Give scientific reasons:
$(1)$ There is no physical connection between sequential neurons,yet nerve impulses are conducted through them.
$(2)$ The neuroplasm of a neuron contains a high $K^+$ concentration during the maintenance of the resting potential.

(N/A) $(1)$ At the end of a branched axon,a knob-like swollen structure called the synaptic knob is present. It contains secretory vesicles that produce neurotransmitter substances,such as acetylcholine.
Acetylcholine is released into the synaptic cleft and binds to receptors on the postsynaptic membrane,allowing the conduction of nerve impulses across the synapse.
$(2)$ For the maintenance of the resting membrane potential,ion pumps and ion channels play a significant role. Through the $Na^+-K^+$ pump,$3 Na^+$ ions are actively transported out of the neuroplasm,while $2 K^+$ ions are transported inside. This active transport,combined with the selective permeability of the membrane,results in a higher concentration of $K^+$ ions inside the neuron compared to the extracellular fluid.