PBI288 - Final review

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Psychology

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119 Terms

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Transduction

Process of changing stimulus ( energy, force, chemical...) from the environment into an electrochemical signal for the nervous system; Requires appropriate receptors & biochemical process in receptors that activate neurons

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Sensory receptor

Specialized type of cell that responds to environmental stimulation (photoreceptors, cutaneous touch receptors)

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Cell membrane receptor

Specialized type of protein on a cell that responds to biochemical activation (ionotropic receptors, metabotropic receptors)

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Receptor Potential

Slow, moderate change in electrical state of a cell ( passive change, EPSP or IPSP)

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Action Potential

Rapid, large change in electrical state of a cell (“all or none“ event, active propagation)

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Summarize how activation of photoreceptors in the retina is transmitted to the lateral geniculate nucleus (LGN) in the thalamus

  • Photoreceptors in retina activated by light

  • Signals transmitted from photoreceptors to bipolar cells then ganglion cells

  • Ganglion cells form optic nerve, carry signals to brain

  • Signals reach LGN in thalamus

  • Within LGN signals undergo processing

  • Processed signals relayed to primary visual cortex in occipital lobe

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Compare/contrast two types of photoreceptors in the human eye

Cones: most prevalent in central retina; found in fovea; sensitive to moderate-high levels of light; provide info about hue; provide excellent acuity.

Rods: most prevalent in peripheral retina; not found in fovea; sensitive in low levels of light; provide only monochromatic info; provide poor acuity.

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Describe how differences in light-sensitive receptor proteins contribute to colour blindness

  • Colour blindness results from malfunction/absence of one or more types of cone cells in retina

  • Differences in opsin genes, which code for cone cell proteins, contribute to colour blindness

  • Variations in opsin can lead to: missing/non-functioning red, green or blue cone cells & reduced sensitivity/altered spectral sensitivity of cone cells

  • Types of colour blindness: red-green (protanopia & deuteranopia)& blue-yellow (tritanopia)

  • Affected individuals may have trouble distinguishing certain colours/perceive them differently

  • Colour blindness can impact daily tasks such as interpreting traffic signals/selecting ripe fruits

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Summarize how information from left & right visual fields is directed to the right & left brain hemispheres

  • Each eye receives input from both left & right visual fields

  • Optic nerves from both eyes meet at optic chiasm (some fibers cross to opposite side, some continue straight)

  • Fibers carrying information from nasal (inner) retina of each eye cross at optic chiasm to opposite side of brain

  • Fibers carrying information from temporal (outer) retina of each eye stay straight on to same side of brain

  • Visual information from left visual field of both eyes processed in right hemisphere of brain & visual information from right visual field of both eyes processed in left hemisphere of brain

  • Arrangement ensures that each hemisphere processes information from both visual fields, enabling integrated perception of entire visual field in each hemisphere

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<p>Anatomy of the eye</p>

Anatomy of the eye

<p></p>
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Properties of light

  • Hue → specific/dominant wavelength (colour)

  • Brightness → intensity of light (amount of light present)

  • Saturation → “purity“ of light, richness of colour (just one wavelength vs many other wavelengths)

<ul><li><p>Hue → specific/dominant wavelength (colour)</p></li><li><p>Brightness → intensity of light (amount of light present)</p></li><li><p>Saturation → “purity“ of light, richness of colour (just one wavelength vs many other wavelengths)</p></li></ul>
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Binocular vision

  • Each eye has slightly different view of a given object, because of small difference between eyes

  • Merging images helps us perceive depth

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Rhodopsin

Photopigment in rods that responds to light

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Opsin

Photopigment in cones

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Photopigment

  • Made up of opsin (protein) & retinal (lipid)

  • Light strikes photopigment molecules & splits it into opsin & retinal components

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“Dark current”

In darkness, photoreceptors release glutamate at synapses with bipolar neurons

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Receptive fields

  • Represents part of visual field that it responds to (changes its firing rate)

  • Constituency of cells that provide info to retinal ganglion cell MP (think of it as government)

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Organization of receptive fields

  • On-centre/off-surround cells: likes light in middle of its receptive field

  • Off-centre/on-surround cells: likes light around perimeter of its receptive field

