construction of a model demonstrating neural pathways and reflex arcs

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INNOVATIONS A N D I D E A S J. When the action potential is relayed to the cerebral cortex, the buzzer will sound. This signifies that the cerebral cortex has received information concerning the painful stimulus. You are now aware of pain in your body, and you also know exactly where that pain is located. Again, discuss with your partner what is happening along this pathway. QUESTIONS. 2) Describe the difference between the monosynaptic reflex/patellar tendon reflex and the withdrawal reflex upon painful stimulus. 2) Explain why both lamps light up in the withdrawal reflex upon painful stimulus when the system is initially turned on. 3) In the pain reflex, discuss the advantages of a pathway that reaches higher brain centers over a monosynaptic pathway. 4) How is the cerebral cortex involved in a pain/ temperature reflex? Explain your answer thoroughly. 5)WHATWOULDHAPPENIF:... the receptor were nonfunctional? . . . the afferent (sensory) neuron were cut? . . .the efferent (motor) neuron were cut? . ..the neuron between the thalamus and cerebral cortex were cut? When answering this question, use the approach that cutting a neuron would be equivalent to driving down a road that suddenly dead-ended. ANSWERS (WITHDRAWAL REFLEX UPON PAINFIJL STIMULUS). 1) There are two major differences between the two reflexes. Obviously, the polysynaptic withdrawal reflex upon painful stimulus is more complex. It con- tains an interneuron between the sensory neuron and motor neuron. In contrast, the corresponding part of the patellar tendon reflex is monosynaptic with a direct link between the alfimxt and e@erent neurons. The second difference involves the conscious awareness of pain. This leads to further processing for learning and memory. This second component of the pathway involves the thalamus and the cerebral cortex. Note that the monosynaptic reflex does not involve the brain at all. 2) Two synaptic junctions are simultaneously stimu- lated by the axon of the initial sensory neuron. This allows two action potentials to be initiated at the same time. One will cause an immediate withdrawal of the limb at which the stimulus is received, and the other informs the brain that pain has occurred somewhere in the body. It also causes subsequent actions as needed. 3) Because the cortex has the ability to store memo- ries and interpret information over time, this will lead to the avoidance of situations that cause pain. If the pain withdrawal reflex did not involve the cerebral cortex, there would be no previous knowledge about pain or learning involved. We would therefore not know to avoid painful sensations, and we would be destined to repeat them. 4) The involvement of the cerebral cortex provides an awareness of pain and simultaneously pinpoints the location of pain in the body. This can lead to a secondary reaction such as grabbing the injured body part or placing a burned finger in your mouth or holding it under cold water. The cerebral cortex can also interpret more information over time that leads to the creation of a memory. This leads to the avoidance of a situation that involves a painful stimulus. 5) WHAT WOIJI,D HAPPEN TF.. the receptor were nonfunctional? If the receptor were nonfunctional, there would be no sensory input received. Therefore, there would be no withdrawal from the harmful stimulus. Bodily harm could occur. For example, someone without a functional receptor might severely burn or cut their hand without realizing it. Note that the muscle would still be functional, and other neural impulses that caused the muscle to move, such as during exercise, would function normally. . . .the afferent (sensory) neuron were cut? If the afferent (sensory) neuron were cut, the receptor would be able to receive the stimulus. The receptor could also pass on the information it received to the sensory neuron, but the sensory neuron would not be able to transmit its information. So, no sensory information would be passed on to the interneuron or to the VOLUME 16 : NUMBER 1 - ADVANCES IN PHYSIOLOGY EDUCATION - DECEMBER 1996 s41
cerebral cortex. All of the also hold true he re. I N N 0 V A T I 0 N S A N D I D E A S above information would . . .the efferent (motor) neuron were cut? If the efferent (motor) neuron were cut, the withdrawal reaction would not occur because the muscle would not get the message to contract. The information would be received normally through the sensory receptor, sensory neuron, and interneuron. However, at the interneuron, the information would not be able to pass through the injured motor neuron. So, the muscle would not be moved away from the painful stimulus. The perception of pain in the cerebral cortex would exist because that component of the pathway would remain intact. Information can still pass from the sensory receptor to the sensory neuron and on to the neuron in the tract carrying information about pain, (external) temperature, and deep touch sensations. People can avoid excessive bodily damage with this injury by using their other functional limbs to jerk the damaged one away from the painful stimulus. They would be able to do this because they would be aware of the pain sensation and where it occurred. They could then do something about it. . . .the neuron between the thalamus and cerebral cortex were cut? If the neuron between the thalamus and the cerebral cortex were cut, the withdrawal part of the pathway would not be affected. Therefore, the automatic, reflexive component would exist. Destroying this specific connection between the cerebral cortex and thalamus would result in not knowing where the pain had occurred. Recall that the thalamus has a relay function, and it directs information to the appropriate area of cerebral cortex. Because of its relay function, the thalamus is still able to relay the information it received about the painful stimulus to the cerebral cortex. Whereas the specific connection going to the region of the cerebral cortex that deals with pinpointing pain does not exist, the thalamus can still send the information to other areas of the brain. Thus a general awareness of a painful sensation results, but you would be unable to pinpoint its location. DISCUSSION One of the authors (J. M. Pisegna) used this model in her senior-level biology class. The following will be a brief discussion of how the material was received by her students. In general, the students had no difficulty in following the directions as written. They found the actual experience of constructing the model enjoy- able and seemed genuinely surprised when they realized they understood the model. It was apparent that constructing and manipulating the model made it much easier for the students to grasp the concepts. This was due, we believe, in part to the hands-on, concrete nature of model building as well as the ability to keep the students attention and interest. The students truly appeared to be immersed in the entire process. Similar observations were noted by a col- league who used this same model construction experience with her anatomy and physiology class. On the basis of these experiences, we believe that more teachers should use model construction in teaching advanced concepts. V. Chan was supported by the Summer Fellowship Program at Northeastern Ohio Universities College of Medicine. J. Pisegna was supported by the American Physiological Society’s Frontiers in Physiology Science Research Program for Teachers. Address for reprint requests: S. E. DiCarlo, Dept. of Physiology, Northeastern Ohio Universities, College of Medicine, PO Box 95, Rootstown, OH 44272 (E-mail:sdicarlo@riker.neoucom.edu). Received 25 August 1995; accepted in final form 14 August 1996. References 1. Bredderman, T. What research says-Activity science-The evidence shows it matters. Science Children 20: 41, 1982. 2. Kandel, E. A., J. H Schwartz, and T. M. Jessel. Principles of NWWUZ Science (3rd en.). New York: Elsevier, 1991. 3. Teyler, T. J., and T. J. Voneida. Use of computer-assisted courseware in teaching neuroscience: the Graphic Brain. Am, J Physiol. 263 (Adv. Pbysiol. Educ. 8): S37-S44, 1992. 4. Tobin, K. The Practice of Constructivism in Science Education. Washington. DC: AAAS Press, 1993. VOLUME 16 : NUMBER 1 - ADVANCES IN PHYSIOLOGY EDUCATION - DECEMBER 1996 S42
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