Assertion: On stimulation, a muscle cell releases calcium ions (Ca²⁺) from sarcoplasmic
reticulum.
Reason: By reacting with a protein complex, Ca²⁺ uncover active sites on the actin filaments

If both assertion and reason are true and reason is the correct explanation of assertion.

If both assertion and reason are true but reason is not the correct explanation of assertion.

If assertion is true but reason is false.

If both assertion and reason are false.

Solution

If both assertion and reason are true but reason is not the correct explanation of assertion.

A neural signal reaching this junction releases a neurotransmitter (Acetyl choline) which generates an action potential in the sarcolemma. This spreads through the muscle fibre and causes the release of calcium ions into the sarcoplasm. Increase in Ca²⁺ level leads to the binding of calcium with a subunit of troponin on actin filaments and thereby remove the masking of active sites for myosin.