sensing the world: chemical sensation Flashcards
olfaction and behavioru
olfaction cues support diverse behaviours:
- food or mate seeking
- feeding
- co-specific identification [group or non-group
- marking territories
- reproduction
- aggression and early warning
how relevant is smell to humans
- Is generally accepted that animals rely more on olfaction than humans.
- Dogs can detect odors 100x less concentrated than humans.
- But, human and dog olfactory receptors are equally sensitive = respond to one single odor molecule!
- Dogs have 100 times more receptors.
So, are we able to use scents as dogs do? At least for somebehaviours…?
olfaction -> human nose
- Primary function: humidify and warm air going into the lungs.
- Secondary function: olfaction.
- Air flows into the nose cavity.
- Odorants interact with the olfactory epithelium.
- Mucus in the epithelium captures odorants.
what do olfactory sensory neurons do
detect odors +produce mucus
olfactory receptors
- Odorants are recognised by specific receptors in the cilia of OSNs.
- Olfactory receptors are G- coupled proteins whose activation opens Na+/Ca2+ channels.
- OSN is depolarized by Na+/Ca2+ influx, firing action potentials.
**olfactory epithelium **
the tissue in the nose that enables the sense of smell
olfactory pathways
- Axons from OSNs pass through the tiny holes in the cribriform plate (bone) to enter the brain.
- Each type of OSN projects its axon to a single glomerulus within the olfactory bulb.
- OSN axons make synapsis with mitral and tufted cells, that project to the primary olfactory cortex and other brain regions
shape pattern theory
olfactory receptors
- each scent—as a function of odorant-shape to OR-shape fit —activate unique arrays of olfactory receptors in the olfactory epithelium.
- These various arrays produce specific firing patterns of neurons in the olfactory bulb, which then determine the scent we perceive.
modulation of olfaction
- Olfaction is a subjective experience.
- Detection threshold can be affected by several factors:
- Gender: women generally lower threshold than men, especially during ovulatory periods of menstrual cycles, but their sensitivity is not heightened during pregnancy.
- Training: professional perfumers and wine tasters can distinguish up to 100,000 odorants.
- Age: By 85, 50% of population is effectively anosmic (sense of smell loss).
what 3 things effect olfaction
- gender
- training
- age
taste and behavioru
- Short range information (inside the mouth).
- Taste recognition guide appetite and trigger physiological processes for absorbing nutrients.
- Important for identifying nutrients and avoiding chemical threats.
- Good taste = usually good. → greatly influenced by culture
- Bad or bitter taste = potentially harmful. → greatly influenced by culture
- Taste liking/disliking already present in newborns.
definition of taste
detection of chemical compounds in the mouth by direct contact with chemoreceptors on the tongue and the roof mouth. Taste categories: sweet, salty, sour, bitter, and umami.
what are the taste categories
sweet, salty, sour, bitter, and umami.
what is retronasal olfactory sensation
perception of odorants while chewing and swallowing food.
what is flavour
combination of taste and olfaction [retronasal]
structure and function of taste sensors
- Taste receptors are arranged in taste buds, distributed along the tongue, palate, pharynx, epiglottis, and upper third of the oesophagus.
- Taste buds arranged in three kind of papillae, distributed in specific regions of the tongue.
- Receptors for different tastes group together in the same bud.
- Receptor activation sends neural signal through taste nerves.
taste buds & taste receptors
- Each taste bud contains several types of taste receptor cells.
- Receptor cells are specialised cells containing microvilli (extensions of cellular membrane) containing receptor proteins.
what are the 3 main receptor types
- type 1
- type 2
- type 3
type 1
3 main receptor types
support function
type 2
3 main receptor types
detect bitter, sweet and unami
- chemical signal to neighbouring cells [including type 3]
type 3
3 main receptor types
detect sour. synaptic communication with afferent fibers
taste buds + taste receptors
- G-coupled protein receptors (like in olfactory neurons) T1R and T2R.
- T1R detects sweet and umami taste.
- T2R detects bitter taste.
- Ion (Na+) channel ENaC detects salty taste.
taste neural pathway
- Three cranial nerves collect taste information:
- Chorda tympani
- Glosso-pharyngeal
- Vagus
- Synapse at nucleus of the solitary tract (medulla) → hypothalamus → insula or gustatory primary cortex → orbitofrontal cortex
taste- mediated behaviour
- Odour detection helps us find food, but taste determines if the food is nutritious or a potential chemical threat.
- Bitter taste might signal poisonous food. While intense sour might be related to harming acidic substances.
- Sweet and salty tastes normally induce seeking behaviour since such substances increase survival.
- Infants’ behaviour and facial expressions reveal innate taste preferences.
