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A&P I IPAP 3-17 > Exam 7 Vision Special Senses 73X > Flashcards

Exam 7 Vision Special Senses 73X Flashcards

1
Q

In broad terms give the overview of Image formation?

A

1) Light refracted through refractive structures of eye
2) Receptor potential produced by retinal photoreceptors
3) Neural layer processes visual data, sends nerve impulses to optic nerve
4) Impulses conveyed to thalamus and onto the cerebral cortex for interpretation as images

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2
Q

What is refraction and what causes it?

A

Light bending as it travels through different transparent substances of different densities

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3
Q

What provides refraction of light rays entering the eye? Which structure provides the majority?

A

Cornea (Most)
Lens
Aqueous Humor (Minor Role)
Vitreous Body (Minor Role)

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4
Q

An images formed on the retina has what orientation?

A

Upside Down

Left-to-right reversal

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5
Q

The variable refraction of light rays reflected form objects further than about 20 feet from the viewer are essentially parallel, what does this mean regarding the ciliary muscle and lens?

A

Ciliary Muscle is relaxed

Lens is fairly flat

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6
Q

The variable refraction of light rays reflected from objects closer than 20 feet from the viewer are not parallel, what does this mean regarding the ciliary muscle and lens?

A

Ciliary Muscle Contracts–> reducing tension on suspensory ligaments –>
Lens shape is more spherical (thicker)

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7
Q

The increase in curvature of the lens for near vision is called what?

A

Accommodation

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8
Q

What shape will the lens have if tension is reduced via the suspensory ligaments (zonular fibers)?

A

Convex shape

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9
Q

If the ciliary muscles relax and tension is restored to the suspensory ligaments via the choroid (acts like a spring), what shape will the lens take?

A

Flat (less convex)

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10
Q

How is tension released from the suspensory ligaments allowing the lens to thicken and take on a more convex shape?

A

Ciliary muscle contracts, stretching choroid and releasing tension

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11
Q

What is the minimum distance from the eye an object can be clearly focused w/maximum accommodation?

A

Near Point of Vision

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12
Q

What term is used to describe the loss of elasticity of the lens w/aging, and therefore cannot accommodate and focus the light?

A

Presbyopia

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13
Q

The normal eye in which is able to refract light rays from an object 20 ft (6meters) away and form a clear image on the retina is called?

A

Emmetropic

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14
Q

Refraction abnormalities that prevent a clear image to form on the retina are?

A

Myopia (Nearsightedness)\
Hypermetropia (Farsightedness)
Astigmatism (Irregular curvature of cornea)

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15
Q

What occurs when the eyeball is too long relative to the focusing power of the cornea and lens?

A

Myopia

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16
Q

Where does the image focus for a person suffering from Myopia?

A

In Front of the Retina

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17
Q

Myopia may be caused by what and how is it corrected?

A

Elongated Eyeball or thickened Lens

Corrected: Use of Concave Lens

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18
Q

What refraction abnormality is characterized by an eyeball that is too short relative to the focusing power of the cornea and lens (thin) and in which the image is focused behind the retina?

A

Hypermetropia

-Convex lens to correct

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19
Q

What refractive abnormality is caused by irregular curvature of either the cornea or lens and results in parts of the image blurred or distorted, and correction is by a lens that rotates the axis of the light going into the eye?

A

Astigmatism

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20
Q

What is the other part of the overall accommodation mechanism that occurs simultaneously w/changes in thickness of the lens and will allow the light rays to enter the eye in a more parallel orientation for better focus?

A

Pupil Constriction (circular muscles of the iris constrict)

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21
Q

Since humans are only able to focus on one set of objects at a time this provides what type of vision?

A

Binocular Vision: Depth perception, three-dimensional perspective

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22
Q

How is Binocular vision created in our human perception?

A

1) Two retinas see an object from slightly different angles

2) Brain fuses the two slightly different images creating stereoscopic vision (seeing solid)

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23
Q

The eyes must move medially so that both are directed toward the object being viewed as we move closer and rotate medially so light rays strike the same point on both retinas, this is called?

A

Convergence

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24
Q

The microscope view of rods and cones consists of what? Term given in the 1830’s due to their shape

A

Rods: Outer Segments cylindrical or rod-shaped
Cones: Tapered or cone-shaped

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25
Q

Where are cones most highly concentrated and in which dramatically decrease in density moving away from this area?

A

Central Fovea (Cone Peak)

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26
Q

Where are rods most highly concentrated?

A

Ring around the foveal pit (18 degrees, 4.5mm)

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27
Q

Which photoreceptor tends to be more densely concentrated?

A

Rods more so than cones

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28
Q

What area of the retina of the eye is receptor free?

A

Optic Disc (blind Spot)

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29
Q

The outer segment of rods and cones are next to the pigmented layer and is responsible for what?

