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... nt of hearing loss based on the amplitudes of the signals (fifth wave). With this information, physicians can decide how to treat the hearing loss and to what degree. A person who is completely deaf would exhibit flat-line responses. The BAEP can also detect lesions in the auditory cortex or any place in the auditory pathway. These abnormalities could also be attributed to tumors or acoustic neuromas, which are non-cancerous growths on the vestibulocochlear nerve in the brain.
The BAEP is especially useful in detecting brain tumors on the brainstem; however, the BAEP will only recognize tumors once they are larger than one centimeter. For this reason, the MRI is more useful when attempting to detect tumors in the brain. For infants, the BAEP is extremely useful. Since it is difficult to tell when an infant has any hearing loss, the BAEP is an objective method to discover if a child is partially or completely deaf. Furthermore, it can determine if a child needs to have special hearing aids. If a child grows up with impaired hearing, they can develop irregular speaking voices.
The BAEP test will prevent children from developing these speech disorders. When children have sustained serious injury to their head, they fall into a post-traumatic coma. The BAEP can be used to determine the likelihood of survival. Although the normal and abnormal BAEP signals varied with survival rates, all children who do not show any responses to the stimuli have died. When a person undergoes general anesthesia, he / she loses consciousness; however, there can be different degrees to the depth of anesthesia. Recently, the BAEP has been being used to determine the level of anesthesia.
An Auditory Evoked Potential Index (Apex) is being used to set a system to determine depth of anesthesia and it is being programmed into the anesthesia monitors in operating rooms. This method is still in its experimental stages. Altogether, the brainstem auditory evoked potential is a very important clinical tool as well as a method to understand other conditions of the body. A third type of evoked potential is the somatosensory evoked potential (SSEP). In this test, the body is stimulated by touch or electrical signal and electrodes are able to record the signals created by the brain. The basic physiology of the somatosensory system is slightly more complicated.
While the eyes and ears send their nerves directly to the brain, the somatosensory system must travel farther to reach its destination. The peripheral receptors in the body pick up stimuli and these nerves lead to the spinal cord. From the spinal cord, the response is then directed to the brain where it reaches the primary somatosensory cortex. In the body, there are different kinds of receptors for different kinds of stimuli. There are thermo receptors which respond to changes in temperature, nociceptors which monitor pain, proprioceptor's which monitor the position of the body, chemoreceptors which are sensitive to chemicals, and mechanoreceptors which deal with mechanical changes in the body. There are two main types of somatosensory evoked potential tests: the upper limb SSEP and the lower limb SSEP.
In the upper limb SSEP, an electrode is placed on the wrist as well as electrodes on the head and back. The patients fingers would be stimulated with low voltage stimulation. Since placing the electrode on the wrist would only monitor from one point on the spinal cord, the electrode is also placed on other parts of the arm including closer to the elbow to read signals going to the lower spinal cord as well. The lower limb SSEP is done by placing the electrode on the lower leg and the stimulation on the ankle. To test other parts of the spinal cord, the electrode can be placed on the thigh and stimulation can occur at the knee. Although the thought of sending a current into a patient may seem extreme, the voltage is kept very low and the electric pulse only causes the patient a small twitch in the limb that was stimulated.
Many of the clinical motivations of SSEP are similar to those of auditory and visual evoked potentials. The SSEP can be used to detect lesions in the entire pathway leading up to the brain including those in the spinal cord. Furthermore, it can trace the location of a tumor if the amplitudes of an SSEP are depressed. One of Ssep's primary advantages are found inside the operating room.
The SSEP can monitor the status of the spinal chord through stimulation. During surgery on the spinal chord, the surgeon can keep track of the condition of the spinal chord. If the SSEP begins to depress, the surgeon can retrace and repair. This is a common technique in scoliosis repair surgery and any other surgeries directly affecting the spinal cord.
The SSEP has a second role in the operating room. When operating on the brain, the exact location of the primary somatosensory cortex needs to be established. This is done by placing electrodes directly on the brain. The lips or fingers are used as points of stimulation.
By monitoring the responses, surgeons can determine where the somatosensory cortex is. In addition to its functions in the operating room, the SSEP has an assortment of other diseases and syndromes in which it can be used as a form of diagnosing. Although many of the Ssep's functions have been replaced by the MRI, it still has many valuable functions in the medical field. The disease that is associated with all three types of evoked potentials is multiple sclerosis. Although the visual evoked potential is the most useful in diagnosing MS, somatosensory and auditory evoked potentials are not far behind.
When the three methods are used together, they can become very useful. The three tests are usually in sync with each other when determining if a patient has MS. Unfortunately, each test takes about an hour to perform, so conducting all three tests would take a very long time (as they are rarely done together). In conclusion, the evoked potential is a very useful form of imaging. In addition to the many other types of imaging today, the evoked potential is crucial for diagnosing such things as multiple sclerosis as well as lesions on nervous tissue. The fundamental basis for the entire technique is the neuron and its ability to transmit signals.
Using electrodes and a form of stimulating the senses, the evoked potential is able to accurately determine the response of the brain to certain stimuli by recording the signals of neurons. Visual evoked potentials being the most prevalent, they are the most capable for helping to diagnose multiple sclerosis because of the visual episodes of optic neuritis. The brainstem auditory evoked potentials are very important for diagnosing hearing loss in infants and determining levels of anesthesia in the operating room. Lastly, the somatosensory evoked potential, although useful in diagnosing lesions, is most useful in the operating room to navigate the brain and to maintain the spinal cords vitals. The three techniques are useful both in diagnosing disorders as well as serving as a useful tool in surgery. In conclusion, the evoked potential is an enormously valuable technology that is widely used in todays medical profession.
Works Cited 1. Aitkin, Lindsay. The Auditory Cortex. New York: Chapman and Hall, 1990. 2. Bear, Mark F. Neuroscience: Exploring the Brain.
Baltimore: Williams & Wilkins, 1996. 3. Desert, John E. Visual Evoked Potentials in Man: New Developments. Oxford: Clarendon Press, 1977. 4. Hood, Donald C. , Greenstein, Vivienne C. Multifocal VEP and Ganglion Cell Damage: Applications and Limitations for the Study of Glaucoma.
Progress in Retinal and Eye Research 22 (2003). 5. Hood, Donald C. , Odel, Jefferey G. Tracking the Recovery of Local Optic Nerve Function after Optic Neuritis: A Multifocal VEP Study. Investigative Ophthalmology & Visual Science November 2000, vol. 41, no. 12. 6. web 7.
web 8. web 9. web 10. McIlwain, James T. An Introduction to the Biology of Vision. Cambridge: Cambridge University Press, 1996. 11.
Nelson, Randall J. The Somatosensory System. New York: CRC Press, 2002. Regan, D.
Evoked Potentials in Psychology, Sensory Physiology and Clinical Medicine. London: Chapman and Hall Ltd, 1972
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Research essay sample on Spinal Cord Multiple Sclerosis
