Palomar College

Physiological

Psychology

DAY COURSE

 

 

 

Roger N. Morrissette, PhD

 

 

Visual System

Objectives: 

  

      By the end of this laboratory you should be able to understand the following concepts associated with the:

 Human Visual Sensory System:

        By the end of this laboratory you should be able to do the following:

        This laboratory investigates the many facets of the sensory system.  We will begin the lab with a lecture on The Visual System. Please print out these slides ahead of time and be prepared to take notes. The content of which will be on your next quiz or examination. The body’s homeostatic process begins with its sensory receptors.  These receptors monitor many aspects of the internal and external environment and relay that information to the nervous system. The body uses that information to adequately respond to the environment.  Sensory receptors come in many types: Mechanoreceptors interpret physical deformation of different body parts; Chemoreceptors monitor different chemical concentrations; Photoreceptors record light energy; and Thermoreceptors send information about temperature to the brain.  In today’s laboratory we will be conducting exercises with a specific sensory system - The Visual System. Please choose a single partner to work with and read the exercise directions carefully. Please also take excellent notes of your findings so that I can check them at the end of the class.  Good luck.

 Human Visual Sensory System

Blind Spot Detection:
 
To measure your blind spot you will need to use the small strip of paper that has both a black dot and a black cross on it.
 
1. Hold the paper in your right hand with the black dot on the right side of the cross.
 
2. Fully extend your right arm and position the paper so that it is at your eye level.
 
3. Close your left eye and focus your right eye only on the cross.
 
4. Now very slowly bring the paper closer to your eyeball.
 
5. At a certain distance, you will see the spot disappear from your field of vision - that is your blind spot.
 
6. At that point, have your partner measure the distance between your eye and the paper.      
 

Blind Spot ________________  from the eye.

Dominant Eye Determination:

 
Most people do not use their two eyes equally. Typically one eye is more dominant than the other. 
 
To determine which is your dominant eye, start by:
 
1. Rolling up an 8 1/2" x 11" sheet of paper into a long tube about 4 cm in diameter.
 
2. Hold the tube at arms length between both of your eyes and notice the image you see through the tube.
 
3. Now close one eye and then the other. Your dominant eye will see the same image as the one both of your eyes sees.
 
Which eye is your dominant eye? _____________________
 
What is your dominant hand? ___________________
 
 
Visual Accommodation Exercises

Proper focusing on objects of varying distances requires the eye to accommodate by adjusting both the lens shape and the size of the opening. In the following exercises you will observe some conditions under which these automatic accommodations take place.

Near Point of Vision:

The distance from the eye to the nearest object that can be focused clearly is called the near point of vision. To identify your near point of vision for each of your eyes you must first: 

 
1. Pick up a straight pin with your right hand and hold it vertically at arm's length and at the level of your eyes.
 
2. Place your left hand over your left eye.
 
3. Gradually bring the pin closer to your eye, focusing continually on the pin until it begins to blur.
 
4. Have your partner measure the distance between your eye and the point where the pin began to blur - this is your near point vision.
 
What is your near point vision for your right eye? _____________________
 
5. Repeat the procedure with your left eye.
 
What is your near point vision for your left eye? _____________________

 

Pupil Reactions:

 
For this exercise you will be observing your partners pupils. If they have a light colored iris this should be pretty easy, but if they have a dark colored iris you may have to get pretty close to see the pupil changes.  
 
1. Grab a penlight and turn it on.
 
2. Look closely at the shape of your partners right eye pupil.
 
3. Now quickly flash the penlight over and away from your partners right eye.
 
What do you observe about their pupil? _______________________________
 
4. Repeat the procedure for their left eye.
 
Can you observe any difference in the response? _________________________________
 
5. Take another close look at your partner's right eye pupil.
 
6. While still observing your partner's right eye pupil, have them place their hand over their left eye for 1 minute and then remove it.
 
What do you observe about their pupil? _______________________________
 
7. Repeat the procedure for their left eye.
 
Can you observe any difference in the response? _________________________________

 

            Today’s laboratory also involves the dissection of a sheep eye.  Since this laboratory involves dissection of animal tissue it is important to remember to be thankful, respectful, and subsequently take your studies, and in this case, your dissections seriously. Once again you will be using extremely sharp scalpels and probes so be careful with them. Please proceed with caution and care during your dissections.  Work in groups of no more than two. Use the dull and sharp probes to try to identify all of the brain regions discussed.  Follow the instructions carefully before you cut into your eyeballs.  A single clean slice will make viewing clearer.  I will be asking you to identify the different regions and parts of your sheep eyes so study while you dissect.  When you have completed your dissection you will need to do the exercises on the last pages of the handout (which will be given to you in class) in order to complete the laboratory.  Good Luck in your explorations.

 

Successfully dissect, sketch, and identify the superficial aspect of the eyeball.

    We receive the majority of our information through our visual senses. There is much integration of the images by our retina prior to getting to our visual cortex. The rods are critical for dim light discrimination and periphery viewing. The cones are located near the fovea and are important for color discrimination and fine details. Both the left and right eye work together to give you a clear view of the world. These exercises should help you gain a better respect for your visual system.

 

Step 1: Trim away excess adipose tissue (yellow material), the extrinsic eye muscles (tan material), and the connective (conjunctiva) tissue (white/clear material).  If you pull with the tweezers you will see the clear connective tissue holding the muscle and fat in place. In this taught position you can simply cut all of the muscle and fat off of the eyeball.

 

Step 2: Draw and color a side view of your eye specimen. Label all of the listed terms.

 

   

    optic nerve

    sclera

    cornea

    pupil

    conjunctiva

 

 

Step 3: Give the function of the five terms you identified.

    optic nerve: _________________________________

    sclera: _____________________________________

    cornea: ____________________________________

    pupil: ______________________________________

    conjunctiva: _________________________________

Successfully dissect, sketch, and identify the deep aspect of the eyeball.

 

Step 1: Puncture the sclera with the tip of the scissors or pointer and cut a circle parallel with the cornea about 1 cm beyond the edge of the cornea and sclera. See the diagram to the right for details.

 

Step 2: Gently tease apart the anterior and posterior portions of the eyeball. The fluid that escapes is the aqueous humor. Be careful not to disturb the fine tissue layer in the posterior section. That is the retina.

 

Step 3: Draw and color the anterior view of your eye specimen. Label all of the listed terms.

 

   

    aqueous humor

    lens

    iris

    cilliary muscles

    pupil

    cornea

 

 

Step 4: Give the function of the four undefined terms you identified.

    aqueous humor: _______________________________________

    iris: _________________________________________________

    lens: _________________________________________________

    cilliary muscles: ________________________________________

Step 5: Draw and color the posterior view of your eye specimen. Label all of the listed terms.

 

   

    vitreous humor

 

    retina

 

    blind spot

 

    tapetum

 

    fovea

 

    choroid coat

 

 

 

Step 6: Give the function of the six terms you identified.

    vitreous humor: _________________________________

    retina: _________________________________________

    blind spot: ______________________________________

    tapetum: _______________________________________

    fovea: _________________________________________

    choroid coat: ____________________________________

 

Successfully dissect, sketch, and identify the lens.

Dissect out the lens so it is separate from all other tissue. Use the scalpel to cleanly bisect the lens. Draw a sketch below of what you find.

 

   

 

 

 

 

rmorrissette@palomar.edu