3.6.3 Skeletal muscles

Front

What is the primary function of antagonistic muscle pairs?

Back

To work against each other to move bones

Answer explanation

Antagonistic muscle pairs work against each other to create movement by contracting and relaxing, allowing bones to move at joints. This is essential for coordinated motion, making the correct answer 'To work against each other to move bones'.

Front

What best describes the ultrastructure of a myofibril?

Back

A bundle of actin and myosin filaments

Answer explanation

A myofibril is best described as a bundle of actin and myosin filaments, which are the key proteins involved in muscle contraction. This structure is essential for the function of muscle fibers.

Front

What role does calcium ions play in myofibril contraction?

Back

They bind to tropomyosin to expose binding sites

Answer explanation

Calcium ions bind to tropomyosin, causing a conformational change that exposes the binding sites on actin for myosin. This is crucial for initiating muscle contraction.

Front

Which molecule is directly responsible for the power stroke in muscle contraction?

Back

ATP

Answer explanation

ATP is crucial for muscle contraction as it provides the energy needed for the myosin heads to perform the power stroke, pulling actin filaments and causing muscle shortening.

Front

What is the role of phosphocreatine in muscle contraction?

Back

It provides a rapid source of ATP

Answer explanation

Phosphocreatine serves as a rapid source of ATP during muscle contraction, allowing for quick energy replenishment. This is crucial for sustaining high-intensity activities, making it essential for muscle function.

Front

Characteristic of slow skeletal muscle fibres?

Back

They have a high density of mitochondria

Answer explanation

Slow skeletal muscle fibres are characterized by a high density of mitochondria, which supports endurance activities by providing sustained energy. In contrast, they fatigue slowly and are not primarily used for short bursts of power.

Front

Where are fast skeletal muscle fibres typically located?

Back

In muscles used for quick, powerful movements

Answer explanation

Fast skeletal muscle fibers are primarily found in muscles responsible for quick, powerful movements, such as sprinting or weightlifting, due to their ability to contract rapidly and generate high force.

Front

What is the primary role of myosin in muscle contraction?

Back

To form cross-bridges with actin

Answer explanation

The primary role of myosin in muscle contraction is to form cross-bridges with actin. This interaction is crucial for muscle contraction, as it allows myosin to pull on actin filaments, leading to muscle shortening.

Front

How does ATP contribute to muscle relaxation?

Back

By detaching myosin heads from actin

Answer explanation

ATP contributes to muscle relaxation by detaching myosin heads from actin. When ATP binds to myosin, it causes the myosin heads to release from the actin filaments, allowing the muscle to relax.

Front

What is the role of tropomyosin in muscle contraction?

Back

It covers binding sites on actin

Answer explanation

Tropomyosin plays a crucial role in muscle contraction by covering the binding sites on actin filaments. When calcium ions bind to troponin, it causes tropomyosin to shift, exposing these sites for myosin to attach and initiate contraction.