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Human Physiology with Vernier14A - 1Experiment14ANeuromuscular ReflexesThe automatic response of a muscle to a stimulus is called a reflex. The patellar reflex results fromtapping the patellar tendon below the knee with a reflex hammer. This causes contraction of the quadriceps muscle and extension of the leg. Stretching of the muscle activates nerve impulses which travel to the spinal cord. Here the incoming impulses activate motor neurons, which travel back to the muscle and result in muscle contraction. This reflex arc is primarily a spinal reflex, but is influenced by other pathways to and from the brain (Figure 1).A reflex may be reinforced(a term used by neurologists) by slight voluntary contraction of muscles other than the one being tested. For example, voluntary activation of arm muscles by motor neurons in the central nervous system “spills over” to cause a slight activation of the leg muscles as well. This results in the enhancement of the patellar reflex. There are other examples ofcentral nervous system influences on reflexes. Health care professionals use knowledge of these influences to aid in diagnosis of conditions such as acute stroke and herniated lumbar disk, where reflexes may be absent; and spinal cord injury and multiple sclerosis, which may result in exuberant reflexes.In this experiment, you will use an EKG Sensor to compare the speed of a voluntary vs. a reflex muscle action and to measure the relative strength (amplitude) of the impulse generated by a stimulus with and without reinforcement. You will make a rough calculation of nerve impulse speed using data generated by an Accelerometer used in conjunction with the EKG sensor.Important: Do not attempt this experiment if you have pain in or around the knee. Inform your instructor of any possible health problems that might be exacerbated if you participate in this exercise.Figure 1
14A - 2Human Physiology with VernierExperiment 14AOBJECTIVESIn this experiment, you willGraph the electrical activity of a muscle activated by a reflex arc through nerves to and fromthe spinal cord.Compare the relative speeds of voluntary and reflex muscle activation. Associate muscle activity with involuntary activation.Observe the effect of central nervous system influence on reflex amplitude.Calculate the approximate speed of a nerve impulse.Compare reflex response and electrical amplitude in different subjects.MATERIALSLabQuestreflex hammerLabQuest Appcable tie, 10 cm longVernier EKG Sensorcloth tape measureVernier 25-gAccelerometerpenelectrode tabsPROCEDUREEach person in the group will take turns being subject and tester. Part I Voluntary Activation of the Quadriceps Muscle1.Connect the EKG Sensor and Accelerometer to LabQuest. Choose New from the File menu.