Module 1 Lesson 1 - 3

Lesson 1 — Sensory Perception

Gustation - Taste (pages 425-426)

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Taste buds on the surface of the tongue can detect a taste only when chemicals are dissolved in saliva so that chemoreceptors can send impulses to the brain. The five basic tastes are salty, sweet, sour, bitter, and umami. Current scientific studies show that every taste bud is capable of detecting each taste (sweet, salty, sour, bitter, and umami), but each taste bud responds best to a certain taste.

Taste sensory pathway

1. Chemoreceptors in taste buds detect chemicals in food.
2. Sensory neurons are triggered.
   
3. Nerve impulses occur.
   
4. Brain receives the nerve impulses (cerebrum - parietal lobe).
5. Brain interprets nerve impulses as a sensation (perception).
   

Going Beyond

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Interested in learning more about taste? Check these websites for more information: 

BBC News Article: Same taste bud for 'bitter - sweet'

BBC Science: Human Body & Mind

Olfaction - Smell (page 426)

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Smell is detected when odour particles stimulate olfactory receptor cells.  A sensory nerve communicates this information to the olfactory cortex (located in the frontal and temporal lobes of the brain) and the limbic system where memories are stored. Have you ever notice that a scent can bring memories?

Cells in the olfactory epithelium produce a continuous secretion of mucous in which molecules of airborne chemicals dissolve. Mucous is secreted continuously to flush away old odour chemicals so that new odour chemicals may gain access to the receptors. Smells associated with dangers (such as smoke, natural gas, or skunk musk) trigger the sympathetic nervous system. The perception of unpleasant odours can trigger sneezing or gag reflexes.

Much of the sensation we perceive as taste is actually olfactory. This is why, when you have a cold, everything tastes bland.

Olfactory sensory pathway

1. Odour molecules are breathed into the nasal cavity.
   
2. Odour molecules dissolve in mucous produced by olfactory glands of the nasal epithelium.
3. The molecules in solution attach to receptors on the cilia (hairs) of olfactory cells.
   
4. The sensory receptors or olfactory cells (specialized neurons) initiate nerve impulses.
5. Sensory neurons conduct nerve impulses.
   
6. Olfactory bulb receives the impulses and sends them to the brain - limbic system (emotional center) and cerebrum (frontal and temporal lobes).
   
7. Brain interprets the impulses.
8. Sensations are interpreted as a scent (perception).