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Across 4. A class of large neuroglial (macroglial) cells in the central nervous system. 9. an organ having nerve endings (in the skin or viscera or eye or ear or nose or mouth) that respond to stimulation 10. neuroglial tissue of mesodermal origin that can become phagocytic 11. a nerve fiber that carries impulses toward the muscles or glands 12. holds all of the general parts of a cell as well as the nucleus, which is the control center. 15. The nervous system outside the brain and spinal cord 16. The portion of the nervous system concerned with the control of voluntary muscle. 21. a cell of the neuroglia 22. A junction between two nerve cells, consisting of a minute gap across which impulses pass by diffusion of a neurotransmitter. 23. An organ or cell that acts in response to a stimulus: "effector cells". 24. 1.A structure containing a number of nerve cell bodies, typically linked by synapses, and often forming a swelling on a nerve fiber. 25. A type of neuroglia cell lining the central canal of the spinal cord or the brain. 26. The long threadlike part of a nerve cell along which impulses are conducted from the cell. 27. Any of the cordlike bundles of fibers made up of neurons through which sensory stimuli and motor impulses pass between the brain or other.

Down 1. any cell that covers the nerve fibers in the peripheral nervous system and forms the myelin sheath 2. 1.A short branched extension of a nerve cell, along which impulses received from other cells at synapses are transmitted to the cell body. 3. Part of the nervous system that was once thought to be functionally independent of the brain. 5. The complex of nerve tissues that controls the activities of the body. In vertebrates it comprises the brain and spinal cord 6. A specialized cell transmitting nerve impulses; a nerve cell. 7. A star-shaped glial cell of the central nervous system 8. 1.A chemical substance that is released at the end of a nerve fiber by the arrival of a nerve impulse and, by diffusing across the synapse or junction, causes the transfer of the impulse to another nerve fiber, a muscle fiber, or some other structure 13. the membrane potential to which a membrane must be depolarized to initiate an action potential 14. 1.The electrical potential of a neuron or other excitable cell relative to its surroundings when not stimulated or involved in passage of an impulse 17. 1.The change in electrical potential associated with the passage of an impulse along the membrane of a muscle cell or nerve cell 18. A gap in the myelin sheath of a nerve, between adjacent Schwann cells 19. a nerve fiber that carries impulses toward the central nervous system 20. a layer of myelin encasing (and insulating) the axons of medullated nerve fibers