Muscle fibre

Muscle Fibre

A muscle fibre is a single cell within a muscle that has the ability to contract. Muscle fibres are the building blocks of muscles and are responsible for the movement and strength of the body. They are classified into three main types: Type I, Type IIa, and Type IIb, each with distinct characteristics and functions.

Structure

Each muscle fibre is a long, cylindrical cell with multiple nuclei located at the periphery. The fibre is filled with myofibrils, which are the contractile elements of the cell. These myofibrils are made up of repeating units called sarcomeres, which contain the proteins actin and myosin. These proteins slide past each other during muscle contraction, shortening the sarcomere and causing the muscle fibre to contract.

Types of Muscle Fibres

Type I

Type I muscle fibres, also known as slow-twitch fibres, are designed for endurance and sustained contraction. They have a high capacity for aerobic metabolism and are resistant to fatigue. These fibres are found in large numbers in muscles used for posture and endurance activities.

Type IIa

Type IIa muscle fibres, or fast-twitch oxidative fibres, are a hybrid of Type I and Type IIb fibres. They have a high capacity for both aerobic and anaerobic metabolism, making them suitable for activities that require both strength and endurance.

Type IIb

Type IIb muscle fibres, or fast-twitch glycolytic fibres, are designed for short, intense bursts of power. They have a high capacity for anaerobic metabolism and fatigue quickly. These fibres are found in large numbers in muscles used for power and speed.

Function

Muscle fibres contract in response to signals from the nervous system. The type of muscle fibre activated depends on the nature of the activity. For example, during a marathon, the body primarily uses Type I fibres, while during a sprint, it primarily uses Type IIb fibres.

See Also

• Muscle
• Myofibril
• Sarcomere
• Actin
• Myosin