If a substance can move across a membrane than it is said to be

It's permeable to the membrane. The membrane has enough space for it to move through, the partials of the substance is small enough.

Neurotransmitters are messengers responsible for communication between neurons. they are released from synaptic vesicles and are received by receptors.  the communication is referred to as neurotransmission. the following statement is true about neurotransmitters: a. they're stored in synaptic vesicles in the axon.