Lecture_11 - Lecture 11 •  Online Handouts: – ...

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Unformatted text preview: Lecture 11 •  Online Handouts: –  Lec 11 Notes •  Review –  Auditory system –  Ves<bular system •  Announcements: –  None •  Visual System •  Reading (Recommended): –  Relevant por<ons of Chapter 6 REV: Ear – Auditory & Ves<bular •  Hair cells respond similarly in both sensory systems: •  Stereocilia bending toward the kinocilium: Depolariza<on •  Stereocilia bending away from the kinocilium: Hyperpolariza<on Fig. 6 ­32, pg. 215; 6 ­41d, pg. 225 The Visual System Visible Light Fig. 6 ­15, pg. 197 The Eye Fig. 6 ­11, pg. 195 Eye Op<cs •  Convex structures of eye produce convergence of diverging light rays that reach eye Fig. 6 ­16, pg. 198 Eye •  Two structures most important in eye’s refrac<ve ability are –  Cornea •  Contributes most extensively to eye’s total refrac<ve ability •  Refrac<ve ability remains constant because curvature never changes –  Lens •  Refrac<ve ability can be adjusted by changing curvature as needed for near or far vision Accommoda<on (Focus) •  Change in strength and shape of lens •  Accomplished by ac<on of ciliary muscle and suspensory ligaments •  Age ­related reduc<on in accommoda<on ability Fig. 6 ­21bc, pg. 200 The Pupil (Amount of light) Fig. 6 ­13, pg. 196 Re<na •  Receptor containing por<on of the eye –  actually an extension of the CNS •  Neural por<on of re<na consists of three layers of excitable cells –  Outermost layer containing rods and cones –  Middle layer of bipolar cells –  Inner layer of ganglion cells •  Axons of ganglion cells join to form op<c nerve –  Point on re<na at which op<c nerve leaves is the op<c disc »  Region o`en called the blind spot because no image can be detected here because of lack of rods and cones The Re<na Vitreous Humor Fig. 6 ­23, pg. 203 Photoreceptors •  Rod and cone cells –  Rods = low light & gray scale –  Cones = color vision –  Outer segment –  Inner segment •  Consist of three parts •  Detects light s<mulus •  Contains metabolic machinery of cell •  Transmits signal generated in photoreceptor on light s<mula<on to next cells in visual pathway –  Synap<c terminal Fig. 6 ­26a, pg. 204 Photopigments •  Undergo chemical altera<ons when ac<vated by light •  Consists of two components –  Opsin –  Re<nene •  Protein that is integral part of disc membrane •  Deriva<ve of vitamin A •  Light ­absorbing part of photopigment •  Four different photopigments –  Rod pigment •  Provide vision only in shades of gray •  Rhodopsin –  Absorbs all visible wavelengths –  Cone pigments •  Respond selec<vely to various wavelengths of light •  Make color vision possible –  Red cones –  Green cones –  Blue cones Fig. 6 ­26b, pg. 204 Photo ­ Transduc<on Fig. 6 ­27, pg. 206 Photo ­Transduc<on (Dark) Fig. 6 ­27, pg. 206 Photoreceptors Release Glutamate onto Bipolar Cells in the Dark •  The receptor releases glutamate onto a bipolar cell in the DARK. –  Some bipolar cells are hyperpolarized by NT –  NT closes ca<on channel –  Some bipolar cells are depolarized by NT –  NT opens ca<on channel NT Release DARKNESS Fig. 6 ­26a, pg. 204 Photo ­Transduc<on (Light) Fig. 6 ­27, pg. 206 Photoreceptors Decrease Glutamate Release onto Bipolar Cells in the Light •  So, in the light: –  Receptors hyperpolarize and reduce glutamate NT release •  Some bipolars depolarize –  “On Bipolars” –  DBC (depolarizing bipolar cells) •  Some bipolars hyperpolarize –  “Off Bipolars” –  HBC (hyperpolarizing bipolar cells) NT Release Blocked LIGHT Fig. 6 ­26a, pg. 204 Cones Sensi<ve to Different Wavelengths •  Each cone expresses a photopigment with a unique absorbance spectrum –  Blue (Short) –  Green (Medium) –  Red (Long) Fig. 6 ­29, pg. 208 Ganglion Cells Are Similarly Classified •  “On Ganglion” cells depolarize in the light •  “Off Ganglion” cells hyperpolarize in the light Fig. 6 ­23, pg. 203 ...
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This note was uploaded on 02/10/2010 for the course BIO NPB taught by Professor Furlow during the Spring '10 term at UC Davis.

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