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Chapter 8

Psych 2NF3 Chapter 8

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Andrew Wade

03/10/2014 03/10/2014 Chapter 8- Organization of the Sensory Systems Portrait: effects of a sensory loss on movement Ian waterman, cut finger Hot/cold spells He could not move, no sense of pressure or touch in hands or feet – felt tingling sensations tho and trouble talking Diagnosis= neuropathy (disorder of periphery nerves) Sensitive to temp and pain He lost fine touch and pressure fibers from sensory nerves that provided his nervous system with info about the position of his limbs and their movements Sixth sense= gone Never recovered but did learn to walk and drive- did so by replacing body awareness with vision General principles of sensory-system function Each sensory system organize don similar plan Sensory receptors Cells that transduce sensory energy into neural activity Receptors are energy filters Respond only to a narrow band of energy Electromagnetic spectrum- visible to human eye (400-700 nm) Ppl who lack receptors for parts of visual spectrum= color blind 03/10/2014 60% of men have one form of the red receptor and 40% of another- females may have both audition- human ears respond to (20-20,000 Hz) elephants can hear below 20 Hz and bats as high as 120, 000Hz receptors transduce energy vision: light energy converted into chemical energy in photoreceptors of retina. This chem energy turned intoA.P auditory: air pressure waves converted into a number of forms of mechanical energy, last which activates auditory receptors▯ A.P somatosensory: mechanical energy activates mechanoreceptors, cells that are sensitive to touch and pain ex. Somato in turn generateA.P taste and olfaction: various chem molecules carried by the air or contained in food fit themselves into receptors of various shapes to activateA.P pain sensation: tissue damage releases a chm that acts like a neurotrans to activate pain fibers receptive fields locate sensory events every cell has receptive field, spec part of world to which it respond photoreceptors point into diff directions- so has unique receptive field receptive fields also help locate sensory events in space receptors identify change and constancy sens receptors differ in sensitivity- may adapt rapidly or slowly to stimulation rapidly adapting receptors- detect whether something is there. Easy to activate but stop responding after a very short time ex. Touching arm with finger, immediately feel but then it will fade Slowly adapting receptors- adapt slowly to stimulation. Ex. Touch arm harder with finger and u will feel touch much longer Rapidly adapting rod-shaped receptors- respond to visible light of any wavelength and have lower response thresholds than cone-shaped receptors (sensitive to color and position) Receptors distinguish self from other Receptors that respond to external stimuli= exteroceptive 03/10/2014 Receptors that respond to our own activity= interoceptive Also help us interpret the meaning of external stimuli Optic flow- apparent motion of visual info when animal in motion Auditory flow- changes in intensity of the sound When interoceptive receptors in inner ear inform your visual system that your head is moving, the visual system responds by compensating for the head movements, and u observe the hand as a stationary image Receptor density determines sensitivity Tactile receptors of the fingers are numerous compared to those on the arm▯ why fingers can discriminate well Two-point sensitivity- ability to discriminate 2 indv points on the skin highest on parts having most touch receptors fovea- where color photoreceptors are concentrated-ALL CONE CELLS- small and densely packed periphery- ROD CELLS- black/white vision- larger and scattered. Sensitivity to light is remarkable Neural Relays Receptors connect to cortex through 3-4 neurons Visual and somato= 3 Auditory= 4 Relays determine hierarchy of motor responses Some 3-4 relays in each sensory system are in spine, others in brainstem and neocortex First relay for pain receptors in spine is related to reflexes that prod withdrawn movements Pain pathway also has relay in brainstem- midbrain ▯Periaqueductal gray matter (PAG) Pain in neocortex- identify pain felt and localize pain, external cause and remedies 03/10/2014 Message modification takes place at relays Ex. Playing sport, u are exited and get injured but may not notice only to find later that its quite severe▯ inhibition called gating of sensory info can be prod by descending signals from cortex, through periaqueductal gray matter and onto lower sensory relays Relays allow sensory interaction Rub area around an injury to reduce pain- increase activitiy in fine touch and pressure pathways, blocking transmission of info in spinal-cord relays of pain pathway mcGurke effect- speech “ba” played by recorder same time observing someone whos lips are articulating “da”, listener does not hear actual sound but articulated sound “da”▯ lip movements modify auditory perceptions Central organization of sensory systems Sensory info = coded After it has been transduced, all sensory info from all sensory systems is encoded byA.P that travel along peripheral-system nerves until they enter brain or spine and then tracts within CNS Synesthesia= mixing of senses▯ ex. Shivering from noise that fingernails make on chalk board- u have FELT sound Each sensory system is composed of subsystems Each pathway from eye to brain traces visual subsystem that culminates in a visual center, numbered 1-7 (1) eye- suprachiasmatic nucleus of hypo controls daily rhythms- feeding sleeping and response to light changes (2) pretectum-midbrain- pupillary responses to light (3) pineal gland- long term circadian rhythms (4) superior colliculus- midbrain- head orientations to objects (5) accessory optic nucleus- moves eyes to compensate for head movements (6) visual cortex- patter perception, depth perception, colour vision and tracking of moving objects (7)frontal cortex- controls voluntary eye movements all these modalities contain subsystems tat perform distinct roles ex. Taste has more than one modality- existence of separate pathways for taste 03/10/2014 taste receptors located in front 2 thirds of tongue send ino to brain through facial nerves taste receptors in posterior third of tongue send info to brain through glossopharyngeal sensory systems have multiple representations topographic organization- neural-spatial rep of the body perceived by sensory organ owl monkey has 14 rep of the visual world all mammals have at least one primary cortical area for each sensory system Vision Photoreceptors Rays enter eye through cornea, which bends them and then through lens, which bends them to a much greater degree so that visual image is focused on the receptors at the back of the eye Light then passes through photoreceptors to sclera which reflects light back into photoreceptors Retina contains 2 photoreceptors Rods- sensitive to dim lights- used for night vision Absent from fovea and distributed in rest of retina Cones- better able to transduce bright light and used for daytime vision 3 types of cones, max responsive to a diff set of wavelengths (R,B,Y), mediate colour vision in fovea, packed densely thus, to see in bright light, acuity is best when looking directly at things and to see dim light, acuity is best when looking slightly away bipolar induceA.P in ganglion cells (retinal gang send axons into brain proper) horizontal and amacrine cells- retinas encoding of info 03/10/2014 visual pathways axons of gang cells leave retina and form optic nerve before entering brain, optic nerves meet and form optic chiasm having entered the brain proper, the optic tract, still consisting of gang cells, diverges to form 2 main pathways to visual cortex. Both relay through thalamus Larger projection synapses in LGN of thalamus, on neurons that then project to the V1 LGN has 6 layers Layers 2, 3 and 5 receive fibers from ipsilateral eye and layers 1,4,6 from contralateral Topography is reproduced in LGN LGN cells project mainly to layer 4 of Primary Visual cortex- striate cortex (layer= large in primates) Region V1 –broadmanns area 17 Central part of visual field is rep at back of visual cortex and peripheral is rep towards the front Central vision field projects to the periphera
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