<ul><li><p>On-centre/off-surround cells: likes light in middle of its receptive field</p></li><li><p>Off-centre/on-surround cells: likes light around perimeter of its receptive field</p></li></ul>
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Lateral Geniculate Nucleus

  • Bilateral, multilayered structure (6 )

  • Each layer receives specific types of info from retina

  • Layers distinguished by cell size ( magnocellular = large, parvocellular =small, koniocellular = tiny)

<ul><li><p>Bilateral, multilayered structure (6 )</p></li><li><p>Each layer receives specific types of info from retina</p></li><li><p>Layers distinguished by cell size ( magnocellular = large, parvocellular =small, koniocellular = tiny)</p></li></ul>
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Optic chiasm

  • Splitter

  • Axons coming from medial/nasal part of retina cross to opposite hemisphere at optic chiasm

  • Axons coming from lateral/peripheral part of retina do not cross

  • Info from left visual field is directed to right LGN (& right visual cortex)

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From retina to brain

  1. RGC axons leave eye (optic nerve)

  2. Optic chiasm

  3. 1st synapse in LGN in thalamus

  4. 2nd synapse in primary visual cortex (V1)

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V1: organization

  • Striate cortex

  • 6 layers: inputs from LGN enter at layer 4 of V1, inputs from ipsilateral & contralateral eyes kept separate in layer 4

  • Organized into modules or small ‘columns‘ of cortex

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V1: representation of visual field

  • Retinotopic map preserved in V1 & fovea processed by proportionally more cells than in any other area of retina

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List the characteristics of visual information processed by cells in V1 (primary visual cortex)

  1. Orientation: most neurons in V1 sensitive to specific orientations of light-dark information in its receptive field, sensitive= more neuron firing when light/dark boundary oriented at specific angle

  2. Spatial frequency: changes in brightness, refers to # of times area of visual information shifts (light→dark→light→dark), high frequency information= lots of small details & large objects with clear edges/contours, low frequency information=visual scenes with large objects & blurry/ not too much detail

  3. Retinal disparity: binocular cells become very active when image of an object appears on slightly different areas of left & right retinas (difference in location between eyes), crossed-disparity=objects close to us, uncrossed-disparity= objects far away from us

  4. Colour: third stage of colour processing occurs in V1→ colour-sensitive cells in blobs

  5. Movement

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V1: modules

  • Each module contains a tiny region of all 6 layers of V1 ( 0.5mm diameter)

  • Each module ‘sees‘ information from tiny part of the retina

  • Cells within single module specialize for orientation (180°), left-right eye (binocular & monocular preference, disparity gives info about distance)

  • 4 colour blobs per module

  • Movement

  • Spatial frequency

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Extrastriate visual cortex

  • Areas of visual cortex outside V1 (visual association cortex,~ 25% of human cerebral cortex)

  • Each area specialized for aspects of visual information

  • Receive info from V1→process →pass on information to higher areas of extrastriate cortex ( area V4→colour processing, area V5→movement)

  • V2 & V3 cells→similar properties to V1 (retinotropic organization, cells selective for angle/direction of motion, cortical magnification, most are binocular)

  • Ventral vs dorsal stream

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Visual processing

  • ~ 25-30% of human cerebral cortex involved in visual processing

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Ventral stream (extrastriate visual cortex)

  • ”what“ pathway

  • Allows for object recognition

  • P pathway, some K pathway (colour, texture, detail)

  • Signals forwarded to parts of inferior temporal lobes

  • Vision for recognition (1. Cells in each region respond to more complex stimuli 2. Cases of IT cortex damage→agnosias 3. Very large receptive fields)

<ul><li><p>”what“ pathway</p></li><li><p>Allows for object recognition</p></li><li><p>P pathway, some K pathway (colour, texture, detail)</p></li><li><p>Signals forwarded to parts of inferior temporal lobes</p></li><li><p>Vision for recognition (1. Cells in each region respond to more complex stimuli 2. Cases of IT cortex damage→agnosias 3. Very large receptive fields)</p></li></ul>
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Dorsal pathway (extrastriate visual cortex)

