PYSO 1: Lab 4ALAB 4A NERVOUS SYSTEM:

SENSORY PHYSIOLOGY

READING in HUMAN PHYSIOLOGY, 7th Edition, Silverthorn.2-point discrimination: pp. 310-313Touch receptors: pp. 319-321Hearing pp. 329-336Equilibrium pp. 337-8Vision: pp. 340-352

OBJECTIVES1. Perform two-point discrimination to demonstrate that areas of the body vary in sensitivity2. Describe the relative density of touch and temperature receptors on the skin 3. Identify the “blind spot” and test visual acuity, astigmatism, binocular vision, color blindness4. Investigate the presence of afterimages5. Explore the complex receptors of the ear by testing hearing and equilibrium

The nervous system is responsible for coordinating body function to maintain homeostasis. To do this, an organism must be able to recognize various stimuli and respond appropriately. A stimulus is perceived by a receptor, which sends an electrical message along sensory afferent neurons to the CNS where integration occurs in either the spinal cord or brain. Motor output travels along efferent neurons to effectors that cause a response. In this lab (4A) you will investigate some general and special senses. In Lab 4B, you will explore somatic and autonomic reflexes.

Sensory Physiology – General & Special Senses

Sensory physiology encompasses both conscious and subconscious processing. The five “special” senses (sight, hearing, taste, smell, and equilibrium) typically mentioned, fall under conscious control. The lesser known conscious senses include the “somatic” senses (touch-pressure, temperature, pain, and proprioception). The subconscious senses include somatic stimuli and visceral stimuli. Somatic stimuli include muscle length and tension or force. Whereas, the visceral stimuli include: blood pressure, pH and O2 content of blood, pH of cerebrospinal fluid, lung inflation, osmolarity of body fluids, temperature, blood glucose, and distention of the gastrointestinal tract.

In general, afferent sensory pathways begin by sensing a stimulus (external or internal) via a sensory neuron. The sensory receptor transduces or changes the signal to an electrical graded signal. If the

signals are strong and frequent enough, the neuron will reach threshold and produce action potentials. In response, the central nervous system (CNS) will tell the efferent motor neuron to have an appropriate action.

There are several ways in which classification of sensory receptors is done. For example, some divide the receptors into structural, regional, or functional. Receptors can have very simple, widely dispersed sensor organs such as the tactile (touch) corpuscles of the skin, to highly complex organs, such as the eyes and ears. Receptors may also detect stimuli from far off distances (eyes, ears, nasal membrane, etc.) to within the body itself (mechanoreceptors, chemoreceptors, baroreceptors, etc.).

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PYSO 1: Lab 4A

This lab will help us understand/ demonstrate the following sensory terms and concepts: Proprioreceptors : A somatic sensory receptor activated by movement of the limbs Nociceptor : A receptor that detects painful stimuli Chemoreceptor : Responds to chemicals that bind to the receptor such as O2, pH, and glucose Mechanoreceptor : Responds to mechanical stimuli such as pressure, vibration, and sound Receptive Field : The area that each neuron can receive information on, which may vary in shape

and overlap with neighboring receptive fields Transduction : The conversion of a stimulus energy into a change in membrane potential Threshold : The minimum amount of depolarization needed to trigger an action potential Accommodation : Process in which the eye adjusts the shape of the lens to keep objects in focus Two-point Discrimination : In some regions of skin, for example the arms and legs, two pins placed

within 40 mm of each other will be interpreted by the brain as a single pinprick; this is an example of a large receptive field, with many 1° neurons converging on a 2° sensory neuron.

Activity 1: Determining 2-point Threshold Using an Esthesiometer

The density of touch receptors in some parts of the body is greater than in other parts; therefore, the areas of the sensory cortex of the brain that correspond to different regions of the body are of different sizes. Those areas of the body that have the largest density of touch receptors also receive the greatest motor innervation; the areas of the motor cortex of the brain that serve these regions are correspondingly larger than other areas. A map of the sensory and motor areas of the brain therefore reveals that large areas are devoted to the touch perception and motor activity of the face and hands, whereas smaller areas are devoted to the trunk, hips, and legs.The density of touch receptors is measured by the two-point threshold test. The two points of a pair of adjustable calipers (esthesiometer) are simultaneously placed on a subject's skin with equal pressure, and the subject is asked if two separate contacts are felt. If so, the points of the divider are brought closer together, and the test is repeated until only one point is felt. The minimum distance at which two points of contact can be discriminated is the 2-point threshold.

