Human skeletal and muscular systems Student Learning Outcomes After completing this exercise the student will be able to: 1. Define bones, ligaments, joints, skeletal muscles, tendons, muscle tone, posture, sutures synovial joints, diaphysis, epiphyses, compact bone, spongy bone, marrow cavity, lever: 2. Identify the major bones of the human skeleton; 3. Describe the structure of a typical bone; 4. Define origin, insertion, and action as these terms apply to skeletal muscles and their tendons; 5. Distinguish between isometric and isotonic contractions of skeletal muscles; 6. Give every day and anatomical examples of the three classes of levers; 7. Present a simple biochemical analysis of walking. Introduction The skeletal system and muscular system are often considered together to stress their close structural and functional ties. These two systems referred to as the musculoskeletal system. They determine the basic shape of your body, support your other systems, and provide the means by which you move in the external environment. Bones are the main organ of the skeletal system. They are primarily bone tissue, although all four basic tissue types are present. The places in the body where two or more bones are connected are called joints. The joints you are most familiar with are the shoulder, elbow, wrist, hip, knee, and ankle. However, there are many others. Around many joints, bones are held together by strap like structures called ligaments. Ligaments are primarily dense connective tissue that is more or less elastic. Elastic ligaments around mobile joints stretch to allow movement. Skeletal muscles are the main organs of the muscular system and are composed primarily of skeletal muscle tissue. Skeletal muscles are connected to bones by dense fibrous connective tissue structures called tendons. Tendons are inelastic, so all of the force of skeletal muscle contraction is transferred to the skeleton. When a skeletal muscle contracts, movements may or may not occur. If the skeletal muscle is allowed to shorten, the bone moves, and in doing so it moves some body part. On the other hand, if the skeletal muscle does not shorten, the tension is that muscle and in its tendons increase. All skeletal muscles exhibit tension or muscle tone except when you are asleep. This tension maintains posture-the ability to hold the boy erect and to keep the position of its parts, all against the pull of gravity. The organs of the skeletal and muscular systems have other functions. Bones protect internal organs (for example, the skull protects the brain, eyes, and ears). Bones also store minerals and produce blood cells in the bone marrow, when body temperature drops below a certain level, skeletal muscles produce heat by shivering. 1
39.1 Adult human skeleton An articulated human skeleton is prepared by joining together the degreased and bleached bones an individual so that many of the bones can be moved as they were in life. Often, plastic casts of the original bones are used. Although bone tissue predominates, fresh bones are composed of all four basic tissues types. However, when they are prepared for study, their organic portion is lost. These bones consist only of the mineral portion of the bones tissue. Original details remain, but the bones are brittle. Therefore, you must handle bones gently. Use a pipe cleaner to point out details and never use a pencil or pen because it is very difficult to remove marks. Materials - - - - - - - Pipe cleaner Compound microscope, lens paper, a bottle of lens-cleaning solution, a lint-free cloth. Prepared slides of o A synovial joint o A ground cross section of compact bone (optional) o A cross section of skeletal muscle Articulated adult human skeleton (natural bone or plastic) Femur Femur that has been sawed into two halves lengthwise Labeled chart and illustration of the adult human skeleton Procedure A. Identification of some bones There are 206 separate bones in the adult human skeleton. Using the labeled chart and illustrations of the human skeleton, identify the following bones on the articulated human skeleton and label them in Figure 38-1. 1. Axial skeleton: a) Skull (28 separate bones, including middle ear bones)(fig. 38-2) b) Vertebrae (singular, vertebra; 26 separate bones, including the sacrum, which is composed of five fused vertebrae, and the coccyx, which is usually composed of four fused vertebrae) (Fig. 38-3) c) Ribs (12 pairs of ribs for a total of 24 separate bones) (Fig. 38-4) d) Sternum (three fused bones) (Fig. 38-4) e) Hyoid (only bone that does not form a joint with another bone) (Fig. 38-4). 2
