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Human Physiology 2 - Unit 1 - Zach H. > Lecture 7: Vision I > Flashcards

Lecture 7: Vision I Flashcards

1
Q

What is the definition of refraction?

A

Is the bending of light waves at an angulated surface of a transparent material.

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2
Q

What is the definition of refractive index?

A

Is the ratio of the velocity of light in air to the velocity of light traveling in the substance. RI of air = 1.00

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3
Q

What is the definition of refractive power?

A

Is a measure of how much a lens bends light waves. It is measured in diopters.

* 1 diopter = 1 meter divided by the focal length of a lens. *

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4
Q

What is the definition of focal point?

A

The point through which all parallel rays of light will pass after passing through each part of the lens.

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5
Q

What is the definition of focal length?

A

The distance from the center of the lens to the focal point.

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6
Q

What is the definition of emmetropia?

A
  • This refers to the normal eye with regard to depth of focus.
  • Parallel light rays from distant objects are in sharp focus on the retina when the ciliary muscle is completely relaxed.
  • ALL distant objects can be seen clearly.
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7
Q

What is the definition of hyperopia?

A
  • Farsightedness
  • Usually due to an eyeball that is too short or, occasionally a lens system that is too weak.
  • ALL distant objects can be seen clearly.
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8
Q

What is the definition of myopia?

A
  • Nearsightedness
  • When ciliary muscle is completely relaxed, light rays coming from distant objects are focused in front of the retina.
  • Usually due to too long of an eyeball.
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9
Q

What is a diopter?

A
  • 1 diopter = 1 meter divided by the focal length of a lens.
  • Diopters are used to measure how much a lens bends light waves.
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10
Q

What does the degree of refraction (amount of bending) depend on?

A
  • The ratio of the two refractive indices of the two transparent media.
  • The degree of angulation between the interface and the entering wave front of the light waves.
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11
Q

True or False:

Light striking a perpendicular surface continues on through without bending.

A

True

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12
Q

What is the function of the iris?

A
  • The iris of the eye functions in a similar manner to the iris diaphragm of a camera.
  • The iris controls the amount of light entering the eye from darkness to light conditions.
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13
Q

What is the relationship between the depth of focus of the lens and pupillary diameter?

A

Depth of focus of the lens increases as the pupillary diameter decreases.

* Thus, have a inverse relationship. *

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14
Q

True or False:

The object as projected on the retina will be reversed and inverted.

A

True

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15
Q

What is the maximum visual acuity of the human eye for two-point light sources?

A
  • Light from a distant point source will normally create a spot with a diameter of about 11 micrometers and a center that is brighter than the periphery.
  • The average diameter of a cone in the retina is 1.5 micrometers.
  • Therefore, the maximum visual acuity for two-point sources of light is 1.5 to 2.0 mm.
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16
Q

How is aqueous humor formed?

A

Formed by the ciliary processes.

  • The ciliary apparatus consists of two opposing layers of epithelial cells with a space between them.
    • sodium ions are actively transported into this space and are accompanied by chloride and bicarbonate ions.
  • The above ions draw water (via osmosis) into the space and the aqueous solution is then passed into the anterior chamber.
17
Q

What is the flow of fluid in the eye?

A
  • Fluid flows from the anterior chamber into the canal of Schlemm and from there into aqueous veins in the sclera.
  • A tonometer is used to measure the intraocular pressure.
  • Normal pressure is 15 mmHg
18
Q

How is a tonometer used?

A
  • The cornea of the eye is anesthetized with a local anesthetic, and the footplate of the tonometer is placed on the cornea.
    • a small force is then applied to a central plunger; causing the part of the cornea beneath the plunger to be displaced inward.
  • The amount of displacement is recorded on the scale of the tonometer; and this is calibrated in terms of intraocular pressure.
19
Q

What is glaucoma and why is it so dangerous?

A
  • Glaucoma, one of the most common causes of blindness, is a disease of the eye in which the intraocular pressure becomes pathologically high, sometimes rising acutely to 60 to 70 mmHg.
  • As the pressure rises, the axons of the optic nerve are compressed where they leave the eyeball at the optic disc.
    • the compression is believed to block axonal flow of cytoplasm from the retinal neuronal cell bodies into the optic nerve fibers leading to the brain.
      • the result is lack of appropriate nutrition of the fibers, which eventually causes death of the involved fibers.
20
Q

What are the visual pigments found in rods and cones?

A
  • Rods:
    • rhodopsin
  • Cones:
    • three different color pigments
21
Q

True or False:

Photosensitive pigments of the rods and cones are transmembrane conjugated proteins.

A

True

22
Q

Of the major functional segments, which is the site of light-sensitive photochemicals?

A

Outer segment

23
Q

Of the major functional segments, which contains orgaelles, especially mitochondria?

A

Inner Segment

24
Q

Of the major functional segments, what does the synaptic body connect?

A

connects with horizontal and bipolar cells

25
Q

True or False:

Cones are similar to rods except that the protein portions (opsins) of the photochemicals are different from the scotopsin in the rod photochemicals.

A

True

26
Q

Which colors are cone senitive to?

A
  • Blue
  • Green
  • Red
27
Q

What happens to rhodopsin when it is exposed to light?

A

It begins to decompose.

28
Q

What does transducin activate when it is stimulated by the retinal portion of the rhodopsin complex?

A

Actiates cGMP phosphodiesterase.

29
Q

What does cGMP phosphodiesterase catalyze?

A

cGMP -> 5’ GMP

30
Q

What causes the closure of sodium channels?

A

reduction of cGMP

31
Q

When does the photoreceptor become hyperpolarized?

A

When the reduction of cGMP cause cloure of sodium channels.

32
Q

True or False:

When rhodopsin is activated, a few sodium channels close for each rhodopsin molecule activated.

A

False - when rhodopsin is activated, several hundred channels close for each rhodopsin molecule activated.

33
Q

Under dark conditions, what happens to the electronegativity inside the membrane?

A

Under dark conditions, there is reduced electronegativity inside the membrane (-40 mV rather than the expected -70 to -80 mV).

*this is caused by sodium ions leaking into the cell and neutralizing much of the negativity on the inside of the entire cell. The membrane is leaky to sodium ions that flow through cGMP-gated channels. *

34
Q

What does the excitation of the rod cause?

A

Increased negativity of the intrarod membrane potential (= hyperpolarization).

35
Q

What does decomposition of rhodopsin decrease?

A

Rod membrane conductance for sodium ions in the outer segment.

** this results in the hyperpolarization of entire rod membrane **

36
Q

Look over the rhodopsin-retinal visual cycle.

A

figure 51-5

37
Q
A

Human Physiology 2 - Unit 1 - Zach H. (9 decks)

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