  • ”where/how“ pathway

  • Allows for locating objects in space, perceiving motion relative to other objects, making actions in relation to object

  • M & K pathway inputs

  • Vision for action pathway (1.Cells in V5 direction-selective 2.Cases of V5 parietal cortex damage→akinetopsia, apraxias)

  • From V1, info sent to parts of posterior parietal lobes & dorsal temporal lobes

  • Different regions specialized for identifying low-detail, movement-related visual info

<ul><li><p>”where/how“ pathway</p></li><li><p>Allows for locating objects in space, perceiving motion relative to other objects, making actions in relation to object</p></li><li><p>M &amp; K pathway inputs</p></li><li><p>Vision for action pathway (1.Cells in V5 direction-selective 2.Cases of V5 parietal cortex damage→akinetopsia, apraxias)</p></li><li><p>From V1, info sent to parts of posterior parietal lobes &amp; dorsal temporal lobes</p></li><li><p>Different regions specialized for identifying low-detail, movement-related visual info</p></li></ul>
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Visual agnosia

  • Difficulty recognizing/interpreting visual information despite perfect vision

  • Often caused by damage to brain's visual processing areas

  • Various types affecting different aspects of visual perception

  • Object agnosia: difficulty recognizing objects

  • Prosopagnosia: difficulty recognizing faces

  • Spatial agnosia: difficulty perceiving spatial awareness

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IT cortex

  • Face recognition region

  • Fusiform face area (FFA) in inferior temporal lobe activated in primates when viewing faces

  • Reduced FFA activity associated with poor face recognition (propropagnosia)

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Akinetopsia

  • Motion blindness (stroboscopic vision→only snapshots of visual scenes, no continuous movement)

  • Caused by damage to V5 area (medial superior temporal lobe)

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Ablation

  • Destruction of tissue

  • Electrolytic: electrode used to burn small area of tissue

  • Non-selective: all tissue at site destroyed

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Exitotoxic ablation/lesions

  • Injection of excitatory agonist drugs directly into brain tissue

  • Selective way → only dentrites, cell bodies that have receptors for drug are affected

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Temporary ablation/lesions

  • Injection of inhibitory agonists like muscimol (gaba-a agonist)

  • Way of inhibiting regional activity, drug effect washes out with time

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Light microscopy

  • Resolution up to 1500x

<ul><li><p>Resolution up to 1500x</p></li></ul>
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Electron microscopy

  • Resolution up to the nanoscale (x10-9)

  • Synapses & individual organelles visible

<ul><li><p>Resolution up to the nanoscale (x10<span style="color: black"><sup>-9</sup></span>)</p></li><li><p>Synapses &amp; individual organelles visible</p></li></ul>
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Scanning electron microscopy

  • Resolution up to the nanoscale (x10-9)

  • Gives 3D view

<ul><li><p>Resolution up to the nanoscale (x10<span style="color: black"><sup>-9</sup></span>)</p></li><li><p>Gives 3D view</p></li></ul>
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Tracers

  • Used to identify projections by injection

  • Anterograde: dendrites→axons (eg. Phaseolus vulgaris leucoagglutinin)

  • Retrograde: axons→dendrites (eg. Fluoro-gold/ hydroxystilbamidine)

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Computerized axial tomography (CAT or CT)

  • Pass x-rays through head

  • Shows tissue density

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Magnetic resonance imaging (MRI)

  • Uses magnets & radio waves to determine tissue density in brain

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Diffusion tensor imaging (DTI)

  • Form of MRI

  • Tracks water movement along myelinated axons to show where white matter bundles are

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Positron emission tomography (PET)

  • Radioactive glucose injected into bloodstream

  • Brain tissue that is active uses more glucose

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Functional MRI (fMRI)

  • Detects small changes in oxygen use in active brain areas

  • No radioactivity needed

  • Regions of tissue that are active require more oxygen & more oxygenated blood flows to active brain regions

  • Measures blood oxygenation level-dependent (BOLD) levels

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Microdialysis

  • Measures release of neurotransmitters within brain region

  • Dialysis probe inserted into a brain region

  • Substances in extracellular fluid can diffuse across membrane into tube

  • Analyze fluid sample for content

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Electrophysiological recordings

