That reflex is called the crossed extensor reflex. These actions are all done without you thinking or planning, but your brain helps to assess the situation as an afterthought. Who left the Lego there? Did you notice how the brain was not on the five-part list of what makes up a reflex? Well, reflexes are functions of the nervous system, which coordinates our actions. The nervous system is the network of neurons that transmits the action potentials.
The sensor and neurons are outside the spinal cord, in what is called the peripheral nervous system PNS. The other part of the system is called the central nervous system CNS , and it consists of the brain and spinal cord. The CNS is used to think, plan, and learn.
Remember the earlier examples when you ducked down in response to a loud noise or lifted your foot after stepping on the Lego? In those examples, the CNS is what helped you understand what the noise was or why you moved automatically. It did not create the initial movement, but the CNS allowed you to understand why you ducked down or that you stepped on a Lego.
The CNS also plans the voluntary movements that come after the initial involuntary reflex. Perhaps you will bend down and pick up the Lego—that is a voluntary movement. Do you remember the example of the doctor tapping your knee? That is a test to see how well your body is prepared to react. There are many different types of reflexes that protect your body. The doctor tapping your tendon is a test of the simple monosynaptic reflex, which consists of a sensor, a sensory neuron, a motor neuron, and a muscle.
Once the sensory neuron is activated, an action potential travels along the sensory neuron to the spinal cord. The action potential then moves across the synapse to a motor neuron and leaves the spinal cord. More advanced reflex responses will use an interneuron, and these are called polysynaptic reflexes. Reflexes do not involve the CNS at first, but after the reflex has occurred in the body to keep it safe, the brain assists in understanding what happened.
Although we do not think about reflexes, they are important parts of our nervous system. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
Dingman weaves classic studies with modern research into easily digestible sections, to provide an excellent primer on the rapidly advancing field of neuroscience. Receive New Content by Email. Changes in the angle can be read by the computer. A hammer is connected to the goniometer and acts as a signal to the computer to begin gathering data when it impacts the patellar tendon. Have the subject sit on the edge of the table with right leg dangling freely. With the straps provided, attach the transducer on the outer side of the right knee with the box facing outwards; make sure the transducer hinge coincides with the knee joint, and that the levers are parallel to the leg bones.
The goniometer should be as close to 90 degrees with the legs dangling freely. You should first practice obtaining the patellar reflex using the rubber reflex mallet provided at your lab station: hit the patellar ligament just below the knee-cap with the pointed end of the mallet.
You may mark the area on the knee as a guide for subsequent data collection. Practice getting the hand of a good involuntary knee jerk using the white hammer. When you are ready to obtain data, press the white RUN arrow in the top left corner of the screen. Data collection will begin only after the button on the end of the white hammer is depressed. Strike the patellar ligament with the button end of the hammer.
You will then see your knee jerks on the bottom left screen. When you are ready to take measurements of the latent period the time it takes between hammer blow and movement and magnitude of the knee jerk angle change you just recorded, press the STOP DATA button. The knee jerk trace will then be transferred to the upper right hand screen. Your instructor will show you how to take measurements for latent period and magnitude of the knee jerk in class.
For each of the following exercises, you will examine two basic features of the reflex: maximum rotation and latent period. Consult the following figure below to make your maximum rotation and latent period measurements. Figure 4: Making the measurements for Latent period.
Measure the time in seconds it takes for the reflex to begin by starting where the trace levels off the trace moves up the y axis when the mallet is hit to the time when the trace goes down. Magnitude measured in degrees is measure as the dip in the trace as indicated on the graph. Each group will do parts A-E. Record the data as you perform the experiments, then enter the data into the excel spreadsheet on the instructor's computer when you have collected all of your trials.
The data will be pooled from all the lab sections and posted on e-mailed to you or posted on Blackboard. Record Electricity from your Muscles - You should read this experiment first to learn about electromyography and motor units. Reaction Time - This experiment also explains the difference between reactions and reflexes.
Reflexes require no thought. They are automatic, fast, and of huge importance to a human's ability to successfully respond to their environment. Despite the magnificent information-processing power of the billions of neurons in our brain, we need a lot of stuff to be done automatically.
Without reflexes, our brains would be overloaded with worrying about constantly updating the position of our unstable bodies to keep us upright. Without reflexes, our ability to engage in complex thought black holes, neuroscience, what to do this weekend, how do I make an instrumented reflex hammer? Without reflexes, your reactions to painful stimuli would require thought, and Don't feel bad, all humans are slow thinkers, and we need more speed to respond to dangerous painful stimuli.
So we let our spinal cord do that fast work for us. One example of a reflex is the patellar stretch reflex. Our spinal cord partners with sensors in our muscles, called muscle spindles, to keep track of where our bodies are in space and how stretched or contracted our muscles are. The way that these sensors interact with our spinal cord is through a reflex pathway.
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