"Topic B.1 � Muscles and Movement"
Topic B.1 – Muscles and Movement IBSL Biology S. Dosman B.1.1 - State the roles of bones, ligaments, muscles, tendons and nerves in human movement. • A joint is where two or more bones come in contact with one another. • Joints provide our skeleton with mobility and hold the skeletal system together. • Joints include bones, ligaments, muscles, tendons and nerves. Bones • Bones are composed of many different tissues which make them organs. • There are 206 bones in the human body. They provide the following functions: • A hard framework to support the body • Protection of vulnerable tissues and organs • Acting as levers so the body can move • Blood cells are formed in the marrow • Storage area for minerals such as calcium and phosphorus Ligaments • Ligaments are tough, band-like structures that connect bone to bone and strengthen the joint. • They restrict movement at the joints to prevent over extension and dislocation. Muscles • Muscles provide the force necessary or needed to move a joint by contracting. • Muscles can move joints only when they contract so they must work in pairs. One muscle contracts and moves the joint in one direction while the other relaxes, and vice versa. • This combination of muscles is known as antagonistic pairs and the biceps and triceps are an example of an antagonistic pair. Tendons • Tendons are dense cords of connective tissue that connect muscle to bone. • Tendons are what allow muscles to pull on a bone. Nerves • The role of nerves is to stimulate the muscles. • This will cause contraction of the muscle and the joint will move. • The nerves also sense the contraction and the relative position of the limbs and this can help prevent overextension of the joint. B.1.2 - Label a diagram of the human elbow joint, including cartilage, synovial fluid, joint capsule, named bones and antagonistic muscles (biceps and triceps). B.1.3 - Outline the functions of the structures in the human elbow joint named in B.1.2. • The human elbow joint is a hinge joint which means it can move similar to the action of a door; open and close. • It involves three bones; the humerus is located in the upper arm and the lower arm consists of the radius and ulna. • The following chart summarizes the structures and functions of the human elbow joint. Structure Function Cartilage Cartilage provides the bones with a smooth surface which allows for easy movement, reduces friction and absorbs shock. Synovial fluid Lubricates the joint to reduce friction and also provides nutrients and oxygen to the cells of the cartilage. Joint capsule Surrounds the joint, encloses the synovial cavity, and unites the connecting bones. Tendons Attach muscle to bones. The biceps are attached to the scapula and the radius. The triceps are attached to the scapula and the ulna. Ligaments Connect bone to bone. The radius and ulna are connected to the humerus by ligaments. Biceps muscle Contraction of the bicep muscle pulls on the lower arm causes flexion (bending) of the arm. Triceps muscle Contraction of the triceps causes extension (straightening) of the arm. Humerus Acts as a lever that allows for the anchoring of the muscles of the elbow. Radius Acts as a lever for the biceps muscle. Ulna Acts as a lever for the triceps muscle. B.1.4 - Compare the movements of the hip joint and the knee joint. • Both the hip and knee joints are diarthrotic joints which mean they are freely moveable. • The knee joint, like the elbow joint, is also a hinge joint. • It allows for movement in one plane and this includes flexion and extension. A hinge joint does not allow for much movement in the other two planes. Hip Joint • The hip joint is known as a ball-and-socket joint. This type of joint permits movement in three planes. The motions possble are flexion, extension, abduction, adduction, circumduction, and rotation. • These types of movements can occur because the head of the femur is shaped like a ball and there is a cup-like depression known as the acetabulum in the hip bone that the head of the femur sits in. B.1.5 - Describe the structure of striated muscle fibres, including the myofibrils with light and dark bands, mitochondria, the sarcoplasmic reticulum, nuclei and the sarcolemma. • Striated muscle can also be referred to as skeletal muscle because it is responsible for the movement of the skeleton. • Striated muscle consists of thousands of cells referred to as muscle fibres because they are such long, multinucleate cells. • The muscle fibres are covered by a plasma membrane known as the sarcolemma which has many tunnel-like extensions known as transverse tubules that penetrate into the muscle cell. Structure of Striated Muscles • Muscle cells contain cytoplasm known as sarcoplasm. It contains a high number of glycosomes; organelles that store glycogen. It also contains large amounts of a red-colored protein known as myoglobin. • Striated muscle also contains sarcoplasmic reticulum which is similar to the endoplasmic reticulum studied earlier. It is a fluid filled system of membranous sacs that surround the myofibrils. Structure of Striated Muscles • Inside each muscle fibre are cylindrical structures known as myofibrils. These are composed of repeating units called sarcomeres; the unit that allows for movement. • They are rod-shaped and they run the length of the cell parallel to one another. In between the closely packed myofibrils are many mitochondria. • Sarcomeres have light and dark bands which extend across the myofibrils of the muscle fibre giving it its characteristic striated or stripped appearance. Actin and Myosin • Actin and myosin are two types of myofilaments composed of actin and myosin, two contractile proteins. They are compared in the table below. Actin Myosin Thin filaments (8 nm in diameter) Thick filaments (16 nm in diameter) Contains myosin binding sites Contains myosin heads that have actin binding sites Individual molecules form helical Individual molecules form a common structures shaft-like region with outward protruding heads Includes two regulatory proteins, Heads are referred to as cross-bridges tropomyosin and troponin and contain ATP binding sites and ATPase enzymes B.1.6 - Draw and label a diagram to show the structure of a sarcomere, including Z lines, actin filaments, myosin filaments with heads, and the resultant light and dark bands. B.1.7 - Explain how skeletal muscle contracts, including the release of calcium ions from the sarcoplasmic reticulum, the formation of cross- bridges, the sliding of actin and myosin filaments, and the use of ATP to break cross-bridges and re-set myosin heads. • Refer to handout given in class and the following animation: http://bcs.whfreeman.com/thelifewire/content/ chp47/4702001.html B.1.8 - Analyse electron micrographs to find the state of contraction of muscle fibres.