L11_NPB_101 - Lecture 11 •  SmartSite: – ...

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Unformatted text preview: Lecture 11 •  SmartSite: –  Lecture 11 Notes •  Review –  Auditory system –  Ves?bular system •  Announcements: –  Tomorrow is the last day to Add •  Visual System •  Reading (Recommended): –  Relevant por?ons of Chapter 6 1 REV: Ear – Auditory & Ves?bular •  Hair cells respond similarly in both sensory systems: 2 REV: Ves?bule Fig. 6 ­41a, pg. 225 3 Ves?bular Input ­Output Rela?ons Fig. 6 ­43, pg. 227 4 The Visual System 5 Visible Light Fig. 6 ­15, pg. 197 6 Structure of The Eye Fig. 6 ­11, pg. 195 7 Eye Op?cs •  Convex structures of eye produce convergence of diverging light rays that reach eye Fig. 6 ­16, pg. 198 8 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 9 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 10 The Pupil (Amount of light) Fig. 6 ­13, pg. 196 11 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 12 The Re?na Vitreous Humor Fig. 6 ­23, pg. 203 13 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 14 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 15 Photo ­ Transduc?on Fig. 6 ­27, pg. 206 16 Photo ­Transduc?on (Dark) Fig. 6 ­27, pg. 206 17 Photoreceptors Release L ­Glutamate onto Bipolar Cells in the Dark •  The receptor releases L ­glutamate onto a bipolar cell in the DARK. –  Some bipolar cells are hyperpolarized by NT –  NT closes ca?on channel –  On ­Center Bipolar Cells –  Some bipolar cells are depolarized by NT –  NT opens ca?on channel –  Off ­Center Bipolar Cells NT Release DARKNESS Fig. 6 ­26a, pg. 204 18 Photo ­Transduc?on (Light) Fig. 6 ­27, pg. 206 19 Photoreceptors Decrease L ­Glutamate Release onto Bipolar Cells in the Light •  So, in the Light: –  Receptors hyperpolarize and reduce L ­glutamate NT release •  Some bipolars depolarize –  “On Bipolar Cells” –  DBC (depolarizing bipolar cells) •  Some bipolars hyperpolarize –  “Off Bipolar Cells” –  HBC (hyperpolarizing bipolar cells) NT Release Blocked LIGHT Fig. 6 ­26a, pg. 204 20 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 21 Ganglion Cells Are Similarly Classified •  “On Ganglion” cells depolarize in the light •  “Off Ganglion” cells hyperpolarize in the light Fig. 6 ­23, pg. 203 22 ...
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