Motile Organisms. Name: Lab section: BACKGROUND READING: This lab handout Chapter 49, pp

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1 Name: Motile Organisms Lab section: BACKGROUND READING: This lab handout Chapter 49, pp PRE-LAB: Do the pre-lab reading and carefully read through the lab. Come to lab with a clear idea of what you will be doing. If you're not prepared, it could take a really long time. OBJECTIVES To examine how skeletons and contractile elements (muscles) bring about motion in animals. To compare the structure and function of rigid endo- and exoskeletons. To apply your knowledge of mechanical advantage to real vertebrate limbs. To make observations of fluid-filled hydrostatic skeletal systems in action. To look closely at the structure of the muscular hydrostatic skeleton of the squid. To examine some biomechanical factors which determine the efficiency of bipedal locomotion. INTRODUCTION Movement in animals is incredibly complex, requiring the interaction of muscles, skeletal elements and nerves. To illustrate this complexity, let's evaluate the processes that occur EVERY time that you take a step with your right foot: 0. Your right leg swings forward in about 0.5 seconds. During this time, the following events will occur: 1. The large muscle in the front of your right thigh (quadriceps) will contract and shorten, bringing the right leg forward and straightening it out; 2. Your large calf muscles in your left leg (gastrocnemius) will contract and shorten, lifting your heel and pushing your mass onto your right toe; 3. Your right heel is timed to strike the ground at about the same time as your left toes leave the ground for the next step; 4. During this time, the muscles in your abdomen, thorax, and buttocks must all constantly adjust their activity to keep your upper body from falling over. It should be clear from this brief description that many muscles throughout the body are recruited to generate even the "simplest" movement. The timing of contractions is crucial and the need for sensory feedback is profound. In this lab we will focus primarily on the skeletal elements involved. If you are interested in knowing more about muscles, nerves, and movement, you should consider taking comparative animal physiology, human anatomy and physiology and/or neurobiology. THE LAB: You're responsible for completing the numbered drawings, experiments, and questions. The lab will be due at the end of the lab period. You may work in pairs and turn in one lab. ** It would be helpful to have a calculator in lab.

2 I. JOINTS AND LEVERS IN RIGID SKELETAL SYSTEMS A. Endoskeletal Joint DISSECTION: Examine the wing of a chicken by locating the bones through the skin to note how the appendage is organized. Remove the skin and select an antagonistic muscle pair. Note how the contraction of either element (i.e., pulling on either muscle) causes movement about a joint. Tease apart the other muscles and note the two ends of one of the antagonists. One end (the one that doesn t move when the muscle contracts) is called the origin; the other is called the insertion. Now tease apart all of the muscles to examine the joint. It is surrounded by very tough, elastic ligaments (ligaments run from bone to bone; tendons run from muscle to bone.) 1. DRAWING: On a separate sheet of paper, make a simple drawing of this joint and muscle system and indicate the planes in which that joint can easily move and which muscle produces which movement. B. Exoskeletal Joint Animals with a hardened outer layer (such as insects and lobsters) are said to have an exoskeleton, or outside skeleton. The skeleton is often set up as a series of hollow rigid tubes connected with more flexible portions of skeletal material. The muscles within these tubes are anchored to the inner surface of the skeleton or inward extensions of the surface called apodemes. Apodemes are analogous to the tendons of vertebrate endoskeletons. As with endoskeletons, the end of a muscle that remains stationary during contraction is called the origin the other end, the one that moves, is called the insertion. External and internal morphology DISSECTION: Examine a crab leg. Remove part of the exoskeleton and observe the muscles, their attachments, and the hinges at the leg joints to answer the following questions: 2. In how many planes can a particular joint of the crab s leg move? Open up the leg segment and find the apodeme and identify an antagonistic muscle pair. 3. DRAWING: On a separate sheet of paper, make a simple drawing of the exoskeleton, muscles, attachments, apodemes, and joint; indicate the direction that each muscle moves the limb. C. Homologies among vertebrate skeletal systems The vertebrates have endoskeletons in which the basic components bones are shared by all major groups. The flipper of a seal, the human arm, and the wing of a bird may look very different, and may serve quite different functions, but the skeleton within all three of these appendages contains the same basic bones. These strong similarities in structure are called homologies. An excellent illustration of such homologies is shown on page 439 (Fig ) of your text, in which the forelimb bones of various mammals are illustrated. Mammals vs. Birds: Examine the bones in a forelimb of a mammalian skeleton (actual or illustrations), and compare them with the bones of a chicken wing. In making these comparisons you should recognize homologies among the different vertebrate groups. For a clearer view of the major bones of the human arm and leg, refer to the human skeletons in the lab. 4. The joint you examined in #1 is homologous to which joint in you? D. Lever mechanics and the mechanical advantage of different mammalian limbs.

