Locomotion and Movement MCQ Practice for Biology

For NEET-level clarity, their roles are distinct but coordinated. The T-tubules (transverse tubules) are invaginations of the sarcolemma that carry the action potential deep into the muscle fibre. This signal triggers the sarcoplasmic reticulum, which is a specialised endoplasmic reticulum that acts as a reservoir for calcium ions (Ca²⁺). Upon stimulation, it releases these calcium ions into the sarcoplasm, which then initiates the cross-bridge cycle and muscle contraction.

This is a common concept trap. The sliding filament theory states that muscle contraction results from the thin actin filaments sliding past the thick myosin filaments. The individual lengths of actin and myosin filaments do not change. Instead, the sarcomere as a whole shortens because the Z-lines are pulled closer together. This process reduces the width of the I-band and the H-zone, while the A-band, which represents the length of the myosin filament, remains constant.

For effective preparation for NEET 2026, focus your MCQ practice on these high-yield areas from the chapter Locomotion and Movement:

• Sliding Filament Theory: The roles of actin, myosin, troponin, tropomyosin, ATP, and Ca²⁺.
• Sarcomere Structure: Identifying and understanding the changes in A-band, I-band, H-zone, and Z-line during contraction.
• Joints: Classification of synovial, fibrous, and cartilaginous joints with specific examples (e.g., pivot joint, saddle joint).
• Disorders: The specific causes and physiological effects of Myasthenia Gravis, Gout, Arthritis, and Osteoporosis.
• Skeletal System: The vertebral column formula and the bones of the axial and appendicular skeleton.

The primary difference lies in their metabolism and function. Red muscle fibres are rich in myoglobin and mitochondria, making them specialised for aerobic respiration. This allows them to sustain contractions for long periods, making them ideal for endurance activities. In contrast, white muscle fibres have less myoglobin and fewer mitochondria but a high amount of sarcoplasmic reticulum. They rely on anaerobic glycolysis for rapid energy, enabling powerful, short-duration contractions, such as in sprinting.

The human vertebral column is composed of 26 serially arranged units called vertebrae. It is differentiated into the following regions:

• Cervical: 7 vertebrae (C1 to C7) in the neck region.
• Thoracic: 12 vertebrae (T1 to T12) in the chest region, which articulate with the ribs.
• Lumbar: 5 vertebrae (L1 to L5) in the lower back.
• Sacral: 1 fused vertebra (formed from 5 sacral bones in an infant).
• Coccygeal: 1 fused vertebra (formed from 4 coccygeal bones in an infant) at the tail end.

This 7-12-5-1-1 formula is crucial for NEET MCQs.

Myasthenia Gravis is classified as an autoimmune disorder because the body's immune system mistakenly produces antibodies that attack its own proteins. Specifically, these antibodies block, alter, or destroy the acetylcholine (ACh) receptors at the neuromuscular junction. This prevents or reduces the binding of acetylcholine released from the motor neuron, leading to a failure in nerve impulse transmission to the muscle fibre. The result is progressive fatigue and severe weakness of skeletal muscles.

This scenario tests a deep understanding of the muscle contraction cycle. If ATP were depleted, the myosin heads, which are already attached to the actin filaments (forming cross-bridges), would be unable to detach. The binding of a new ATP molecule is required to break the cross-bridge. Therefore, even with high calcium levels keeping the actin binding sites exposed, the muscles would enter a state of continuous contraction known as rigor. This is the physiological basis for rigor mortis, which occurs after death when ATP production ceases.