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1
Q

sensory system

A

gives rise to sensory perceptions. basic functions include transduction and coding.

2
Q

trandsduction

A

transformation of physical energy into neuronal activity. Occurs in receptor neurons.

3
Q

coding

A

Information about stimuli (e.g., intensity, duration) are represented (coded) in the pattern of activity (action potentials) of the neurons.

4
Q

laws of specific sense energies

A

Johannes Muller (1826). labeled pathways.

5
Q

sensory receptor

A

A specialized neuron that detects a particular category of physical energy. Some transduce and encode (somatosensory, olfaction); some only transduce (vision, audition, taste).

6
Q

sensory transduction

A

The process by which sensory stimuli are transduced into slow, graded receptor potentials.

7
Q

receptor potential

A

A slow, graded electrical potential produced by a receptor cell in response to a physical stimulus.

8
Q

receptive field

A

The region of the sensory surface that modulates the activity of sensory neurons.

9
Q

visual system

A

answers what it is (recognition) and where it is (location). transforms a 2D and upside-down retinal image into the 3D world we perceive.

10
Q

Wavelength (frequency)

A

perception of color

11
Q

Intensity (amplitude)

A

perception of brightness

12
Q

electromagnetic spectrum

A

colors and wavelengths visible to humans. violet (shortest, 400 nm) to red (longest 700nm)

13
Q

lens

A

focuses light on the retina

14
Q

ciliary muscles

A

alter the shape of the lens to focus

15
Q

accommodation

A

adjusting the lens to bring images into focus

16
Q

optic disk

A

produces a blind spot. normally solved by the phenomenon called completion. the person does not perceive a blind spot because it is filled with the information around it.

17
Q

choroid membrane

A

has blood vessels and pigments

18
Q

the retina is “inside-out”

A

light passes through several cell layers before reaching its receptors

19
Q

travel of light through the retina

A

light -> retinal ganglion cells -> bipolar cells -> receptor cells

20
Q

lateral communication

A

horizontal and amacrine cells

21
Q

duplexity theory of vision

A

cones and rod mediate different kinds of vision

22
Q

cones (8 mill)

A

photopic vision; lower sensitivity, high-acuity in day light. color information in good lighting.

23
Q

rods (120 mill)

A

scotopic vision; high-sensitivity, low-acuity vision in dim light. lacks detail and color information.

24
Q

high converge in rod system

A

increasing sensitivity while decreasing acuity

25
Q

only cones are found at the fovea

A

low converge and low sensitivity but high acuity

26
Q

scanning the visual world

A

because only the central region of the retina provides high resolution, we see the world by moving our eyes.

27
Q

saccades

A

quick eye movements

28
Q

perception of color and detail decrease beyond

A

20 degrees from the fixation point, unless you move your eyes

29
Q

spectral sensitivity curve

A

shows how sensitivity depends on wavelength

30
Q

phototransduction

A

conversion of light to neural signals by visual receptors. relatively slow.

31
Q

when light strikes the retina

A

it interacts with light-sensitive photopigments in the rods and cones

32
Q

photopigments

A

are contained in discs located in the rod and cone outer segments

33
Q

rhodopsin

A

photopigment in rods; responds to light rather than neurotransmitters. made of retinal (from Vitamin A) and opsin, a protein.

34
Q

rhodopsin (in the dark or DARK CURRENT)

A

phototransduction; Na+ channels are maintained partially open by cGMP. this partial depolarization (-40 mV/-50 mV) releases glutamate out of the synaptic terminal.

35
Q

rhodopsin (when light strikes)

A

phototransduction; split rhodopsin activates a G-protein. Na+ channels close (cGMP is degraded). Rods hyperpolarize (returns to resting potential of -70 mV), inhibiting glutamate release.

36
Q

amplification during transduction

A

one rhodopsin activates hundreds of transducin (G-proteins) molecules per second. each transducin activates a single phosphodiesterase. each phosphodiesterase degrades over 100 cGMP molecules per second. overall, one photon degrades over 105 cGMP molecules per second.

37
Q

the visual pathway in humans

A

optic nerve -> optic chiasm -> optic tract -> LGN -> optic radiations -> occipital cortex

38
Q

lateral geniculate nuclei layers (6-1)

A

contra, ipsi, contra, ipsi, ipsi, contra

39
Q

dorsal lateral geniculate nucleus (dLGN)

A

layers are monocular. maps are in register. each layer only receives input from one eye.

40
Q

cortical layers

A

1, 2, 3, 4a, 4b, 4c, 5, 6

41
Q

lateral geniculate nuclei

A

neurons project to cells in layer IV (monocular) in V1.

42
Q

layers II-III

A

biocular cells appear

43
Q

layer V

A

projects to SC in mesencephalon

44
Q

layer VI

A

projects back to the LGN.

45
Q

retinotopic map in human V1

A

systematic organization of RF position. representation of fovea is magnified.

46
Q

receptive fields of visual neurons

A

The area of the visual field within which it is possible for a visual stimulus to influence the firing of a given neuron in the retina or central visual system.

