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Across 4. A constriction in the myelin sheath, occurring at varying intervals along the length of a nerve fiber. 6. Fatty layers formed from certain neuroglia that surround axons,providing insulation. 8. A bundle of axons in the peripheral nervous system. 19. A nerve composed of sensory nerve fibers. 20. A type of neuroglial cell that connects neurons to blood vessels. 21. Mortor pathways of the peripheral nervous system that led to the skin and skeletal muscles. 23. Chemicals that axons secrete on effectors or other neurons. 24. The functional connection between the axon of a neuron and the dendrite or cell body of another neuron or the membrane of another cell type. 25. Nerve Cells. 26. The brain and spinal cord.

Down 1. Muscles or glands that effect changes in the body. 2. Part of the nervous system outside the central nervous system. 3. Process of a neuron that recieves input from other neurons. 5. Masses of neuron cell bodies,usually outside the central nervous system. 6. A neuroglial cell that supports neurons and phagocytizes. 7. Neuroglial cells that line the ventricles of the brain. 9. A momentary change in electrical potential on the surface of a cell, especially of a nerve or muscle cell, that occurs when it is stimulated, resulting in the transmission of an electrical impulse. 10. Stimulation level that must be exceeded to elicit a nerve impulse or a muscle contraction 11. A type of neuroglial cell that forms myelin. 12. Part of the nervous system that controls the viscera 13. The difference in electrical charge between the inside and outside of an undisturbed nerve cell membrane. 14. Specialized stuctures associated with the peripheral ends of sensory neurons specific to detecting a particular sensation and triggering nerve impulses in response,which are transmitted to the central nervous system. 15. A nerve that consist of mortor neuron axons. 16. The supportive tissue of the nervous system, including the network of branched cells in the central nervous system,and the supporting cells of the peripheral nervous system 17. A type of neuroglial cell that surronds an axon of peripheral neuron,forming the neurilemmal sheath and mylein. 18. Portion of the nerve cell that includes a cytoplasmic mass and nucleus,and from which nerve fibers extend. 22. A nerve fiber. It conducts a nerve impulse away from the neuron cell body.