1. NEUROMUSCULA R CONTROL OF MUSCLES 2. NERVOUS CONTROL OF MUSCLES 3. A MOTOR UNIT A motor unit consists of one motor neuron and the muscle fibre it stimulates (Each neuron may stimulate a number of muscle fibres) Depending on the size and function of a muscle will depend on the number of motor units it has Example: The quadriceps are responsible for gross movement such as kicking and jumping. They have a very large number of motor units The muscles that control movements like writing and typing have only a small 4. THE ALL OR NOTHING PRINCIPLE The nerve impulse will not stimulate the muscle fibres until it reaches a certain threshold level. Once the nerve impulse reaches this threshold, all fibres of the motor unit will contract at the same time and maximally. If the impulse is too weak, no fibres will contract. Therefore depending on the force required for a movement will impact the number and speed of nerve impulses sent. 5. UNDERSTANDING MUSCLE Muscles never work on their own, and always work in teams. A muscle belly will have tendons at either end to attach them to bone A muscle is always attached to 2 or more bones (by tendons) to allow a stable and strong surface to pull against. These connections are called the origin and insertion. 6. STRUCTURE The muscle belly consists of thousands of muscle fibres known as fascicles which run side by side along the length of the muscle Each of these fibres is encased in and surrounded by connective tissue known as perimysium, which assists in keeping the fascicles together. 7. MUSCLE FIBRES Each fascicle is made up of several muscle fibres, which are made up of even smaller fibres called myofibrils, which are similar to the many wires within a telephone cable. These have many units, known as sarcomeres, which are arranged end to end for their entire length of the myofibril 8. SARCOMERE Is a contractile unit, and each end is designated by a line called a Z-line. Each sarcomere consists of two proteins myofilaments called actin and myosin. Actin is a thin filament which is attached to the Z-line Myosin is a thick filament which is situated between 9. THE LINES AND ZONES OF A SARCOMERE 10. The Z-line: Marks the two ends of a sarcomere The I-band: Where only actin is found The A-band: Where both actin and myosin are found and equates to the length of the myosin filaments The H-zone: Where only myosin is found and is the gap between the ends of the actin THE LINES AND ZONES OF A SARCOMERE 11. A MUSCULAR CONTRACTION The myosin filaments have cross bridges (oar-like structures) that are attracted to the actin filaments At rest, there is little contact between the actin and the myosin However, when the sarcomere contracts, the cross bridges attach to the actin filaments and pull them into the centre of the sarcomere in a rowing action The cross bridges continue to detach and reattach themselves from the actin filaments, shortening the sarcomere. Every sarcomere along the muscle fibre shortens, leading the whole muscle to contract. The muscle will relax when the actin and myosin filaments lose contact with each other that is, when the cross bridges detach from the actin. 12. MUSCLE TONE Not all the myosin filaments detach themselves from the actin. Some may stay in contact, so the muscle is never completely relaxed. If this is the case, the muscle is said to have tone The advantage of muscle tone is that the actin and