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PYSO 1: Lab 4AProcedure: (One test subject/pair)

1. Starting with the calipers wide apart and the subject's eyes closed, determine the two-point threshold on the back of the hand (i.e. measure distance using calipers). Randomly alternate the two-point touch with one-point contacts, so that the subject will not be able to predict/guess.

2. Repeat this procedure with the face, fingertip, lips, back of neck and anterior forearm.3. Record and discuss the results of your measurements on the data sheet (p. 9).

Activity 2: Relative Density and Location of Touch and Temperature Receptors

Specialized sensory organs and free nerve endings in the skin allow us to feel a variety of sensations including touch and hot and cold temperatures. The type and location of each sensation is determined by the specific sensory pathway in the brain. Sensitivity depends on the density of the cutaneous receptors.

Procedure: (One test subject/pair)1. Draw or use an ink pad to mark a square 4 x 4 cm on the ventral surface of the forearm. 2. With the subject's eyes closed, you will gently and randomly touch at least 30 different points (~10X

with the ice cold, dry probe, ~10X with the warm (45°C), dry probe, and ~10X the thin bristle) on the grid, making sure to vary the order of the hot and cold probes and bristles. As you gently touch the subject, the subject should state whether they perceive the sensation of warm, cold or touch only.

3. Record the results as follows:a. On the grid, mark the points where the subject perceived cold with a blue dot, mark the

points where the subject perceived warm with a red dot, and mark the points where the subject perceived touch with a black dot.

b. In the table, record the number of times the subject was touched with each stimulus and record the number of times that they perceived the correct sensation. Then calculate the percent correct.

Note: If the subject perceives touch only when you use the warm or cold probe, you should record it as touch on the grid and in the table. This would still be considered a correct response for touch, but an incorrect response for that temperature.

4. Evaluate your findings for the density and location of receptor types. See data sheet (p.9-10).

Activity 3: Testing Tactile Localization

Touch localization is the ability to determine where exactly the skin has been touched. Depending on the density and distribution of the receptors, localization varies with body parts. Areas with higher concentrations of touch receptors should be more accurate in pinpointing the spot touched.

Procedure: (One test subject/pair)1. Close eyes and have your lab partner touch the palm of your hand with a pencil (or pen).2. Keep eyes closed. Try to place the eraser of the pencil on the spot touched by your lab partner.3. Have your lab partner measure and record the difference in distance between the two spots. 4. Repeat the steps two more times and average the results. 5. Repeat the experiment on a fingertip, the forearm, and back of neck.6. How do the various regions of the body compare? Record and discuss your results on the data

sheet (p.10)3

PYSO 1: Lab 4AActivity 4: Adaptation of Sensory Receptors

Adaptation is the ability of the sensory system to filter out old information and basically ignore it in an attempt to be prepared for new incoming sensory stimuli. 

Procedure: (One test subject/group)1. Close your eyes and have your lab partner place a coin on the ventral surface of your forearm.  Note

how long it takes for accommodation to occur.  (When do you no longer feel the coin?)2. Record the time in the table on the data sheets.3. After the sensation disappears, add three more coins of the same size on the first coin.  If the

sensation returns, note how long the sensation lasts.4. Record and discuss results in the data sheet (p. 11).

Activity 5: Adaptation of Hot and Cold Temperature Receptors While your brain can filter out certain input, certain types of sensory receptors also play a role in filtering out continuous stimuli. Phasic receptors send bursts of impulses when a stimulus is first applied, but then quickly decrease or stop their firing rate if the stimulation persists. Sensory adaptation refers to the phenomenon in which you stop noticing certain continuous stimulation due to the decreased firing rate of phasic sensory receptors. Since your receptors are no longer sending the impulse to the brain, the brain does not receive the input necessary to create the perception of the stimulus, and therefore you are no longer aware of the stimulus. This phenomenon occurs for receptors that detect odor, touch, temperature and light.

