heat receptors causing the brain to interpret the sensation as heat or spicy. This can lead to physiological responses like sweating, an effort by the body to counter excessive heat. Although such false stimuli are rare, they are avoided by sensory cells which mainly respond to appropriate sensory stimuli. Temperature receptors detect temperature changes, and light-sensitive cells, light stimuli. Sensory cells can usually only detect specific sensory input. **Grouping Sensory Cells** Sensory cells are often grouped together within sensory organs. Classically, the five senses—sight, hearing, smell, taste, and touch—are distinguished. However, other senses like temperature, pain, and balance are also integral to the experience. Alternatively, sensory cells can be categorized based on the form of energy they detect. This leads to the following classifications: chemoreceptors, photoreceptors, mechanoreceptors, and thermoreceptors. Touch and balance are controlled by mechanoreceptors; sight is mediated through photoreceptors; smell and taste depend on chemoreceptors; and temperature perception is handled by thermoreceptors. **Conversion of Sensory Stimuli to Electrical Signals:** Sensory cells convert chemical or physical stimuli into electrical signals. In all sensory cells, the stimuli evoke a receptor potential that can spread along the cell body. This receptor potential is converted to an action potential at the axon hillock. The signals are conveyed along the axon of the sensory cells. The sensory signal eventually reaches the synapses with the postsynaptic neuron where neurotransmitter is released. **Diagram Description:** The image includes diagrams illustrating the conversion of stimuli into action potentials and diagrams of the various structures involved. There is a flowchart detailing the pathway of a piece of pizza from the hand directly to its perception in the brain. These diagrams and text discuss processes and structures relevant to sensory processing.