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Reflexes Biol 335 Lab Rhode Island College Dr. J. Montvilo 1 Reflexes • A reflex is an automatic response by an effector (usually a muscle) to some stimulus (such as the stretching of a muscle or tendon) • A basic reflex usually involves a receptor (such as a stretch receptor), an afferent (sensory) neuron, the spinal cord, an efferent (motor) neuron, and an effector (usually a muscle) • Other reflexes may be more complicated 2 Electromyogram • An electromyogram is the recording of the electrical activity that occurs during the contraction of a muscle; it is similar to the electrocardiogram recorded from heart muscles as they contract • This lab will involve recording electromyograms of leg muscles as they respond reflexively to stretch stimuli 3 Achilles Tendon Reflex (1) • Carefully follow the directions in the lab manual • Place electrodes and attach leads to the following areas: • green — slightly above the main portion of the Achilles tendon • black — middle of the gastrocnemius (calf) muscle • red — 6 cm below the back of the knee 4 Achilles Tendon Reflex (2) • Practice generating the reflex until it can be done consistently: • the subject should sit with the leg dangling • push up lightly on the bottom of the foot • tap the Achilles (calcaneal) tendon with a reflex hammer • the foot should respond by moving downwards as the gastrocnemius contracts in response 5 Achilles Tendon Reflex (3) • Make sure that the iWorx recording system is set up properly • Check to make sure that it is recording properly by hitting Record and having the subject bend his or her foot downward several times, with a pause in between; make sure a good recording of these is seen and copied into the journal 6 Achilles Tendon Reflex (4) • Using the pressure-sensitive reflex hammer, produce and record at least five good actual reflex recordings; paste one of these into the journal • Calculate the average of five response times for the reflex from the recordings 7 Achilles Tendon Reflex (5) • Measure the impulse distance (path length) in millimeters from the middle of the black electrode to the spinal cord at the level of the top of the hips • Calculate the nerve impulse conduction velocity using the following equation 8 Patellar Tendon Reflex (1) • Carefully follow the directions in the lab manual • Place electrodes and attach leads to the following areas: • green — on the lateral side of the knee • black — on the top middle of the quadriceps (anterior thigh) muscle, 12 cm above the knee • red — 10 cm above the black lead 9 Patellar Tendon Reflex (2) • Practice generating the reflex until it can be done consistently: • the subject should sit with the leg dangling • tap the patellar (kneecap) tendon with a reflex hammer • the lower leg should respond by moving outwards as the quadriceps contracts in response 10 Patellar Tendon Reflex (3) 11 Patellar Tendon Reflex (4) • Make sure that the iWorx recording system is set up properly • Check to make sure that it is recording properly by hitting Record and having the subject lift his or her lower leg several times, with a pause in between; make sure a good recording of these is seen and copied into the journal 12 Patellar Tendon Reflex (5) • Using the pressure-sensitive reflex hammer, produce and record at least five good actual reflex recordings; paste one of these into the journal • Calculate the average of five response times for the reflex from the recordings 13 Patellar Tendon Reflex (6) • Measure the impulse distance (path length) in millimeters from the middle of the black electrode to the spinal cord at the level of the top of the hips • Calculate the nerve impulse conduction velocity using the following equation 14 • Jendrassik’s Maneuver (1) Erno Jendrassik (1858-1921) discovered that if a patient hooked his or her fingers together and pulled the patellar reflex was enhanced 15 • • Jendrassik’s Maneuver (2) Test the effect of Jendrassik’s maneuver on the patellar reflex by repeating the patellar tendon reflex experiment while the subject is hooking their fingers together and pulling (It is unclear whether this maneuver is simply a distraction to the subject so that the reflex is not inhibited by a conscious act of the subject or whether a more neurological mechanism is at work) 16 Any questions? 17