Answer:
a). Voltage-gated Ca2+ channels
b). the motor end plate
c). Threshold, voltage-gated Na channels
d). sodium ions
Explanation:
a). The voltage-gated [tex]Ca^{2+}[/tex] channels are the key transducers of the membrane potential that changes into a intracellular [tex]Ca^{2+}[/tex] transients which initiates the physiological events. When the action potential makes a contact with axon terminal, the voltage-gated [tex]Ca^{2+}[/tex] channels opens.
b). The acetylcholine is the main neurotransmitter of the parasympathetic nervous system. It helps in blood vessels dilation, muscle contraction, and perform many more functions.
It diffuses with the synaptic cleft that is located on the motor end plate of the nervous system.
c). The membrane potential is also known as the membrane voltage or the transmembrane potential. When it recaches the threshold, the voltage-gated Na channels opens to spread the action potential across sarcolemma.
d). The sodium ions in case of acetylcholine binding moves to the muscle fiber due to which the membrane potential rises.