Match List I with List II related to muscular/skeletal system:

List I	List II
A. Tetany	I. Inflammation of joints
B. Arthritis	II. Autoimmune disorder affecting neuromuscular junction
C. Myasthenia gravis	III. Wild contraction in muscle due to low Ca⁺⁺$Ca^{++}$ in body fluid
D. Muscular dystrophy	IV. Progressive degeneration of skeletal muscle

Choose the correct answer from the options given below:

Core Logic

(A) Incorrect: Human skull is dicondylic. The skull region articulates with the superior region of the vertebral column with the help of two occipital condyles. (B) Correct: The joint present between the adjacent vertebrae of vertebral column is cartilaginous joints. (C) Correct: There are 7 cervical vertebrae in almost all mammals including human beings. (D) Incorrect: All ribs of humans are bicephalic, i.e., they have two articulation surfaces on their dorsal end. (E) Correct: The occipital bone of the skull articulates with the atlas vertebra via occipital condyles, forming the atlanto-occipital joint.

Step 1: Final Conclusion

The correct statements are B, C, and E.

Pattern Recognition

Humans are dicondylic. All ribs are bicephalic dorsally. 7 cervical vertebrae is a defining mammalian trait.

Chapter Mix

Class 11 Biology: Locomotion and Movement

Core Logic

Statements A, B, D and E are correct while statement C is incorrect. A neural signal reaching the neuromuscular junction releases a neurotransmitter (Acetylcholine) which generates an action potential in the sarcolemma. This spreads through the muscle fibre and causes the release of Ca⁺⁺$Ca^{++}$ into the sarcoplasm. This Ca⁺⁺$Ca^{++}$ binds to the subunit of troponin on actin filaments and thereby removes the masking of active sites for myosin on actin, facilitating the FORMATION of a cross bridge (not breaking them). Thus, increase in Ca⁺⁺$Ca^{++}$ activates actin, contrary to statement C.

Pattern Recognition

Calcium binding to troponin exposes myosin-binding sites. This initiates the sliding filament mechanism. Calcium does not break cross-bridges; ATP does.

Chapter Mix

Class 11 Biology: Locomotion and Movement