2. Appendicular skeleton (these are all paired bones found on the right and left sides of the body) I. pectoral girdle (shoulder) (Fig. 38-5) a) Scapula b) Clavicle Arm (Fig. 38-5, 38-6) a) Humerus b) Radius c) Ulna d) Carpals (8) e) Metacarpals (5) f) Phalanges (14) g) Pelvic girdle (hip) (Fig. 38-7) II. Coxal bone (three fused bones- pubis, ishium, ilium) Leg (Fig. 38.8) a) Femur b) Tibia c) Fibula d) Patella e) Tarsals (7) f) Metatarsals (5) g) Phalanges (14) 3
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B. Joints The degree of movements allowed at different joints ranges from none to freely movable (Fig. 38-9). Examples of immovable joints are the sutures that connect the bones of the roof of the skull of young adults. Joints that allow the freest movement are synovial joints such as the ones listed in Table 38-1. 1. Examine a prepared section of a synovial joint with your compound microscope. Identify the structures labeled in Fig. 38-9. The fibrous capsule of synovial joints is lined by a synovial membrane, which secretes lubricating synovial fluid. The fibrous capsule and ligaments function to stabilize synovial joints. Ligaments can be located outside and inside the capsule, and they may be thickening of its wall. 2. Identify the synovial joints listed in Fig. 38-1 and list the adjacent bones that form them in Table 39-1 page 6. 5
TABLE 38.1 Bones that form the major synovial joints Joint Wrist Elbow Shoulder Hip Knee Ankle Adjacent bones 6
C. Surface features There are many places on your body surface where bones can be felt. However, it is often difficult to tell specifically which bone you are feeling. Some are easy 1. Feel the bone supporting your lower jaw, the mandible. This is the only bone of the skull that forms a synovial joint with another skull bone. 2. Let s try a harder example, the piece of bone that projects from the point of the elbow joint. Touch it and alternately extend and flex the forearm, increasing and decreasing the angle between the forearm and upper arm, respectively. (a) Which part of the arm does the projection move with, forearm or upper arm? (b) While still touching this projection, alternately turn the hand palm down and up. Does the projection move? (yes or no) (c) Which bone belongs to this projection? In general, to identify a portion of a bone near a joint, move the body parts adjacent to the joint while touching the bone. 1. Identify the bones that have the surface features listed in Table 39-2 on page 10. 7
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Table 39-2 Features and Bones Surface Feature Bone Knuckles Bump next to the wrist and on the same side of the upper appendage as the little finger Smaller bump next to the wrist and on the same side of the upper appendage as the thumb Bump next to and outside the ankle Bump next to and inside the ankle D. Structure of a bone 1. Look at the femur, the longest bone of the skeleton (Fig. 39-10). It consist of shaft, or diaphysis, with two knobby ends, or epiphyses (singular, epiphysis). One end has a narrow neck and a round head. (a) Which bone does the femur join? (b) To which bone of the skeleton does the other end join? Note the other surface features on the femur, such as projections of various sizes and lines. These surface features are attachment sites for tendons and ligaments. Are these small tunnels openings onto the surface of the femur? (yes or no) In life these nutrient canals serves as routes for blood vessels and nerves. 2. Examine a femur that has been sawed in half lengthwise. There are two kinds of adult bone tissue: compact bone and spongy bone. Compact bone is solid and dense and is found on the surface of the femur. Spongy bone is lattice like and is found on the inside of the femur, primarily in the epiphyses and surrounding the marrow cavity. (a) Which kind of bone tissue looks denser? (b) Comparing pieces of equal size, which kind of bone tissue looks lighter? 10
E. Structures of a skeletal Muscle Like bones, skeletal muscles are composed of all four tissue types. Skeletal muscles are mostly skeletal muscle tissue with the individual skeletal muscle fibers arranged parallel to the axis along which the muscle shortens when contracting. A substantial amount of connective tissue surrounds the fibers and connects them to the tendons. Use your compound microscope to examine a section of a skeletal muscle. Look for fibers, fiber bundles the more or less loose connective tissue located between fibers and between bundles of fibers, and the fibrous connective tissue that surrounds the entire organ (Fig. 39-11) 39. 2 Leverage and Movements Much of the skeletal system is a system of levers, in which each bone is a lever and the joints are fulcrums. During a typical movement, one end of a skeletal muscle, the origin, remains stationary. The other end, the insertion moves along with the bone and surrounding body part. The movement produced by the contraction is the action of the skeletal muscle. Most insertions are close to their joints, and the advantage gained by this is that the muscle has to shorten a small distance to produce a large movement of the corresponding body part. Materials h) Pair of scissors i) Toggle switch mounted on a board (Alternatively, you can use any light switch present in the room.) j) Pair of forceps k) Pencil l) Textbook 11
