Earthworms (3 per student or group of students)--Worms can be purchased at large department store or bait shops. In this article, we focus on the application of these experiments as teaching tools for basic neurobiology courses. Mechanical stimulation of the worm front end, activating the MGF pathway. After the gallery walk, the class will come back together and have a discussion about their findings. Stronger stimuli often activate the already described positive feedback loop (see Introduction, Fig. Temperature Investigation: How Do Earthworms React to Different Temperatures? Although necessary equipment has become cheaper and more widely available, dissections remain a major obstacle because they are time-consuming, raise ethical concerns about animal experiments, have lower success rates, or fail to meet the curriculum requirements. If more time is available in a course, we also conduct double recordings and let students measure the conduction velocity, as well as obtain more data points between 0.5 and 3 ms. Plotting and comparing the conduction velocities of both elicited APs (Fig. In contrast, a decreased distance of 5 mm or 2 mm usually leads to decreased AP amplitudes (often better observed in the MGF responses) - the distance of the electrodes is smaller than the spatial dimensions of the negative potential wave. The ion channels engaged in such phenomena and their possible role in shaping the patterned motor output of neural networks are currently under investigation in the crustacean stomatogastric nervous system (Ballo and Bucher, 2009). At very short intervals (15 ms), the second AP not only gets smaller, but slows down in conduction velocity. Earthworms possess three giant fibers within their ventral nerve cord, one median and two lateral fibers. Because the skin and body muscle wall are thin, it is sufficient to place worms upon arrays of electrodes that make contact with the outer ventral part of the body (Fig. This species comes to the surface to mate. In this experiment, students analyze the reversible (synaptic) depression of these giant motorneurons using frequent stimulation (Guenther, 1972). Once the data is collected, the numbers should indicate that the worms prefer the moist paper towel. (a) Representative student measurements of the MGF strength-duration curve. Groups can work on the poster while they are waiting on worms to react. With repeated stimulation, the response diminishes in magnitude and eventually disappears. However WH Thorpe restricts its use to more permanent effects. action potentials, giant fibers, earthworms, extracellular recordings, threshold, refractory period, conduction velocity, facilitation of conduction velocity, spatial size of action potentials, flight reflexes, synaptic depression and facilitation, giant motorneuron. Overall, we present nine experiments that each focus on specific theoretical topics: In the described experiments, earthworms (Lumbricus terrestris) are used. 1 Collect the worms well in advance. A pile of castings outside a burrow. Reactions to Light and Mechanical Stimuli in the Earthworm Perichta Das Experiment: Neurophysiologische Versuche am intakten Regenwurm. However, most times only two or three steps are seen and not six. Isolated stimulator for electrical stimuli with adjustable stimulus amplitude (010 V) and optimal a stimulus duration between 50 s and 50 ms, hardware & software trigger, functionality to deliver double-pulses with pulse intervals between 1 and 50 ms. Oscilloscope or analog-digital converter and PC/software interfaces with a minimum of two channels. As much as possible of the body wall should be touching the surface. We usually use the categories weak, medium and strong. This suggests that more than one process may be responsible for waning. Click on a file type icon to download an attachment. In the following sections, we describe the two basic setups that are required to conduct the experiments, with detailed descriptions of stimulus parameters and experimental conditions for each experiment being presented in the Results section. Structure and function in the nervous systems of invertebrates. Dig up a section of ground 12 inches by 12 inches and about 6 to 7 . Paired, representative classroom data. This workstation should consist of two amplifiers for differential recordings, a unit for electrical stimulation, and any kind of visualization equipment (e.g., oscilloscope or computer). As they share out, record a list of notices and a list of wonderings somewhere that is visible to all students. This is also true for recordings of giant fibers in earthworms, with experiments using dissected worms already being a standard classroom exercise. Quest Kickoff: Make a Human Body Road Map, 336-337 Although they are simple organisms which may not 'suffer' in the same way as higher animals, they still deserve respect. The second method determines the refractory period through the thresholds that are required to generate a second AP at different stimulus intervals (Fig. They analyze the main features of an action potential and the influence of the fiber diameter on the threshold for action potential generation (Fig. Each experiment needs its own data table, so each poster should have four data tables on it. All these experiments use awake, moving earthworms and apply mechanical stimuli to elicit giant fiber activity. Place an earthworm on a wet paper towel on the Doc Cam (be careful it does not dry out.) They are asked about a stimulus and response on the lab sheets, but students were not given a definition. There are 10 handouts with this lesson. Usually, a >10% increase in conduction velocity can be observed if the first two APs following medium or strong stimuli are compared. At the very least, they will move away from the source of the vibrations. How do earthworms respond to stimuli? - Project Sports The measurement was performed using method 1, varying intervals but constant width and strength (0.5 ms, 2.8 mA). Inclusion in an NLM database does not imply endorsement of, or agreement with, The rheobase is the minimal electric current of a stimulus with infinite duration that results in an AP, while the chronaxy is the shortest duration of an electrical stimulus where the threshold amplitude is twice the rheobase (Woodbury, 1965). 