Reflex Arc Lab
Name: AbdulhamitTANRISEVEN
Purpose
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To study the simplest functional unit of the nervous system: the reflex arc.
Materials
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ruler, glass rod, piece of paper, nail, flashlight, piece of paper with writing on it, beaker
Method : For the duration of this lab students should work in pairs
Patellar (knee-jerk) Reflex
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Have the subject sit on the edge of a table with one leg dangling freely. Strike the tendon just
below the knee-cap with the edge of a ruler
Record the results in your lab book
The leg rised 2-5 cm when we hit on tendon with edge of ruler.
Uvular Reflex
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Have the subject open his/her mouth widely and touch the uvula with a clean Q-tip.
Record the results in your lab book
Of what value is this response to humans?
When person touched on the uvula, other one felt likely to vomit.
Pupillar Reflex
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Have the subject close his/her eyes for 2 minutes
Observe the pupils of both eyes as they open their eyes and record the response.
Explain the results in your lab book
Place a piece of paper along the bridge of your subject’s nose, Shine light only into the left eye
using a small flashlight
Observe the pupils of both eyes as they open their eyes and record the response.
Explain the results in your lab book
What could happen if this reflex did NOT exist?
When the person kept his eyes closed for two minutes, his pupils got smaller.
But the left pupil get smaller size when the light shone on that eye.
When we Place a piece of paper along the bridge of his nose and Shine light only got into the left
eye, the observation is that left pupil is smaller than the right one.
If it is not exist, we cannot adapt the changing condition any time and excess light could enter the
eye and damage it.
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a) Accomodation Reflex
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Focus both eyes on the tip of a pencil held at eye level and at arm's length. While focussing on the
pencil tip, indicate whether or not the objects in the background are in focus.
Keeping the same line of sight, focus on the objects in the background. What happens to the image
of the pencil tip.
When we focus on tip of the pencil, rest of the visuals cannot be seen clearly. Also , when we
focus on other background, this time the pencil tip cannot be seen clearly.
b) Near Point vision (The distance from the eye to the nearest object that can be focussed on clearly)
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Cover one eye, and focus on a piece of paper with writing on it. Gradually bring the paper closer
and closer to your eye until the letters just go out of focus.
Have your partner measure the distance (in cm) between the paper and your eye in your lab book
Repeat these last two steps with the other eye.
Record the near point for both eyes.
Give a physiological explanation for what has occurred in both parts of this experiment.
Why can a person not see objects clearly when they are positioned closer to the eye than the near
point?
What happens to the near point as a person ages? Why does this occur?
When cover one of eye and focus on a writing that is coming closer to that eye,
the eye can’t read the writing clearly.
The distance between the eye and the paper is almost 3 cm and same for each eye.
This is because after the near point the lens of eye cannot bend the light enough
and focus on the object anymore.