Muscles and Movement Structures involved in human movement Bone – rigid structure for anchoring muscles Muscle – contract and relax to allow movement of bone Tendon – joins muscle to bone Ligaments – joins bone Nerves – provide the impulse that causes muscle to contract - sense relative position of the limbs

Antagonistic pairs of muscle often work together on opposite sides of a bone to bring about movement eg/ biceps and triceps The Elbow joint The end of each bone in the elbow is made of spongy bone, which is light but strong. Cartilage covering the end of the bones helps to provide smooth movement and also absorbs shock. The bursa contains synovial fluid. This contains glucose and oxygen to maintain the cartilage and to act as a lubricant for the joint.

Synovial fluid is contained within the synovial membrane which secretes synovial fluid and keeps it within the joint. The Hip and the Knee Similarities: Both are synovial joints Both are required to move the leg Both are required for walking

Differences: Abduction and adduction refers to sideways movement of the leg away from the centre of the body. Hip Joint Knee Joint Type of Joint Ball and socket Hinge Axes of movement Multi axial Moves in one axis only Kinds of movement Flex and extend Abduction and adduction Rotation Small amount of rotation

Striated Muscle Muscle cell Each muscle cell was originally many cells which fused and so the resulting cell contains many nuclei. The cytoplasm of the muscle cell is called sarcoplasm and the internal membrane is sarcoplasmic reticulum. Its role is to store and release calcium ions. Myofibril contraction requires a lot of energy, so many mitochondria are found between the myofibrils.

Sarcomere structure The sarcomere is the functional unit of the muscle Sarcomere structure The sarcomere is the functional unit of the muscle. The striped appearance of skeletal muscle is due to the arrangement of two types of protein filaments. Thin actin filaments are attached to the Z line and form the I band – the light section. Thick myosin filaments are in the centre of the sarcomere, sandwiched between thin actin filaments.

Muscle Contraction Skeletal muscle contraction is explained by the sliding filament theory which states that actin and myosin filaments slide over each other to make the muscle shorter. When the muscle is Contracted, the distance between the Z lines becomes shorter. In addition, both the I bands and H zone become smaller.

The filament slide over each other due to the action of myosin heads, attached to the thick myosin filament. When contraction begins, these myosin heads attach to the actin filaments, forming a cross bridge, and pull them closer. They then release the actin filament, swing through a cycle and re-attach. This is repeated until the muscle is contracted. This process is referred to as the ratchet mechanism. Actin filaments contain two additional proteins – tropomyosin and troponin. Tropomyosin exists as two strands wound around the actin. When muscle is in the relaxed state, these cover the binding sites for the myosin heads.

When a nerve impulse arrives, the depolarisation of the nerve ending (motor end plate) is passed on to the sarcoplasmic reticulum, which in turn releases Ca2+ into the sarcoplasm. The calcium ions attach to the troponin, which is attached to the tropomyosin. This causes the tropomyosin to shift and in so doing, exposes the binding sites for the myosin heads. As long as calcium is present in the sarcoplasm, the muscle will continue to contract. When nerve impulses stop arriving at the muscle, Ca2+ are actively transported back into the vesicles of the sarcoplasmic reticulum. The tropomyosin moves back into its original position and covers the binding sites, allowing the muscle to relax. Sliding Filament - YouTube

Electron micrograph analysis Right next to the Z line is a white band of only actin (I band). Further towards the centre of the sarcomere is the darkest band, the A band, which is where actin and myosin overlap. In the centre of the dark A band is a grey H zone of myosin filaments only. When the muscle contracts, the distance between the Z lines becomes shorter.

In addition, both the I band and the H zone become smaller.