Sensation and Perception

Chapter 4: Sensation and Perception

4.1 Smell (Olfaction)

  • Definition: Olfaction is the response to molecular structures of substances (odorant molecules) entering the nasal cavity.

  • Characteristics:

    • Least understood of the senses.

    • Only sense directly connected to the forebrain, indicating a relationship with emotional and social behavior.

4.2 Anatomy of Smell

  • Olfactory Epithelium:

    • A mucus membrane located at the top of the nasal cavity.

    • Contains around 10 million olfactory receptor neurons (ORNs) which are essential for the sense of smell.

    • Odorant molecules bind to sites on ORNs, sending action potentials into the olfactory nerve when enough binding occurs.

  • Olfactory Bulb:

    • Receives axons from groups of ORNs.

    • Located above the nasal cavity beneath the frontal lobes.

    • Each specific type of ORN converges at a glomerulus within the olfactory bulb.

    • Humans have about 350 glomeruli.

    • Outputs from the olfactory bulb go to various brain centers responsible for basic drives, emotions, and memories.

    • Subject to sensory adaptation.

4.3 Role of Smell in Behavior

  • Social Behavior: Smell influences social behavior through chemical signals.

  • Pheromones:

    • Biochemical odorants emitted by members of a species that can affect another’s behavior or physiology.

    • There may be a link between sexual orientation and responses to specific odors.

    • For instance, testosterone-based odors activate the hypothalamus in heterosexual women and homosexual men, but not in heterosexual men.

    • The same is noted in homosexual women and estrogen.

4.4 Taste

  • Definition: Taste involves conditioned taste aversion and is facilitated by taste buds located within papillae on the tongue.

  • Structure:

    • Each papilla contains hundreds of taste buds, each functioning as the organ of taste transduction.

    • 5,000 to 10,000 taste buds are distributed across the tongue, roof of the mouth, and upper throat.

    • Around 50% of taste receptors are lost by the age of 20.

  • Taste Buds:

    • Contain various types of taste receptor cells which react with tastant molecules through their microvilli tips.

4.5 Types of Taste Receptors

  • Main Types:

    • Salty

    • Sour

    • Bitter

    • Sweet

    • Umami (savory)

  • Smell and Taste:

    • Taste experience is also influenced by smell.

    • There are individual differences:

      • 50% tasters

      • 25% non-tasters

      • 25% super-tasters

    • Different groups can be subjected to varying health conditions.