3a, red dots, method 2) - this is the classical textbook approach. Furthermore, the duration of an experiment might exceed available time or the level of required expertise is too high to successfully complete the experiment. Figure 1: Earthworm on the Duplo board. A typical classroom example of measurements using a double recording is shown in Table 3. In this case the experiment starts at room temperature and over time, the worm is cooled down to 2 C. The minimal electric current (rheobase) of the MGF is at 0.19 mA and the chronaxy is at 129 s. This work is licensed under a Creative Commons CC BY-SA 4.0 License. As mechanical stimulation would not work in anesthetized worms, electrical stimuli are used to generate action potentials in the giant fibers. Depending on the specific experiment, we either apply mechanical or electrical stimuli, and this requires slight changes to the setup. In the described experiments, differential, extracellular recordings are performed, i.e., voltage differences are measured over distant recording sites. 2019, Royal Society of Biology, 1 Naoroji Street, London WC1X 0GB Registered Charity No. Originally, experiments that measure giant nerve fiber activity in awake, moving earthworms were introduced by Charles Drewes and colleagues (Drewes et al., 1978). An earthworm is placed in a cage that (I) allows external recording from the giant fibers, (II) prevents awake worms from crawling away, and (III) serves as a simple Faradays cage. Students should note that no MGF responses can be observed in this case and, again, explain how this differs from electrical stimulation. Danny Mattox, Alexandra Parsons | Published: May 17th, 2022 by K20 Center. Inspired by the first descriptions of C. Drewes, a German publication by Hans-Georg Heinzel introduced similar experiments that used anesthetized earthworms and electrical stimulation (Heinzel, 1990). These gigantic potentials can be distinguished from APs by their size and duration (Fig. They should cover the containers because earthworms are sensitive to light, but that is an investigation they will conduct later. 1 in Fig. Action potential recordings in giant fibers of intact earthworms (Lumbricus terrestris) circumvent many of these problems and result in a nearly 100% success rate. 1Institut fuer Zoologie, University of Bonn, Poppelsdorfer Schloss, 53115 Bonn, Germany; 2Janelia Farm Research Campus, HHMI, Ashburn VA 20147, U. S. Introductory neurobiology courses face the problem that practical exercises often require expensive equipment, dissections, and a favorable student-instructor ratio. To prevent superposition of the MGF and LGF responses, the stimulus amplitude is set to a value between their previously determined thresholds. Earthworms respond rapidly to electrical stimuli, becoming U-shaped with both ends directed toward the cathode when a low . An electrical stimulus leads to the generation of an action potential by depolarizing the membrane; in this case the median giant fiber. 9b). In the past, we have applied both, custom made equipment as well as packaged workstations for education purposes (see Discussion). In this article, we describe our experience using such experiments in introductory animal physiology and various neurobiology courses at the University of Bonn. sharing sensitive information, make sure youre on a federal This keeps the worms alive and improves recording and stimulation. Avoidingstrong smelling substances protects them from ingesting harmful substances. Nervous system - Annelids | Britannica How Wolves Shape Rivers. If students use notebooks (as suggested at the beginning of this lesson), they should use the handout as a template for their data collection in their notebooks. Federal government websites often end in .gov or .mil. This decrease in latency illustrates that an increase in fiber diameter increases the conduction velocity of action potentials along the fiber. After the experiments are conducted and the data gathered, students should display their results from each experiment. Read our standard health & safety guidance. Paper towel/Microwaved or using hot water. Accessibility Facilitation of conduction rate in nerve fibers. You will know they are at the right temperature if they are bendable. If this does not help, change the position of the stimulation electrodes (if applicable). A behavior can be considered a habit an organism exhibits repeatedly in response to conditions it regularly experiences. Oxygen dissolves in the moisture on the earthworm'sbody and maintaining moisture in the soil is important for this process. Spatial dimensions of the MGF and LGF responses. The worms have to be left for significant periods of time between stimulations in this investigation. The lower trace shows the action of the positive feedback loop. To ensure students collect appropriate data, each poster should be based on the handout for each experiment. However, if students follow the guidelines below for conducting thisinvestigation, undue harm should not occur to earthworms. A stimulus is anenvironmental change that directly influences the activity of an organism. After a break of 12 minutes, slow stimulation (0.5 Hz) usually allows the recovery of all or at least some of the six motoneurons. They will then construct a poster to share their findings with the class. Performing the labs in this lesson will help them construct answers for the worms' actions. In this experiment, stimuli are applied to the very front end of the earthworm to analyze the MGF pathway (Fig. A list of suggestions for successful experiments is provided in the supplementary material. Earthworms do not like sunlight because of its relationship to giving off heat whichapplies to the next experiment. Materials: Earthworms Estimates of the absolute and relative refractory period durations obtained by method 1 (observing the amplitude of the second AP).
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