Membrane Transport, Heat, and Neuron Function Lab

Introduction

Eggs are a great way to study the movement of substances through cell membranes because an egg is essentially a giant cell surrounded by a double plasma membrane. In this lab, we will explore the movement of water through the egg membrane with eggs whose shells have been previously dissolved with vinegar.

Neurons or nerve cells send and receive signals from your brain and central nervous system. There are three main types of neurons that work together to help your body respond to stimuli: sensory neurons, motor neurons, and interneurons. Sensory neurons are triggered by external chemical or physical inputs, such as heat, light, sound, touch, smell, and taste. They carry this information to your brain and spinal cord. Motor neurons allow the brain and spinal cord to communicate with muscles, organs, and glands across your body. Some motor neurons carry signals between your spinal cord and muscles, and others carry signals between your brain and spinal cord. The most common type of neuron are interneurons. They function as intermediaries to pass signals between sensory and motor neurons and are found in your brain and spinal cord.

In this lab, we will explore different types of neuron functions, including spinal reflexes, and conscious reacting to stimuli. We will be measuring neuron speed and reflex magnitude and using various methods to see what might increase or decrease the speed and magnitude.

Most animals must regulate their body temperatures. Many animals thermoregulate using behaviors such as basking or retreating to the shade, and huddling together for warmth. Some animals have adapted insulation or water evaporation mechanisms to help them thermoregulate. In this lab, we will be exploring the two main types of insulation that mammals have evolved. All mammals have skin covered in hair that helps them regulate their body heat. Others, especially marine mammals, rely on large amounts of blubber to act as insulation against frigid waters. Other animals have some of both. In this lab, we will explore the differences and similarities of blubber and fur as insulation and their relative efficiency.

Materials

• Tape measures (1 per group)
• Infrared thermometers (1 per group)
• Masking tape
• Rulers (2-3)
• Scales or balances (2-3)
• Vernier Labquest 2 (1 per group)
• Vernier Go Direct Dual-Range Force Sensor and Reflex hammer accessory kit. (1 per group)
• Vernier Go Direct EKG Sensor (1 per group)
• Electrode tabs (6 per group)
• De-shelled eggs (2 per group)
• Different types of animal fur (1 per group)
• Slabs of animal fat (1 – 2 of different thicknesses)

Pre-Lab Questions

1. Describe the reflex arc (pathway the neurons travel) for the patellar reflex.

2. What is the difference between a spinal reflex and a conscious reaction?

3. Briefly describe the functions of motor neurons, sensory neurons, and interneurons.

4. How does fur act as an insulator for animals?

5. What are two ways that blubber helps animals keep warm?

Activity 1

Egg Membrane Transport via Osmosis.

Hypothesis: The egg placed in the water solution will swell, and the egg placed in the corn syrup solution will shrink. (Experiment 1)

Experiment 1 – Egg membrane transport via osmosis.

1. At the beginning of lab, obtain 2 eggs whose shells have previously been dissolved using vinegar.
2. Carefully weigh each egg (they are very fragile) and record weight in table 1, and on a piece of masking tape.
3. Place each egg in a small beaker and label the beakers with the eggs’ starting weight.
4. Into one beaker, pour water until it completely covers the egg.
5. Into the other, pour corn syrup until the egg is completely covered.
6. Record the time.
7. Take the 2 beakers to your table and let them sit.
8. At the end of lab, record the time, and carefully take the eggs out, dry them off and weigh them. Record the final weights in table 1 and determine the change in weight.
9. Calculate rate of change of weight using the starting and ending times.

