Chapter 8: Special Senses

1. Chapter 8: Special Senses

2. Taste • Chemoreceptors are sensory receptors that respond to chemicalssuch as taste and smell. • Taste buds detect at least five basic chemical substances: sugars (sweet), acids (sour), alkaloids (bitter), salts (salty), and umami/proteins (savory). • Food molecules dissolved in saliva flow into the taste pores and bind to taste cells, which generate nerve impulses that are sent to the brain for interpretation.

4. Taste cont. • We have ~10,000 taste buds; most are on the tongue, but a few are scattered on the soft palate and inner cheeks. Because of location, taste buds are exposed to friction and burning, but are replaced every 7-10 days. • Gustatory cells- specific cells that respond to chemicals dissolved in saliva. • Taste likes and dislikes have homeostatic value. Affinity for sugar and salt satisfies the needs for carbohydrates and minerals. Sour foods provide vitamin C. Unami guides the intake of proteins. Our aversion for bitter protects us from poison and spoiled foods.

5. Smell • Chemicals in the air stimulate olfactory receptors, chemoreceptors located deep in your nostrils. • These sensory receptors produce nerve impulses that are sent to and interpreted by the brain. • When you have a bad cold and your nose is stuffed up, your food may seem to have little taste. Your ability to taste food directly depends on your ability to smell it!

6. Smell cont. • The thousands of olfactory receptors occupy a space the size of a postage stamp on the roof of each nasal cavity. • Olfactory hairs extend from the receptors cells and are continuously bathed in mucus secreted by underlying glands. This allows inhaled chemicals to be dissolved and recognized. • Odor recognition is closely tied to the limbic system- emotions. • Olfactory receptors are extremely sensitive- just a few molecules can activate them, but tend to adapt quickly!

7. Touch • The skin is responsible for our sense of touch and our ability to quickly sense changes in the surrounding temperature. • Painful sensations are also detected by the skin. • Pressure receptors are found in the skin, muscle, and joints. • The sensory receptors that detect these phenomena send nerve impulses directly to the brain.

8. Processing Sensory Information • Most sense organs send signals through nerves of the PNS into the CNS. • The thalamus then relays this information to specific regions of the cortex. • Specialized regions of the cerebral cortex detect differentsensory information. • The parietal lobe of the cortex receives somatosensory (“body sense”) stimuli. • In the rear portion of the frontal lobe, immediately in front of the somatosensory cortex is the motor cortex. • The frontal lobe also regulates intellectual function and aspects of our personality. Most visual processing occurs in the occipital lobe, located at the back of the head. • The temporal lobe processes sound information.

9. Developmental Aspects of the Special Senses • All babies are born hyperopic (farsighted) and can only see in gray tones. By 5 months, visual acuity has improved to about 20/200 and color vision is developing. By 5 years, visual acuity is 20/30 on average and color vision is well developed. • We lose taste buds as we age, which is why children tend to prefer bland foods (chicken nuggets) and adults prefer more flavorful foods.