  • Listen in on cell firing patterns from single cell all the way up to multiple brain regions at once

  • Use electrodes to directly stimulate cells/specific parts of brain

  • Lateral hypothalamic stimulation: animals will self-administer stimulation to electrodes near lateral hypothalamus (activate dopamine cells in ventral tegmental area)

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Transcranial magnetic stimulation (TMS)

  • Generates mild magnetic fields to trigger changes in activity of localized brain regions

  • Used for research & therapeutic purposes

  • Allows for non-invasive manipulation of neural activity

  • Device held near skull surface, pulsed current through device creates magnetic field which alters neural activity in tissue below the skull

  • Vs TDCS → pulsed current directly through

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Deep brain stimulation (DBS)

  • Brain stimulation techniques increasingly used for therapeutic purposes in humans

  • Implantation of chronic electrodes for some movement disorders (Parkinson's), severe depression, epilepsy

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Optogenetics

  • Activate parts of brain without electricity or drugs

  • Provides selective way of activating/inhibiting specific neurons by “injecting“ light into brain

  • Infect cells with viruses so they make “light-sensitive” receptor protein

  • Channel Rhodopsin 2→activated by blue light→ opens Na+ channel

  • Halorhodopsin→activated by yellow/orange light → open Cl- channel

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Genetic methods

  • Manipulating gene expression allows targeting of specific proteins in nervous system

  • Multiple approaches (genetic mutation→delete gene, add extra copies, modify it; RNA manipulations→block production of proteins from gene transcription)

  • Manipulation/mutation: targeted deletion of a gene (‘knockout‘) can tell us about role a gene may normally have

  • Crispr-CAS9, knockouts/knock-ins, upregulation|downregulation, cross-breeding

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Experimental controls

  • An equivalent experience of all steps of a manipulation/treatment except for step that is thought to have an effect

  • For surgery→’ sham’ surgery

  • For drug injections→vehicle injection (eg. Saline)

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Recognize different ways of lesioning brain tissue

  • Electrolytic

  • Excitotoxic

  • Temporary

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Recognize different ways of imaging/recording activity of live brain tissue

  • Microscopy: light microscopy, electron microscopy, scanning electron microscopy

  • Tracers: anterograde, retrograde

  • Brain imaging: CAT, CT, MRI, fMRI, DTI, PET

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Recognize different ways of manipulating of live brain tissue

  • Lateral hypothalamic stimulation

  • Transcranial magnetic stimulation

  • Transcranial direct current stimulation

  • Deep brain stimulation

  • Optogenetics

  • Genetic manipulation/mutation

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Physical properties of sound

  • Produced by objects that vibrate & set molecules of air into motion

  • Vibrations cause molecules of air to move in waves that travel away from object

  • Frequency, measured in hertz (Hz), cycles/sound

  • Hz determines pitch of sound (high→soprano, low→bases)

  • Loudness/volume reflects how ‘big‘ sound waves were

  • Timbre is complexity of sound waves

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Anatomy of auditory system

  1. Outer

  2. Middle

  3. Inner

<ol><li><p>Outer </p></li><li><p>Middle</p></li><li><p>Inner</p></li></ol>
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Outer ear

  • Pinna funnels sound waves into auditory canal

  • Tympanic membrane (eardrum) at end of canal

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Middle ear

  • Tympanic membrane→ossicles: hammer (malleus), anvil (incus), & stirrup (stapes) bones

  • Stirrup pushes on oval window membrane

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Inner ear

  • Oval window→opening into cochlea

  • Fluid filled→ fluid movement creates travelling wave in membranes inside cochlea

  • Specialized membranes inside

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Organ of Corti

  • Region where sound wave transduction happens

  • Basilar membrane (bottom)

  • Tectorial membrane (tap)

  • Hair cells (outer & inner)→attached to basilar membrane, some touch the tectorial membrane above

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Hair cells (auditory system)

  • Sound receptors

  • Inner & outer rows of hair cells on basilar membrane

<ul><li><p>Sound receptors</p></li><li><p>Inner &amp; outer rows of hair cells on basilar membrane</p></li></ul>
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Sound transduction

