Taste & Smell: Crash Course Anatomy & Physiology #16

CrashCourse
27 Apr 201510:30
EducationalLearning
32 Likes 10 Comments

TLDRThe video script presents a detailed exploration of the human senses of smell and taste, using the case of Olivia, a woman who lost her sense of smell due to head trauma, as a starting point. It explains the biological processes behind these senses, highlighting the importance of chemoreceptors in detecting molecules in food and air. The script delves into the science of how smell and taste are linked, with taste being 80% dependent on the sense of smell. It also debunks the myth of the tongue's taste map, showing that all tastes can be detected across the entire tongue. The video emphasizes the role of these senses in memory, emotion, and survival, and concludes with a reminder of the complexity and wonder of human sensory perception.

Takeaways
  • 🚑 Olivia's case illustrates the impact of anosmia, a condition resulting from head trauma that led to the loss of the sense of smell and most of the sense of taste.
  • 🌸 The sense of smell is crucial for enjoying life's simple pleasures and plays a significant role in memory, emotion, and safety.
  • 🧠 Sensory transduction is the process by which sensory cells convert stimuli into action potentials that the nervous system can interpret.
  • 👃 Olfaction (smell) relies on chemoreceptors in the nasal passages that detect airborne molecules, which must be volatile to be perceived.
  • 🧫 The olfactory epithelium contains specialized olfactory sensory neurons, each with receptors for a specific type of smell.
  • 🔬 Each odorant is a combination of various chemicals, and our olfactory system can identify thousands of different smells.
  • 🧶 The olfactory signal is processed through a structure called a glomerulus, which acts as a transfer station for sensory information.
  • 🎶 The combination of olfactory neurons and mitral cells forms a complex pattern of signals, likened to a musical chord of smells.
  • 👅 Taste (gustation) is closely linked to smell, with the majority of taste sensations being processed through the sense of smell.
  • 🔍 The traditional tongue map, which suggests different areas of the tongue detect specific tastes, has been debunked.
  • 🍕 Taste buds are located in pockets behind the tongue's surface, and each contains cells that respond to different molecules in food.
  • 💡 The gustatory system involves taste receptor cells that, once triggered, send signals through cranial nerves to the brain for processing.
Q & A

  • What is anosmia and how did it affect Olivia's life?

    -Anosmia is a partial or complete loss of the sense of smell, and with it, most of the ability to taste. It affected Olivia by making her life less interesting, causing her to get depressed, and leading to practical issues like not being able to smell burnt food or expired milk.

  • What is the process of sensory transduction?

    -Sensory transduction is the process by which sensory cells translate chemical, electromagnetic, and mechanical stimuli into action potentials that the nervous system can interpret.

  • How do our chemical senses of taste and smell work?

    -Taste and smell are chemical senses that use chemoreceptors in our taste buds and nasal passages to detect molecules in our food and the air. These senses are our most primitive and fundamental, and they play a crucial role in memory, emotion, and danger alerting.

  • What are the main components involved in the process of smelling?

    -The main components in the process of smelling include odorant molecules, the olfactory epithelium, olfactory sensory neurons, the olfactory bulb, and the brain's olfactory cortex.

  • How do olfactory neurons specialize in detecting smells?

    -Each olfactory neuron has receptors for just one kind of smell, allowing for the detection of a wide range of odors. When an odorant is present, it triggers a specific combination of olfactory neurons, forming a unique pattern that the brain interprets as a particular smell.

  • What role does the glomerulus play in the olfactory system?

    -The glomerulus serves as a transfer station where the nose information turns into brain information. It is where olfactory axons meet with the dendrites of mitral cells, which then relay the signal to the brain.

  • How many different smells are humans estimated to be able to identify?

    -Scientists estimate that our 40 million different olfactory receptor neurons help us identify about 10,000 different smells, possibly even more.

  • How does the sense of taste relate to the sense of smell?

    -Taste is closely related to smell because when we chew food, air is forced up our nasal passages, allowing our olfactory receptor cells to register information simultaneously with our taste receptors. This means that a significant portion of what we perceive as taste is actually smell.

  • What is the debunked myth about the human tongue and taste?

