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Read pgs. 516-519 Do #1-3 pg.521 Section 11.1: The Role of the Nervous System Section 11.1 Questions, page 521 1. (a) Afferent neurons receive signals from sensory receptors; efferent neurons transmit neural messages to effector tissues; interneurons transmit and integrate neural messages from the afferent neurons to the efferent neurons; effectors are the tissues where the appropriate response/stimulus takes place (for example, muscles, glands, and organs). (b) Afferent neurons, interneurons, efferent neurons, and effectors all work together to complete a neural circuit. (1) Afferent neurons receive a signal from sensory receptors (for example, on your skin); (2) the message is transmitted from afferent neurons to interneurons in the spinal cord; (3) integration of neural messages occurs in interneurons; and (4) there is response transmission of neural messages by efferent neurons to effectors (muscles or glands) where action appropriate to the stimulus occurs. 2. The nodes of Ranvier are gaps between sections of the myelin sheath, which expose the neuron to extracellular fluid. The alternating exposure and insulation from the fluid increases the rate of nerve impulse transmission. 3. The nervous system cells that provide a supporting role rather than a transmitting role are the Schwann cells, which produce the myelin sheath, and the glial cells, which provide nutritional and structural support for neurons. They facilitate the transmission of nerve impulses via neurons but do not provide nerve transmission themselves. 4. Reflexes have evolved to occur without the need for the brain to process the information because processing by the brain requires more time, possibly resulting in damage or injury to the body. The reflex arc is so quick that one experiences pain only after removing the finger from the hot element or sharp object. 5. A reflex arc is the process by which the body’s nervous system performs an automatic reaction to a stimulus by routing the neural transmissions through the spinal cord, but not to the brain. It usually operates very quickly and without the need for processing by the brain. An example is touching something hot or sharp with your finger, which results in the rapid pulling away of the finger from the source of the heat or sharp object. 6. Reports will vary. Student reports should include the following information on the causes, symptoms, and treatments of the disorder: Neurofibromatosis type 1 (NF-1) is a disease that causes the formation of a multitude of tumours. It occurs because of a malfunction of a gene on chromosome 17. This gene encodes a protein called neurofibromin, which plays a role in the control of cell signalling. Symptoms of NF-1 include six or more “cafe-au-lait” spots, which are areas of darkened skin that are greater than 5 mm in diameter, two or more neurofibromas (which are tumors of the nervous system), freckling of the armpit or groin, two or more growths in the eye, a tumor of the optic nerve (glioma), and/or scoliosis of the spine (curvature of the spine). Treatment of NF-1 can be complicated. There is no cure for the disease itself. Surgery is often used to remove tumours. In some cases, treatment of tumours with radiation and chemotherapy is required, if the tumours become cancerous. Other treatments for NF-1 are directed towards relieving symptoms associated with this disorder such as assistance with overcoming learning disorders that are often associated with NF-1 or treatment of headaches and seizures, which can also be experienced as a result of the disease. Neurofibromatosis may be underdiagnosed because its symptoms are so diverse and non-specific. Many of them can have other, more common causes. Copyright © 2012 Nelson Education Ltd. Chapter 11: The Nervous System 11.1-1