  • Each hair cell contains cilia

  • Side-by-side, attached to one another by flexible tips links (movement of one cilium pushes/pulls the ones around us)

  • Site where tip links attach to each cilium called insertional plaque

  • Insertional plaques contain ion channels

  • Movement of cilia opens ion channels in insertionnal plaques

  • Ion channels open→ ions flow→electrical changes inside hair cell (receptor potential)

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Pitch

  • 2 mechanisms used in cochlea: Place coding & Rate coding

  • Place coding: high frequency (high pitches) move only part of basilar membrane closer to oval window

  • Rate coding: hair cells on basilar membrane match firing rate to frequency of sound ( 100 Hz → hair cells fire 100 times/second), rate of cell firing in auditory nerve gives us info about sound pitch

  • Evidence shows that both place & rate coding happen in cochlea (place coding→higher pitches, rate coding→ lower pitches)

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Auditory pathway in brain

  • Auditory nerve activated

  • To medulla (cochlear nucleus)

  • To tectum in midbrain (inferior colliculus)

  • To thalamus (medial geniculate nucleus)

  • To primary auditory cortex (temporal lobe)

  • Each hemisphere ‘hears‘ from both ears, but ‘hears more‘ from contralateral ear (left ear→right temporal lobe)

<ul><li><p> Auditory nerve activated</p></li><li><p>To medulla (cochlear nucleus)</p></li><li><p>To tectum in midbrain (inferior colliculus)</p></li><li><p>To thalamus (medial geniculate nucleus)</p></li><li><p>To primary auditory cortex (temporal lobe)</p></li><li><p>Each hemisphere ‘hears‘ from both ears, but ‘hears more‘ from contralateral ear (left ear→right temporal lobe)</p></li></ul>
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Causes of deafness

  1. Conduction deafness: ears do not conduct sound to nervous system

  2. Sensorineural deafness: problems with structures that convert sound vibrations into neural activity

  3. Central deafness: hearing loss caused by brain damage (variable forms)

    Causes of deafness in aging:

  4. Presbycusis: most common form of a hearing loss in older adults, hearing loss greater for high pitched sounds

  5. Hair cell loss: noise, genetic variation, some medications (aspirin & certain antibiotics)

  6. Loss of blood supply to ear: heart disease, high blood pressure, diabetes

  7. Damage to middle ear (membrane or bones conducting sounds)

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Treating deafness

  • Cochlear implants used to treat deafness due to hair cell loss (sensorineural or central deafness)

  • Electrical currents stimulate the auditory nerve

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Complex sound processing

  • Hearing in cerebral cortex occurs through 2 pathways (anterior & posterior)

  • Anterior pathway: ‘what‘ pathway, helps us recognize what sounds are, judge if familiar/ unfamiliar

  • Posterior pathway: ‘where‘ pathway, helps us identify where sounds are coming from

  • Evidence shows that these system are plastic

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Music/pitch perception

  • Musicians have larger neural response to pitch info than non-musicians (shown for both musical & speech sounds)

  • Musician’s brains look different & respond differently to music (activation of motor regions when listening to familiar piece)

<ul><li><p>Musicians have larger neural response to pitch info than non-musicians (shown for both musical &amp; speech sounds)</p></li><li><p>Musician’s brains look different &amp; respond differently to music (activation of motor regions when listening to familiar piece)</p></li></ul>
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Taste: physical stimulus

  • Taste involves perception of chemical compounds (tastants) dissolved in medium (not same as flavour)

  • Humans perceive only a limited range of tastants (each may have own adaptive/survival value, responses to each can change with age/experience/cultural influences)

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Taste (anatomy)

  • Tastant receptors found in taste buds on tongue, mouth & throat (on tongue, taste buds located on sides of papillae)

  • No tastant-specific ‘map‘ of tongue

<ul><li><p>Tastant receptors found in taste buds on tongue, mouth &amp; throat (on tongue, taste buds located on sides of papillae)</p></li><li><p>No tastant-specific ‘map‘ of tongue</p></li></ul>
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Taste: transduction

