Taste & Smell

• Anosmia


  Partial or complete loss of the sense of smell
• Anosmia can be caused by head trauma, respiratory infections, and aging
• Our six major special senses translate stimuli into action potentials
• Transduction


  The process of sensory cells translating stimuli into action potentials
• Photoreceptors


  Cells that detect light waves
• Mechanoreceptors


  Cells that detect sound waves and pressure
• Chemical senses


  Include taste (gustation) and smell (olfaction)
• Chemical senses are our most primitive and fundamental
• Newborns can orient themselves chiefly by scent
• Tastes and smells are powerful at activating memories and triggering emotions
• Smelling process


  1. Sniff molecules

  2. Molecules must be volatile

  3. Molecules filtered by nose hairs

  4. Molecules hit olfactory epithelium

  5. Bind to receptors on olfactory sensory neurons

  6. Fire action potentials to olfactory bulb
• Olfactory epithelium


  Main organ of the olfactory system
• The olfactory epithelium contains millions of olfactory sensory neurons
• Mitral cells


  Relay signals from olfactory neurons to the brain
• Each olfactory neuron has receptors for just one kind of smell
• Scientists estimate that our 40 million olfactory receptor neurons help us identify about 10,000 different smells
• Signal processing in the brain

  1. Mitral cell picks up signal

  2. Sends signal to olfactory cortex

  3. Data reaches frontal lobe

  4. Data reaches limbic system
• Taste is 80 percent smell
• When you chew food, air is forced up your nasal passages
• Taste maps of the tongue are bogus
• Taste buds


  Cover the tongue, mouth, and upper throat
• Taste buds are tucked into tiny pockets behind stratified squamous epithelial cells
• Gustatory cells


  Cells that actually do the tasting
• Basal cells


  Stem cells that replace gustatory cells
• Tasting process


  1. Tastants dissolve in saliva

  2. Diffuse through taste pores

  3. Bind to receptors on gustatory cells

  4. Trigger action potentials
• Each tastant is sensed differently
• Salty foods cause sodium channels in gustatory cells to open
• Sour foods activate proton channels
• Action potential relay


  1. Action potential activated

  2. Relayed through cranial nerves

  3. Sent to taste area of cerebral cortex
• Olivia's anosmia prevented her from accessing emotional memories associated with scents
• Each gustatory cell projects a gustatory hair down to a taste pore
• Gustatory cells synapse to sensory neurons that carry taste information to the brain
• Gustatory cells are replaced every week or so
• Action potentials trigger the release of digestive enzymes in saliva and gastric juices
• This episode was filmed in the Doctor Cheryl C. Kinney Crash Course Studio
• The episode was written by Kathleen Yale and edited by Blake de Pastino
• Thomas Frank contributed to the production of this episode