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Chemoreceptors Taste Smell 20-Nov-18 Taste & Smell.

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Presentation on theme: "Chemoreceptors Taste Smell 20-Nov-18 Taste & Smell."— Presentation transcript:

1 Chemoreceptors Taste Smell 20-Nov-18 Taste & Smell

2 Chemoreceptors Respond to chemical change Internal receptors
Detect changes in chemical composition of blood & body fluids Oxygen, H+, glucose Osmoreceptors, carotid & aortic bodies 20-Nov-18 Taste & Smell

3 Chemoreceptors External receptors Taste
Help us to be in contact with external environmment Taste Give us indication of what is being passed through the mouth Proximal external environment 20-Nov-18 Taste & Smell

4 Chemoreceptors Smell Make us aware of distant external environment
Odorous substances disperse in air 20-Nov-18 Taste & Smell

5 Taste Sensory modality Taste qualities Sour taste
Mediated by chemoreceptors of Tongue, mouth, pharynx Taste qualities Sour taste Associated with acids Intensity is proportional to log [H+] 20-Nov-18 Taste & Smell

6 Taste Salty taste Elicited by ionized salts (Na+)
Cations mainly responsible for salty taste But anions also contribute 20-Nov-18 Taste & Smell

7 Taste Sweet taste Associated with naturally occurring sugars
Sucrose, glucose Glycol, alcohol, aldehydes, ketones Synthetic substances Saccharin P-4000 is 5000 times more sweet than sucrose But extremely poisonous 20-Nov-18 Taste & Smell

8 Taste Bitter taste Associated with alkaloids, organic compounds
Quinine, caffeine, nicotine 20-Nov-18 Taste & Smell

9 Taste Umami taste quality New taste quality Meaty, savoury taste
Identified by Japanese in 1909 Meaty, savoury taste Drive our appetite for amino acids 20-Nov-18 Taste & Smell

10 Importance of Taste Taste We like taste of sugar Drives appetite and
Protects us from poisons We like taste of sugar Because we require carbohydrate (sugars) 20-Nov-18 Taste & Smell

11 Importance of Taste We get craving for salt Bitter or sour
Because we must have sodium chloride in our diet Bitter or sour Cause avoidance reaction Most poisons are bitter 20-Nov-18 Taste & Smell

12 Importance of Taste Food which has turned bad
Is sour (acids) Most medicines tastes bitter Because most of them are poisons 20-Nov-18 Taste & Smell

13 Taste Receptors Receptors are Each taste bud Modified epithelial cells
Microvili Taste bud Receptors are Modified epithelial cells Each taste bud Made up of 50 to 150 taste cells Lifespan is 10 to 14 days Microvili Receptor cells Transmitter 20-Nov-18 Taste & Smell

14 Taste Receptors One nerve innervates several receptors
Microvili Taste bud One nerve innervates several receptors One receptor may be innervated by several nerves Trophic effect of nerves on receptors Microvili Receptor cells Transmitter 20-Nov-18 Taste & Smell

15 Other Cells in Taste Buds
Microvilli Taste bud Supporting cells Contain microvilli Appear to secrete substances into lumen of taste buds Supporting cells Basal cells Receptor cells Microvilli Transmitter 20-Nov-18 Taste & Smell

16 Other Cells in Taste Buds
Microvilli Taste bud Sensory receptors Contain microvilli Contain sites for taste transduction Supporting cells Basal cells Receptor cells Microvilli Transmitter 20-Nov-18 Taste & Smell

17 Other Cells in Taste Buds
Microvilli Taste bud Basal cells Differentiate into receptor cells Cells Continually renewed every 10 days Supporting cells Basal cells Receptor cells Microvilli Transmitter 20-Nov-18 Taste & Smell

18 Taste Transduction General Taste substances
Taste stimuli chemicals Receptor protein General Taste substances Bind to receptor protein on receptor cells Change in membrane properties Opening of ionic channels Voltage gated Na+ channels Na+ Ca++ Voltage gated Ca++ channels Neurotransmitter release AP 20-Nov-18 Taste & Smell

19 Taste Transduction This leads to depolarization
Taste stimuli chemicals Receptor protein This leads to depolarization Followed by ca++ influx Release of neurotransmitter Excitation of sensory nerve Voltage gated Na+ channels Na+ Ca++ Voltage gated Ca++ channels Neurotransmitter release AP 20-Nov-18 Taste & Smell