  • A taste bud is a cluster of receptor cells (constantly regenerating)

  • Each cell extends microvilli into ‘taste pore‘ (gap between papillae)

  • Microvilli contain ion channels/receptors

  • Tastants bind to receptors→triggering transduction

  • Change in electrical state of taste cells, synapse with sensory nerve fibers in tongue

  • Each taste cell responds to only one type of tastant

<ul><li><p>A taste bud is a cluster of receptor cells (constantly regenerating)</p></li><li><p>Each cell extends microvilli into ‘taste pore‘ (gap between papillae)</p></li><li><p>Microvilli contain ion channels/receptors</p></li><li><p>Tastants bind to receptors→triggering transduction</p></li><li><p>Change in electrical state of taste cells, synapse with sensory nerve fibers in tongue</p></li><li><p>Each taste cell responds to only one type of tastant</p></li></ul>
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Taste: trajectory

  • Taste signals carried to brain via cranial nerves

  • Brainstem: nucleus of solitary tract

  • Ventral posteriomedial thalamus→primary gustatory cortex= frontal cortex (insula) →orbitofrontal cortex

  • Ventral posteriomedial thalamus→somatosensory cortex

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What affects the sensitivity of our sense of taste?

  • Absolute thresholds very low for bitter tastants

  • Higher for sweet tastants

  • Combinations can modify perceived intensity of each

  • Interactions with other senses (smell)

  • A factory triggered by airborne molecules: may be inhaled directly from outside air or pushed up through back of mouth/throat into naval cavity

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Smell: anatomy

  • OIfactory receptor cells are bipolar cells

  • Axons project up through cribiform bone ( axons terminate in glomerulus, small clustered region of axons)

  • Mitral cells in olfactory bulb, brain tissue above cribiform bone (mitral cells send their dendrites into glomerulus, axons of mitral cells form olfactory tract into brain)

<ul><li><p>OIfactory receptor cells are bipolar cells</p></li><li><p>Axons project up through cribiform bone ( axons terminate in glomerulus, small clustered region of axons)</p></li><li><p>Mitral cells in olfactory bulb, brain tissue above cribiform bone (mitral cells send their dendrites into glomerulus, axons of mitral cells form olfactory tract into brain)</p></li></ul>
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Olfactory epithelium

<p></p>
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Olfactory epithelium

  • Layer of tissue at top of nasal cavity

  • Receptor cells embeddedin epithelium

  • Cilia project into mucosal layer

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Smell: transduction

  • We can distinguish between 1000s of different smells

  • In humans,~350 different olfactory receptors made (all metabotropic)

  • Each receptor can bind to more than one type of odorant molecule

  • Each odorant can bind to more than one type of receptor

  • Individual smells created by unique patterns of receptor activation

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What affects our sensitivity in our sense of smell?

  • Type of odorant (different absolute thresholds for different odorants)

  • Developmental differences (hyposmia-decreased ability to smell-more common in older age)

  • Sex differences (women > men, small differences for some odorants)

  • Experience ( adaptation, rapid sensitivity decreases with prolonged exposure to odorants)

  • Influenced by attention (less adaptation to noxious smells)

  • Recognition thresholds influenced by familiarity/experience (also affected by verbal abilities, greater vocabulary = greater recognition)

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Multimodal nature of flavours

  • Vision: visual can affect how flavour is perceived (eg. White wine with tasteless/odourless red dye described by oenologists as red wine), reported sweetness enhanced by red; saltiness by white, congruence between visual cues & smells, flavours affect judgements of un/pleasantness

  • Hearing: ’sonic chip’ experiment (higher crispness, freshness ratings with louder, high-frequency sounds), high-frequency sounds increase ’fizziness’ ratings of carbonated drinks, high levels of background noise may reduce perceived saltiness

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Hedonic value of flavours (like/dislike)

  • Orbital frontal cortex is key

  • Activity in OFC correlates with motivation to consume, ratings of pleasantness of foods

  • Activity in OFC correlates with expectation of quality & with rated ‘liking‘ of wine & with believed price

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Vestibular system

  • Allows perception of ‘linear translational movements’ in space & rotational movements of head

