When acetylcholine binds to receptors at the motor end plate, the end plate membrane becames: . repolarized. b. more permeable to calcium ions. c. less permeable to potassium ions. d. more permeable to sodium ions. e. less permeable to sodium ions.

d. more permeable to sodium ions.

Explanation:

The binding of Acetylcholine  with the receptors at  motor end plate facilitate   membrane permeability to sodium ions therefore  opening of voltage gated channels for sodium ions.

Sodium ions diffused into the synapse of post synaptic neuron at the neuromuscular junction.

If  the  stimulus is up to threshold levels; more chemical(neurotransmitter) gated sodium channels opens, and sodium ions move into the  synapse to depolarize the membrane with  reversal of charges to generate action potential.

The continuous  binding of Acetycholine , leads to permanent opening of sodium ions,and over excitation from depolarization.  Acetycholinesterase enzymes breakdown Acetycholine to choline  and Acetyl Co -A. These are recycle back to Acetycholiine