How do muscle tissues contribute to movement?

Muscle tissues contribute to movement by contracting and relaxing in response to nerve signals.

Muscle tissues are specialised to contract, and this contraction is what enables movement. They are made up of individual muscle cells, also known as muscle fibres, which are long and cylindrical in shape. These fibres contain numerous myofibrils, which are the contractile units of the muscle. Myofibrils are made up of two types of protein filaments: actin (thin filaments) and myosin (thick filaments). The interaction between these filaments during contraction and relaxation is what drives movement.

The process of muscle contraction is initiated by a nerve impulse. When this impulse reaches the muscle, it triggers the release of calcium ions. These ions bind to a protein in the actin filaments, causing them to change shape and expose binding sites for the myosin filaments. The myosin heads then bind to these sites, forming cross-bridges. Using energy from ATP (adenosine triphosphate), the myosin heads pull the actin filaments towards the centre of the muscle fibre, causing it to shorten or contract. This is known as the sliding filament theory of muscle contraction.

Relaxation occurs when the nerve impulse stops. Calcium ions are pumped back into the storage areas, the myosin heads detach from the actin filaments, and the muscle fibre returns to its original length.

In terms of movement, different muscle tissues play different roles. Skeletal muscles, which are attached to bones by tendons, are responsible for all voluntary movements. When they contract, they pull on the bones, causing them to move. Smooth muscles, found in organs like the stomach and intestines, contract to move substances through these organs. Cardiac muscle, found only in the heart, contracts to pump blood around the body.

In summary, muscle tissues contribute to movement through the process of contraction and relaxation, which is controlled by nerve impulses and involves the interaction of protein filaments within the muscle fibres.