Lab Assignment: Neuromuscular Reflexes

The automatic response of a muscle to a stimulus is called a reflex. The patellar reflex results from tapping the patellar tendon below the knee with a reflex hammer. This causes contraction of the quadriceps muscle and extension of the leg. Stretching of the muscle activates nerve impulses which travel to the spinal cord. Here the incoming impulses activate motor neurons, which travel back to the muscle and result in muscle contraction. This reflex arc is primarily a spinal reflex, but is influenced by other pathways to and from the brain (Figure 1).

OBJECTIVES

In this experiment, you will

• Graph the electrical activity of a muscle activated by a reflex arc through nerves to and from the spinal cord.
• Compare the relative speeds of voluntary and reflex muscle activation.
• Associate muscle activity with involuntary activation.
• Observe the effect of central nervous system influence on reflex amplitude.
• Calculate the approximate speed of a nerve impulse.
• Compare reflex response and electrical amplitude in different subjects.

DATA ANALYSIS

1. Compare the reaction times for voluntary vs. involuntary activation of the quadriceps muscle. What might account for the observed differences in reaction times?

2. Using data from Table 2, calculate speed at which a stimulus traveled from the patellar tendon to the spinal cord and back to the quadriceps muscle (a complete reflex arc). To do this, you must estimate the distance traveled. Using a cloth tape measure, measure the distance in cm from the mark on the patellar tendon to the spinal cord at waist level (straight across from the anterior-superior iliac spine-see Figure 9). Multiply the distance by two to obtain the total distance traveled in the reflex arc. Once this value has been obtained, divide by the average ?t from Table 2 and divide by 100 to obtain the speed, in m/s, at which the stimulus traveled.

3. Nerve impulses have been found to travel as fast as 100 m/s. What could account for the difference between your answer to Question 2 and this value obtained by researchers?

4. Assume the speed of a nerve impulse is 100 m/s. How does this compare to the speed of electricity in a copper wire (approx. 3.00 x 108 m/s)?

5. Compare the data you obtained in this experiment with other members of your group/class. Can individual differences be attributed to any physical differences (body shape/size, muscle mass, physical fitness level)?

EXTENSION

1. Explore the ankle and elbow reflexes.

2. Perform the experiment with the subject watching the reflex hammer as it hits the patellar tendon. Compare this data to data gathered while the subject is focusing on an object elsewhere in the room.

Attachment:- Lab_Reflexes.rar