Taste And Smell

Cornea

Pupil Iris

Optic nerve

Lens

Cornea

Pupil Iris

Retina

Sclera

Choroid figure 49-12

Light entering the eye travels through the cornea, the pupil, and the lens to the retina, which contains millions of photoreceptors. Activation of these specialized sensory receptors sends a signal through the optic nerve to the optic centers of the brain—first to the thalamus and eventually to the visual cortex in the occipital lobe.

Retina

Sclera

Choroid

People perceive variations in tastes and odors because of specialized chemoreceptors. The chemoreceptors for taste are clustered in taste buds. Most of the 10,000 taste buds are embedded between bumps called papillae (puh-PIL-ee) on the tongue. Additional taste buds are found in the throat and on the roof of the mouth. Chemicals from food dissolved in saliva enter a taste bud through a small opening. The chemicals bind to receptors and stimulate the neurons that line the inner surface of the taste buds. As shown in Figure 49-13, taste signals travel through a relay in the brain stem, to the thalamus, and finally to the cortex for interpretation.

Receptors in the nasal passages detect chemicals in the air. Specialized chemoreceptors called olfactory (ahl-FAK-tuh-ree) receptors are located in the mucous lining of the epithelium in the nasal passages. The binding of odor molecules to specific receptor molecules in the olfactory receptors stimulates the receptors. Signals from olfactory receptors travel to the olfactory bulb, a structure of the limbic system. Then, signals travel to olfactory areas of the cortex and to the amygdala, another limbic structure.

figure 49-12

Light entering the eye travels through the cornea, the pupil, and the lens to the retina, which contains millions of photoreceptors. Activation of these specialized sensory receptors sends a signal through the optic nerve to the optic centers of the brain—first to the thalamus and eventually to the visual cortex in the occipital lobe.

figure 49-13

Taste and smell are chemical senses. Sensory receptors in the mouth and nasal passages bind to molecules from the environment, initiating neural signals that travel to the brain.

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