construction of a model demonstrating neural pathways and reflex arcs

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#4 I N N 0 V A T I 0 N S A N D IDEAS #2 FIG. 19. Polysynaptic withdrawal reflex upon painful stimulus is illustrated. Arrange the 4 sheets of paper ln the order shown here. Trace the path of the reflex by following the numbered sheets clockwise. Sheet 1 contains the skin receptor that senses the painful stimulus. Sensory neuron extends from the skin receptor to the spinal cord illustrated on sheet 3. Sensory neuron synapses with an interneuron in the spinal cord at the S-l unit and with a second interneuron in the spinal cord at the S-2 unit. Interneuron from the S-2 unit passes its information to the ascending tract for pain and temperature. S-4 unit is a synapse in the thalamus that continues to the cerebral cortex illustrated on sheet 2. The interneuron from the S-l unit synapses with the motor neuron at the S-3 unit on sheet 3. Motor neuron travels to the muscle effector shown in sheet 4, which allows an individual to pull away from the painful stimulus. understanding of neural pathways and the monosynaptic reflex. Objectives On completion of this laboratory unit, students should be able to l Diagram and describe the neural pathways in- volved in the withdrawal reflex upon painful stimulus and the monosynaptic reflex/patellar tendon reflex l Construct a working model of a monosynaptic reflex arc (knee jerk/patellar tendon reflex) l Use the model to explain what happens during the monosynaptic portion of the patellar tendon reflex * Construct a working model of the withdrawal reflex upon painful stimulus l List the components and describe the function of a l Use the model to explain what happens at each monosynaptic reflex stage of the withdrawal reflex upon painful stimulus VOLUME 16 : NUMBER 1 - ADVANCES IN PHYSIOLOGY EDUCATION - DECEMBER 1996 s35
INNOVATIONS AN D ID EAS l Compare a monosynaptic reflex as illustrated by the patellar tendon reflex to the polysynaptic withdrawal reflex upon painful stimulus. Introduction This model is designed to illustrate reflex mechanisms of the nervous system. It is important to realize that this model is only an electrical representation of what happens in the nervous system. In the body, both electrical current and chemical transmission are in- volved in information transfer. Chemical synaptic transmission cannot be shown by this solely electrical model. Constructing the Models Part I: monosynaptic reJex/patellar tendon reflex. MATERIALS NEEDED. The materials needed are the monosynaptic reflex diagram sheets, monosynaptic wire packet, one synaptic junction (lamp/switch connec- tions), four AA batteries with holder, one motor, tape (masking or clear), and a Phillips screwdriver. INSTRUCTIONS. A. The monosynaptic reflex diagram sheets are numbered l-4 in the upper left-hand corner. Arrange the four sheets on the lab table in the order shown below and in Fig. 18. Tape the four pages together and tape the entire diagram to the table. &I B. Place the synaptic junction unit (switch/lamp) on the diagram at the site labeled SYNAPSE. The knife switch should be in the perpendicular position. c. Loosen the screws on either side of the bulb on the synaptic junction unit. Attach the wires designated as SENSORY NEURON to each of the screws. To do this, wrap the bare end of the wire around the screw and tighten the screw to secure the wire, or, if connectors have been attached to the ends of the wire, slide the D. Place the wires labeled SENSORY NEURON over the area labeled SENSORY NEURON on the diagram. Tape the wires to the paper. Do not connect the wire ends to the power source (stimulus/sensory receptor) until the model has been completed and checked by your teacher. E. Loosen the two screws on the synaptic junction unit farthest from the lamp/bulb. Attach one end of the wire labeled MOTOR NEURON to one of the screws and tighten. Repeat this procedure for the remaining wire labeled MOTOR NEURON. Tape the wires on the diagram over the area labeled MOTOR NEURON. F. Place the motor on the diagram at the site labeled MUSCLE EFFECTOR. Connect the muscle effector to the motor neuron by attaching an alligator clip on the muscle effector to one wire representing the motor neuron. Do the same with the remaining alligator clip and wire. Your model is complete and should re- semble Fig. 20. Check Fig. 20 before asking your teacher to check your model. DEMONSTRATION OF THE PATELLAR TENDoN REFLEX. A. COIl- nect the wires labeled SENSORY NEURON to the power source. The power source is the battery pack. The battery pack represents the stimulus in this reflex: tapping the patellar tendon with a reflex hammer. The stimulus is picked up by stretch receptors located in the quadriceps muscle. The stimulus is transmitted by the sensory receptor to the sensory neuron. The sensory neuron is represented by the wires labeled SENSORY NEURON. All of this happens when you connect the wires to the battery pack. B. Notice that the first light bulb (in the S-l unit) lights up. This signifies that synaptic transmission has oc- curred. Chemical neurotransmitters from the axon of the sensory neuron have been released to the next neuron in line, the motor neuron. c. Push down the switch/lever. The flow of energy in the model mimics the flow of nerve signals in the body. When you flip the switch, you are making the decision in the all-or-none phenomenon that occurs at the axon hillock. Recall that the chemical neurotrans- connector under the head of the screw and tighten mitters released by the axon of the sensory neuron the screw to secure the wire. have been picked up by the dendrites of the motor VOLUME 16 : NUMBER 1 - ADVANCES IN PHYSIOLOGY EDUCATION - DECEMBER 1996 s36
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