Procedure: (One or more test subjects/pair)1. Place the subject’s right hand in 45˚C water and left hand in cold water ~5˚C for 1-2 minutes. What

happens to the sensation of hot and cold and which hand seems to adapt the fastest? 2. Place both hands in room temperature 25˚C water immediately after removing from the hot and cold.

How does the water feel to each hand? Are receptors for temperature relative or absolute? 3. Record and explain your results on data sheet (p. 11).

Activity 6: Demonstrating the Blind SpotThe optic disc is the area on the retina that lacks photoreceptors and therefore any image that falls on this region will NOT be seen. It is in this region that the optic nerves come together and exit the eye on their way to the brain. To demonstrate this effect, look at the image below (on the following page):

Procedure: (Test individually )

1. Close your left eye. 2. Place your head about 50 cm from the paper. 3. With your right eye, look at the +. Slowly move your head closer while looking at the +. At a certain

distance, the dot will disappear from sight. This is when the dot falls on the blind spot of your retina. 4. Reverse the process. Close your right eye and look at the dot with your left eye. 5. Move slowly closer to the image and the + should disappear. 6. What is occurring when the dot disappears? Answer the questions on p. 11

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PYSO 1: Lab 4A

Activity 7: Testing For Color Blindness

Procedure: (Test individually)1. Test each group member for color blindness. What number (or figure) do you see immediately when

looking at one of the Ishihara plates? Note: If you use the book, you’ll want to begin with panel 3, since the answers and scoring begin there.

2. Look at the key to determine what subjects with normal vision should see. 3. Observe the scribble on the back of the cards to demonstrate the effects of color blindness.4. Now place the plastic filter over the scribble to make the object within the scribble visible.5. What did you learn? Record and explain your results on the data sheet (p. 13-14).

Activity 8: Testing Vision: Visual Acuity, Astigmatism, Near Point Vision , & After-Image

8A. Visual Acuity: Snellen ChartRefraction is the bending of light waves. Light waves entering your eye from a specific point on an object must be focused on a specific point of your retina. If this light is not focused on a particular point, you will not see the image clearly. Your lens and your cornea are the principle parts of your eye involved in refraction of light. Some of the exercises you do will be to investigate this refraction and visual acuity. For instance, Myopia is the condition of near-sightedness. This is usually due to having an eyeball that is a bit too long. Thus, the light waves focus in front of the retina rather than right on it. You can treat this condition with lenses that are concave and pre-bend the light waves. Hyperopia is far-sightedness. You can treat this condition with a convex lens. With hyperopia, the light waves focus behind the retina because the eyeball is too short. The concave lens bends the light a bit more to compensate for the short eyeball.

Procedure: (Test individually) Stand 20 feet from the Snellen chart1. Cover your right eye, and read aloud the letters of each row, beginning at the top.2. The smallest row that can be read accurately indicates the subject’s visual acuity in that eye.3. Repeat the procedure with your left eye and record on the data sheet (p.12).

If you wear contact lenses, you do not need to record “uncorrected” values

8B. Astigmatism: the Spoke Chart5

PYSO 1: Lab 4AAstigmatism is just an abnormality in the surface of your eye (your cornea) or in your lens that causes abnormal refraction of light in one or the other planes. A circular lens can be used to correct astigmatism. Use the circular spoke chart to determine if you have astigmatism.

Procedure: (Test individually) Stand 20 feet from the Snellen chart1. Stand about 10 feet from the astigmatism chart. If you wear glasses, remove them. You may leave

you contacts in if you where them.2. Cover one eye.3. Determine if all of the spokes on the chart are clear or if some are fuzzy and blurred. 4. Repeat this procedure for the other eye. Answer the question on p. 12.

8C. Accommodation and Near-Point Vision TestAccommodation is the ability of your eye to focus on objects that are variable distances from your eyes.

Accommodation is due to the ability of your lens to change shape depending on whether or not the ciliary muscles within the eyeball are contracted. In order to bring distant objects into focus, the ciliary muscles relax, which places tension on the lens, causing the lens to stretch and become thin. In order to bring near objects into focus, the ciliary muscles contract, which reduces tension on the lens and allows the lens to return to a rounder shape. However, as we age, our lens begins to lose elasticity and is no longer able to become round enough to allow for good near point vision. The term for this loss of near point vision with age is presbyopia.Use a meter stick, and the tip of a pen or a pencil to determine your near point vision.