A

Transducing light energy into receptor potential

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30
Q

How do Rods and cones increase the surface area available for trapping light?

A

Outer Segments are layered

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31
Q

How do the layers of the outer segment of rods and cones differ?

A

Rods: Stack Discs w/fold near base membrane
Cones: Folds (long pleated fabric)

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32
Q

What destroys the outer segments of rods and cones and what occurs to the destroyed portions?

A

Light Destroys the outer segments of rods and cones

-Sloughed off and phagocytized by pigment epithelial cells

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33
Q

How/When does the Phagocytic activity of Rod and Cone tips occur?

A

Circadian Rhythm:
-Rod tips: morning after first exposure to light
-Cone tips: triggered by darkness (occurs at night)
(Turnover of outer segment is fairly rapid)

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34
Q

what is contained in the inner segment of rods and cones?

A

Cell Nucleus
Golgi Apparatus
Mitochondria (Many)

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35
Q

The proximal end of rods and cones expands into what?

A

Synaptic terminal containing numerous synaptic vesicles

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36
Q

What are the colored, integral proteins in the plasma membrane of the outer segment of rods and cones?

A

Photopigments

37
Q

Photopigments undergo structural changes when they absorb light and are contain two parts, what are the two parts?

A

Retinal: Derivative of Vit. A formed from Carotene
Opsin: Glycoprotein

38
Q

The photopigment in rods is called what and absorbs what light most effectively?

A

Rhodopsin (Retinal + Opsin = Rhodopsin_)

Blue to Green Light

39
Q

Cones have three different photopigments due to the three types of cones, what are they called and what light do they absorb?

A 
Photopsin I (Yellowish Absorption Maximum)
Photopsin II (Green Absorption Maximum)
Photopsin III (Blue-Violet Absorption Maximum)
40
Q

Which portion of the Photopigment is essential for transducing light energy into electrical signals and which portion is different in each?

A
  • Retinal: Same in all photopigments and essential in transducing light energy to electrical signal
  • Opsin: Different in each
41
Q

In darkness what shape does retinal have and what is it called? This allows for what regarding Opsin?

A

Cis-Retinal (Bent Shape)

Opsin and Retinal fit together nicely

42
Q

What occurs when the Cis-retinal absorbs a photon of light?

A

Straightens to trans-retinal and Opsin and retinal no longer fit, they dissociate

43
Q

The conversion from cis-retinal to trans-retinal is called?

A

Isomerization

44
Q

In the dark what ion flows into the photoreceptor outer segment through what channels?

A

Sodium

Via Ligand-gated Sodium Channels

45
Q

The Ligand-gated Sodium Channels are held open by what? What effect does this have?

A

Ligand Cyclic GMP (cGMP)

-Partially depolarizes photoreceptor (Sodium-Potassium Pump expels Sodium ions out of the cell)

46
Q

What does the Partial Depolarization during darkness trigger?

A

Continual Release of Glutamate (Neurotransmitter) at Synaptic Terminal

47
Q

What is significant about Glutamate at the synaptic terminal?

A

Inhibitory of bipolar cell (usually it is excitatory)

48
Q

Glutamate triggers inhibitory postsynaptic potentials that have what effect?

A

Hyperpolarize the Bipolar cells, preventing them from sending signals to ganglion cells when it is dark

49
Q

What occurs when light strikes the retina?

A

Isomerization of cis-retinal activates enzymes that break down cGMP

50
Q

Lack of cGMP causes what to happen?

A

Ligand-gated sodium channels close

51
Q

What is the enzyme that breaks down cGMP?

A

Phosphodiesterase

52
Q

The closing of cGMP channels has what effect?

A

Sodium ion inflow decreases
Membrane potential becomes more negative
(resulting in hyperpolarizing receptor potential decreasing release of glutamate)

53
Q

The decrease in the inhibitory glutamate neurotransmitter allows for what?

A

Graded Potential produced by activated Bipolar Cells

54
Q

Rhodopsin has a reddish color, in the presence of light cis-retinal is converted to trans-retinal and the Opsin minus the retinal have what color? What is this termed?

A

Colorless

Bleaching of Photopigment

55
Q

What enzyme converts trans-retinal back to cis-retinal which allows it to rebind to Opsin reforming a functional photopigment? what is this called?

A

Enzyme: Retinal Isomerase
Called: Regeneration

56
Q

What photopigment contributes little to daylight vision and why?

A

Rods: regeneration is to slow

Cones regenerate rapidly

57
Q

What is dark adaptation and how long does it take?

A
  • Photopigments able to regenerate in the dark without being bleached by light
  • 30-40 minutes for bleached rhodopsin to fully regenerate
58
Q

What is an inability to distinguish between certain colors due to an absence or deficiency of one of the three cone photopigments? What is the most common?