    -The debunked myth is the tongue map from elementary school that suggests different areas of the tongue are responsible for detecting specific tastes. Research has shown that all tastes can be detected all over the tongue.

  • Where are the taste buds actually located on the tongue?

    -Taste buds are located in tiny pockets hidden behind the stratified squamous epithelial cells on the tongue, not in the visible fungiform papillae.

  • How do taste receptor cells respond to different molecules in food?

    -Taste receptor cells, specifically the gustatory cells, bind to different molecules in food, known as tastants. This binding triggers an action potential that is then relayed to the brain via the seventh, ninth, and tenth cranial nerves.

  • What are the five basic tastes that humans can detect?

    -The five basic tastes that humans can detect are sweet, salty, sour, bitter, and umami.

Outlines
00:00
🏥 Olivia's Anosmia and Sensory Transduction

This paragraph introduces Olivia, a previously healthy 35-year-old woman who experiences a loss of smell (anosmia) following a serious bike accident resulting in head trauma. The loss of smell impacts her ability to taste and leads to a diminished quality of life. The paragraph delves into the science of sensory transduction, explaining how sensory cells convert various stimuli into action potentials that the nervous system can interpret. It also distinguishes between the different types of sensory receptors, such as photoreceptors for vision and mechanoreceptors for touch, hearing, and balance, and highlights chemoreceptors' role in detecting molecules related to taste and smell. The importance of these senses in memory, emotion, and danger detection is emphasized, along with the innate nature of these senses in newborns.

05:03
🍕 The Olfactory System and the Experience of Smelling

This section details the process of smelling, starting with the necessity for odorants to be volatile to reach the olfactory epithelium in the nasal cavity. It explains how different molecules are filtered and how some reach the olfactory sensory neurons. Each neuron is specialized to detect a single type of smell, and when activated, they send signals to the olfactory bulb in the brain through the ethmoid bone. The paragraph also describes the structure of the olfactory epithelium and how the signals from various smell-specific neurons converge in the glomerulus, which then relays the signal to the brain via mitral cells. The complexity of the olfactory system is highlighted by the vast number of combinations of olfactory neurons and mitral cells, likened to a piano with thousands of keys, and the ability of humans to identify thousands of different smells.

10:04
🍕 Taste and the Interplay with Smell

The paragraph discusses the close relationship between taste and smell, emphasizing that taste is largely dependent on the sense of smell. It explains how the process of chewing food forces air up the nasal passages, allowing for simultaneous smelling and tasting. The paragraph dispels the myth of the tongue's taste map, explaining that all tastes can be detected across the entire tongue. It then describes the anatomy of taste buds, located in the papillae on the tongue, and the role of gustatory and basal epithelial cells within them. The process of how food chemicals (tastants) interact with taste receptor cells to trigger action potentials is outlined, and how these signals are sent to the brain via various cranial nerves. The paragraph concludes with a humorous note on the difficulty of resisting eating pizza while discussing the topic.

🎬 Behind the Scenes of Crash Course Production

This final paragraph provides credits and acknowledgments for the production of the video. It names the writer, Kathleen Yale, the editor, Blake de Pastino, and the consultant, Dr. Brandon Jackson. It also mentions the director, Nicholas Jenkins, the script supervisor and editor, Nicole Sweeney, the sound designer, Michael Aranda, and the graphics team, Thought Café. The paragraph acknowledges the support of Thomas Frank, a Patreon contributor, and invites others to contribute to keep Crash Course sustainable.