Procedure: (Test individually)A. Obtain a meter stick and place the meter stick at the edge of your desk. Cover one eye and

crouch down next to the meter stick such that the end of the meter stick is under the open eye.B. Hold the tip of a pen or pencil at arm’s length along the meter stick and slowly bring the tip of

the pen or pencil closer. In the table on p. 12, record the distance at which the tip of the pen or pencil becomes blurry.

C. Repeat the test for the other eye. Below are typical near point accommodation results based on age.

Age (years) 10 20 30 40 50 60Near point 7 cm 10 cm 13 cm 20 cm 45 cm 90 cm

Record your data and answer the questions on p. 12.

8D. Afterimages Afterimages are images that continue to persist after you are no longer looking at the original object. Positive afterimages occur when you continue to perceive a bright light after a brief but intense exposure to bright light. A good example would be when someone takes your picture and you continue to see the bright flash even after the camera flash is no longer there. Positive afterimages occur because

it takes photopigments, such as rhodopsin, some time to return to their original 3D conformation, so as long as they remain in the stimulated conformation, the ganglia will continue to fire and send input to the brain even in the absence of the original stimulus.

In contrast, if you stare at an object for a prolonged period of time and then look away, you might experience a negative afterimage, which would be the continued perception of that object but in the different colors than the original object. For instance, have you ever stared at the words on a page for a long time and then glanced away to look at a white wall, and the words and page appear in the opposite colors? With negative afterimages, the rods and cones that have been stimulated for a prolonged period of time begin to sensory adapt and become desensitized, while the rods and cones that were not being

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PYSO 1: Lab 4Astimulated become more sensitive due to lack of stimulation. When you then look away at something that is white, you actually have all of the colors of light refracting off the white object and entering your eye. Even though the stimulus is there, the desensitized rods or cones do not fire, while those that had not been stimulated now do fire. For instance, if you stare at something red, your red cones are working very hard but your blue and green cones are not. In fact, your blue and green cones are becoming more sensitive due to lack of stimulation. If, after starting at a red image for some time, you shift your vision to a white surface of paper, only the ganglia associated with you blue and green cones will fire and the image you will see an image but it will not be red, but instead cyan, since your brain is only receiving input from the ganglia associated with the blue and green cones.

Procedure: After-Image With Colored Squares1. Gather up a few of the colored squares on black backgrounds that are available in the lab.2. Stare at one of the colored squares (start with red) for about a minute. The black paper must be about

1-1.5 feet from your face and you have to look at the red square for about 30 seconds or more for this to work well.

3. Look quickly at a white piece of paper about 1-2 feet away from your face, in the light.4. Record the color of the square that you see on the white piece of paper on p. 13.5. Now do the same experiment with the other colors (blue and yellow) and record the colors you see

when shifting to the white paper.6. Look at the eyes of the cartoon green person for about 20-30 seconds and then shift your gaze to the

white paper again. What color is the image or part of the person you see on the white paper?

Procedure: After-Image With Bright Light1. Look into the light bulb for a second and quickly look away.2. Shift your gaze toward the dark wall and record what you see. (Record on p. 13)

Activity 9: Binocular Vision

Procedure: (One test subject/pair)1. Have your lab partner hold a test tube erect about arm’s length in front of you. With both eyes open,

quickly insert a pencil into the test tube. Remove the pencil, bring it back close to your body, close one eye, and quickly insert the pencil into the test tube. (Do not feel for the test tube with the pencil!) Repeat with the other eye closed.

2. What do you think is the value of binocular vision? Record your results on data sheet (p. 14).

Activity 10: Hearing and Equilibrium

10A. Hearing. The ear serves the body in two important ways, for hearing and for balance. The cochlea, a coiled tube found in the inner ear, receives impulses originating as sound waves from the external environment and changes them into chemical-electrical impulses that are transmitted to the brain and interpreted as sound. The vestibular apparatus, the second part of the inner ear including the utricle, saccule, and semicircular canals, contains complex receptors that are sensitive to changes in the position of the body, changes in linear and rotational acceleration.

