[ad_1]
Nerve reaction and reflexes Lab Exercise Name___________________________
Adapted and modified from backyardbrains.com
https://backyardbrains.com/experiments/reactiontime
The speed of your reactions play a large part of your everyday life. Fast reaction times can produce big rewards. For example, a goalie must react fast to saving a speeding soccer ball from entering the goal. Having slow reactions to stimuli may have big consequences such as losing the match for the team or in real life for all of us, an automobile accident.
Reaction time is a measure of the quickness an organism responds to some sort of stimulus. You also have “reflexes” too. Reflexes and reactions, while seeming similar, are quite different. Reflexes are involuntary, used to protect the body, and are faster than a reaction. Reflexes are usually a negative feedback loop and act to help return the body to its normal functioning stability, or homeostasis. The classic example of a reflex is one you have seen at your doctor’s office: the patellar reflex.
This reflex is also known as a “reflex arc”. It is a negative feedback circuit that is comprised of three main components:
- A sensory component or afferent neuron. These neurons take in information and translate it to an electrical signal that gets sent to the central nervous system, much like the spikes you hear when doing the cockroach leg experiments.
- Integrating center or interneuron. These neurons act as sensory processing centers that determine the magnitude of the response to the incoming stimulus. They are located in the central nervous system (your spinal cord).
- The efferent portion or motor neuron takes the information from the interneuron and sends it to the effectors which activate a response. The effectors are usually muscle fibers as in the patellar reflex or a gland such as the salivary gland.
The knee reflex arc is a spinal reflex, and the circuit is drawn above. This picture shows how the sensory (afferent) neuron sends information through the dorsal root ganglion into the spinal cord; where the signal splits into two different paths. The first is the motor neuron (efferent) leading back to the quadriceps. When your quad muscle’s motor neuron receives the information it fires and causes your lower leg to spring forward up in the air. The second signal from the sensory neuron travels to an interneuron which sends a signal to the motor neuron (efferent) leading to the hamstring. This signal tells your hamstring to relax so there is no negative force acting on the quadriceps muscle when it contracts. Both signals work together and all of this happens in the spinal cord without going to the brain. It never needs the brain.
You may be asking how a knee reflex arc and a soccer player dealing with an oncoming ball are different. Are both not reflexes? While it may seem that a soccer player negotiating an oncoming ball is a simple fast reflex, it is actually a symphony of hundreds of thousands of neurons working together to produce a conscious decision. Does the player catch, dodge, or bat away the ball? This choice is what makes a reaction.
When a soccer player realizes the ball is blistering towards him, there is visual information that has to be processed and decisions regarding a correct course of action. The brain then needs to send many signals to various muscles. Feet begin to move, hands might travel in front of the face, and eyes may close shut, along with many more processes. This is the work of many neurons as well as numerous systems and circuits in the brain, and what’s more, you can train and enhance your skill through practice. This is how you get better at sports over time.
Like all science, the history of the reaction time discovery is peculiar. Dutch physiologist F.C. Donders in 1865 began to think about human reaction time and if it was measurable. Prior to his studies scientists thought that human mental processes were too fast to be measured. This assumption was proved incorrect with the help of Charles Wheatstone, an English scientist and inventor. In 1840 Wheatstone invented a device, much like his early telegraph system invention, that recorded the velocity of artillery shells. Donders used that device to measure the time it took from when a shock occurred on a patient’s foot until when that patient pressed a button. The button had to be pressed by the left or right hand matching the left or right foot that was shocked. His study tested 2 conditions: in the first, the patient knew in advance which foot was to be shocked; in the other condition, the patient did not know. Donders discovered a 1/15 second delay between patients who knew which foot was to be shocked versus patients that did not know. Notably, this was the first account of the human mind being measured!
Procedure
This experiment will be broken into two phases. The first test will use one ruler or meter stick (or if you don’t have one, use a folded sheet of paper with one-centimeter increments drawn from 0-30cm), while the second test will use two.Each exercise will be conducted three times: First as a baseline control and second using a cold-water bath (ice cold)and warm-water bath (like warm bath water temperature).You will need to find a partner for the activity (ask relative or sibling or friend or classmate to assist).
Experiment 1: In this phase you and your partner will test visual, auditory, and tactile reaction times using one ruler as shown below (or sheet of paper if you do not have a ruler).
Demonstration | Nerve conduction speed test
Visual Test
- Subject one (You) will rest the forearm of your dominant hand with your hand projecting off the edge of a table (see diagram above).
- Subject two (Your partner) holds a 30-centimeter (12 inch) ruler between two fingers at the 30 cm mark, having the 0 mark touching subject one’s index finger.
- Subject two tells subject one to grab the ruler as fast as possible, when they SEE it being released.
