1. Transduction Input into the brain
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.