  • Sense of balance

  • Keep head in an upright position

  • Adjusts eye movement to compensate for head movements

  • 2 parts: semicircular canals & vestibular sacs

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Semicircular canals

  • Orientation of head space

  • 3 fluid-filled canals

  • Movement of head causes movement of endolymph

  • Ampulla at base of each canal

  • Cupula within each ampulla contains hair cells

  • Movement of cupula causes movement of hair cells (bending of hair cells causes receptor potential, receptor potential activates auditory cranial nerve

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Vestibular sacs

  • Utricle & saccule → balance & equilibrium

  • 2 fluid-filled compartments next to semicircular canals (tissues on sides of sacs contain layer of hair cell receptors - otoconia on top of this layer)

  • Movement of fluid within sacs pushes on ocotonia, pushes hair cell cilia

  • Receptor potential activates auditory cranial nerves

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Somatic perception

  • Different aspects to somatic perception (perception of the body) → 1. Cutaneous perception 2. Proprioception & kinesthesia

  • 3 types of info received through cutaneous perception: touch, temperature, pain

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Touch

  • Different types of touch (tactile) receptors give us different types of touch sensations → pressure, vibration, stretching, movement, textures

  • Tactile receptor types differ in:

  1. What type of stimulation they respond to best

  2. How fast they adapt (stop responding to stimulation)

  3. Which type of skin they are found in (hairy vs glabrous) & where

  4. Receptive field size

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Cutaneous perception

  • 4 key types of ‘encapsulated mechanoreceptors‘, or tactile receptors

  1. Merkel's discs

  2. Meissner's corpuscle

  3. Ruffini's ending

  4. Pacinian corpuscle

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Merkel's discs

  • Touch

  • Fingertips, lips, tongues

  • Pressure info

  • Form perception, edges, fine details

  • Slow adapting

  • Small receptive fields

<ul><li><p>Touch</p></li><li><p>Fingertips, lips, tongues</p></li><li><p>Pressure info</p></li><li><p>Form perception, edges, fine details</p></li><li><p>Slow adapting</p></li><li><p>Small receptive fields</p></li></ul>
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Meissner's corpuscle

  • Fingertips, lips, tongue

  • Pressure & movement info

  • Form perception, texture

  • Fast adapting

  • Small receptive fields

<ul><li><p>Fingertips, lips, tongue</p></li><li><p>Pressure &amp; movement info</p></li><li><p>Form perception, texture</p></li><li><p>Fast adapting</p></li><li><p>Small receptive fields</p></li></ul>
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Ruffini's ending

  • Deeper, in hypodermis

  • Stronger pressure

  • Stretch info

  • Slow adapting

  • Large receptive fields

<ul><li><p>Deeper, in hypodermis</p></li><li><p>Stronger pressure</p></li><li><p>Stretch info</p></li><li><p>Slow adapting</p></li><li><p>Large receptive fields</p></li></ul>
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Pacinian corpuscle

  • Deeper, in hypodermis

  • Strong, vibrating pressure or movement

  • Texture info

  • Large receptive fields

<ul><li><p>Deeper, in hypodermis</p></li><li><p>Strong, vibrating pressure or movement</p></li><li><p>Texture info</p></li><li><p>Large receptive fields</p></li></ul>
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Temperature perception

  • Temperature receptors in skin respond to changes in skin temperature from 34°C (normal)

  • ’Transient receptor potential‘ (TPR) receptor family

<ul><li><p>Temperature receptors in skin respond to changes in skin temperature from 34°C (normal)</p></li><li><p>’Transient receptor potential‘ (TPR) receptor family</p></li></ul>
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Transient receptor potential (TPR)

  • Cold sensors in skin closer to epidermis, warmth sensors located more

  • Warmth sensors located more deeply

  • Each TPR receptor type has a ’preferred‘ range of temperature

  • Some can be activated by chemical chemical compounds

<ul><li><p>Cold sensors in skin closer to epidermis, warmth sensors located more </p></li><li><p>Warmth sensors located more deeply</p></li><li><p>Each TPR receptor type has a ’preferred‘ range of temperature </p></li><li><p>Some can be activated by chemical chemical compounds </p></li></ul>
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Nociception

