Sense system Introduction The visual system Hearing Introduction to sensory mechanisms Sensory receptors & sense organs Sensory neurons & Receptor cells Adequate stimulus threshold Transduction Receptor potential Generator potential Adaptation Physic receptors rapidly Tonic receptors slowly College of Life Sciences, Beijing Normal University 1
Coding of sensory information Modality Labeled line theory Localization Receptive fields Acuity Two-point threshold Intensity Receptive field size Innervation density Central convergence Lateral inhibition Contrast enhancement Frequency modulation Recruitment The visual system Light: 380 ~800nm The dioptric system Eye structure Visual reflex Visual accommodation Accommodation reflex Vergence reflex Pupil reflex *Pupil light reflex Refractory disorder Myopia,hyperopia, presbyopia College of Life Sciences, Beijing Normal University 2
The retina Structure of the retina pigment cells light Photoreceptor cells Bipolar cells Ganglion cells Properties of photoreceptors Rods Scotopic vision 120 million Photopic vision Cones 6.5 million Horizontal cells Amacrine cells Periphery, High sensitivity, Poor acuity (High convergence),lack of color vision Center, Low sensitivity, Color vision, High acuity(low convergence) Transduction Light Activated rhodopsin (Isomerization of retinal) Ati Activation of fg-protein (transducin) by opsin Activation of cgmpphosphodiesterase cgmp Closure of cgmp-gated ion channels Hyperpolarization of photoreceptors Secretion of glutamate by photoreceptor College of Life Sciences, Beijing Normal University 3
Receptive field of ganglion cells Adaptation Dark adaptation Light adaptation Color vision Trichromatic theory by Young-Helmholz Three different cones Color opponent theory *The visual pathways Hearing *Sound: Loudness (Intensity) db Pitch (Frequency) Timbre (Quality) Auditory threshold Sound transmission External ear Middle ear Ear drum Ossicles 17 1.3=22 College of Life Sciences, Beijing Normal University 4
Sound transduction Structure of the cochlea The organ of Corti Innerhaircells(IHC) : 3500 Divergence innervation Out hair cells(ohc) : 12000 Convergence ~ Bioelectric phenomenon in cochlea Resting potential Perilymph 0mV high Na + Endolymph +80mv high K + Hair cells -70~-80mV Cochlear receptor potential Hair cells: Mechanical gated ion channels Action potential Sound analysis Basilar member Traveling wave theory: The peak amplitude for High-frequencies is near to the base Low-frequencies is near to the helicotrema Hair cells IHC Tuning curve Characteristic frequency OHC Cochlear amplification:voltage-dependent p p contract Primary auditory afferents Tuning curve Central auditory pathways College of Life Sciences, Beijing Normal University 5
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