A

Color Blindness
Common: Red-Green Color Blindness
Generally inherited trait

59
Q

What is another term for night blindness in which refers to the inability to see well at low light levels?

A

Nyctalopia

60
Q

What is a typical cause of Nyctalopia?

A

Prolonged Vit. A deficiency and consequent below normal amount of rhodopsin, rod degeneration
-Supplement will restore as long as before degenerative changes

61
Q

The reina processing of images at synapses causes inputs to be enhanced and others discarded, why is the pathway typically one of convergence rather than divergence?

A

Photoreceptors vastly outnumber ganglion cells

62
Q

A Single bipolar cell will synapse with how many Rods? what is the significance of this?

A

6-600 rods per bipolar cell

Convergence increase light sensitivity but decreases acuity of image

63
Q

A single bipolar cell will typically synapse with how many cones?

A

One, less sensitive but higher acuity

64
Q

What cells attenuate the differences between parts of the retina that are strongly stimulated and parts that are less stimulated, as well as assist in the differentiation of colors?

A

Horizontal cells

Amacrine Cells

65
Q

What is the visual pathway from Optic Nerve to Occipital Lobe?

A 
Optic Nerve
Optic Chiasm
Optic Tract
Lateral Geniculate Nucleus of Thalamus
Optic Radiations
Primary Visual Area of Cortex (area 17) in Occipital Lobe
66
Q

What provides output from the retina to the brain and via what structure is this accomplished?

A

Axons of Retinal Ganglion cells via Optic Nerve

67
Q

Axons of the Optic Nerve pass through what and at this location what occurs?

A

Pass through: Optic Chiasm

Some cross to opposite side, some do not

68
Q

What are the axons considered once they pass through the Optic Chiasm?

A

Optic Tract

69
Q

The Optic tract terminates where?

A

Lateral Geniculate Nucleus of the Thalamus

70
Q

Lateral Geniculate Nucleus of the Thalamus synapse w/neurons having axons that form what and in which those have projections that travel where?

A

Optic Radiations which project to the primary visual area (17) in the occipital lobes of the cerebral cortex

71
Q

The Visual Field refers to what?

A

Everything that can be seen by that eye

72
Q

The visual fields of our eyes overlap and provide binocular vision, each eye has two regions of their visual field?

A

Nasal (Central) Half

Temporal (Peripheral) Half

73
Q

The light rays from objects in the nasal half of the visual field fall on what portion of the retina?

A

Temporal half of the retina

74
Q

The light from objects in the Temporal Half of the visual field fall on what portion of the retina?

A

Nasal Half of the retina

75
Q

What visual information is conveyed to the left side of the brain due to the crossing/not crossing over pattern at the optic chiasma?

A

Right half of each visual field

Left eye: Nasal Half, Right eye: Temporal Half

76
Q

What visual information is conveyed to the right side of the brain due to the crossing/not crossing over at the optic chiasma?

A

Left half of each visual field

Left eye: Temporal half, Right eye: Nasal Half

77
Q

What axons do not cross at the Optic Chiasma but continue directly to the lateral geniculate nucleus of the thalamus on the same side?

A

Temporal half of each retina (which field of vision is Nasal half)

78
Q

Axons of collaterals of retinal ganglion cells project to the midbrain and are involved in what?

A

Circuits that constrict pupils and coordinate head and eye movement

79
Q

Collaterals will also travel to what portion of the brain in which establishes circadian rhythms based in part on impulses of light perception from the eyes?

A

Suprachiasmatic nucleus

80
Q

What are the projection of axons from the thalamus to the primary visual area of the cortex on the same side?

A

Optic Radiations

81
Q

Loss of vision in an otherwise normal eye, caused by either no transmission or poor transmission of visual stimulation through the optic nerve to the brain during early childhood or for sustained period due to strabismus, anisometropia cataract, trauma, is called?

A

Amblyopia

82
Q

What is the name of the fissure slightly above the occipital pole and travels along the middle cerebrum between the cuneus (cuneate) and lingual (linguate) gyrus?

A

Calcarine Sulcus

83
Q

What is concentrated on the banks of the calcarine Sulcus?

A

Primary Visual Cortex

84
Q

Central Visual Field is located on what portion of the Calcarine Sulcus?

A

Posterior Portion

85
Q

Peripheral Visual Field is located on what portion of the Calcarine Sulcus?

A

Anterior Portion

86
Q

The upper bank of the calcarine sulcus responds strongly to which portion of the visual field?

A

Lower half (below center)

87
Q

The lower bank of the calcarine sulcus responds strongly to which portion of the visual field?

A

Upper Half (Above Center)

88
Q

Processing of visual signals involves a number of separate systems within the cerebral cortex and to operate in concert to interpret what different aspects of visual images?

A

1) Process information related to shape
2) Process information related to color
3) Process information related to movement, location, and spatial organizaiton

A&P I IPAP 3-17 (16 decks)

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