DO NOT HIT TUNING FORKS ON THE COUNTERS 7

PYSO 1: Lab 4AUse a rubber mallet or the heal of your hand to vibrate the tuning forks

Frequency Rangelow freq. 128 Hzmedium freq. 512 Hzhigh freq. 4096 Hz

Rinne Test for Comparing Bone and Air Conduction Hearing (Use 512 Hz tuning fork)The Rinne test compares air conduction to bone conduction.

Normal: Air Conduction is better than Bone Conduction. Air conduction usually persists twice as long as bone – referred to as "positive test"

Abnormal: Bone conduction better than air conduction. Suggests Conductive Hearing Loss – referred to as "negative test"

Procedure: (Test individually)1. Hit the tuning fork firmly on the palm of your hand and place the butt of the tuning fork on the

mastoid bone firmly. The test subject should indicate when they can no longer hear the vibration. Record the time (seconds).

2. When this happens, remove the butt of the tuning fork and place the U of the tuning fork approximately 1 inch from the ear without touching it. Have the subject tell you when they can no longer hear anything. Record the time (seconds).

3. Repeat the Rinne test with the other ear.4. Evaluate and record results on the data sheet (p. 14).

10B. Equilibrium: (One or more test subjects/pair) Equilibrium is centered in the three semicircular canals located in each inner ear. These are fluid

filled tubes, with sensory hairs oriented in three planes: horizontal, vertical, and lateral. With any movement in these planes, the cupula surrounding the hairs moves causing distortion of the hairs triggering the nerve impulse. This information is transmitted to the brain so you know that your head is moving and in what plane.

Vision and Balance: Do this away from any edges/corners of desks, etc. that you could fall on. 1. The role of vision in maintaining body balance can be demonstrated by standing erect on one foot

with your eyes open for one minute. 2. Repeat the same procedure, but with your eyes closed. 3. What difference do you note? EXPLAIN. Answer questions on data sheet (p. 14).

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PYSO 1: Lab 4ANAME: Frankie Guevara LAB PARTNERS: Christy Balderrama

LAB DAY & TIME: Monday 7:00-10:10AM

Lab 4A: Sensory Results & Questions Worksheets(to be turned in as a GROUP or in PAIRS – check w/your instructor)

Activity 1: Determining 2-Point Threshold (from pp.2-3)

1. Record your measurements in the table below:

Body AreaTested

Two PointThreshold (mm)

Back of Hand 15mmFingertip 0mm

Back of Neck 23mmAnterior Forearm 18mm

a) Which area was most sensitive to the test? Are these results expected?The most sensitive area to the test was my fingertip. Based on these results, they are expected since my fingertips have a small area. There wasn’t much room on my fingertips for the two-point threshold to be precise.

b) For a relatively SMALL 2-point threshold, you would expect that the density of sensory receptors in that area would be relatively (high or low?) high, and the proportion of the somatosensory cortex in the brain devoted to perception for that part of the body would be relatively (large or small?) small.

c) Explain why it is, that at a certain distance between the two points, you perceive the two points as a single point rather than as two distinct points.

The certain distance between the two points are perceived to be two points as a single point rather than as two distinct points because

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PYSO 1: Lab 4A

Activity 3: Testing Tactile Localization (from p.3)

a) How do the various regions of the body compare? (i.e. Which body part showed the most accurate tactile localization (lowest error) and which showed the least accurate tactile localization (greatest error)?)

Comparing the palm of the hand and fingertips to the anterior forearm and the back of the neck there is a huge difference. The body part that showed the most accurate tactile localization was the fingertip and the least accurate tactile localization was the anterior forearm.

b) Explain why there were differences in error in one body part versus another.There is a difference in error from one body part versus another because of the receptors that are found in each. The receptors all responded to being poked by a marker/pen, but when the portion of the brain, specifically the parietal lobe responded to the sense of touch/pain for each body part it responded differently since visual perception plays a key role in determining where exactly since it is a big area (body part).

c) Explain what adaptation is and what is occurring here.

Adaptation is the process of adapting or an adjustment to a stimulus and their effects. In this activity, we were testing tactile localization in four different locations on the body. The stimulus is being poked by a pen/marker and the test subject adapting by being able to figure out where specifically the stimulus was. In the environment, this would help an organism survive because it would easily adjust in ecological, social, or economic systems.

