Distinguish between:
$(1)$ Synapse and Neurotransmitters.
$(2)$ Myelinated nerve fiber and Non-myelinated nerve fiber.

(N/A) $(1)$ Synapse: The functional junction between the axon terminal of one neuron and the dendrite of the next neuron is called a synapse.
Neurotransmitter: These are chemical substances (e.g.,acetylcholine) released from the synaptic vesicles at the synaptic knob into the synaptic cleft to transmit nerve impulses.
$(2)$ Myelinated nerve fiber: These axons are enveloped by a fatty myelin sheath,which is secreted by Schwann cells.
Non-myelinated nerve fiber: These axons are not surrounded by a myelin sheath,although Schwann cells are present on their outer side.