3 In this part of the lab, you will compare the mechanical advantage of the homologous joint system among different mammals. The following is a brief review of lever mechanics and mechanical advantage. As discussed in lecture, a large mechanical advantage means that a relatively small muscle force (F M ) produces a relatively large force of movement (F E ; the subscript E is used to indicate that this force is applied to the environment). Recall from lecture that we can calculate the mechanical advantage (MA) by measuring "lever arms" around a pivot point. A formal definition of mechanical advantage is: MA = F E /F M = L M /L E (where L M = the lever arm from the pivot point to the muscle and L E = is the lever arm from the pivot point to where the limb interacts with the environment) What does mechanical advantage mean? A mechanical advantage greater than 1 means that you get more force out than you put in (F E > F M ). Conversely, a mechanical advantage less than 1 means that you get less force out than you put in (F E < F M ). In the figure below, the ratio L M /L E is clearly greater than 1 (this is how a crowbar works, where F M is the muscle force applied by a person) pivot point L M F E F M L E Load What would be the advantage of having a mechanical advantage less than 1? As it turns out, a low mechanical advantage increases the speed of movement, but at the expense of force production. Use the following figure to convince yourself why this is the case. pivot point L M F E L E F M Although obviously much more complex, vertebrate limbs can be broken down into a system of lever arms and pivot points and analyzed like the "see-saw" models above. Calculate the mechanical advantage of your foot using your ankle joint as the pivot point. In calculating L E, think about where your foot pushes off the substrate when you walk or run (i.e., do you push off with the tips of your toes or with the ball of your foot?). Rather than taking all the flesh off your foot to see the pivot point, get oriented by examining the human skeleton. 5. What is the mechanical advantage of your foot? Include your calculations.

4 6. Find the homologous joint system in the three mammals on display (illustrations or actual skeletons). Calculate the mechanical advantage for this joint in each of the mammals giving adequate consideration to the points discussed above in reference to your skeleton. Compile your measurements and results in the following table: ANIMAL L M L E MA Force Speed 7. Based only on your results above, the limb of which animal has the greatest capacity to produce force? the least? The limb of which animal has the greatest capacity for speed? the least? Use a 1 for the greatest capacity and a 3 for the least. Do these results agree with what you know about the biology of these animals? Please explain. 8. Compare the mechanical advantage of your foot with those of the limbs above. What can you conclude about the relative force producing ability of your joint system? Do you believe that this result corresponds with what you know about your locomotor capacity relative to that of these other animals? If not, please provide a plausible and testable reason for this discrepancy. II. HYDROSTATIC SKELETAL SYSTEMS A. Fluid filled hydrostatic skeletons Earthworms have no rigid exoskeleton or endoskeleton and yet they move by means of muscle contraction. How do they manage to do this? Watch the movements of an earthworm as it crawls across a damp paper towel. Note the changes in proportion of width to length of the segments as it moves. The segments of this creature are covered with tiny bristles called setae that give the worm some traction. They all tend to point toward the tail so that when the worm crawls forward, they provide resistance to backwards sliding. You can feel this by performing the following simple test. Run your fingers from head to tail over the surface of the worm and then run them backwards. Examine a prepared cross-section of an earthworm under a microscope to determine the arrangement of muscles in the body wall of a worm. There is a layer of circular muscles surrounding each segment and a layer of longitudinal muscles that run parallel to the long axis of the worm. Each segment of a worm can be considered similar to a water balloon. When longitudinal muscles contract, it gets shorter and fatter.

5 9. Armed with (1) your observations of segment motions of a live worm, (2) your observations of how setae provide traction, and (3) the muscle arrangement, propose a mechanism for how worms move. To do this, you will need to clearly indicate the role of antagonistic muscle pairs. 10a.Do you think that setae increase the efficiency of earthworm locomotion? YES / NO EXPERIMENT: Test your assertion by setting up an experiment that tests locomotion of the worms on different substrates. Choose your substrates to test your hypothesis. b. Describe your experimental set-up and tests. c. Describe your results. d. What do your results suggest about your initial hypothesis in (11a)? B. Muscular hydrostatic skeletal systems The mantle, arms and tentacles of squid will serve as our example of muscular hydrostats. 11. To which phylum and class do squid belong? Working with no more than one other person, dissect a squid. You are also welcome to work alone on your own specimen. DISSECTION: Examine the squid s external structure. Be sure that you can identify the eyes, arms, tentacles, fins, mantle, funnel, dorsal, ventral anterior and posterior (see pictures at the end of the lab). NOTE: All cephalopods have 8 arms (unless some have broken off) but only some have 2 tentacles and fins. Use scissors to cut open the mantle cavity along the ventral surface (the funnel is ventral). Make your cut either to the right or to the left of the ventral mid-line. 12. DRAWING: Make a sketch of your specimen on a sheet of plain paper. Label the eyes, funnel, arms, tentacles, pen, gills, ink sac, and gonads, and include the name of the animal and a scale bar. Cephalopods are active predators, and they use their tentacles to capture fast moving prey such as fish and shrimp. The arms then hold the prey while it is devoured. Both the tentacles and arms are muscular hydrostats. Examine the structures at the ends of the arms and tentacles using a dissecting microscope. If you find the tentacles and arms particularly interesting, include sketches of their structure on your drawing.

