Laboratory Guide Anatomy and Physiology TBME04, Fall 2010 Name: Passed: Last updated 2010-08-13 Department of Biomedical Engineering Linköpings Universitet
Introduction This laboratory session is intended to increase the students knowledge of the physiology and anatomy of the nervous system. This is done by independent laboratory work in four steps: 1. to decide the time from a stimulus to a conscious response. 2. to decide the refractory period of the ulnar nerve. 3. to decide the propagation speed of motor neuron in the median nerve 4. to decide the time from the release of the reflex of Achilles to the response of the muscle, both theoretically and practically To take part in the laboratory session, you must be prepared both by answering the questions in this document, and also by planning how the tasks can be solved with the available equipment. If this is not done, you are not allowed to carry out the laboratory session. There will be an oral test in the beginning of the session. Keep in mind that in some cases, reasonable assumptions that are not explicitly stated in the course literature regarding, for example, nerve transmission speed are required in order to solve the given tasks. You will work in groups of three, and you are supposed to follow your own plan. A laboratory assistant will be present to answer specific questions, and to demonstrate the laboratory equipment at the start of the session. Four laboratory tasks will be performed by each group, and each task takes about 30-45 minutes to complete. At the end of the session, there will be a discussion concerning the results. As an aid in this discussion, please consider the following aspects for each laboratory task: What is it that you measure? Are there parameters that affect the results that you didn t think of at first? Is the equipment influencing the results? Are the results reasonable? The laboratory session will be held at IMT, in the computer lab on floor 12. A map can be found at the course home page. For further questions, please contact Elin Diczfalusy, elidi@imt.liu.se. 1
Basic setup of experiments This is a description of the basic setup used in the laboratory tasks and not a comprehensive instruction on how to use it. This description is supposed to be a support when planning the laboratory work. At the lab session you will get a thorough user instruction of all devices. Note that additional, task-specific equipment will be presented for each laboratory task. In order to measure the nervous activity explicitly, direct contact with the nerves would be necessary. However since this is not feasible here, it can be measured indirectly by studying how the muscles respond to the nervous signals. The signal consisting of the electrical activity of muscular tissue is called the electromyogram (EMG). The EMG is captured by placing electrodes on the skin over the muscle. In this lab, adhesive skin electrodes are used, but there are a variety of electrodes for example needle electrodes which can be inserted in the muscle in order to measure the response of single motor units. The electrode consists of a contact gel in contact with a metal plate. Normally when measuring bioelectrical events, a differential amplifier is used. It measures the potential difference between two electrodes (red and blue in Figure 1). To reduce disturbances it also uses a third electrode (black) to ground the patient. The results are either captured and stored or visualized on a screen. Electrodes placed on the body red black blue out In this lab, signals are shown on an oscilloscope. Two channels are used Figure 1 Differential amplifier simultaneously, for either comparison between signals or for triggering. Triggering is used to display repeating waveforms in a way that they appear to be static. It can also be used to capture single events following a certain trigger. Commonly, the triggering function is based on a threshold or slope (either positive or negative) depending on the application. In this setup, the single event triggering mode will be used. Make sure that you understand how to use this function on the oscilloscope before you start the laboratory task, and note which input channel that is used. 2
Laboratory task 1: Reaction time Task: To experimentally decide the reaction time from an outer stimuli to a conscious reaction. Vary the stimuli between sight, hearing and sensation. Equipment: Reaction time indicator The reaction time indicator is a simple circuit as shown in Figure 2. Practically, it consists of two pushbuttons and a light emitting diode. The diode emits light only when both buttons are pressed. Oscilloscope Measuring tape Preparation questions (to be answered before the laboration): How can the equipment be used to create stimuli for sight, hearing and sensation? Draw the nerve signal pathways in the body from stimulus to conscious reaction for the different stimuli, using Figure 3. Describe the laboratory procedure. Questions to answer during the laboratory task: Does the reaction time differ between different stimuli? Can you think of any way to isolate the signal processing time in the brain? How? How can the nerve propagation velocity in a sensory nerve be isolated with the available equipment? Possible sources of error? Figure 2. Reaction time indicator Figure 3 3