  • Pain perception = ‘nociception‘, noxious or harmful

  • Several types of pain receptors in skin on free nerve endings

  • TRPV1, TRPV2 receptors activated by strong heat chemical compounds

  • At least 4 types of pain receptors in skin

  1. High-threshold mechanoreceptors

  2. TRPV1 receptors: heat (burns) & chemicals (eg. Capsaicin), burning sensation

  3. TRPA1 receptors: chemicals that cause inflammation

  4. TRPM3 receptors: activated by very high h eat ( around > 45°C → higher TRPV1), axons of nerves large diameter (myelinated)

  • Activation of receptors→A delta or C fibers in spinothalamic path (special kind of sodium channel found in these axons: Nax 1.7)

  • Cingulate cortex activity correlates with amount of pain reported

  • Cingulate activity decreases when painkillers (analgesics) or placebos taken & reported pain decreases

<ul><li><p>Pain perception = ‘nociception‘, noxious or harmful</p></li><li><p>Several types of pain receptors in skin on free nerve endings</p></li><li><p>TRPV1, TRPV2 receptors activated by strong heat chemical compounds</p></li><li><p>At least 4 types of pain receptors in skin</p></li></ul><ol><li><p>High-threshold mechanoreceptors</p></li><li><p>TRPV1 receptors: heat (burns) &amp; chemicals (eg. Capsaicin), burning sensation</p></li><li><p>TRPA1 receptors: chemicals that cause inflammation</p></li><li><p>TRPM3 receptors: activated by very high h eat ( around &gt; 45°C → higher TRPV1), axons of nerves large diameter (myelinated)</p></li></ol><ul><li><p>Activation of receptors→A delta or C fibers in spinothalamic path (special kind of sodium channel found in these axons: Nax 1.7)</p></li><li><p>Cingulate cortex activity correlates with amount of pain reported</p></li><li><p>Cingulate activity decreases when painkillers (analgesics) or placebos taken &amp; reported pain decreases</p></li></ul>
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Somatosensory pathways

  • Somatosensory receptors (touch, temperature, pain) activated

  • From receptors in body below head, axons enter CNS via spinal nerves (dorsal root ganglia)

  • From face & head, via cranial nerves (mostly trigeminal nerve)

  • Route in CNS depends on type of info carried: dorsal column (touch) & spinothalamic (pain, temperature)

  • Both pathways send axons to: ventral posterior thalamus→primary somatosensory cortex

<ul><li><p>Somatosensory receptors (touch, temperature, pain) activated</p></li><li><p>From receptors in body below head, axons enter CNS via spinal nerves (dorsal root ganglia)</p></li><li><p>From face &amp; head, via cranial nerves (mostly trigeminal nerve)</p></li><li><p>Route in CNS depends on type of info carried: dorsal column (touch) &amp; spinothalamic (pain, temperature)</p></li><li><p>Both pathways send axons to: ventral posterior thalamus→primary somatosensory cortex</p></li></ul>
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Primary somatosensory cortex

  • Somatic map of body in parietal cortex

  • Bigger parts → more sensitive to touch/temperature /pain perception

<ul><li><p>Somatic map of body in parietal cortex</p></li><li><p>Bigger parts → more sensitive to touch/temperature /pain perception</p></li></ul>
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Somatic nerves

  • Tactile information is carried by different types of nerves than temperature or pain info

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What happens if transduction pathway mutated (Nax 1.7)

  • Ashlyn Blocker → “ pain is a gift, she doesn't have it”

  • Inherited erythromelalgia “man on fire”syndrome →hyperactivation of nerves carrying pain signals to spinal cord

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Pain perception

  • Pain information also activates other regions of cerebral cortex: anterior cingulate cortex (ACC) & insular cortex (frontal lobe)

  • Different parts to experience pain:

  1. Touch, sensory → primary somatosensory cortex

  2. Emotional response → ACC & insular cortex

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Touch & pain interaction

  • Touch, pressure can sometimes suppress pain, at least temporarily

  • “Gate Theory“ of pain perception

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Gate Theory

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