BIOL 4380 Lecture Notes - Lecture 7: Retinal Pigment Epithelium, Photoreceptor Cell, Amacrine Cell

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13 May 2018

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• There are 2 types of photoreceptors: rods and cones. Second type of type of neuron is called a

bipolar cell which cell bodies are located in the inner nuclear layer. Toward the distal we have

horizontal neurons, are innervated by multiple photoreceptor neurons. On the other side of

axons we have amacrine cells which are similar to horizontal cells.bipolar cells can be considered

interneurons.

• At the very proximal layer we have ganglion cells which are the ones that contribute their axons

to the optic nerve that ultimately to the brain.

• Is horizontal cell pre or postsynaptic to the bipolar cell synapse? Presynaptic. Horizontal cells

synapse with photoreceptors. The signals the receptors send to bipolars are modified by

horizontal cells.

• The receptors outer segets otai disks, i ase of rods it’s erae eapsulated

organelles. In cones, there are no inner membrane enclosed, they form protrusions with PM of

the cell. The region where the rod or the cone meets the rest of the cytoplasm is called the

cilium. Each one produces a single axon with multiple processes at the terminal.

• Reeptors are faig away fro the light! Not partiularly itelliget desig. It’s ot etirely

understood this is the way it is, but one of the reason is because the interphase between the

pigment epithelium and the receptors is a very special place that can only be located distally. As

these disks (which contain photoreceptor molecules) are hit with light, the molecule that

catches the photon irreversably changes. Therefore, all of the disks have to be recharged

somehow with retinal. The pigment cells form encapsulating covers around the rods and the

disks are generated closer to the cell body, keep regenerating dorsally and as they move dorsally

they separate form the rod and are ultimately endocytosed by the pigment cell. Once they are in

the pigment cell, they can be recycled, are removed and the new ones are formed. Pigment cells

a’t e loated i the frot of rods ad oes, eause the ost of the light would e

absorbed by epithelium.

• They took a student and injected him with radioactive something! And then followed over 12

day period and noticed that radioactivity moves along the rod into the pigment cell and

accumulates in the epithelial cells.

• There’s soethig uusual about the way that a receptor responds to a photon. What is

unusual here? The resting potential is not in the normal range is at -40 and the stimulus instead

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Document Summary

There are 2 types of photoreceptors: rods and cones. Second type of type of neuron is called a bipolar cell which cell bodies are located in the inner nuclear layer. Toward the distal we have horizontal neurons, are innervated by multiple photoreceptor neurons. The signals the receptors send to bipolars are modified by horizontal cells: the receptors outer seg(cid:373)e(cid:374)ts (cid:272)o(cid:374)tai(cid:374) disks, i(cid:374) (cid:272)ase of rods it"s (cid:373)e(cid:373)(cid:271)ra(cid:374)e e(cid:374)(cid:272)apsulated organelles. In cones, there are no inner membrane enclosed, they form protrusions with pm of the cell. The region where the rod or the cone meets the rest of the cytoplasm is called the cilium. Each one produces a single axon with multiple processes at the terminal: re(cid:272)eptors are fa(cid:272)i(cid:374)g away fro(cid:373) the light! It"s (cid:374)ot e(cid:374)tirely understood this is the way it is, but one of the reason is because the interphase between the pigment epithelium and the receptors is a very special place that can only be located distally.

Related Questions

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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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

Which of the following statements is TRUE regarding sea anemones?

	None of the answer options is correct.
	Spongesânot sea anemonesâpossess what is considered to be the âsimplestâ nervous system found in animals.
	Because sea anemones are âsimpleâ organisms, these animals only possess motor neurons; sensory neurons or interneurons are never found in sea anemones.
	Although sea anemones possess ânet-likeâ nervous systems, these animals have brains located at their bases (near where they would attach to rocks).
	Although sea anemones lack definitive brains, they do possess ganglia that serve a similar function to the paired ganglia of flatworms.

Some people have low levels of calcium circulating in the blood, a condition known as hypocalcemia. While for many this disorder has little to no effect, for some it can be life-threatening. How could low levels of calcium harm an individual?

	Low levels of calcium would not have any effect on synaptic transmission.
	Low levels of calcium would cause sustained depolarization of the presynaptic cell.
	Low levels of calcium would result in fewer signals sent between the pre- and postsynaptic cell.

Cephalization is: the

	All of these choices are correct.
	development of a brain within the head of an animal.
	concentration of sensory organs within the head end of an animal.
	development of a âhead endâ in an organism.

Which of the following are TRUE about the resting membrane potential? (Select all that apply.)

	It results from voltage-gated sodium channels remaining open for long periods of time.
	It results from K⁺ ions diffusing out of the cell.
	It results from the sodium-potassium pump moving more Na⁺ ions out of the cell than K⁺ ions into the cell.

Afferent and efferent neurons differ in:

	their size.
	the directionality of the information they send.
	their pattern of myelination.

A neuron that responds to the environment is a(n):

	interneuron.
	homeostatic neuron.
	motor neuron.
	sensory neuron.

Which of the following is NOT the role of an interneuron?

	stimulating a muscle to contract
	conveying information from the internal environment of an animal
	relaying information from sensory to motor neurons
	maintaining homeostasis

Where are postsynaptic cell receptor proteins synthesized?

	the Golgi apparatus
	the lysosome
	the cytoplasm
	the rough endoplasmic reticulum

Inhibition of the flexor muscle during the knee-extension reflex is an example of:

	homeostasis.
	reciprocal inhibition.
	negative feedback.
	All of these choices are correct.

10.

What type of cells produce myelin for sensory neurons?

	pyramidal neurons
	glial cells
	melanocytes
	astrocytes

BIOL 4380 Lecture Notes - Lecture 7: Retinal Pigment Epithelium, Photoreceptor Cell, Amacrine Cell

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