Name: Bone Structure and Types
Uploaded: 2019-07-19
Duration: 4 min 55 s
Description: Bones are living tissue with blood vessels made of various cells, proteins, minerals and vitamins. Let's learn about bone structure and types in this video.

Question

Explain the sliding- filament theory of muscle contraction.

Accepted Answer

The Sarcomere is the basic unit of muscle that can undergo contraction. Each sarcomere extends from one Z line to the other. It consists of thick actin and thin myosin filaments. According to the sliding filament theory of muscle contraction, overlapping actin and myosin filaments of a fixed length that slide past one another in an energy-requiring process results in muscle contraction.

The contraction of a muscle can be best explained by the sliding filament theory of muscle contraction. It states that the contraction of a muscle fibre occurs due to the sliding of the thin actin filaments over thick myosin filaments.

Mechanism of muscle contraction is best explained as follows:

1. Depolarisation of Sarcolemma - The central nervous system(CNS) sends a signal to the neuromuscular junction, which is the point of contact between the sarcolemma of the muscle fibre and the motor neuron. It stimulates the release of a neurotransmitter known as acetylcholine which sets the action potential in the sarcolemma.

2. Release of calcium ions - The above action potential reaches the sarcolemma and to the organelle sarcoplasmic reticulum through the T-tubule and triggers the release of the calcium ions in the sarcoplasm.

3. Confirmation change in the Actin Filaments- The calcium ions bind to the tropomyosin and troponin that are located on the actin myofilaments, which causes a modification in the three-dimensional structure of the actin-troponin-tropomyosin complex. Thus, the active site for myosin located on the actin filament is exposed.

4. Activation of Myosin heads - When the myosin heads get activated, the hydrolysis of ATP occurs. It releases energy that causes the binding of myosin heads to the active sites on the actin filaments, forming a cross-bridge in between them.

5. Sliding of Actin Filaments over Myosin heads- Formation of cross-bridge causes the myosin head to rotate which pulls the actin filaments to the centre of the A-band and the H zone disappears. The z-line that is attached to the actin filaments is also pulled inwards, which results in the contraction of the sarcomere. The I-band also shortens during the process of contraction, whereas the A-band maintains its length.

Explain the sliding- filament theory of muscle contraction.

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