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Chapter 7

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PSYC 2410
Elena Choleris

Chapter 7 Summary Audition: Amplitude = loudness Frequency = pitch Pureness = timbre Fourier Analysis: can break down complex sound wave in to simpler frequency, amplitude, timbre waves and adding up these simple waves gives you back the complex wave Fundamental Frequency: highest frequency for which all other frequencies of the sound are multiples (e.g. sound with 100, 200 and 400 Hz, fundamental is 100 Hz), fundamental frequency can also be missing (e.g. sound with 200, 300 and 400 Hz) Compressed wave: sound particles are close together Rarefaction: sound particles are far apart (negative pressure)  Humans hear from 20 – 20,000 Hz but can feel lower Hz, lose high frequencies first when we age (membrane becomes less flexible and the width of the cochlea at that point is small to begin with) and babies can hear even higher  Infrasounds (below perception) vs. ultrasounds (above perception) Outer Ear (pinnae, auditory canal)  tympanic membrane (ear drum)  middle ear (3 ossicles – malleus, incus, stapes, eustachian tube from throat – equalization, cold, air filled)  oval window  cochlea (contains organ of Corti – basilar and tectorial membranes, fluid filled)  hair cells (receptors, graded lengths, respond to mechanical stimulus, K+ and Ca2+ ion channels)  auditory nerve (VIII) OR  round window (vibration dissipates)  Don’t know much about chemical basis of channels because the protein is low in abundance and they are hard to grow in vitro Higher frequency sound waves peak closer to the oval window while lower frequencies peak closer to the apex (Tonotopic organization) Due to location of auditory cortex, damage from blows to the head are uncommon (embedded in lateral sulcus, more likely to have visual damage), major permanent effects are loss of ability to localize sounds and impairment to ability to discriminate frequencies  Deafness (~1%), rare because other pathways remain  Conductive deafness: due to damaged, malformed, inhibited by cold, ossicles  Nerve deafness: due to damage to auditory nerve / hair cells (tumour, congenital, stroke)  Tinnitus: ringing in the ear, temporary or permanent, can cause stress / anxiety, used to cut the auditory nerve as treatment but ringing persists therefore changes to auditory system that are causes of deafness are not the cause of tinnitus Cochlear Implant: implant is surgically placed on bone, electrodes from implant extend to cochlea and when given stimulus from external head piece, stimulate corresponding points on the cochlea, the sooner after deafness your receive the implant, the better – disuse leads to degeneration Localization : Medial Superior Olives: detect changes in phase difference (what part of the wave we are at / timing) vs. Lateral Superior Olives detect changes in loudness Superior Colliculus – deep layers – auditory map, this in combination with superficial layers allows us to orient head and eyes to stimulus that we are hearing Chapter 7 Summary Echolocation – using time differences to detect distance Vestibular System: Semicircular Canals: 3, fluid (endolymph) filled, horizontal – spin, 3 – cart wheels and vertical – front flips Ampulla: enlargement at base of each canal, contains receptors for angular acceleration Vestibular Sacs: where canals converge into, contains receptors on wall of saccule and floor of utricle, respond to linear acceleration  Receptors are embedded in cupola where otoconia (crystals of calcium carbonate) move and then stimulate action potential  Cranial nerve VIII (audiovestibular nerve) projects to medullar vestibular nuclei then to either the eye muscles (to keep eye muscles still in space while head moves) or other projections  Visual capture – when visual input and vestibular input conflict with one another, we trust our vision, why we can get motion sickness Somatosensation: Exteroceptive system: external stimuli applied to skin Proprioceptive system: stimuli on body position (from muscles and vestibular system) Interceptive System: general information about body conditions (blood pressure, internal temperature, ANS) Free Nerve Endings  Fast adapting, respond to pain and changes in temperature, simplest (no special structure), close to surface  High threshold pain, inflammatory responses in pain receptors, need to actually apply heat or cold to skin to see difference in temperature nerve endings because anatomically they look the same  3 receptor for pain is ATP-dependent ionotropic receptor Pacinian Capsules  Fast adapting, looks like onion (lots of layers), largest and deepest in skin, respond to changes in skin displacement (vibrations > constant pressure) Merkel Disks  Slow adapting, close to Ruffini endings, respond to gradual skin indentation (pressure) Ruffini Endings  Slow adapting, close to Merkel disks, respond to gradual skin stretch Different receptors adapt at different rates (a moderate constant stimulus will stop producing sensation after a short time), why in stereognosis (identification of an object by touch) you must be constantly moving the object in your hands Dermatomes: chunks of body that are innervated by sensory nerves that enter through same dorsal root, large degree of overlap (why complete loss of 1 sensory nerve does not often result in loss of sensation from part of body not common) Dorsal-Column Medial-Lemniscus System: carries information about touch and proprioception, dorsal columns  dorsal columns nuclei  decussate  medial lemniscus  ventral posterior nucleus of thalamus  secondary and primary somatosensory cortexes Chapter 7 Summary Anterolateral System: carries information about pain and temperature, decussates as soon as it reaches the spinal cord  either take spinothalamic tract, spinorectiular tract or the spinotectal tract  ventral posterior nucleus of the thalamus  primary and secondary cortex projections Primary Somatosensory Cortex (SI)  Post central gyrus  4 strips, somatotopic, contralateral sensations  Horizontal electrode: same body part, different sensation, increasingly more complex,
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