PPT The Chemical Senses

The Chemical Senses

Overview of Topics

  • Taste

  • Olfaction

  • Pheromones

  • Synesthesia

Understanding Taste

  • Role of Taste: Informs whether to swallow or reject substances.

  • Taste Buds: Stimulation occurs via taste buds on the tongue.

  • Flavor: A combination of taste and smell. Axons for taste and smell in the endopiriform cortex(part of the brain for processing smell & memory related to odor)

    ↓

    not important to memorize

Taste Receptors

  • Nature of Taste Receptors: Modified skin cells, not true neurons that release neurotransmitters to excite neighboring neurons. Last about 10-14 days, gradually sloughed off.

  • Location: Found in papillae on the tongue surface, with each papilla having up to 10 taste buds, each containing ~50 receptor cells. Mainly located along the tongue's edge.

Types of Taste Receptors

  • Common tastes in Western society: Sweet, Sour, Salty, Bitter.

  • Determining Taste Variety: Identify how taste receptor work and how they can be influenced by certain substances

    • Example: Miracle berry changes the sweet perception of acids temporarily.

Taste Adaptation

  • Adaptation: Fatigue of receptors leads to altered taste perception.

    • Example: Soaking tongue in sour solution reduces sour taste in subsequent tests.

  • Cross Adaptation: Exposure to one taste can lessen response to another.

  • Other Tastes: Glutamate receptor for umami; detection of fats as a distinct taste

    -Glutamate receptor=special proteins in the brain and nervous system respond to glutamate, the most common excitatory neurotransmitter(chemicals that helps sends signals between nerve cells) in the brain.

Mechanisms of Taste Reception

  1. Saltiness & Sour(Use directly through ion channel):

    • saltiness detection=the process of salt which is a sodium is detected on your toungue by taste receptor cells

    • Sour Detection: Triggered by the presence of acids.

  2. Sweetness, Bitterness, Umami(use G proteins):

    • Resemble metabotropic synapses=brain connection where receptors (on neurons) do not directly control but activate G proteins which trigger other processes inside the cell.

      >receptors activate G proteins that send a signal to your brain about what your tasting

    • Over 30 bitter receptors detect toxins, also stimulating nasal receptors leading to physiological responses like sneezing.

    -G proteins=messengers inside cells, When a signal (like a taste or smell) reaches the receptor G protein it helps pass the message inside the cell to create a response.

Taste Information Pathway

  • 2/3 of the front Tongue's: Information travels via the chorda tympani (7th cranial nerve; nerve that carries taste information).

  • Back of tongue and throat: Utilizes branches of 9th and 10th cranial nerves; nerve that carries taste information

  • Central Pathway: NTS → Pons → Lateral hypothalamus → Amygdala → Ventral posterior thalamus → Cerebral cortex (Somatosensory and Insula).

Variations in Taste Sensitivity

  • Taste Bud Variation: Some individuals may have three times as many taste buds.

  • Gender Differences: Women’s taste sensitivity can change with hormonal levels.

  • Supertasters: Dislike strong flavors. Nontasters have fewest taste buds; tasters have a normal amount.

Understanding Olfaction

  • Definition: Response to chemicals that contact nasal membranes.

  • Importance: Crucial for finding food, mates, and avoiding danger for mammals.

Relationship Between Olfaction and Taste

  • Flavor Connection: Much of food's flavor depends on its odor.

Smell and Emotions

  • "Smell of Fear" Study: Collection of sweat odors during emotional videos. Women’s facial expressions reflected emotions evoked by smells.

  • Social Preferences: Preference for people with different smells may reduce inbreeding risks.

Olfaction and COVID-19

  • Anosmia: Loss of smell as a neurological symptom of COVID-19. Affects over half of patients; often temporary rehabilitation.

Olfactory Receptors

  • Distinction Ability: Humans can distinguish over a trillion smells.

  • Olfactory Cells Location:these smell detectors are found on a special layer of tissue inside your nose called the olfactory epithelium

  • Receptor Mechanism: Respond to external chemicals, triggering G protein changes. Multiple receptor proteins in humans enhance smell discrimination.

Olfactory Information Processing

  • Olfactory Bulb Function:

    • Function=helps carry the smell signals from your nose to your brain so you can recognize smells. If smells are similar, they activate nearby cells in your brain.

      *the smell receptors in your nose don't last long—they only live for about a month before being replaced

Individual Olfactory Differences

  • Gender Sensitivity: Women generally detect odors more readily than men. Young adult women show increased sensitivity to previously ignored scents; influenced by hormones. Effects diminish in men and women post-menopause.

Understanding Pheromones

  • Vomeronasal Organ (VNO): A specialized region for pheromone detection.

  • Pheromone Effects: Unconscious influence on behavior among the same species. Effects on hormonally driven behaviors like testosterone and cortisol secretion. Synchronization of menstrual cycles in females due to pheromones.

Understanding Synesthesia

  • Definition: Stimulation of one sense evokes perceptions in others.

  • Examples of Synesthesia: Colors perceived with letters, tastes associated with shapes or colors.

Brain Structure and Synesthesia

  • Gray Matter and Connections:

    • grey matter= the brain does a lot of its thinking and processing

    • If you use your senses a lot(seeing or hearing) the brain builds up more gray matter in the areas that handle those senses, making them work better.

  • Cortical Interaction: Enhanced connections between color and number/letter processing areas. Main occurrence in the cerebral cortex rather than in sensory receptors.