the junction between two neurons (axon-to-dendrite) or between a neuron and a muscle; "nerve impulses cross a synapse through the action of neurotransmitters"
a major part of the central nervous system which conducts sensory and motor nerve impulses to and from the brain; a long tubelike structure extending from the base of the brain through the vertebral canal to the upper lumbar region
the outer boundary of an artifact or a material layer constituting or resembling such a boundary; "there is a special cleaner for these surfaces"; "the cloth had a pattern of red dots on a white surface"
a superficial aspect as opposed to the real nature of something; "it was not what it appeared to be on the surface"
the extended two-dimensional outer boundary of a three-dimensional object; "they skimmed over the surface of the water"; "a brush small enough to clean every dental surface"; "the sun has no distinct surface"
the outermost level of the land or sea; "earthquakes originate far below the surface"; "three quarters of the Earth's surface is covered by water"