Sensing the World - Chemical Senses

Emotional and behavioural responses are influenced by the presence of Chemical signals.

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Olfaction and Taste

Dogs can detect 100x less concentrated odours than humans. While receptors are equally sensitive in both dogs have 100x more.

Scent Tracking   

Olfaction Human Nose

Primary function is to warm and humidify air going into the lungs

Secondary function is olfaction: air flows in and odorants interact with the epithelium. Mucus in the epithelium captures odorants.

Three cell Types of Epithelium

·        Supporting cells

·        Basal cells

·        Olfactory sensory neurons (detectors of odours)

Olfactory receptors

Odorants are recognised by specific receptors in the cilia.  

Odorant binding to receptors activates sodium and calcium channels in neurons causing action potentials to fire.

Shape Pattern theory: Each scent has a specific shape that activate (fit) a unique receptor in the epithelium. The various arrays produce firing patterns of neurons (in the olfactory bulb) that determine which scent we perceive.

Olfactory is subjective and is affected by:

·        Gender

·        Training

·        Age7

Olfactory fatigue

Smell detection stops during continuous exposure to odorant. Receptor adaptation = continuous exposure to odorant makes the receptor stop working.

Taste

Taste is the detection of chemical compounds in the mouth by direct contact with chemoreceptors on the tongue and the roof of the mouth

Retronasal olfactory sensation = perception of odorants while chewy and swallowing.

The brain processes odors from the nose and mouth differently.

Flavour

Flavour is the combination of taste (sweet, salty) and olfaction (smell)

Structure and function of taste sensors

Taste receptors are arranged in taste buds and distributed along the tongue and other areas.

Each taste bud contains many taste receptors cells. These are specialised and have microvilli containing receptor proteins.

Type 1: support function

Type 2 detect bitter, sweet and umami

Type 3 detect sour

T1R detects sweet and umami and T2R detects bitter

Ion channels detect salty

The three cranial nerves collect taste information. The synapse at the nucleus at the medulla moves information to the hypothalamus to the gustatory primary cortex and thre **

Salt

Animals have an appetite for salt. High concentration of salt is bad and leads to dehydration. ENaC detects salt.

Sour

Comes from acidic substances. At high concentrations it causes damage.

Sweet

Evoked by sugars. T1R receptors responsible

Bitter

Bitter substances usually poisonous. Quinine (bitter substance). T2R Receptor.

Taste mediated behaviours

Helps us find food. Sweet and salty initates seeking behaviour. Bitter taste signals poisonous food and sour may indicate harmfulness.