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E.2 Perception of Stimuli Types of Sensory Receptors • Mechanoreceptors respond to mechanical energy in the form of movement, sound, pressure or gravity EX. Hair cells in inner ear move due to sound waves and conduct impulse to brain. • Chemoreceptors response to chemical substance EX. Nerve cells in tongue send impulses to brain when specific chemicals bind to receptor cells Types of Sensory Receptors cont. • Thermoreceptors response to temperature EX. Warm and cold nerve endings in the skin conduct message to brain or spinal cord at a • Photoreceptors respond to electromagnetic radiation usually in the form of light • EX. Rods and cones in the eye send messages to the brain, when they absorb light Structure of the Human Eye • Sclera- tough, white layer of connective tissue that protects the eye • Cornea- where sclera becomes transparent at the front of the eye to let light in • Choroid- thin pigmented layer under sclera that provides nourishment to retina • Iris- the black screen that regulates the size of the pupil. • Conjuctiva – very thin membrane that covers the sclera and keeps it moist • Pupil – opening in the middle of iris that allows light to pass through • Lens – transparent protein disk that focuses light onto the retina • Retina – photosensitive layer of the eyeball. Contains the photoreceptor cells • Fovea – center of visual field. On retina at back of eye • Optic nerve – nerve that transmits messages from retina to brain • Blind spot – place where optic nerve attaches to retina. Does not contain photoreceptors • Lens divides the eye into two cavities • Aqueous humour – watery liquid between the lens and cornea (blockage in this causes glaucoma which can lead to retina damage) • Vitreous humour – jelly like fluid that transmits light from lens to optic nerve. Acts as a liquid support. Diagram of Retina – Rods and cones synapse with bipolar neurons – Bipolar neurons synapse with a ganglion cell – Axons of the ganglion cells make up the optic nerve Transfer of stimulus at Retina • Light must pass through cornea, lens and the humours before it reaches the retina • Light then strikes the photoreceptors (rods and cones) • Rods and cones then transmit the information to bipolar neurons that combine the information • The bipolar cells transmit information to ganglion cells that feed into the optic nerve RETINA • The more photoreceptors that feed a ganglion cell, the blurred the image because the optic nerve can’t perceive ______ where the stimulus is coming from • Thus rod information is ________ and cone info. is ___________ Rods cells vs. Cone cells • Rods • Cones – A group of rods send impulses along a single neuron – Work well in dim light – Each has an individual neuron – Black and white vision – Three types(named by colour that they absorb) – Does not work well in dim light • Red • Green • Blue Rods and Cones • Both are photoreceptor cells found on the retina of the eye • Both pass their information to the optic nerve • Account for ______ of all sensory receptors in the human body Rods • ~125 million rod cells/retina • Absorb all visible wavelengths of light which results in dim light vision (black and white) • More numerous than cones • Function better in dim light • In greatest density in the peripheral retina • _many cells transmit information to one neuron of optic nerve Cones • ~6 million per retina • 3 types, each absorbs different wavelength of light (blue, green, red) gives color vision • Function better in bright light • Have better visual perception • One cone cell transmits to one neuron of optic nerve • Very dense at fovea Perception of visual stimuli The Hermann grid Edge Enhancement • Part of retina where image is projected is called receptive field • If different parts of an image fall onto different receptive fields in the retina, stimulation is reduced • This will lead to _________ when trying to focus on one diagram • To compensate, stimulation of some receptors may actually ________ neighboring ones so that you can get ____________ Contra-lateral processing • Some impulses from _________ actually travel to __________ (and vice versa) • Exchange occurs in ________________ • Right side _________ images from left eye, and vice versa Processing of Visual Stimuli • Right optic nerve carries information from the right eye :left optic nerve from left eye • At a place in the brain called the optic chiasmata impulses from both eyes cross over • ½ of the right optic nerve fibers cross over to left side of brain, and vice versa • For this reason each side of the brain receives input from the __________________ • Optic nerves feed into the where they are processed • It is finally carried to visual cortex in the _____________ of the brain where the image is finally formed • Discovered by ___________ patients with brain lesions Ear Detection of sound • • • • Sound waves collected by pinna Passed into ear canal Cause reverberations of ear drum _Ear ossicles (bones of middle ear) vibrate against each other due to movement of eardrum • Final ossicle (Stapes) moves against oval window of cochlea causing movement of fluid inside • Round window provides ________________ of fluid in cochlea In the inner ear • Fluid moves across hair cells in Cochlea • These hairs cells release chemical messages to the _______________ that relay messages to brain • Hair movement then analyzed and interpreted into a sound by analyzing the ___________ of the sound (pitch) and the ____________ of hair movement (volume)