Muscles and Movement

• Myoglobin is a ready and fast supplier of oxygen to muscles when they need it.
• The bony skeleton supports your whole body, allowing you to move around as a result of the way the bones of your skeleton and other skeletal tissues work together.
• The main tissue of the skeleton is bone, which is strong and hard, made of bone cells fixed firmly in a matrix of collagen and calcium salts.
• Bone is strong under compression force and needs to be hard but as light as possible to reduce the weight you have to move about.
• Compact bone is dense and heavy, found in the long bones of your body.
• Spongy bone has a more open structure, is much lighter, and is found in large masses of bones such as pelvis and head of the femur (thigh bone).
• The skeletal tissue, cartilage, is hard but flexible, made of cells called chondrocytes within an organic matrix made of collagen fibrils.
• Cartilage is elastic and able to withstand compression forces, acting as a shock absorber.
• Cartilage is found between bones to prevent friction during movement.
• There are two main types of cartilage found in the skeleton: Hyaline cartilage is found at the ends of bones, tip of the nose, parts of the ear and in airway passages.
• White fibrous cartilage has bundles of densely packed collagen in the matrix, has great tensile strength and is less flexible than other forms of cartilage.
• Tendons are made of white fibrous tissue, consist of bundles of collagen fibres to form a strong and inelastic tissue, and join the muscles to the bones securely.
• Ligaments hold the bones together and form a capsule around the joint, are elastic to allow movement of the bones at the joints, and are formed of yellow elastic tissue which gives strength and elasticity.
• Types of joints include Ball and socket joint, which allows a wide range of movement such as the shoulder joint, and Hinge joint, which allows a narrow range of movement as the elbow joint.
• If the joints are just bone on bone, this leads to wearing away of both bones due to friction, to prevent this, the joint is lined with a layer of cartilage to allow smooth articulation.
• Some joints produce an oily synovial fluid for lubrication to ensure friction-free movement.
• Movement happens due to the action of muscles on bones, each skeletal muscle is attached by tendons to two bones, spanning at least one joint.
• Different muscle fibers have different proportions of slow and fast twitch fibers.
• The two types of muscle fibers have different properties.
• Most people have equal amounts of both muscle fibers.
• Endurance athletes have high proportions of slow twitch fibers.
• In weightlifters and sprinters, there is a higher proportion of fast twitch fibers because they need maximum strength of their muscles in short activities.
• Training can change the number of muscle fibers, but the size and type of fibers can change with exercise.
• Different genes which affect the components of the muscle can be enhanced with further training.
• Superfast twitch fibers contract more quickly and strongly than usual.
• Muscle contraction is explained by Sliding Filament Theory.
• Myosin and actin filaments slide over one another to make the sarcomeres contract.
• The simultaneous contraction of lots of sarcomeres means the myofibrils and muscle fibres contract.
• Sarcomeres return to their original length as the muscles relaxes.
• Myosin filaments have globular heads that are hinged, so they can move back and forth.
• Each myosin head has a binding site for actin and a binding site for ATP.
• Actin filaments have binding sites for myosin heads, called actin - myosin binding sites.
• Two other proteins called tropomyosin and troponin are found between actin filaments.
• These proteins are attached to each other and they help myofilaments move past each other.
• In a resting (unstimulated) muscle, the actin - myosin binding site is blocked by tropomyosin, which is held in place by troponin.
• When an action potential from a motor neuron stimulates a muscle cell, it depolarizes the sarcolemma, spreading down the T- tubules to the sarcoplasmic reticulum.
• This causes the sarcoplasmic reticulum to release stored calcium ions (Ca2+) into the sarcoplasm.
• Calcium ions bind to troponin, causing it to change shape, which pulls the attached tropomyosin out of the actin – myosin binding site on the actin filament.
• The bond formed when a myosin head binds to an actin filament is called an actin - myosin cross bridge.
• After actin - myosin cross-bridges are formed, phosphate ion is released from the myosin head.