Unformatted text preview: Lecture 11 SmartSite: Lecture 11 Notes Review Auditory system Ves;bular system Announcements: None 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 The Visual System 4 Visible Light Fig. 6-15, pg. 197 5 The Eye Fig. 6-11, pg. 195 6 Eye Op;cs Convex structures of eye produce convergence of diverging light rays that reach eye Fig. 6-16, pg. 198 7 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 8 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 9 The Pupil (Amount of light) Fig. 6-13, pg. 196 10 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 11 The Re;na Vitreous Humor Fig. 6-23, pg. 203 12 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 13 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 14 Photo- Transduc;on Fig. 6-27, pg. 206 15 Photo-Transduc;on (Dark) Fig. 6-27, pg. 206 16 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 17 Photo-Transduc;on (Light) Fig. 6-27, pg. 206 18 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 19 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 20 Ganglion Cells Are Similarly Classified "On Ganglion" cells depolarize in the light "Off Ganglion" cells hyperpolarize in the light Fig. 6-23, pg. 203 21 ...
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