BBMB 405 1st Edition Lecture 40 Outline of Last Lecture XVIII Chapter 33 Sensory Systems A A wide variety of organic compounds are detected by olfaction B Taste is a combination of senses that function by different mechanisms C Touch includes the sensing of pressure temperature and other factors Outline of Current Lecture XVIII Chapter 33 Sensory Systems D Hearing depends on the speedy detection of mechanical stimuli E Photoreceptor molecules in the eye detect visible light XIX Chapter 35 Molecular Motors A Introduction Current Lecture XVIII Chapter 33 Sensory Systems D Hearing depends on the speedy detection of mechanical stimuli 1 Hearing Detection of vibrations by audition a Sound waves of 200 to 20 000 Hz is the stimulant b Mechanical stimulus like modalities of touch c Detection of sound and sound location These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute d located in inner ear coclia 2 Mechanical stimulation of hair cells causes changes in membrane potential a Movement of hair bundle acts on ion channels directly membrane depolarization leads to rapid response b Tension along tip link extracellular filaments that connect stereocilia increases the depolarization c d e From 200 to 0 Tension decrease and from 0 to 200 tension increase 3 Touch and hearing rely on mechanoreceptor proteins a Mechanosensitive ion channels mechanical deformations of cell membrane switch ion channels from closed to open b Made of ankyrin repeats potential gating springs 4 Model for mechanosensitivity No mechanoreceptor potential C nompC gene when gene deleted mechanoreceptor doesn t work 5 Recent advances in our understanding of touch receptors a Piezo2 is major transducer of mechanical forces for touch sensation in mice b Piezo2 is expressed in sensory neurons innervate skin of mice and involved in lowthreshold mechanosensitivity light touch c Loss of function results in loss of touch sensation d Loss of function has not effect on pain receptors nociceptors E Photoreceptor molecules in eye detect visible light 1 Sight Detection of visible light a Rod cells express Rhodopsin GPCR recognize light opsin linked to chromosome 11cis retinal retinal is aldehyde form of vitamin A b Cone cells express rhodopsin homologs Absorb light at different wavelengths 2 Rod cells detect dim light a Light absorption causes isomerization of cis to trans b c Retinal isomerization causes rhodopsin conformational change 3 Signal transduction by rhodopsin a Occurs on millisecond scale b Rhodopsin activation leads to transducing nucleotide exchange c Activated transducing activates phosphdiesterase that converts cGMP to GMP d Decrease in cGMP levels lead to reduction in ion flow through cGMP gated ion channel e Membrane hyperpolarization and neuronal signaling results f Closing of cGMP gated ion channel and Ca2 efflux leads to guanylatecyclase activation inhibited by Ca2 and restoration to initial state g 4 Cone cells detect brighter light in color a Types of cone cells L cones long wavelengths red M cones medium wavelength green S cones short wavelength blue b Each type of cell contains different pigment c Associated with photopsins d Three different sites cause changes in what wavelength is detected 5 Red green color blindness a Highly similarity between red and green photoreceptors 98 identical including introns and UTRs b Susceptible to unequal homologous recombination c 5 of human males have this condition d XIX Chapter 35 Molecular Motors A Introduction 1 Examples E coli chemotaxing to sugar white blood cell chasing bacteria human heart muscle cell beating movement of animal 2 Three major families of eukaryotic motor proteins a Motor device that converts energy into mechanical work b Motor domains Head domains bind ATP and track c Actin motor myosin d Microtubule motor kinesin and dynein 3 Cytoskeletal motor proteins utilize a track a Kinesin pulls vesicle along cytoskeletal microtubule filament b Myosin molecules form thick filament at center of actin filaments c Cytoskeletal fibers are tracks actin filaments microtubules
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