a sharp rigid animal process or appendage; as a porcupine quill or a ridge on a bone or a ray of a fish fin
the part of a book's cover that encloses the inner side of the book's pages and that faces outward when the book is shelved; "the title and author were printed on the spine of the book"
a small sharp-pointed tip resembling a spike on a stem or leaf
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