Mindmap
Keywords
💡Anosmia
Anosmia is a medical condition characterized by the partial or complete loss of the sense of smell. It is a significant impairment since the sense of smell is closely linked to the sense of taste, and it plays a crucial role in experiencing flavors and warning of potential dangers. In the video, Olivia's anosmia led to a diminished ability to taste, a less interesting world, and even depression.
💡Transduction
Transduction is the process by which sensory cells convert one form of energy into another, such as translating chemical, electromagnetic, or mechanical stimuli into electrical signals (action potentials) that the nervous system can interpret. In the context of the video, transduction is central to how we perceive our environment through our senses, including the sense of smell and taste.
💡Olfactory epithelium
The olfactory epithelium is the primary organ of the olfactory system, located in the nasal cavity. It contains millions of olfactory sensory neurons that are responsible for detecting odorant molecules. When these molecules reach the olfactory epithelium, they dissolve in mucus and bind to receptors on the neurons, initiating the process of smell perception.
💡Glomerulus
A glomerulus is a structure in the olfactory bulb where olfactory axons meet dendrites of mitral cells. It serves as a transfer station where information from the nose is transformed into brain information. The video uses the analogy of a 'ball of yarn' to describe its appearance and function, emphasizing the complexity of the smell signals being processed.
💡Taste buds
Taste buds are sensory structures found in the mouth that contain taste receptor cells. They are responsible for detecting the basic tastes of sweet, salty, sour, bitter, and umami. The video dispels the myth of the tongue map, explaining that taste buds are not located in specific areas of the tongue but are distributed across it.
💡Gustatory cells
Gustatory cells are the specialized epithelial cells within taste buds that are responsible for the actual act of tasting. They have receptors that bind to molecules in food, triggering an action potential that signals the brain about the type and intensity of the taste. These cells are distinct from basal cells, which are stem cells that regenerate gustatory cells.
💡Tastants
Tastants are the chemical compounds in food that are responsible for triggering taste sensations when they bind to receptors on gustatory cells. The video explains that tastants must dissolve in saliva to reach and interact with the taste receptors, leading to the perception of different tastes.
💡Action potentials
Action potentials are electrical signals generated by neurons in response to a stimulus. In the context of taste and smell, action potentials are the means by which sensory information is transmitted from the sensory cells to the brain. The video emphasizes the importance of action potentials in the process of sensory perception.
💡Limbic system
The limbic system is a group of brain structures involved in emotion, memory, and the fight-or-flight response. The video highlights the limbic system's role in processing the emotional and memory aspects of smells, explaining how the loss of the sense of smell can impact a person's emotional well-being.
💡Olfactory receptor neurons
Olfactory receptor neurons are specialized sensory neurons in the olfactory epithelium that have receptors for specific odorant molecules. Each neuron is tuned to one type of smell, and when an odorant binds to these receptors, it generates an action potential that contributes to the perception of that particular smell.
💡Mitral cells
Mitral cells are a type of nerve cell in the olfactory bulb that receive signals from olfactory receptor neurons. These cells play a crucial role in relaying the smell information to the brain. The video illustrates how each mitral cell can receive input from multiple olfactory axons, each representing a single volatile chemical, contributing to the complex perception of smell.
Highlights

Olivia suffered from anosmia, a partial or complete loss of the sense of smell, after a bike accident.

Anosmia can be caused by head trauma, respiratory infections, or aging.

Our six major senses involve sensory cells translating stimuli into action potentials.

Taste and smell are chemical senses, using chemoreceptors to detect molecules.

Newborns orient themselves primarily by scent, able to distinguish their mother's milk and smell her from across the room.

Tastes and smells are powerful at activating memories, triggering emotions, and alerting us to danger.

Smelling begins as molecules are sniffed into the nose, with volatile odorants getting pulled into the nostrils.

The olfactory epithelium in the nasal cavity contains millions of olfactory sensory neurons.

Each olfactory neuron has receptors for just one kind of smell, detecting specific chemicals.

Olfactory signals travel through the olfactory bulb to the brain, forming a complex pattern of smell.

Our 40 million olfactory receptor neurons help us identify around 10,000 different smells.

The emotional pathway for smell quickly triggers memories and activates the fight or flight response for dangerous odors.

Taste is 80% smell, with air forced up nasal passages allowing simultaneous smelling and tasting.

Taste buds are located in pockets behind the fungiform papillae on the tongue.

Tongue taste maps showing specific areas for different tastes are bogus.

Taste receptor cells are specialized epithelial cells that synapse with sensory neurons to transmit taste information to the brain.

Different types of taste (salty, sour, etc.) activate different channels and receptors on gustatory cells.

Taste messages are relayed to the cerebral cortex via the 7th, 9th, and 10th cranial nerves.

Transcripts

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Related Tags
Sensory PerceptionSmell LossTaste MechanicsAnosmiaOlfactory SystemChemical SensesMemory TriggerEmotional ResponseNeurological ProcessHealth ImpactAnatomy of Taste