Question

Study the following and choose the correct statements:
• During muscle contraction, whenever action potential reaches the sarcoplasmic reticulum, \(Ca^{++}\) ions are released into the sarcoplasm.
• Accumulation of lactic acid in sarcoplasm leads to muscle fatigue.
• Ethmoid is considered as the keystone bone of the cranium.
• Sacrum is formed by the fusion of four sacral vertebrae.

• A. I, III
• B. II, IV
• C. I, II
• D. III, IV

Hint:

Sphenoid = Keystone bone of skull Sacrum = Fusion of 5 sacral vertebrae Calcium release from SR initiates muscle contraction.

Answer 1

The Correct Option is C

Concept: This question combines concepts from muscular physiology and skeletal system. Each statement should be examined independently.

Step 1: Check Statement I. Action potential travels through T-tubules. This stimulates sarcoplasmic reticulum. Sarcoplasmic reticulum releases: \[ Ca^{++} \] into sarcoplasm. Calcium binds troponin and initiates contraction. Hence Statement I is correct.

Step 2: Check Statement II. During vigorous exercise: \[ \text{Glucose} \rightarrow \text{Lactic Acid} \] Lactic acid accumulates in muscle fibers. This causes temporary muscle fatigue. Hence Statement II is correct.

Step 3: Check Statement III. The keystone bone of cranium is: \[ \boxed{\text{Sphenoid bone}} \] not Ethmoid bone. Hence Statement III is incorrect.

Step 4: Check Statement IV. Sacrum is formed by fusion of: \[ 5 \text{ sacral vertebrae} \] and not four. Therefore Statement IV is incorrect.

Step 5: Select correct statements. Only Statements I and II are correct. \[ \boxed{\text{Option (C)}} \]