TASTE & SMELL

Chapter 1: Introduction: Anosmia

  • Olivia, a healthy 35-year-old woman, lost her sense of smell after a bike accident and head trauma

  • Anosmia is a partial or complete loss of the sense of smell, which also affects taste

  • Anosmia can be caused by head trauma, respiratory infections, and aging

  • Our senses inform who we are and how we experience the world

Chapter 2: How Smell Works

  • To smell something, odorants must be volatile and in a gaseous state

  • Molecules are sniffed up into the nose and vacuumed up by sniffing deeper

  • Molecules are filtered by nose hairs, but some reach the olfactory epithelium

Chapter 3: Olfactory Epithelium

  • The olfactory epithelium is the main organ of the olfactory system

  • It is a small yellowish patch of tissue on the roof of the nasal cavity

  • It contains olfactory sensory neurons and insulating columnar supporting cells

  • Pizza molecules dissolve in the mucus on the olfactory epithelium

Chapter 4: Olfactory Sensory Neurons

  • Odorant molecules bind to receptors on olfactory sensory neurons

  • Each olfactory neuron has receptors for one kind of smell

  • Different chemicals in an odorant create different smells

  • Olfactory sensory neurons fire action potentials to the olfactory bulb in the brain

Chapter 5: Glomerulus

  • Olfactory axons converge with mitral cells in a structure called a glomerulus

  • Glomerulus looks like a tangle of fibers and serves as a transfer station

  • Each olfactory neuron and mitral cell combination represents a single volatile chemical

  • The combination of olfactory neurons and mitral cells forms a chord of smells

Chapter 6: How the Brain Processes Smell

  • Mitral cells send signals to the olfactory cortex and emotional areas of the brain

  • Smells can be consciously identified in the frontal lobe

  • Smells also trigger emotional responses and memories in the limbic system

  • Anosmia affects emotional memories and the ability to detect danger

Chapter 7: How Taste Works

  • Taste buds on the tongue, mouth, and upper throat sort sensory information

  • Taste buds are located between fungiform papillae

  • Taste and smell work together to create the perception of flavor

  • Holding the nose impairs the ability to taste subtle flavors

Chapter 8: What Are Taste Buds (Taste Receptor Epithelial Cells)?

  • Taste maps of the tongue are inaccurate and subjective

    • Tongue diagrams from the early 1900s by D.P. Hanig were based on subjective measurements

    • Research in the 1970s showed that taste sensations can be detected in all parts of the tongue

  • Taste buds are located behind the stratified squamous epithelial cells on the tongue

  • Each taste bud contains 50 to 100 taste receptor epithelial cells

  • Taste buds register and respond to different molecules in food

  • Taste buds are not nervous tissue, they synapse to sensory neurons that carry taste information to the brain

Chapter 9: Types of Taste Receptor Epithelial Cells: Gustatory and Basal

  • There are two major types of taste receptor epithelial cells: gustatory and basal

  • Gustatory cells are responsible for tasting

  • Basal cells are stem cells that replace gustatory cells

  • Basal cells are dynamic and replace gustatory cells every week

  • Gustatory cells have gustatory hairs that project into taste pores

  • Tastants must dissolve in saliva and bind to receptors on gustatory cells to trigger an action potential

Chapter 10: How Different Tastants are Sensed

  • Different tastants are sensed differently

  • Salty tastants contain positively-charged sodium ions that open sodium channels in gustatory cells, generating a graded potential and triggering an action potential

  • Sour tastants, which are acidic, activate proton channels

  • Action potentials are relayed through neurons via cranial nerves to the taste area of the cerebral cortex

  • The brain processes taste information and releases digestive enzymes and gastric juices

Chapter 11: Review

  • Olfactory sensory neurons contain receptors for scent signals

  • Olfactory sensory neurons synapse with mitral cells, which send signals to the brain

  • Taste begins with taste receptor epithelial cells, not nervous cells

  • Tastants bind to receptors on gustatory cells, triggering action potentials in cranial nerves

Chapter 12: Credits

  • The episode was written by Kathleen Yale and edited by Blake de Pastino

  • Dr. Brandon Jackson served as a consultant

  • Nicholas Jenkins directed the episode

  • Nicole Sweeney was the script supervisor and editor

  • Michael Aranda was the sound designer

  • Thought Caf was the graphics team