RD 171 Lecture Notes - Lecture 48: Presbyopia, Ganglion Cell, Chromophore

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amaranthlouse236

14 Jul 2020

School

Irvine Valley College

Department

Reading

Course

RD 171

Professor

Seksi

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Document Summary

Electromagnetic spectrum: continuum of electromagnetic energy produced by electric changes and radiated as waves. Light enters eye through pupil and is focused by cornea & lens. Form sharp images of objects on the retina. Visual receptors rods & cones (named by outer segments) Retina network of neurons that covers the back of the eye and contains the visual receptors. Signals from receptors flow through network of neurons that make up retina. Peripheral retina contains both but much more rods than cones. Fovea only cones when we look directly at an object the image falls directly on it. Blind spot no receptors spot where nerves that make up optic nerve leave the eye. Brain fills in spot by creating a pattern a perception that matches the surrounding pattern so it"s hard to detect the blind spot. Optic nerve conducts signals to brain. Object far away: light reaches eye essentially parallel.

Related Questions

We perceive a change in hue from blue to red when the

		wavelength of the light increases
		wavelength of the light decreases
		amplitude of the light increases
		amplitude of the light decreases

We perceive a decrease in intensity when

		wavelength of the light increases
		wavelength of the light decreases
		amplitude of the light increases
		amplitude of the light decreases

We perceive an increase in intensity when

		wavelength of the light increases
		wavelength of the light decreases
		amplitude of the light increases
		amplitude of the light decreases

A ratio of light reaching a surface to light leaving asurface.

		Illuminance
		Illumination
		Luminance
		Luminous flux
		Luminous intensity
		Reflectance

A measure of the visible light emitted in all directions

		Illuminance
		Illumination
		Luminance
		Luminous flux
		Luminous intensity
		Reflectance

Unit of measure is the lumen.

		Illuminance
		Illumination
		Luminance
		Luminous flux
		Luminous intensity
		Reflectance

Unit of measure is the Lux.

		Illuminance
		Illumination
		Luminance
		Luminous flux
		Luminous intensity
		Reflectance

The rods ... (check all that apply)

		are best for viewing detail
		are located in around the periphery of the retina
		require more light than the cones
		are used for detecting motion in the periphery
		exist in three types: short, medium and long

The cones ... (check all that apply)

		are best for viewing detail
		are located only in the periphery of the retina
		require more light than the rods
		are used for detecting motion in the periphery
		exist in three types: short, medium and long

The fovea is

		where the optic nerve attaches to the eye
		an area of densely packed rods
		an area of densely packed cones
		the back of the eye where the rods and cones are located

The optic disk is

		where the optic nerve attaches to the eye
		an area of densely packed rods
		an area of densely packed cones
		the back of the eye where the rods and cones are located

Visual acuity is

		the ability to adjust to light levels.
		the ability to detect changes in contrast.
		the ability to detect detail.
		the ability to focus light on the retina.

Accommodation is

		the ability to adjust to light levels.
		the ability to detect changes in contrast.
		the ability to detect detail.
		the ability to focus light on the retina.

The retina is

		where the optic nerve attaches to the eye
		an area of densely packed rods
		an area of densely packed cones
		the back of the eye where the rods and cones are located

A eye that focuses light in front of the retina is

		myopic
		hyperopic
		presbyopic
		astigmatic

11.Which sequence of events is required for the brain to interpret sound?
I. Vibration of the basilar membrane relative to the tectorial membrane causes cilia on hair cells to bend and triggers depolarization.

II. Hair cells stimulate the production of action potentials in sensory neurons that project to the brain.

III. Ganglion cell axons transmit action potentials to the occipital lobe.

A. II then I B.III then I then II. C.III then I D.I then II E.I then II then III

12. Which animal became numerous and widespread by using sonar to enable a high level activity in the dark?

A.bats B.whales C.owls D.dolphins E.shrews

13.In the vertebrate eye, what structure is light focused onto?

A.pupil B.lens C.retina D.sclera E.iris

14.Which is NOT a part of the vertebrate eye?

A. cornea B. retina C. iris D. cochlea E. pupil

15. In the vertebrate eye, what structure controls the amount of light that reaches the retina?
A. fovea. B. cornea. C. iris D. lens E. sclera

16.What are the short retinal photoreceptors responsible for color vision called?