Laboratory task 2: Refractory period Task: To experimentally decide the refractory period of the ulnar nerve. Equipment: Nerve stimulator The nerve stimulator used for this task consists of a stimulation device connected to a small probe which can be placed on a superficial nerve. The device generates a series of electrical pulses (a pulse train ), with adjustable frequency and amplitude. Oscilloscope Amplifier Surface electrodes Preparation questions (to be answered before the laboration): In Figure 4, the pulse train from the nerve stimulator is illustrated, with a time interval t s between the pulses. Draw what the corresponding muscle signal can be expected to look like, both when t s is longer and shorter than the refractory period (t ref ) of the nerve. The nerve stimulation probe is preferably placed on the upper arm between the biceps and the elbow, where the ulnar nerve is superficial (The lab instructor will show you the right position). Where should the EMG electrodes be placed? How should the equipment be connected for this task? Use Figure 5 to draw the connections between the different parts. The same setup is used in task 3. Describe the laboratory procedure. Questions to answer during the laboratory task: Do you believe that you ve measured the absolute or the relative refractory period? Why? Possible sources of error? 4
Signal from nerve stimulator t s Corresponding signal from muscle, t s > t ref Corresponding signal from muscle, t s < t ref t Figure 4 Pulse train from nerve stimulator. Figure 5 Available equipment for laboratory task 2. The dark squares represent the connectors through which the different devices can be connected. The upper channel on the oscilloscope represents the trigger channel. 5
Laboratory task 3: Nerve propagation speed Task: To experimentally decide the nerve propagation speed of the median nerve. Equipment: Nerve stimulator The nerve stimulator used for this task consists of a stimulation device connected to a small electrode which can be placed on a superficial nerve. The device generates a single pulse, with adjustable amplitude. Oscilloscope Amplifier Surface electrodes Measuring tape Preparation questions (to be answered before the laboration): Is the median nerve a motor or sensory nerve? Describe the signal pathway in this task. The nerve stimulator electrode is preferably placed under the biceps, where the median nerve is superficial. Where should the EMG electrodes be placed? How should the equipment be connected for this task? Use Figure 5 to draw the connections between the different parts. The same setup is used in task 2. Describe the laboratory procedure. Questions to answer during the laboratory task: Possible sources of error? 6
Laboratory task 4: Reflex Task: To experimentally decide the time from the release of the Achille s reflex (Figure 8) to the response of the muscle. Equipment: Reflex hammer The reflex hammer used here is constructed so that it sends an impulse when it hits the target. Amplifier Surface electrodes Measuring tape Preparation questions (to be answered before the laboration): Describe the nerve signal pathway for the reflex arc involved in this task, using Figure 6. How should the equipment be connected for this task? Use Figure 7 to show the connections between the different parts. Describe the laboratory procedure. Questions to answer during the laboratory task: Are there factors other than the nerve propagation velocities that influence the time between release and muscle response? Possible sources of error? Figure 6 7
Figure 7. The equipment available for laboratory task 4. The dark squares represent the connectors through which the different devices can be connected. The upper channel on the oscilloscope represents the trigger channel. 8
Preparation exercises These exercises, as well as the preparation questions described for the laboratory tasks above, are to be completed prior to the lab session in order for you to participate. In addition to answering the questions, also try to relate them to the laboratory tasks described above. You also need to obtain anatomical and physiological knowledge relevant for this lab session. It is more important to know where to find the various muscles and nerves than their Latin names. Before the lab starts there will be an oral test and discussion concerning the questions below. 1. How does a nervous pulse propagate in a nerve? 2. Describe an action potential and its phases. Which ion channels are involved and how do the open/close relative to the different phases? 3. Which factors determine the propagation speed of nervous pulses? 4. Explain the concepts of absolute and relative refraction period. 5. How do sensory nerves and motor nerves differ in terms of nerve signaling pathways? 6. Give examples of three types of nerve fibers, what is special for the various groups, where they are located, and their propagation speed. 7. Which muscles in the hand contract when the ulnar nerve is stimulated? 8. Which muscles in the hand contract when the median nerve is stimulated? 9. Describe the five components involved in the reflex arc. 10. What is the difference between a reflex and a conscious reaction to a stimulus? 11. In what interval should the nerve propagation velocity be for the median nerve? 12. Give an estimate of how long the refractory period of the ulnar nerve should be. 13. What do you think are reasonable reaction times from a sight, hearing or sensation stimuli to a motoric response? Describe the factors involved in the process. 9
14. How long time do you think it takes from a stimulus on the Achille s tendon until the Achille s reflex is released (Figure )? Make a brief calculation with reasonable assumptions regarding the nerve propagation speed in both the sensory and the motor nerves involved. Where is the nervous signal initiated? What other factors should be taken into consideration? Figure 8. Example of how the Achilles reflex can be released. 10