Actin and Myosin

Actin and myosin are both proteins that are present in all forms of muscle tissue. The interplay of bulky myosin filaments and thin actin filaments is what causes muscle contractions and movement. Myosin is a form of molecular motor that turns ATP’s chemical energy into mechanical energy. The actin filaments are subsequently pulled along by the mechanical energy, causing muscle fibres to contract and generate movement.

Actin and myosin

Myosin and actin are two proteins that are present in every type of muscle tissue. Actin creates smaller filaments, while myosin forms large filaments (15 nm in diameter) (7nm in diameter). The filaments of actin and myosin work together to create force. This force causes muscle cell contractions, which allow muscles and hence bodily structures to move more easily.

Types of Muscle

Muscle is a type of contractile tissue found in animals that is primarily responsible for movement facilitation. Muscle tissue may be divided into three categories in the human body:

Smooth muscle:  Smooth muscle is located in the internal organs (excluding the heart) and blood arteries and contracts automatically.

Cardiac muscle: Cardiac muscle is a kind of muscle that only exists in the heart and contracts automatically.

Skeletal muscle: Skeletal muscle is a type of muscle that is linked to bones. It is the most prevalent kind of muscle tissue in the human body and the only one capable of voluntary movement. Skeletal muscle contractions exert tension on the bones of the skeleton, allowing them to move (together with the bodily structures they support).

Actin and myosin filaments are found in all three muscle types and work together to create muscular contractions.

The Structure of Muscles

Muscular tissue is made up of muscle fibre bundles. Muscle fibres are long, slender cells that can be several inches long and may include several nuclei in skeletal muscle. Myofibrils, which are made up of bundles of strong myosin filaments and thin actin filaments, are long, thread-like structures found in the cytoplasm of muscle fibres. Sarcoplasmic reticulum (SR) is a tubular network that accumulates calcium ions and surrounds actin and myosin filaments. Additionally, the SR plays a role in the propagation of electrical impulses. Neurons transmit these electrical impulses to the muscle cells.

Sarcomeres are repeated contractile units that make up each myofibril. A Z disc is located at the end of each sarcomere.

Two types of bands may be found on sarcomeres. The A bands, which are black in colour and include dense myosin filaments, and the I bands, which are lighter in colour and contain just thin actin filaments, are the two types. The actin filaments are linked to the Z disc, whereas the myosin filaments are tethered to the M line, which runs across the centre of the sarcomere.

Functions of Actin and Myosin

Actin and myosin are two proteins that work together to cause muscle contractions and, as a result, movement. A motor neuron first sends an electrical signal from the brain to the muscle cell. A molecule called acetylcholine is released as a result of this. Calcium ions are released from the sarcoplasmic reticulum when acetylcholine is present. The calcium ions then bond to a protein known as troponin. Troponin is located in muscle tissue between the actin filaments and is connected to another protein termed tropomyosin.

The form of troponin changes as calcium ions attach to it. This ‘unblocks’ tropomyosin from the myosin-binding sites on the actin filament, allowing the myosin heads to connect to the filament.

The myosin heads can bind to the exposed binding sites on the actin filaments once tropomyosin has moved out of the way. This causes muscle contraction to begin by forming actin-myosin cross-bridges.

When ATP is hydrolyzed, energy is released, and myosin acts as a motor to turn this chemical energy into mechanical energy.

That mechanical energy is used by the myosin to drive its head groups towards the sarcomere’s midsection. The actin filaments are pulled towards the sarcomere’s core, causing the sarcomere to shorten and contract. Muscle movement is caused by the contraction of the sarcomere, which causes the muscle fibre to contract.

Conclusion

The filaments of actin and myosin work together to create force. This force causes muscle cell contractions, which allow muscles and hence bodily structures to move more easily.