47
Q

on and off channels

A
  • Rods and cones contact bipolar cells.
  • Bipolar cells contact ganglion cells.
  • Some bipolar cells (off-center) are excited by glutamate and are depolarized by darkness and hyperpolarized by light.
  • Some bipolar cells (on-center) are inhibited by glutamate and
    are depolarized by light
    and hyperpolarized by
    darkness.
48
Q

lateral connections

A

allow cells in one part of the

retina to influence the activity of cells in another part

49
Q

cortical simple cells

A

have elongated RFs with excitatory and inhibitory subregions. simple cell RFs would be formed by the convergence of input from circular, center surround RFs.

50
Q

binocular disparity (retinal disparity)

A

for objects at different distances, each eye sees a slightly different view. grants us info about depth relationships between objects.

51
Q

depth detectors

A

neurons in the visual cortex that are able to detect retinal disparity.

52
Q

steropsis

A

depth perception through binocular vision

53
Q

columnar organization of V1

A
  • Cells with simple receptive fields send information on to cells with more complex receptive fields
  • Functional vertical columns exist such that all cells in a column have the same receptive field and ocular dominance
  • Ocular dominance columns – as you move horizontally, the dominance of the columns changes
  • Retinotopic organization is maintained
54
Q

hypercolumn

A

portion of cortex that has the machinery to analyze all properties of stimuli (orientation, motion, etc), for each point in the visual field, and for each eye.

55
Q

component (trichromatic) theory

A

Proposed by Thomas Young (1802); refined by Hermann von Helmholtz (1852). Three types of receptors, each with a different spectral sensitivity. Color perceived depends on the ratio of activity in these three receptor types.

56
Q

Protanopia (first color defect)

A

An inherited form of defective color vision in which red and green hues are confused; “red” cones are filled with “green” cone opsin. They see the world in shades of yellow and blue; both red and green look yellowish to them. Visual acuity is normal. affects men more.

57
Q

Deuteranopia (second color defect)

A

An inherited form of defective color vision in which red and green hues are confused; “green” cones are filled with “red” cone opsin. Visual acuity is normal. affects men more.

58
Q

Tritanopia (third color defect)

A

An inherited form of defective color vision in which hues with short wavelengths are confused; “blue” cones are either lacking or faulty. See the world in greens and reds. Blue looks green and yellow looks pink. Visual acuity is normal. affects men and women equally.

59
Q

hierarchical organization

A

From receptors to striate (V1) and extrastriate (V2, etc.) cortex

60
Q

functional segregation

A

cortical areas are functionally specific.

61
Q

parallel processing

A

what and where are processed in different pathways that originate from the retina (magno, parvo)

62
Q

Ganglion cells form two main retinal output channels

A

parvo cells and magno cells

63
Q

parvo cells

A

mostly in the fovea and receiving

mainly cone inputs form the parvocellular pathway

64
Q

magno cells

A

mostly in the peripheral retina

and receiving mainly rod inputs from the magnocellular pathway..

65
Q

magnocellular pathway

A

Large ganglion cells in retina project to large neurons in the ventral (magnocellular) division of the dLGN. Information is passed from V1 to parietal cortex (dorsal stream). responds to motion and spatial info.

66
Q

lesion of parietal cortex bilaterally (magnocellular pathway lesion)

A

inability to perceive movement (case LM)

67
Q

balient syndrome (magnocellular pathway lesion)

A

Localization deficit due to lesion in dorsal stream

  • Ataxia: deficit in visually guided movements
  • Ocular apraxia: deficit in the ocular scanning of images
  • Simultagnosia: perception of only one object at a time
68
Q

parvocellular pathway

A

Small ganglion cells in retina project to small neurons in the dorsal (parvocellular) division of the dLGN. Information is passed from V1 to temporal cortex (ventral stream). Responds to shape, details (acuity), color.

69
Q

lesions in temporal cortex (ventral stream) [parvocellular pathway lesion]

A

produce visual agnosias, which in the inability to recognize visual objects.

70
Q

prosopagnosia (parvocellular pathway lesion)

A

inability to recognize faces. Often associated with damage to the ventral stream. Recognition deficits may not limited to faces. Prosopagnosics have different skin conductance responses to familiar faces compared to unfamiliar faces, even though they reported not recognizing any of the faces

71
Q

when presented with face stimuli

A

activity change in the right temporal lobe of normal subjects. lesions in this area produce prosopagnosia.

72
Q

Functional Areas of Extrastriate Visual Cortex

A

Anatomically distinct architecture and borders. Retinotopically organized. Neurons in each area respond to different visual cue: color, movement, shape, etc. Lesions of each area results in specific deficits

73
Q

MT

A

motion area

74
Q

motion is also used for the perception of form

A

breaking camouflage and biological motion

75
Q

Intensity of a light stimulus is coded through

A

through increased frequency of action potential i.e. cells fires more often for intense light

76
Q

After the chiasm, the optic nerve changes name to

A

optic tract

77
Q

Optic nerve carries only

A

ipsilateral information (nasal and temporal)

78
Q

Optic Tract carries

A

ipsilateral (temporal) and contralateral information (nasal)

79
Q

pre-optic chiasm lesion

A

ipsilateral vision loss

80
Q

ost-optic chiasm lesion

A

contralateral vision loss

81
Q

Convergence of on/off bipolar cells-> leads to

A

on/off ganglion cells-> LGN on/off cells-> V1 on/off simple cells->V2 complex cells