A.rods B.cones C.bipolar cells. D.glial cells. E.ganglion cells

17. What sensory equipment is required for an animal to have binocular vision?

A.eyes located to the sides of the head B.forward-facing eyes C.a camera-type eye with multiple lenses

D. infrared vision E.ultraviolet vision

18. Choose the receptor that is NOT correctly matched with its function.

A.proprioceptor - monitors stretch of muscle fibers

B.baroreceptor - monitors hydrostatic pressure in blood vessels

C.nociceptor - transmits signals that the brain interprets as pain

D.chemoreceptor - perceives taste and smell stimuli

E.peripheral chemoreceptor - monitors the pH of the cerebrospinal fluid

19. Where is the visual image in focus for a nearsighted individual?

A.behind the retina B.in front of the retina C.on the retina, but it appears blurred

D.at the lens, forming a shadow on the retina E.on the retina, but it is upside down

20. Since the optic nerve must pass through the retinal layer, we all have a blind spot devoid of light receptors. This normally goes unnoticed, since the brain attempts to compensate for missing sensory information by filling it in based on surrounding patterns. Which step of the sensory pathway is represented by perceptual filling-in of the physiological blind spot?

A. interpretation B. stimulus. C. transduction into receptor potential D.action potential transmission

Exercise #5: The Nervous system and Perception

Task #1: Color vision

Introduction

In the human retina, there are two kinds of light-sensitive cells: rods and cones. These cells are located on the outside of the retina, away from the vitreous humor and against the choroid layer, and are covered by a later of bipolar and ganglion cells as well as neurons. Light enters the posterior chamber through the lens and must pass through several cell layers before it is absorbed by the rods and cones.

Cones are involved in color vision at daylight intensities. Generator potentials in a cone excite one neuron, giving high-level resolution vision. Cones will not cause neural firing at low light intensities and are, therefore, nonfunctional at night.

Rods provoke black-and-white vision at low light intensities. A bipolar cell associates with several rods, so that generator potentials sum in their effect. This assures neuronal firing at low light intensities and provides a highly sensitive vision but with less resolution.

Receptor convergence. A ganglion cell, which receives input from a number of rods, spread out over the retina, cannot pinpoint the source of a light stimulus as well as a ganglion cell, which is stimulated by a single photoreceptor. In the case of a ganglion cell receiving the added input of several rods, light hitting any one of the rods can cause a neural spike in the ganglion cell, but the brain has no way to know which rod was excited. It is therefore harder to pinpoint the location of light stimuli on the retina when the stimulus is detected by rods (as compared to cones). The result is that our ability to see detail, or our resolving power, is considerably lower under dim light conditions than under bright light conditions.

Dark adaptation. If you go from a lighted area to a very dark room, you will not be able to see. After about ten minutes, however, you begin to be able to see again. This occurs because the rhodopsin pigment, which gets broken down when it absorbs light, is continually re-synthesized in the rods. When there is very little light, very little rhodopsin gets broken down and the amount of rhodopsin gradually builds up, making the rod much more sensitive to dim light.

When light strikes a receptor cell, it triggers a photo-chemical reaction that leads to neuronal firing. If a rod or cone receives high-intensity light, the visual pigments will be temporarily bleached and will not absorb any more light. Within a matter of a few seconds, enzyme systems in the cells will restore the visual pigment to its light-absorbing form. This can be easily demonstrated. If, after viewing a bright light, the eye is quickly shut or turned to a dark wall, the bright image will persist as a positive afterimage because the high generator potential causes the continued firing of neurons. If the eye is cast on a lighter background after a few seconds, a negative afterimage, or a dark image of the object will appear. This is because the still bleached cells are not receptive to the light coming from the light background.

According to the Young-Helmholtz theory of color vision, there are three types of cone cells, which respond respectively to red, green, and blue light.

All other colors are perceived as the brain interprets impulses coming from a mix of these receptors. If an object of one color is viewed for a long period of time at high light intensity, the cones for that color will become bleached. The afterimage of the object will be seen in the complementary color.

The Exercise 6 PowerPoint will demonstrate afterimages to you. Use the slide show option to project the square of red light on your entire screen in a dark room. After staring intensely at the square for 30 seconds or so, without shifting your gaze, click enter to change the slide to a soft white. Continue staring at the screen as the change is made. What do you see? What was the color of the afterimage?

Repeat this experiment using a blue square. Before doing the experiment, hypothesize what color the afterimage will be according to the Young-Helmholtz theory.

Hypothesis to be tested: (2 pts)

What did you see when the experiment was conducted? (2 pts)

Was you hypotheses accepted or rejected? (1 pt)

Explain the colors seen in these afterimages using the Young-Helmholtz theory. (5 pts)

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RD 171 Lecture Notes - Lecture 48: Presbyopia, Ganglion Cell, Chromophore

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