6 Squid arms are about the same diameter as the earthworms. Compare how hard squid arms are relative to earthworms. The hardness comes from the fact that the arms are packed with muscle and the worms are filled with fluid. At the base of the ring of arms lies the mouth. Dissect out the beak and try to locate the radula. The beak musculature forms a spherical mass of muscle. The small radula lies within this muscle mass. III. PENDULUM WALKING AND THE BIOMECHANICS OF BIPEDAL LOCOMOTION The simplest physical analysis of human walking is called the pendulum gait model. In this analysis, we model a walking human as a body and two rigid legs... just like upside down pendulum shown below. Direction of locomotion The basic idea here is that forward motion occurs as a series of arcs, with the body swinging around each pendulum. Simple physics tell us that the forward velocity is related to the inward acceleration of the body along the inverted pendulum and the length of the pendulum (recall that the velocity of a swinging pendulum is proportional to the length of the pendulum). If the legs are indeed rigid, the only inward acceleration we have available is that due to earth s gravity. This simple model predicts that the forward velocity (V) must always be less than or equal to the square root of (gravity x leg length). Our hypothesis, therefore, is in the form of a physical equation that states: V (g*l) 1/2 13. EXPERIMENT a. To test this hypothesis, select a lab partner to be the subject. Our hypothesis predicts that the peak speed this person can reach is the square root of the product of earth s gravity (g = 9.8 m/s 2 ) and their leg length. Measure the length of their leg from the top of their femur (where it attaches to the pelvis) to their heel. Use the human skeleton for orientation. Leg length (meters) Write your prediction for the peak pendulum walking speed m/s To insure that the subject obeys the rules of a pendulum walking they must walk with their back straight, arms by their side, and their knees locked in a straight position. At no time may they jump, bend their knees or wiggle their hips. Things get a bit more challenging with the final requirement: they cannot use their whole foot but must, instead, walk only on their heels.

7 b. Go into the hallway and count off 30 tiles on the floor. That corresponds to about 10 meters. Have the person walk in the pendulum style at their fastest speed for those ten meters and time them with either a stopwatch. You may repeat this several times to get a better estimate. Time for 10 meter walk s Average time s Speed m/s Does this result support the pendulum-walking hypothesis? YES / NO In reality, many complex motions are involved in human walking and running. For race-walking, in which the rules of the competition are that at no time are you off the ground (at least one foot in contact all the time), odd postures and body motions are seen. These motions and postures are unconscious methods by which competitors increase the effective leg length. These include spinal flexion, exaggerated hip motions and the like. c. To examine the effects of peculiar limb motions, have the subject perform the following series of activities and time the motion to estimate the velocity. i. With the back straight, and knees locked, walk as fast as possible. You may use your whole foot. Time for 10 meter walk Average time Speed How does this speed compare to that of pure pendulum walking in b? FASTER / SLOWER / ABOUT THE SAME ii. With the back straight, walk as fast as possible. Your knees and feet are free to move as you wish, but you may not run (at least one foot on the ground at all times). Time for 10 meter walk Average time Speed How does this speed compare to that of pure pendulum walking in b? FASTER / SLOWER / ABOUT THE SAME iii. Arch your back and repeat this process. Time for 10 meter walk Average time Speed How does this speed compare to that of pure pendulum walking in b? FASTER / SLOWER / ABOUT THE SAME d. Propose a plausible explanation for each of these three results.

8 IV. THE COMBINATION SKELETON OF ECHINODERMS No need to answer questions, just look, touch, and enjoy. Familiarize yourself with the external body parts of echinoderms by examining Figure on p. 674 of your text. Locate the (1) mouth and anus, (2) tube feet, and (3) madreporite on one of the living starfish we have in the lab. What is the function of the madreporite? Obtain members from the other echinoderm classes that we have in the tanks. Are all of the features that you labeled on the asteroid visible in members of the other classes? If a feature is not visible, has it been lost or is it covered by another structure?. Echinoderms get their name from their typically rough and spiny aboral surface. Examine the aboral surfaces of a sea star and a sea urchin under a dissecting microscope and look for spines and pedicellariae. Compare the pedicellariae of the sea star and the sea urchin. What is the function of these structures in each class? Echinoderms have mutable connective tissue. The stiffness of this unique material is under the control of the organism and can change rapidly depending on the situation. Try to experience the unique properties of this tissue by lightly touching a starfish or sea cucumber. Does the animal feel soft, pliable, and maybe a bit squishy? Now try and lift the animal and bend its arms or body. The organism should now feel much stiffer. There you have it... mutable connective tissue!

-Elastic strain energy (duty factor decreases at higher speeds). Higher forces act on feet. More tendon stretch. More energy stored in tendon.

-Elastic strain energy (duty factor decreases at higher speeds). Higher forces act on feet. More tendon stretch. More energy stored in tendon. As velocity increases ( ) (i.e. increasing Froude number v 2 / gl) the component of the energy cost of transport associated with: -Internal kinetic energy (limbs accelerated to higher angular velocity).