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Procedure A. Classes of levers Levers are simple machines. When pulling force or effort is applied to a lever, it moves about its fulcrum, overcoming a resistance or moving a load. 1. There are three classes of levers (Fig. 39-12): m) Class I. The fulcrum is located between the effort and the load n) Class II. The load is located between the fulcrum and the effort. o) Class III. The effort is located between the fulcrum and the load. Class III levers are the most common in the skeletal system. Test your understanding of the three classes of levers by examining the objects listed in the following table and then matching them with the appropriate class of lever. 2. To remember the relative position of the fulcrum, the load, and the effort for each class of lever use this mnemonic (memory device): 1, 2, 3; F, L, E. For example, because 2 has the same relative position as L in figure 39 112b, the mnemonic tells you that a class II lever has the load in the center, the Effort at one end, and the fulcrum at the other. Try it for the other two classes of levers. Lever Class I. Class II. Class III. Object a. Scissor b. Toggle switch or light switch c. Forceps 13
B. Analysis of simple movements Let s analyze three simple movements: flexion of the forearm, extension of the forearm, and planter flexion of the foot (Fig 39-13). 1. Flexion of forearm. While sitting, turn your hand so the palm is up and place it under the lab bench. Try to flex the forearm (decrease the angle between the forearm and upper arm). Because the skeletal muscle that is attempting to flex the forearm cannot shorten, the tension in it will increase. A contraction of a skeletal muscle in which tension increases but no movement results is called an isometric contraction. Feel with your other hand the front surface of the upper arm. The large tense muscle is the biceps brachii. Its origin is the scapula, and its insertion is the radius. (a) Which joint is the fulcrum? Now place a pencil in the palm of your hand and flex the forearm. A contraction of a skeletal muscle that results in movement is called an isotonic contraction. There is no increase in tension during the movement. 14
Class III Class I Class II Feel the tension in the biceps brachii as you make this movement. Request this procedure, but replace the pencil with a textbook. Both the pencil and the book are adding to the load being lifted, the forearm. (a) In which case: (1) lifting the pencil or (2) the textbook, was the tension in the biceps brachii the greatest? When you lift any object, the tension in the muscle must equal the weight of that object before movement can occur. Therefore, normal movements have an isometric phase followed by an isotonic phase. (b) Where is the pulling force applied? (insertion, origin, or both the insertion and origin) Even simple movements require the coordination of a group of muscles. For example the origin does not move because other skeletal muscles hold the scapula stationary. (c) What class of lever (I, II, or III) is illustrated by this movement? 2. Extension of forearm. Place the hand, still palm up, on the top of the lab bench and try to extend the forearm (increase the angle between the forearm and the upper arm). Feel for a tense muscle on the back surface of the upper arm. This is the triceps brachii. The origin of the triceps brachii is the scapula and the upper humerus: its insertion is the olecranon process of the ulna (Fig. 36-10). The fulcrum is the same as the previous example, example, except that it has shifted position relative to the effort and the load. (a) What class of lever is illustrated by this movement? 15
Extension of the forearm is the opposite movement to flexion of the forearm. Hold the textbook, palm still up, halfway between full flexion and full extension. Feel the tension in the biceps brachii and triceps brachii. Repeat this procedure without the book. (b) Is the tension in the biceps brachii greater with or without book? (c) Is the tension in the triceps brachii greater with or without the book? The state of contraction of a group of skeletal muscles has to be coordinated to accomplish a particular movement or element of posture. Both the tendons of the biceps brachii and the triceps brachii are pulling on their insertions on the bones of the forearm to keep the forearm stationary. Other muscles are keeping the shoulder stationary. 