Starting time:

Ending time:

Rate of change: (Corn syrup):

                            (Water):

Activity 2

Reflex Speed and Magnitude

Hypotheses:

• Reaction time to an auditory stimulus is slower than spinal reflex speed. (Experiments 1 and 2)
• Leg length is negatively correlated with normal patellar reflex speed and magnitude. (Experiment 2)
• Age is negatively correlated with normal patellar reflex speed and magnitude. (Experiment 2)
• Vigorous exercise of the quadriceps muscle will reduce the patellar reflex speed. (Experiment 3)
• Reinforcement on one side via holding a weight will increase patellar reflex magnitude. (Experiment 4)
• Reinforcement on both sides via the Jendrassik maneuver will increase patellar reflex magnitude. (Experiment 4)
• Reflex reinforcement on one side is less effective at increasing the patellar reflex magnitude than reinforcement on both sides. (Experiment 4)

Setup

1. Measure the leg length of each person in your group from the top of the hip joint to the floor (in cm). Record this data, and ages below.
   

   Group Member’s Name	Age	Leg Length (cm)

2. Attach the reflex hammer to the Go Direct Dual-Range Force sensor according to assembly instructions that come with the reflex hammer accessory kit.
3. Connect and set up the sensors.
   • Turn on your Labquest 2 using the power button on the top left. Wait for it to boot up.
   • Be sure your Go Direct Dual Range Force sensor is set to the +-50 N on the front of the sensor. Then plug it into the CH 1 slot on the left-hand side of the Labquest. You should see a red box appear on the screen labeled ‘Force’. (If you don’t see this box after waiting a minute and unplugging and plugging it back in again, click on ‘sensors’ on the top, then click ‘sensor setup’, click on ‘channel 1’, Scroll down to find ‘force’ and click the down arrow, then select the ‘dual range force 50N’, then click ‘ok’ twice. Now you should see the red box and when you push on the sensor, the numbers should get more and more negative).
   • Plug the Go Direct EKG Sensor into the USB slot on the left-hand side of the Labquest 2. You should see a blue box appear labeled ‘GDX: EKG’.
   • Tap the red ‘force’ box on the screen and check the box next to ‘reverse’. Then place the sensor flat horizontally on the table, click the red ‘force’ box again, and select ‘zero’.
   • Tap the blue ‘GDX: EKG’ box on the screen, select ‘Sensor Channels’. Deselect the ‘EKG’ channel and select the ‘EMG Rectified’ channel.
4. Set up data collection mode:
   • Tap ‘Mode’ in the top right, and change ‘Rate’ to 100 samples/s, and change ‘Duration’ to 45 s.
   • Tap ‘ok’.
5. In a sitting position, for each person in your group, attach two electrode tabs above the knee of the subject along the line of the quadricep muscle. The first should be approximately 2 inches above the patella, and the second should be about 5 inches above the patella. Attach a third electrode tab about halfway down the shin.
6. Choose two people from your group to be a part of the first experiment (conscious reaction speed), have the first person sit comfortably in a chair with their legs dangling freely above the ground, and attach the red and green EKG leads to the electrode tabs above the knee with the red lead closest to the knee, and the green further away. Attach the black ground lead to the electrode tab on the lower leg.
7. Write the person’s name next to ‘Subject 1’ in Table 2.1.
8. You are ready to begin data collection.

Experiment 1: Conscious Reaction Speed to Auditory Stimulus

1. Note: any time you collect data for someone, be sure to make a note of whose data it is, so that we can get accurate data correlations between leg length, age, and reflexes.
2. Collect conscious reaction speed from the first member of your group. NOTE: read through entire step before collecting data).
   • Have the subject close their eyes and relax.
   • Tap the play button in the lower left-hand corner to begin recording data.
   • Hit the reflex hammer against the desk or something else that will make a noise.
   • As soon as they hear the sound, the subject should kick his or her foot out.
   • Continue collecting samples for the 45s duration. Aim to collect data for 10 – 15 kicks during the 45 seconds.
3. Determine the time between striking the table with the reflex hammer and the contraction of the subject’s quadriceps muscle.
   • On the labquest 2, tap on the graph as close as possible to the beginning of the first spike on the Force graph.
   • Use the arrow key to toggle forward until you reach the very beginning of the spike. (You’ll see the little black circle on the graph start to move up.)
   • Record the time of the beginning of the spike (from bottom right of screen) in Table 2.1. (Note, there will be some normal up and down fluctuation, what we want here is the very beginning of the spike, not the normal ups and downs.)
   • Continue toggling forward until the little circle on the EMG Rectified graph begins to move up in the first spike. This represents the beginning of the quadricep muscle contraction. Record this time in Table 2.1.
4. Compute the ΔTime (in ms) for each kick and then the average for all 10 kicks.
5. Complete steps 1 and 2 with the second subject. Write their name under ‘subject 2’ in Table 2.1. Record their data in the bottom half of table 2.1.

