Download Reaction Time and Reflexes – Lab #11 - Science-with

Reactions versus Reflexes Lab
Name:
Background: Have you ever had to react to a situation where something was flying at your face? If so,
you probably used two of our body’s most important – as well as fastest – mechanisms for protecting
your eyes: reflexes and reactions. You automatically closed your eyes as the object approached and
you may have ducked your head out of the way.
Closing your eyes automatically is a reflex. A reflex is an autonomic (or involuntary) response to a
stimulus that helps to protect the body from injury. Reflexes are very rapid and of short duration since
they do not rely upon the brain for “decision making”. This entire “decision” to react occurs in the
spinal cord or brain stem.
Other types of reflexes happen all the time. In fact, your last visit to the doctor probably involved one.
When struck just below the knee with a small hammer, your lower leg “kicks” up to protect the
ligaments inside the knee capsule and to keep your quadriceps from being stretched too far. If you pick
up something very hot, you may drop it to prevent a serious burn. All of these are examples of reflexes.
Ducking your head out of the way is a reaction. A reaction is a somatic (voluntary) response to a
stimulus. This decision involves the brain and requires the brain to make a decision about what your
response will be. A reaction is the deliberate or voluntary changing of the body’s position to respond to
the stimulus. Reactions may also be very quick and of short duration, but they aren’t always.
Purpose: the purpose of this laboratory experience is:

to understand the difference between a reflex and a reaction

to demonstrate some human reflexes

to be able to calculate your reaction time
Procedure:
Patellar or Knee Jerk Reflex
1.
The subject is to sit on the edge of the lab table with the legs able
to swing freely. (One partner will be the subject first and the
other partner the tester, then you’ll switch.)
2.
Once the legs are relaxed and swing freely, the tester should use
the side of their hand to “tap” the subject just below the kneecap.
What happened? Record your results in the data table.
3.
Now have the person sit with their leg straight out. Tap the
knee in the same place. Observe and record your results.
4.
Switch places with your partner and repeat steps 1-3.
Record the data for both partners in your data table.
Papillary Reflex
5.
Have the subject close his or her eyes for one minute (no peeking). After one minute, stare into
the subject’s eyes and tell him/her to open his/her eyes. Observe and record what happens to
the pupils.
6.
After the subject has been tested switch places and repeat with the partner.
Babinski’s Response
7.
Have the subject remove one shoe and sock. Have the subject sit on the lab table with his/her
foot extending just over the edge. Using a pen cap or fingernail, the experimenter is to scratch the
subject’s foot in one smooth stroke motion from toe to heel.
8.
Describe the response in the toes in your data table.
9.
After the subject has been tested switch places and repeat with the partner.
Blink Reflex
10.
Have the subject hold a sheet of clear plastic (transparency) in front of their face. Crumple up a
small piece of paper and toss it toward their eyes. Observe what happens and record your data.
11.
After the subject has been tested switch places and repeat with the partner.
Table 1. Data for Reflex Testing:
Stimulus
Knee Tap
(bent leg)
Knee Tap
(straight leg)
Pupil Response to
Light
Touching toe to heel
Object thrown towards
face
My Response
Partner’s Response
Procedure for Reaction Time:
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 the meter stick traveled to where the thumb meets the stick. Repeat the trial three more
times and record your data.
3.
Switch roles and repeat steps 1 and 2.
4.
Determine the average distance that the meter stick fell for all of the trials. Using that average,
calculate the TIME it took for you to react and grab the ruler using the equation on the next page.
Table 2. Data for Reaction Time:
Trial
Distance (cm) of fall
Mine
Partner
Calculation of Reaction Time
t=(2d/a)
1
2
3
4
Average
Where…
t = reaction time
d = average distance of fall
a = acceleration due to gravity = 980 cm/s2
Conclusion:
1.
In the space below calculate your reaction time and your partner’s reaction time. Show your
work for each.
Mine:
Partner’s:
2.
Why doesn’t the patellar reflex happen when your leg is straight?
3.
How does the patellar reflex protect us? How does the papillary response prevent injury? What
would happen without it?
4.
Why is the blinking response effective? What kind of job would you have where you used this
reflex quite often?
5.
What kind of job would you have where you would want to stop the blinking response?
6.
Name three sports or occupations where having a fast reaction time is important.
7.
Give three examples of things that could slow down your reaction time or reflexes.
8.
Say that a person catches a meter stick very slowly when their hands are cold. If that person was
able to average catching the meter stick at 93 cm, what is their reaction time? Show your work
below.
APPENDIX #1
SECTION 1: REFLEXES AND REFLEX ARCS
Nerve impulses follow routes through the nervous system called nerve pathways. Some of the
simplest nerve pathways consist of little more than two neurons that communicate across a single
synapse.
Reflexes are rapid, involuntary responses to stimuli, which are mediated over simple nerve pathways
called reflex arcs. Involuntary reflexes are very fast, traveling in milliseconds. The fastest impulses
can reach 320 miles per hour.
Reflex arcs have five essential components:
1. The receptor at the end of a sensory neuron reacts to a stimulus.
2. The sensory neuron conducts nerve impulses along an afferent pathway towards the CNS.
3. The integration center consists of one or more synapses in the CNS.
4. A motor 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).
Reflexes can be categorized as either autonomic or somatic. Autonomic reflexes are not subject to
conscious control, are mediated by the autonomic division of the nervous system, and usually involve
the activation of smooth muscle, cardiac muscle, and glands. Somatic reflexes involve stimulation of
skeletal muscles by the somatic division of the nervous system.
Most reflexes are polysynaptic (involving more than two neurons) and involve the activity of
interneurons (or association neurons) in the integration center. Some reflexes; however, are
monosynaptic ("one synapse") and only involve two neurons, one sensory and one motor. Since there
is some delay in neural transmission at the synapses, the more synapses that are encountered in a
reflex pathway, the more time that is required to effect the reflex.
SECTION 2: THE IMPORTANCE OF REFLEX TESTING
Reflex testing is an important diagnostic tool for assessing the condition of the nervous system.
Distorted, exaggerated, or absent reflex responses may indicate degeneration or pathology
of
portions of the nervous system, often before other signs are apparent.
If the spinal cord is damaged, then reflex tests can help determine the area of injury. For example,
motor nerves above an injured area may be unaffected, whereas motor nerves at or below the
damaged area may be unable to perform the usual reflex activities.
Closed head injuries, such as bleeding in or around the brain, may be diagnosed by reflex testing.
Remember that the oculomotor nerve stimulates the muscles in and around the eyes. If pressure
increases in the cranium (such as from an increase in blood volume due to brain bleeding), then the
pressure exerted on CN III may cause variations in the eye reflex responses.
SECTION 3: SPINAL REFLEXES
The spinal cord provides a major pathway for ascending and descending neural tracts. In addition to
this function, the spinal cord functions as the integration center for many reflexes. These are called
spinal reflexes because their arcs pass through the spinal cord.