3. Plantar flexion of foot. You need to stand up to do this movement. A lab partner should stand behind you and watch that you do not fall during this procedure. With one hand on the lab bench to steady your balance, stand on the tips of your toes. With your other hand, feel one of the very large tense muscles on the back of each calf. This is the gastrocnemius. The origin of the gastrocnemius is the femur, and its insertion is a tarsal, the calcaneus or heel bone. The fulcrum is the metatarsal-phalangeal joints, and the weight is the weight of the body transmitted through the tibia. (a) What class of lever does this movement exemplify? 39.3 Walking Walking is a complex activity that requires many movement and the coordinated contractions of several groups of skeletal muscles. For each leg, walking involves two phases, which together make up the step cycle. The stance phase occurs when the leg bears weight, and the swing phase occurs when the leg is in the air. Materials p) Safe place to walk Procedure 1. Follow your instructor s direction as to where to walk safely. Walk a few normal steps, concentrating on one leg. (a) What part of the foot (toe or heel) strikes the ground first? (b) What part of your foot leaves the ground first? (c) Does it leave passively, or does it push off? 2. Now put your hands on your hips and concentrate on what your pelvic girdle is doing while you walk. First take short strides and then long ones. (a) Does the pelvic girdle rotate more during short or long strides? 16
Rotation of the pelvic girdle can be demonstrated in a different way. Find a lab partner of about equal height. Walk right next to each other but out of step, that is, with opposite feet leading. First take short strides and then long ones. (a) What happens? This sideways movement is called lateral displacement. Incidentally, females in general have to rotate their pelvic girdles a little more than males for a given length of stride. This is due to differences in the proportions of the female and male pelvic girdles. 3. Vertical displacement also occurs during walking. From the side, observe two individuals of equal height walking out of step and next to each other. (a) Do their heads remain at the same level, or do they bob up and down? Pre Lab Questions 1. Ligaments connect (a) Bones to bones (b) Skeletal muscles to bones (c) Tendons to bones (d) Skeletal muscles to tendons 2. Tendons connect (a) Bones to bones (b) Skeletal muscles to bones (c) Ligaments to bones (d) Skeletal muscles to tendons 3. Which bone is part of the axial skeleton? (a) Clavicle (b) Radius (c) Coxal bone (d) Sternum 4. The two kinds of bones tissue are (a) Compact and loos (b) Compact and spongy (c) Dense and spongy (d) Loose and dense 5. There are classes of levers. (a) 2 (b) 3 (c) 4 (d) More than four 6. The class of lever in which the effort is located between the fulcrum and the load is called (a) Class I (b) Class II (c) Class III (d) Class IV 7. The end of the skeletal muscles that remains stationary during a movement is\ (a) The actin (b) The origin (c) The insertion (d) None of the above 8. In an isotonic contraction of a skeletal muscles, (a) The tension in the muscles increases (b) Movement occurs (c) No movement occurs (d) Both a and c occur 9. In an isometric contraction of a skeletal muscles, (a) The tension in the muscles increases (b) Movement occurs (c) No movement occurs (d) Both a and c occur 10. The step cycle of walking consists of (a) A stance phase (b) A swing phase (c) Both a and b (d) None of the above 17
Last Name, First Name [lab partner N0. 1] Last Name, First Name [lab partner N0. 2] Last Name, First Name [lab partner N0. 3] Last Name, First Name [lab partner N0. 4] Section group # Date Post - lab questions 39.1 Adult human skeleton 1. Match the following bones to their location in the body. Answer Bone Location Radius Coxal bone Ribs Scapula Fibula a. Pectoral girdle b. Leg c. Axial skeleton d. Arm e. Pelvic girdle 2. Label this photo of a femur that has been sawed in half lengthwise (Note: labels found at the bottom of the picture.) 18
3. Identify the bones indicated in this photo. 4. Label the fibrous capsule and synovial membrane of this joint. 39.2 Leverage and movement 5. Define the following term: a. the insertion of a skeletal muscle b. the origin of a skeletal muscle c. the action of a skeletal muscle 19
6. Explain the difference between isometric and isotonic contractions. How are both important to normal body movements? 7. Draw and label the structures of a typical skeletal muscle organ. 39.3 Walking 8. In your own words, describe one step in the walking cycle. Food for thought 9. The skeletal muscle that flexes (bends) the forearm after pronation (palm down position as in a pull-up) is the brachialis. Its origin is the humerus, and the insertion is the upper front of the ulna. Identify the class of lever involved and explain why you made this choice. 20