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Across 1. Colorful, shiny blue material found behind the retina that reflects back light through the retinal giving some animals good night vision 4. Thick clear jelly found in the CENTER of the eye that helps give the eyeball its shape 5. A colorful, circular muscle that controls how much light enters the eye; reason for change in the size of the pupil 9. Another name for a neuron 10. The part of a nerve cell that carries impulses away from the cell body 12. Clear hard but flexible structure that can change its shape while focusing on objects that are close up or far away 14. The small space between two neurons or between a neuron add a muscle cell that an impulse must "hop" 16. Name for the two halves of the brain (cerebrum) 17. Type of photoreceptor cells found in the retina that activate in dim light 19. Made up of the brain and spinal cord 20. Thick, tough, clear protective covering over the iris and pupil; can get cloudy when diseased 21. Thick, tough white outer covering of the eyeball 22. A message carried by a neuron in the form of an electrical signal 23. Reaction to a stimulus 24. Thin, clear fluid that help the cornea keeps its shape

Down 2. Made up of all the nerves coming OFF the brain and spinal cord 3. Hole in the eye that lets light into the inner eye; appears as a white dot; its size is controlled by the iris 6. Nerve cells that carry electrical messages from the brain and spinal cord to the muscles to respond 7. The widest part of a nerve cell that houses the neuron's nucleus 8. Nerve cells that carry messages from the environment to the spinal cord and brain 11. Place where the optic nerve is attached to the retina; does NOT carry messages to the brain about what is being seen 13. Thick, tough bundle of nerve fibers found in the back of each eye that carry messages from the retina to the brain about what we see 15. The largest brain region; its wrinkled surface is divided into two hemispheres and our thinking & learning happens here 18. The parts of a nerve cell that receives impulses from stimuli or another nerve cell 20. Type of photoreceptor cells found in the retina that allow us to see colors in bright light