Taste

1. Taste Transduction Input into the brain

2. Transduction of tastants • Receptors on the apical surface of taste cells • Na+ enters the taste cell • H+ enters the taste cell • Cation selective channels --> inward current, receptor potential--> voltage gated Na channels, voltage gated Ca channels.

4. Sweet and amino acid (glutamate) receptors • Heteromeric G protein coupled receptors • Sweet: T1R3 paired withT1R2 receptors (T1R2/T1R3). • Activates Phospholipase C • Increased IP3 • Opening of TRP channels (transient receptor potential channel) TRPM, allow calcium entry.

6. Amino Acids: • T1R1/T1R3 receptor broadly tuned to 20 L amino acids • Activates Phospholipase C • Increased IP3 • Opening of TRP channels (transient receptor potential channel) TRPM, allow calcium entry.

7. Bitter taste • G-protein couple receptors • T2R receptors • 30 T2R subtypes • 30 genes • Multiple T2R receptors in a single cell type. • Cells with T2R receptors do not express T1R receptors

8. Gustducin - the taste G protein • Found mostly on T2R cells.

9. Taste, labeled line coding • Trigeminal nerve • Audition - the ear.

10. Neural Coding • Pattern of action potentials relayed to the brain.

11. Labeled Line Coding • Specifc pathways carry information quality to the brain. (Is there a “sweet” pathway? • Knock out T1R2, T1R1 • Loose behavioral response to sweet or amino acids • No action potential recorded in response to sweet or aa from VII, IX or X fibers • Consisten with Labeled Line hypothesis

12. Trigeminal chemoreception • Polymodal nociceptive neurons • Axons of trigeminal nerve (cranial nerve V) • Some axons of IX and X

13. Polymodal nociceptors • Free nerve endings • Polymodal, respond to thermal, mechanical and chemical stimuli • Associated with pain • C fibers conduct dull pain

14. Nociception Transduction • TRP channels (TRPV1 binds casaicin) • Transient receptor potential channels • Channel closed under resting conditions • Open - sodium and calcium flow • Receptor opens in response to heat and capsaicin • Endogenous endovanilloids bind to TRPV1 channels

15. Irritants • High concentrations of tastants • Ammonia • Air pollutants (sulfur dioxide) • Acetic acid • Little known about signal transductio of irritants.

16. Auditory System • Sound • External ear • Middle ear • Inner ear

17. Sound • Pressure wave pass in three dimensional space • Amplitude - volume (loud) • Frequency - pitch • Inner ear is like a prism and decomposes sounds into tones

18. Audible spectrum • For humans, 20 Hz to 20 kHz. • Echolocation through high frequency vocal sounds • Low frequency hearing for sensing approaching predator

19. Auditory function • Information about sound waves gets sent as neural activity to the brain. • 1. Collect the sound • 2. Signal transduction • 3. Neural coding in auditory nerve fibers. • 4. Central processing

21. External Ear

22. External ear • Auditory meatus boosts sound pressure • Pinna and concha selectively filter different sound frequencies

23. Middle Ear

24. Middle Ear

25. Middle Ear • Match airbourne sounds to fluid of inner ear. • Fluid is more resistant to movement (high impedance) than air

26. Middle ear • Sound is focused on the oval window, where the bones (ossicles) connect the tympanic membrane to the oval window.

27. Inner Ear • Cochlea • Pressure waves are transferred to neural impulses. • Physical properties of the cochlea are important.