Experiment 2: Normal Reflex Speed and Magnitude

1. Collect normal patellar reflex speed and magnitude from all members of your group. (Note: read entire step before collecting data).
   • Have the subject close his or her eyes and relax. Write their name next to the appropriate ‘subject’ in table 2.2.
   • Click the play button in the lower left corner to begin collecting data.
   • Tap the reflex hammer briskly against the subject’s patellar tendon just below the patella. If this does not elicit a reaction, try aiming toward other areas of the tendon until a good reflex is obtained.
   • Continue collecting reflex samples for the duration of the 45 seconds. Aim for 10-15 samples.
2. Determine the time between striking the patellar tendon and contraction of the quadriceps muscle, and reflex magnitude.
   • Following the same steps as in experiment 1 step 2 to record time data in table 2.2 with this added step:
   • For each kick, continue toggling forward after you get the time of muscle contraction until the circle reaches the highest point of the spike on the EMG rectified graph. This represents the magnitude of the reflex. Record the value (mV) in Table 2.2.
3. Repeat steps 1 and 2 for each member of your group.

Experiment 3: Effect of Exercise on Reflex Speed

1. Collect patellar reflex speed after exercise of the quadriceps muscle from two members of your group.
   • Disconnect the EKG leads and have the first subject do 10-15 jump squats.
   • Have the subject then sit comfortably in the chair with his or her legs dangling freely and close their eyes.
   • Repeat method from experiment 2 step 1 to collect patellar reflex speed samples. Aim for 10-15 kicks over the 45s duration.
   • Following the instructions from experiment 1 step 2, determine time of stimulus and time of muscle contraction and record data in Table 2.3
   • Calculate average speed for all 10 kicks.
2. Repeat step 1 for a second member of your group. Record data in the bottom half of Table 2.3.

Experiment 4: Effect of Jendrassik Maneuver on Reflex Magnitude

1. Choose two people from your group to take part in this experiment.
2. Have the first subject sit comfortably on the chair with their legs dangling freely and close their eyes. Then have them perform the Jendrassik maneuver by interlocking flexing both sets of fingers into a hook-like position, and then interlocking them together in front of the chest, pulling outward toward the elbows without breaking contact at the fingers.
3. Using the same method from the previous experiments, obtain reflex magnitude data.
4. Determine magnitude for each trial, and calculate the average magnitude across all 10 trials, and record in table 2.4.
   • Using the stylus, click and drag on the graph to select an area that encompasses the entire first spike of the EMG rectified graph.
   • At the top of the screen, select ‘Analysis’, then select ‘Statistics’ and check the box next to ‘EMG Rectified’.
   • On the right-hand side, under ‘statistics’ scroll down to find the ‘Max’ mV value. This represents the magnitude of the reflex.
   • Record in table 2.4.
   • Do the same for the next 9 samples (Note: you will have to deselect and reselect ‘EMG Rectified’ under ‘statistics’ each time you select a new area, otherwise the statistics will not change to the new selection.)
   • Calculate the overall average between the 10 samples.
5. Repeat steps 2 – 4 with the second subject.