20 Taste transduction Taste receptor proteins Taste chemicals are soluble
Microvili Taste bud Taste receptor proteins Found on microvilli Taste chemicals are soluble Diffuse to bind to receptors Microvili Receptor cells Different receptor cells: bitter, sour, sweet, salty, umami 20-Nov-18 Taste & Smell

21 Taste transduction Each taste bud Made up of multiple taste cells
Microvili Taste bud Each taste bud Made up of multiple taste cells With different chemical sensitivity Microvili Receptor cells Different receptor cells: bitter, sour, sweet, salty, umami 20-Nov-18 Taste & Smell

22 Taste transduction Within each taste bud
Microvili Taste bud Within each taste bud There are different taste cells Can detect NaCl, sucrose, H+, quinine Microvili Receptor cells Different receptor cells: bitter, sour, sweet, salty, umami 20-Nov-18 Taste & Smell

23 Taste transduction Each taste cell form
Microvili Taste bud Each taste cell form Chemical synapse with sensory nerve Project to the brain Microvili Receptor cells Different receptor cells: bitter, sour, sweet, salty, umami 20-Nov-18 Taste & Smell

24 Sweet Taste Transduction
Receptor protein Sugar Combination of sugar with receptor Activate Gs protein Leads to activation of Adenyl cyclase Formation of cAMP K+ channels K+ Neurotransmitter release AP 20-Nov-18 Taste & Smell

25 Sweet Taste Transduction
Receptor protein Sugar Leads to activation of Protein Kinase A (PKA) This leads to Phosphorylation of K+ channels Closes the channels Depolarization of cells K+ channels K+ Neurotransmitter release AP 20-Nov-18 Taste & Smell

26 Sweet Taste Transduction
Receptor protein Sugar This leads to Release of transmitter  In firing of sensory nerve K+ channels K+ Neurotransmitter release AP 20-Nov-18 Taste & Smell

27 Sour Taste Transduction
Receptor protein H+ The H+ ions block K+ channels K+ channels maintain membrane potential at about –85 mv K+ equilibrium pot When they are blocked Membrane depolarizes K+ channels K+ Ca++ Ca++ Neurotransmitter release AP 20-Nov-18 Taste & Smell

28 Sour Taste Transduction
Receptor protein H+ Voltage gated ca++ channels open Ca++ enters the cell Release of transmitter  In firing of AP in sensory nerve K+ channels K+ Ca++ Ca++ Neurotransmitter release AP 20-Nov-18 Taste & Smell

29 Salty Taste Transduction
ENaC Na+ The Na+ ions enter cell through epithelial sodium channels (ENaC) Membrane depolarizes Voltage gated ca++ channels open Ca++ enters the cell Release of transmitter  In firing of AP in sensory nerve Na+ Voltage gated Ca++ channels Ca++ Ca++ Neurotransmitter release AP 20-Nov-18 Taste & Smell

30 Bitter Taste Transduction
Receptor Chemical Chemical combination with receptor Activation of G protein  In IP3 Leads to release of ca++ from internal sources Release of transmitter  In firing of AP in sensory nerve GS protein Ca++ Neurotransmitter release AP 20-Nov-18 Taste & Smell

31 Transmission to CNS 20-Nov-18 Taste & Smell

32 Abnormalities Ageusia Hypogeusia Dysgeusia Absence of sense of taste
Diminished taste sensitivity Dysgeusia Disturbed sense of taste 20-Nov-18 Taste & Smell

33 Olfactory System Smells are detected in the nose
Olfactory bulb Smells are detected in the nose Through specialized receptor cells Olfactory receptor neuron (ORN) Located in olfactory epithelium Olfactory receptors Olfactory mucosa Odorous chemical 20-Nov-18 Taste & Smell

34 Olfactory System Olfactory bulb Smell makes us aware of the distant external environment Odorous substances are dispersed in air Olfactory receptors Olfactory mucosa Odorous chemical 20-Nov-18 Taste & Smell

35 Olfactory System We continuously sample the air we breath
Olfactory bulb We continuously sample the air we breath To alert us of presence of Potential dangers such as smoke Food Another individual Olfactory receptors Olfactory mucosa Odorous chemical 20-Nov-18 Taste & Smell

