Human Anatomy & Physiology
Influencing Reactions & Reflexes Lab
Name _________________________________
Background: A reflex is an autonomic response to a perturbing stimulus that acts to return the body to
homeostasis or balance. This may be subconscious as in the regulation of blood sugar by the pancreatic
hormones, may be somewhat noticeable as in shivering in response to a drop in body temperature; or may be
quite obvious as in stepping on a nail and immediately withdrawing your foot.
A reflex arc refers to the neural pathway that a nerve impulse follows. The reflex arc typically consists of five
components (3):
1. The receptor at the end of a sensory neuron reacts to a stimulus.
2. The sensory (afferent) neuron conducts nerve impulses along an afferent pathway towards the central
nervous system (CNS).
3. The integration center consists of one or more synapses in the CNS.
4. A motor (efferent) neuron conducts a nerve impulse along an efferent pathway from the integration center
to an effector.
5. An effector responds to the efferent impulses by contracting (if the effector is a muscle fiber) or secreting a
product (if the effector is a gland).
Many people consider only the simplest types of responses "reflexes". Those that are always identical and do
not allow conscious actions. These shouldn’t be confused with "reactions", which are different from reflexes in
that they are voluntary responses to a stimulus from the environment. For example, while you may shiver from
the cold which is a reflex, you may also react to the cold. You could jump up and down to get warm, rub your
arms vigorously or put on more clothes. These are all reactions requiring decision making by the brain. Spinal
reflexes only travel to the spinal cord and back which is a much shorter distance. Because of this and the
complexity of conscious reactions, reactions take more time to complete than a reflex. On average, humans
have a reaction time of 0.25 seconds to a visual stimulus, 0.17 for an audio stimulus, and 0.15 seconds for a
touch stimulus. Reaction times vary from individual to individual. Because of the higher degree of neural
processing, reaction times can be influenced by a variety of factors, especially the number of neurons or
synapses involved. Reaction times can decrease with practice, as often times athletes have faster reaction
times than non-athletes. Sleepiness, emotional distress, or consumption of alcohol can also impact reaction
time.
Purpose:
The purpose of this lab is to see if we can influence reflex and reaction times by varying the conditions of the
testing.
Procedure:
1. Patellar Reflex: While your lab partner sits on the counter with legs dangling, use the side of your hand to
“tap” the subject just below the kneecap. Do this 3 times and watch how quick and how strong (far) the patellar
response is.
2. Patellar Reflex with Mental Distraction: This time have your partner count backwards from 99 by twos
(99, 97, 95, etc) while you perform the knee-jerk test. Do it 3 times and compare the reaction to when s/he was
not counting backwards. Was it faster, slower or the same? Stronger, weaker or the same?
3. Patellar Reflex with Muscle Strain (Jendrassik’s maneuver): This time have your partner lock his/her
fingers together and strain to pull them apart while you perform the knee-jerk test. Do it 3 times and compare
the reaction to the first 2 patellar tests. Was it faster, slower or the same? Stronger, weaker or the same?
4. Patellar Reflex with Iced Quadriceps: Before doing the last patellar test, have your lab partner sit with a
bag of ice on their quadriceps for 7 minutes. Then perform the knee-jerk test 3 times and compare it to the
other three patellar tests. Was it faster, slower or the same? Stronger, weaker or the same?
5. Complete the data table by ranking which patellar test was the strongest and quickest reaction. Then switch
places with your partner and repeat the 4 tests.
Data for Patellar Reflex Testing:
Stimulus
My Response
Partner’s Response
Involuntary or regular
patellar test
Patellar Reflex with
mental distraction
Patellar Reflex with
muscle strain
Patellar Reflex with
iced quadriceps
Ranking of Patellar Reflexes:
Stimulus
Involuntary or regular
patellar test
Patellar Reflex with
mental distraction
Patellar Reflex with
muscle strain
Patellar Reflex with
iced quadriceps
Strongest = 1
Weakest = 4
Fastest = 1
Slowest = 4
Procedure for reaction time with visual stimulus:
1. Have the subject sit comfortably with their forearm resting on a desk. With their index finger and thumb
about two inches apart. Hold a ruler at the 30 cm end and have the “zero” (0 cm) mark lined up
between your partner’s finger and thumb.
2. Without warning, release the ruler and have them grasp it as quickly as they can. Record the distance
in the data table. Repeat the trial and record your data.
Procedure for reaction time with auditory (sound) stimulus:
3. Now repeat this test, but at the same time you release the ruler, say “now”. Run this test 2 times and
record the distance in the data table.
Procedure for reaction time with kinesthetic (touch) stimulus:
4. Repeat this test again, but at the same time you release the ruler, touch your partner’s shoulder. Run
this test 2 times and record the distance in the data table.
5. Switch roles and repeat all three reaction tests.
6. Determine the average distance that the meter stick fell for all of three tests. Using that average,
calculate the TIME it took for you to react and grab the ruler using the equation provided.
Data for Reaction Time:
Trial
Reaction for
visual cue
(mine)
Reaction for
audio cue
(mine)
Reaction for
kinesthetic
cue (mine)
Reaction for
visual cue
(partner)
Reaction for
audio cue
(partner)
Reaction for
kinesthetic
cue (partner)
1
2
Average
Questions:
1. List two differences between reflexes and reactions:
2. Which patellar reflex was the strongest? Which patellar reflex was the fastest? Give a reason why
these reflexes might be the strongest and fastest:
Strongest =
Reason why:
Fastest =
3. Which patellar reflex was the weakest? Which patellar reflex was the slowest? Give a reason why these
reflexes might be the weakest and slowest:
Weakest =
Slowest =
Reason why:
4. What purpose or influence did the three factors have on the patellar testing?
Mental distraction:
Muscle strain:
Iced quadriceps:
5. Calculation of Reaction Time
t=(2d/a)
Where:
t = reaction time
d = average distance of fall
a = acceleration due to gravity = 980 cm/s2
Use the equation above to calculate your 3 reaction times and your partner’s 3 reaction times:
Mine:
Visual
Audio
Kinesthetic
Partner’s:
Visual
Audio
Kinesthetic
5. Which stimulus did you have the fastest reaction to? Which did your partner react the fastest to?
6. Which stimulus did you have the slowest reaction to? Which did your partner react the slowest to?
7. On average, people react the quickest to touch (.15 seconds average) and the slowest to visual (.25
seconds average). While audio is in the middle with an average of .17 seconds. Do you fit this pattern?
Does your partner fit this pattern? Explain
8. Why might visual stimulus be the slowest on average?
9. Why might kinesthetic or touch be the fastest on average?
10. Think about your favorite classes or lessons. Do you prefer a class where you just listen to the teacher,
read material yourself or get up and do things? Is there any connection between how you like to learn
and your reaction times?