Activity 5: Adaptation of Hot and Cold Temperature Receptors (from p.4)

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Body Area Tested Error (mm)Test One

Error (mm)Test Two

Error (mm)Test Three

Average Error (mm)

Palm of Hand 7 9 9 8.33Fingertip 4 1 1 2Anterior Forearm 19 12 22 17.67Back of Neck 17 11 15 14.33

PYSO 1: Lab 4A

5. Fill in the table and answer the questions below:

a) What happens to the sensation of hot and cold over time and which hand seems to adapt the fastest?

The sensation of hot and cold over time differed because my right hand could quickly adapt, however, my left hand upon immersion started to tingle and after 1 minute I felt a lot of discomfort.

b) From a physiological perspective, why does the sensation begin to fade?From a physiological perspective, the sensation begins to fade away because the body is trying to maintain homeostasis by getting to a normal temperature that goes with the outside of the environment.

c) When placed in room temperature water (25˚C) after removing from the hot and cold water baths, how did the water feel to each hand? Are receptors for temperature relative or absolute? Explain.

After removing my hands from both water baths and placing them in room temperature water my right hand tingled, but my hand felt a little cold while my left hand felt a little cold. The receptors for temperature are relative because the body tries to maintain homeostasis with the outside environment.

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Time of Observation Right Hand 45˚C

Quality of SensationLeft Hand 5˚C

Quality of SensationOn

immersionHand felt fine and quickly

adaptedHand became cold and it did

not adaptAfter

1 minuteHand felt fine Hand began to hurt and did

not adaptAfter

2 minutesHand felt fine Hand hurt and felt like a bit

numb Immersion in Room Temp

Hand was tingling a little bit but there was no discomfort and it felt

a little cold.

Hand felt cold and tingled but it felt warm.

PYSO 1: Lab 4A

Activity 6: Demonstrating the Blind Spot (from p.4)

6. Answer the questions regarding the blind spot. a) At what distance (cm) does the dot disappear? Left eye: ~25cm Right eye: ~25cm

b) What is occurring when the dot disappears? In your explanation, include the anatomical term for the part of the eye responsible for the phenomenon and describe why this anatomical part causes this effect.When the dot disappears, the image has reached a point in the eye where the image is obscured. The part of the eye that obscures the image is the optic disk or the optic nerve head within the retina. There are no photoreceptors in the optic disk and therefore there is no image detection in this area. The brain sometimes must fill in what is there by looking at the surrounding area.

Activity 7: Testing for Color Blindness (from p.5)7. Fill in the table below and answer the questions about color blindness.

Number or Figure seen

12 29 3 74 45

“Normal” Actual Number

or Figure

12 29 3 74 45

a) Use the booklet or information sheet to interpret your results. What did you learn?Based on the information sheet, reading 10 or more plates read normally (for this test only 5 were recorded), the color vision is regarded as normal.

b) Is anyone in the group color blind? What causes color blindness?

When the test was conducted in with the rest of the group, everyone had was read as normal. Color blindness is usually inherited. People usually have three types of cone cells in the eye. Each type senses either red, green, or blue light. You see color when your cone cells sense different amounts of these three basic colors. The highest concentration of cone cells is found in the macula, which is the central part of the retina. Inherited color blindness happens when you don't have one of these types of cone cells or they don't work right.

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PYSO 1: Lab 4A

Activity 8: Testing Vision (from p.5-6)8A. Visual Acuity Snellen Chart: Fill in the table and answer the questions below about visual acuity.

a) What do the two numbers in an acuity test mean (interpret the values for uncorrected vision)?20/15 vision is better than 20/20. A person with 20/15 vision can see objects at 20 feet that a person with 20/20 vision can only see at 15 feet. The test subject did not have any uncorrected.

b) Are you myopic in either eye? Explain what causes myopia.I am not myopic in either eye. Myopia is the condition of near-sightedness. This is usually due to having an eyeball that is a bit too long. This the light waves focus in front of the retina rather than the light on it.

8B. Astigmatism: Spoke Chart a) Does anyone in the group have astigmatism? What is the cause of astigmatism?

No one is the group has astigmatism. Astigmatism is just an abnormality in the surface in the eye (cornea) that causes abnormal refraction of light in one or other planes.