36 Olfactory Epithelium The olfactory epithelium Contain Covered by mucus
Olfactory bulb The olfactory epithelium Covered by mucus Contain Olfactory receptor neuron About 10 million in humans Bowman’s glands Secrete solution that bathe surface of receptors Olfactory receptors Olfactory mucosa Odorous chemical 20-Nov-18 Taste & Smell

37 Olfactory Epithelium Bowman’s glands
Olfactory bulb Bowman’s glands Secrete solution that bathe surface of receptors Olfactory receptors Olfactory mucosa Odorous chemical 20-Nov-18 Taste & Smell

38 Olfactory Epithelium Bowman’s gland solution also contains
Olfactory bulb Bowman’s gland solution also contains Mucopolysaccharides Immunoglobulins Lysozymes Various enzymes Olfactory receptors Olfactory mucosa Odorous chemical 20-Nov-18 Taste & Smell

39 Olfactory Epithelium Also contain basal cells
Olfactory bulb Also contain basal cells Stem cells from which new receptors are formed There is continuous replacement of receptors Olfactory receptors Olfactory mucosa Odorous chemical 20-Nov-18 Taste & Smell

40 Olfactory Receptor Neuron
Axon Supporting cell Olfactory cells are Bipolar cells derived from the CNS There ar about 100 mil cells in olfactory epithelium Interspersed with supporting cells Basal cell Receptor Cilia Olfactory mucus 20-Nov-18 Taste & Smell

41 Olfactory Receptor Neuron
Axon Supporting cell The mucous end of ORN forms olfactory hairs or cilia Cilia project into the mucus They are the ones which react to odors Basal cell Receptor Cilia Olfactory mucus 20-Nov-18 Taste & Smell

42 Olfaction Receptors are sensitive to chemicals For olfaction to occur
Chemicals must be airborne Must dissolve in mucus membrane Odorants are Volatile Water soluble To penetrate watery mucous layer 20-Nov-18 Taste & Smell

43 Olfaction Also odorants must be Lipid soluble
To penetrate cell membrane of olfactory receptors 20-Nov-18 Taste & Smell

44 Olfactory Threshold Olfactory sensitivity Very high
Only few molecules need to interact with receptors To excite receptor neurons 20-Nov-18 Taste & Smell

45 Olfactory Discrimination
Remarkable ability Can recognize more than 10,000 different But determination of Differences of intensity within any given odor is poor 20-Nov-18 Taste & Smell

46 Odorant Receptors There are many odorant receptors
But only one or few are expressed in each olfactory receptor neuron All odorant receptors Coupled to G-proteins Some act via adenyl cyclase and cyclic AMP 20-Nov-18 Taste & Smell

47 Odorant Receptors Others act via Most of them
Phospholipase C & products of Phosphatidylinositol hydrolysis Phospholipase C Inositol triphosphate (IP3) Diacylglycerol (DAG) Most of them Open calcium ion channels 20-Nov-18 Taste & Smell

48 Pathway From the olfactory receptor neurons
Lateral olfactory tract From the olfactory receptor neurons ORN synapse with mitral cells Olfactory glomerulus Olfactory bulb Mitral cells Periglomerular cells Olfactory glomerulus Olfactory receptor neuron Olfactory membrane (mucus) 20-Nov-18 Taste & Smell

49 Pathway Mitral cells axons form lateral olfactory tract
Terminate in primary olfactory cortex Pyriform & prepyriform areas Mitral cells Periglomerular cells Olfactory glomerulus Olfactory receptor neuron Olfactory membrane (mucus) 20-Nov-18 Taste & Smell

50 Pathway From here fibers project to Thalamus and then to
Lateral olfactory tract From here fibers project to Thalamus and then to The neocortex Orbitofrontal For recognition Mitral cells Periglomerular cells Olfactory glomerulus Olfactory receptor neuron Olfactory membrane (mucus) 20-Nov-18 Taste & Smell

51 Pathway In addition primates have pathways that
Lateral olfactory tract In addition primates have pathways that Runs via the limbic system to hypothalamus Responsible for “affective” component of smell Mitral cells Periglomerular cells Olfactory glomerulus Olfactory receptor neuron Olfactory membrane (mucus) 20-Nov-18 Taste & Smell

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