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Across 2. a type of neuroglial cell that connects neurons to blood vessels 6. stimulation level that must be exceeded to elicit a nerve impulse or a muscle contraction 7. a nerve fiber; it conducts a nerve impulse away from the neuron cell body 8. a nerve that consists of motor neuron axons 9. motor pathways of the peripheral nervous system that lead to the skin and skeletal muscles 10. the brain and spinal cord 12. nerve cells 16. a nerve composed of sensory nerve fibers 17. fatty layers formed from certain neuroglia that surround axons, providing insulation 18. portion of nerve cell that includes a cytoplasmic mass and a nucleus, and from which nerve fibers extend 19. chemicals that axons secrete on effectors (muscles or glands) or other neurons 21. specialized cells of the nervous system that produce myelin, communicate between cells, maintain the iconic environment, and nurture the differentiation of neurons 22. a neuroglial cell that supports neurons and phagocytes 23. the sequence of electrical changes that occurs in a portion of a nerve cell membrane that is exposed to a stimulus that exceeds the membrane's threshold 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. a type of neuroglial cell that surrounds an axon of a peripheral neuron, forming the neurilemmal sheath and myelin 26. masses of neuron cell bodies, usually outside the central nervous system

Down 1. part of the nervous system outside the central nervous system 2. part of the nervous system that controls the viscera 3. neuroglial cells that line the ventricles of the brain 4. process of a neuron that receives input fro other neurons 5. narrow gaps between schwann cells 11. specialized structures 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 13. the difference in electrical charge between the inside and the outside of an undisturbed nerve cell membrane 14. a type of neuroglial cell that forms myelin 15. muscles or glands that efect changes in the body 20. a bundle of axons in the peripheral nervous system