Itt írjon a(z) SensoryArtificial-ról/ről
Introduction
In this essay we will discuss sensory perception during movement, effects of short term training on sensory and motor function in amputees. Phantom pain and how to ease it and the difficulties in regaining sensory perception and the attempts made to improve the ownership of artificial limbs.
Sensory perception during movement in man
The ability of a person to feel painless stimuli in the existence or absence of motion can be easily gauged with the use of electrical stimulation on the skin. The personal strength of the suprathreshold stimulation is not varied during motion. Inequity of slight changes in the strength of the suprathreshold stimulus is also not changed by motion while, in the same subjects, finding thresholds were raised when the stimulated arm was in motion. The findings indicate that the increase of detection thresholds while in motion can be justified by masking. Active motion and Passive motion of the limb being stimulated increase detection threshold .The active motion having a marginally larger and more constant effect that the passive motion. Therefore, equally central feedback and peripheral feedback factors can simulate in reducing one’s capability to recognise a gentle stimulation during motion (Chapman et al, 1987).
Effects of training on motor and sensory function after injury
There has been extensive research into plastic changes in the central nervous system of mammals prompted by life-changing situations amputation of a limb. Although there has been much research in this field it is still unknown about the degree to which the original pathway keeps continuing function after a limb amputation. Studies have shown that central nervous system pathways established with amputated peripheral nerves contain at minimum a few sensory or motor functions. Studies are currently being carried out to find out if it were possible for these functional networks to be enhanced or stronger if the subject trained and worked on perfecting movement over a period of time. To conduct this research, electrodes are inserted into bundles of split nerves belonging to subjects that are long term amputees. Then, differences in electrically erased feelings and free motor neuron action linked with a subject trying to move a phantom limb. Stimulation of a nerve frequently occurred in discrete, exclusive, sorted feelings of pressure or touch and a sense of joint position. No compelling differences in the amount of stimulation parameters needed to cause the feelings were detected. Furthermore, the subject amputees had the ability to better their free power of motor neuron activity, however, the amount and consistency of difference was comparable to that observed with training in non amputee subjects on normal motor tasks. this research shows that the central plasticity that is observed post amputation is probably due to unmasking, and not restoration of current synaptic connections (Dhillon et al, 2005)Peripheral nerve amputation has been shown to produce changes in cortical sensory and motor representation in various mammalian species, including humans. Contradictory to the general idea that there is a fixed wiring mechanism, there is substantial findings cortical representation of the limbs and body is frequently adjusted in reaction to skills, behavior or activity (Chen et al, 2002). Different findings show that is is feasible to bond microelectrodes at a sub fascicular level to little bundles of motor and sensory neutrons (Branner and Normann, 2000).
Treating phantom pain and providing sensory feedback to an amputee from a prosthetic limb
Phantom Pain is an indirect dysfunctional result that can affect a person after undergoing an amputation of a limb. They feel sensations of pain or discomfort arising from the original limb. The causes are not fully understood, however, several processes are responsible. The sensations are understood to emerge from the missing limb, although, sensory receptors from other parts of the body trigger these "feelings". These sensations are not always related to pain, however, when the pain is present it can be get so agonizing that it becomes insufferable or debilitating. Amputation disrupts or eliminates the usual flow of sensory information originating from other processes of sensory receptors such as muscle receptors transported by large diameter, myelinated axons which usually transmit non-painful information of proprioceptive and cutaneous origin for example, pressure, muscle length, joint position or touch. (see fig 1.)
For transmission in the spinal cord and brain centers, the balance of activity in the large and small diameter sensory nerve fibers has become important. Fiber diameters of a severed nerve are reduced but the nerve cells continue to conduct electrical impulses and maintain their basic synaptic connectivity patterns (Hoffer et al, 1979). Sensory fibers degenerate more than motor fibers and the sensory fibers with small-diameters degenerate less than the large-diameter sensory fibers. "For hind limb nerves of cats that were cut and ligated over a period of 300 days, found that large sensory fibers had a 60% decrease in conduction velocity (CV); small sensory fibers had about a 45% decrease in CV; large motor fibers had a 40% decrease in CV: and small motor fibers had about a 20% decrease in CV. Thus, in amputated nerves, “large” and “small” nerve fibers will gradually become closer in their diameters and consequently closer in their thresholds for electrical stimulation." (Milner and Stein, 1981).