- Record the centimeter measurement (the distance the ruler fell).
- Repeat this three times, for a total of four measurements
- If you want, you may switch places with your partner and redo the above exercise.
In the table on the next page, record your resultsand then repeat entire activity after your hand was in an ice water bath for 1 minute; and then again after hand was in warm water for 1 minute.
| Subject | Visual (cm)
Control |
Ice water (cm) | Warm Water Bath (cm) |
| Average (cm) | |||
| Average (seconds) |
Auditory Test (similar to the above test except close you should have your eyes closed).
- Subject one has eyes closed before dangling dominant hand off the edge of a table.
- Subject two holds a 30 centimeter (12-inch) ruler between two fingers at the 30 cm mark, having the 0 mark touching subject one’s index finger.
- Subject two tells subject one to grab the ruler as fast as possible, when they HEAR the word “release” being said.
- Subject two simultaneously says “release” and lets go of the ruler. Record the centimeter measurement.
- Repeat this three times, for a total of four measurements and then repeat entire activity after your hand was in an ice water bath for 1 minute; and then again after hand was in warm water for 1 minute.
| Subject | Auditory (cm)
Control |
Ice water (cm) | Warm Water Bath (cm) |
| Average (cm) | |||
| Average (seconds) |
Tactile Test
- Subject one is blindfolded before dangling dominant hand off the edge of a table.
- Subject two holds a 30 centimeter (12-inch) ruler between two fingers at the 30 cm mark, having the 0 mark touching subject one’s index finger.
- Subject two tells subject one to grab the ruler as fast as possible, when they FEEL their non-dominant shoulder being touched.
- Subject two simultaneously touches the shoulder and releases the ruler. Record the centimeter measurement.
- Repeat this three times, for a total of four measurements and then repeat entire activity after your hand was in an ice water bath for 1 minute; and then again after hand was in warm water for 1 minute.
| Subject | Visual (cm)
Control |
Ice water (cm) | Warm Water Bath (cm) |
| Average (cm) | |||
| Average (seconds) |
Experiment 2: In this activity, you and your partner will test visual and auditory reaction times using two rulers (or sheets of paper as outlined above).
For the Visual portion of this experiment have your partner sit as the table, like before, but have both of their hands over the edge.
- You will hold both rulers this time instead of just one.
- Tell your partner that you will release just one ruler and they must pick the correct one and grab it as fast as possible. Tell them they must not squeeze both hands, only one.
- When you are ready to begin, randomly decide one ruler to drop. It does not matter which one, you will perform this test 3 more times, but never tell your partner which ruler you will drop.
- Again as before switch roles and redo.
- Finally, we will test the auditory reaction again. This time using both rulers.
- Get in the same position as before with both rulers. Make sure your partner has the eyesclosed.
- You will then proceed to say “left” or “right”. As you say it you will drop the corresponding left or right ruler. Your partner must decide which ruler to grasp based on the auditory cue you give: “left” or “right”. As before, your partner must only squeeze one hand.
- Record the measurement and repeat 3 more times, remember to randomly decide which ruler to drop. Also record if the correct hand was closed by using a + or – sign. Switch roles and repeat.
Here is the table for the second experiment:
Control
| Subject | Visual (cm) | (sec) | Auditory (cm) | (sec) |
| Average |
Math
In your charts above you are going to take all the averages of the centimeter measurements you have collected and convert the measurement in centimeters to seconds. This will tell you how long it takes, in seconds, an object (the ruler) to fall a certain distance. The formula below is comprised of three variables.
Y = the distance you measured in centimeters
g0 = the acceleration due to gravity constant (980 cm/sec2 )
t = time in seconds
Here is an example of the equation being used:
Calculate the average centimeter number for each sensory measurement. It may seem tedious to convert by hand each number you recorded so instead you will be provided with a quick chart to convert your centimeter measurement to seconds. However, there are several values missing in the table. You will need to fill them out to complete the table. Use the equation above to fill out the remainder of the chart. If you are savvy you can also design a computer program to do this.
| Distance (cm) | Seconds (s) | Distance (cm) | Seconds (s) |
| 3.0 | 13.0 | 0.16 | |
| 4.0 | 0.09 | 14.0 | |
| 5.0 | 0.10 | 15.0 | |
| 6.0 | 20.0 | 0.20 | |
| 7.0 | 0.12 | 25.5 | 0.23 |
| 8.0 | 30.5 | 0.25 | |
| 9.0 | 43.0 | 0.30 | |
| 10.0 | 0.14 | 61.0 | 0.35 |
| 11.0 | 0.15 | 79.0 | 0.40 |
| 12.0 |
[ad_2]
Testimonials