8C. Accommodation and Near Point Vision Test Record the values for your near point vision test in the table below:

a) What happens to the ciliary muscles and consequently what happens to the lenses of your eye when you are trying to focus on an object that is close to your face?

The ciliary muscles essentially undergo accommodation which is due to the ability of your lens to change shape depending on whether the ciliary muscles within the eyeball are contracted. To bring distant objects into focus, the ciliary muscles relax, which places tension on the lens, causing the lens to stretch and become thin. But, to bring near objects into focus, the ciliary muscles contract, which reduces tension on the lens and allows the lens to return to a rounder shape.

b) Refer to the typical near point accommodation results on p. 6. Why do the near point vision values increase with age?

As we age, our lens begins to lose elasticity and is no longer able to become round enough to allow for good near point vision. The term for this loss of near point vision with age is presbyopia.

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Visual AcuityUncorrected

Left Eye Right Eye Both Eyes

Visual AcuityCorrected

Left Eye20/15

Right Eye20/15

Both Eyes20/15

Near Point Vision,

Uncorrected (mm)

Left Eye10cm

Right Eye12cm

PYSO 1: Lab 4A

8D. Afterimages (from p. 6)a) What color square did you see on the white paper immediately after prolonged exposure to:

Red square on the black background? Blue

Blue square on the black background? White

The little green man? White

b) Are these examples of positive or negative after-images? EXPLAIN at the physiological level what is occurring to produce the afterimage when you look at the white paper or screen after staring at the GREEN MAN. Be very specific!

These are examples of negative after images, however the other results do not show a result. It may be that we did not conduct the experiment correctly. With negative afterimages, the rods and cones that have been stimulated for a prolonged period begin to sensory adapt and become desensitized, while the rods and cones that were not being stimulated become more sensitive due to lack of stimulation. When you then look away at something that is white, you have all the colors of light refracting off the white object and entering your eye.

c) Was the image you saw after looking into the light bulb a positive or negative after-image?

The image I saw after looking into the light bulb for one of the three images was a negative after-image.

d) EXPLAIN at the biochemical level the cause of this type of afterimage. At a biochemical level the cause of this type of afterimage was that if you stare at something red, your red cones are working very hard but your blue and green cones are not meaning when looking at a white paper are the only ones firing off.

Activity 9: Binocular Vision (from p.7)9. Answer the questions below about binocular vision.

a) Discuss your observations.

When doing the test with both eyes open it was easy to quickly put the pencil into the tube however, with one eye closed it was more difficult because of a smaller field of view that didn’t allow the eyes to have a great depth perception and ability to distinguish the distance.

b) Why might binocular vision be an important adaptation?

Healthy binocular vision produces important visual perceptual skills which are part of normal human vision; the advantage of much greater depth perception, or the ability to distinguish the distance of an object.

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PYSO 1: Lab 4A

Activity 10: Hearing and Equilibrium (from pp. 7-8)10. Answer the questions below about hearing and equilibrium.

a) Rinne Test Comparing Bone and Air Conduction Hearing

Bone conduction time (sec): Left ear: 15 seconds Right ear: 15 seconds

Air conduction time (sec): Left ear: 28 seconds Right ear: 33 seconds

b) Explain why a person with conduction deafness hears the tuning fork better when it rests against the mastoid process than when it is held close to the ear.

A person with conduction deafness hear the tuning fork better when it rests against the mastoid process than when it is held close to the ear because the being that the mastoid process is located under the ear it is also connected to the middle ear. The middle ear transmits sound from the outer ear to the inner ear.

c) What parts of the ear can be affected to cause conduction deafness?Conductive hearing loss occurs when there is a problem conducting sound waves anywhere along the route through the outer ear, eardrum, or middle ear.

Equilibrium – Vision and Balance d) What difference was observed in balance when eyes were open vs closed? Explain results.

Eyes opened on one foot- 2 minutes (2 mins being the maximum)Eyes closed on one foot- 18 seconds

The difference between balance when eyes are close and open is that to maintain balance, the human body relies on three different systems. Your eyes are intrinsic to your sense of balance and spacial awareness. So when I closed my eyes my spacial awareness was taken away and since the brain uses input from these sensors to enable us to balance so by closing your eyes you’re restricting the amount of information that the brain can use to balance.

Note: See instructor for specific activities your class will be covering – some may not be covered

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