The complete question is :
Which of the following best describes how ACh changes the ion permeability of the sarcolemma?
A) ACh activates acetylcholinesterase.
B) ACh entry into the axon terminal causes neurotransmitter release.
C) ACh binds to receptors in the junctional folds.
D) ACh entry into the muscle fiber causes Ca2+ to be released by the sarcoplasmic reticulum.
Answer:
C) ACh binds to receptors in the junctional folds.
Explanation:
Sarcolemma is the term used for the cell membrane of the skeleton muscle fiber cell.
At the motor end plate, there are several folds present in the sarcolemma that are known as junctional folds.
These junctional folds have several acetylcholine (Ach) receptors present on them and these are ion channels that are chemically gated.
These ion channels open upon binding of Ach and thus, the ions can diffuse into the sarcolemma.
Thus, the binding of Ach on the receptors located in the junctional folds increases the ion permeabiltity of the sarcolemma.
