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Taste Transduction Input into the brain 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. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. 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. 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. 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 Gustducin - the taste G protein • Found mostly on T2R cells. • Taste, labeled line coding • Trigeminal nerve • Audition - the ear. Neural Coding • Pattern of action potentials relayed to the brain. 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 Trigeminal chemoreception • Polymodal nociceptive neurons • Axons of trigeminal nerve (cranial nerve V) • Some axons of IX and X Polymodal nociceptors • Free nerve endings • Polymodal, respond to thermal, mechanical and chemical stimuli • Associated with pain • C fibers conduct dull pain 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 Irritants • • • • • High concentrations of tastants Ammonia Air pollutants (sulfur dioxide) Acetic acid Little known about signal transductio of irritants. Auditory System • • • • Sound External ear Middle ear Inner ear Sound • Pressure wave pass in three dimensional space • Amplitude - volume (loud) • Frequency - pitch • Inner ear is like a prism and decomposes sounds into tones Audible spectrum • For humans, 20 Hz to 20 kHz. • Echolocation through high frequency vocal sounds • Low frequency hearing for sensing approaching predator 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 QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. External Ear QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. External ear • Auditory meatus boosts sound pressure • Pinna and concha selectively filter different sound frequencies Middle Ear QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Middle Ear QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Middle Ear • Match airbourne sounds to fluid of inner ear. • Fluid is more resistant to movement (high impedance) than air Middle ear • Sound is focused on the oval window, where the bones (ossicles) connect the tympanic membrane to the oval window. Inner Ear • Cochlea • Pressure waves are transferred to neural impulses. • Physical properties of the cochlea are important. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture.
