Transduction Input into the brain 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.

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

External Ear

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

Middle Ear

Middle Ear

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.