Experiment 5: Effect of One-sided Reinforcement on Reflex Magnitude

1. Use the same two subjects for this experiment that you did for the last one.
2. Obtain a weight of about 5 lbs. Have the subject hold it in their hand to the side like they are setting up to do a bicep curl. One side of their arm muscles should be tense, and the other side should be relaxed. Have them sit in the chair with their legs dangling freely and their eyes closed.
3. Follow the same steps as before to obtain reflex magnitude data.
4. Determine the magnitude (max mV) value of each reflex following the steps from experiment 4 step 4. Record data in table 2.5.
5. Calculate the average magnitude of the 10 kicks and record in Table 2.5.
6. Repeat steps 1 – 3 to collect data from a second subject.

Table 2.5

When you have finished this activity, please come, and enter your averages from each experiment into the excel spreadsheet at the front of the room so that we can graph the class’s data.

Activity 3

Effectiveness of different types of animal insulation.

Hypotheses:

• Thickness of fur is positively and linearly correlated to insulation ability. (Experiment 1)
• Thickness of fat is positively and linearly correlated to insulation ability. (Experiment 2)
• Fur is more effective at insulating than the same thickness of fat. (Experiments 1 and 2).

Experiment 1: Effectiveness of Fur as an Insulator.

1. Obtain a fur from the back of the classroom.
2. Lay it flat on the table and record the thickness (cm) here: ______________ (note: some don’t lay flat, just do your best to get an accurate thickness from the skin to the edge of the fur)
3. Obtain an icepack and lay the fur flat over the icepack on the desk (be sure that the ice pack is making contact with the skin, if your skin is from an entire animal, try to get the ice pack inside so that you can measure cold transference over just one layer of skin/fur).
4. Use an infrared thermometer to take the temperature on the top of the fur every 30 seconds for the first 6 minutes, and record data in table 3.1. Do not touch or move the fur during this time. Try to aim for the same spot from the same angle each time.
5. Calculate the average rate of change of temperature for the first 6 minutes (in °C/min) by subtracting your value from 6 minutes from your starting value, and then dividing by 6.
6. Enter your data into the Excel spreadsheet at the front of the classroom.

Starting Temperature:

Rate of change of temperature:

Experiment 2: Effectiveness of Fat as an Insulator.

1. Obtain a block of fat from the back of the classroom.
2. Lay it flat on the table and record the height (cm) here:
3. Obtain an icepack and lay the fat over the icepack on the desk.
4. Use a heat gun to take the temperature on top of the fat every 30 seconds for the first 6 minutes, and record data in Table 4.2
5. Calculate the average rate of change for the first 6 minutes.
6. Enter data into the excel spreadsheet at the front of the room.

Starting temperature:

Rate of change of temperature:

Post-Lab Questions

Activity 1

1. Describe the changes you observed in your eggs through the lab. Did they grow or shrink? Why?

Activity 2

1. Which was faster: the patellar reflex or the speed of reaction to an auditory stimulus? Why?

2. Was there a difference in the reflex speed after working the quadriceps muscle? Why or why not?

3. Is there a correlation between age and reflex speed? If so, was it positive or negative? What causes this correlation?

4. Was there a correlation between leg length and reflex speed? If so, was it positive or negative? Why do you think this would be the case?

5. Was the magnitude of the reflex higher or lower than normal with reinforcement? Why?

6. Was there a difference between the magnitudes of the reflex with reinforcement on both sides versus just one side? Why do you think this might be the case?

7. Was there a correlation between age and magnitude of the patellar reflex? If so, was it positive or negative? Why?

Activity 3

1. Look at the graph comparing fur and fat insulation. For the same thickness, did the fat or fur cool down more slowly?

2. Using what you have learned about fat vs. fur insulation effectiveness, would it be more effective for terrestrial mammals to use fur or fat as an insulation? What about marine mammals?

3. Sea otters, a marine mammal, have the densest fur of any living mammal. They can have upwards of a million hairs per square inch of their body. Why do they have such thick fur when they live in the water?