Sensory Receptor Sensitivity - Assignment Example

PRACTICAL 1: SENSORY RECEPTOR SENSITIVITY: Name of Student: Student ID: Lecturer: Course: Assignment: Date of Submission: PRACTICAL 1: SENSORY RECEPTOR SENSITIVITY: Aim: To determine the characteristics of cetaceous receptors by studying variations in response of mechanoreceptors and thermoreceptors. To observe variations in localization of touch over various body parts. To observe variations in location and concentration of heat receptors. Introduction. The sensory receptors are widely classified into three categories depending with the origin of the stimulus: Namely; interoceptors, proprioceptors and the exteroceptors. This model of classification though has the limitation of revealing little regarding the sensory apparatus of the general somatic afferent. And for this matter is appropriate that we also base the classification of the kind of stimulation on which the receptor will respond to and are; the thermoreceptors , the nociceptors and the mechanoreceptors. Mechanoreceptors response to receptors or tissues is of similar mechanical deformations of touch, pressure, vibration and stretch. The sensations recorded normally range from the random body position to touch and the orientation in space. In this Laboratory practical session, we are to observe the variation in discrimination over different body parts by deploying two-point discrimination method. Nolar, M.F., (1987} Physiologically, the dermis of the skin has two specialized nerve endings which are the receptors for the temperature. The Krause’s end bulb is more sensitive than the receptors for heat and is specialized for cold reception. To distinguish the heat receptor from the touch receptors when the temperatures are low is always difficult and even when the temperatures are high, distinguishing them with the pain receptors is also difficult. Weinstein, S., (1968) Before going into the details of the composition of each receptor group, the significant to understand the various afferent fiber groups that work hand in hand with the various receptors kinds. There are two kinds of nerve fibers; the myelinated and the non myelinated. The myelinated nerve fibers have a much high velocity of conduction than the non-myelinated nerve fibers. The non myelinated nerve fibers are cuteneous nerves with a diameter of about 0.2 – 1.5 um and their conduction velocity is approximately 0.4-2.0 m/s. The stimuli sensitivity of the non-myelinated nerve fibers varies between the glabrous which are less sensitive and the glabrousskin being more sensitive. It’s the physical motion or the indentations that cause the excitement of the mechanoreceptors. Some mechanoreceptors are situated in the superficial and in the deep areas of the skin. At the superficial section, there is Merkel disk receptors and Meissner’s corpuscles. Schmidt, R.F., (1981) . Part A: Two-Point Discrimination Methodology: 1. Blindfold the subject and ensure he/she is seated and relaxed with hands resting on a bench or arm rest. 2. Commence with a minimum separation of stimuli by using both ends of a two-point compass and stimulate the subject’s finger. Ask the subject to report if he/she feels 1 or 2 stimuli. 3. Increase the separation distance of the compass points by 1 mm until the subject first reports 2 stimuli. RECORD the separation distance. 4. Start with a separation distance of 10 mm and progressively decrease the separation distance by 1 mm until the subject first reports one stimulus. RECORD the separation distance. 5. REPEAT (5 times) and record the separation distance. 6. REPEAT the above procedure on both sides of the body for each test site listed below: (a) Finger, (b) Palm, (c) Shoulder, (d) Forehead, (e) Back, (f) Calf and (g) Forearm Results and Observations. The results are recorded in the table 1. Below. Separation distance (in mm) for each trial, with alternative direction of compass tip movement for each trial Right side Trials Left side BODY PART 1 2 3 4 5 6 7 8 9 10 FINGER 9.5 11.5 13 16 18 9 12 14.5 15 19 PALM 10 12 14.5 15 17 10 12 13 14 16 SHOULDER 9 11 12 14.5 15 8.5 11 12.5 13 14 FOREHEAD 10 12 13 14 17 10 12 14.5 16 17 BACK 10 10.5 12 13 14 9 11 13 15 17 CALF 9.5 12 14 14 15 11 13 13 14 15 FOREARM 10 12 13 15 17 8 10 12 13 15 Table 1. results 2.Graph of ‘two-point discrimination’ (median value). Discussion: The questions as to whether our fingertips are more sensitive than our lips? Or the dermis skin on our legs could have the same sensitivity as to our arms are well answered in this practical experiment. There are tiny pressure sensors all over our body and in some areas of our body, the pressure sensors are many compared to other parts where the pressure sensors are relatively less. In the areas of the body having many clustered pressure sensors respond highly sensitive to touch. The two-point discrimination practical experiment, guides us in obtaining which parts of our skin do have most pressure sensors and in which parts are the pressure sensors less distributed. The experiment encompasses gently and carefully pressing two sharp points of the compass point onto the subjects skin and instructing them to respond whether she feels two or one pressure points. Schmidt, R.F., (1981) Areas that are more sensitive have the pressure sensors more close together, therefore the tips of the compass will activate separate two pressure points. The impulses from both the sensors are conveyed to the brain making the subject feel the one point. Conclusion: The grating orientation role was special in giving measurements that corresponded consistently with the report of the subject. The results are consistent with data of the neurophysiological indicating that most of the primary afferent fiber category reinervation of the skin is at same rate. Part B: Localization of Touch: Methodology: 1. The subject sits with eyes closed. Using a felt-tip pen, the partner touches and marks the back of the subject’s non-preferred hand 2. With eyes still closed, the subject uses a pencil to try to touch the same spot. Move the pencil tip about until you believe you have found it; 3. Record the miss in mm, repeat and average the two trials; 4. Repeat steps 1 - 3 for the forefinger and the forearm. Results The results are shown on the following table 2: BODY PART TRIAL 1 (mm error) TRIAL 2 (mm error) AVERAGE Back of Hand 5 5.5 5.25 Forefinger 8 6.5 6 Forearm 8 7 7.5 Discussion: The report shows the effect of the temporal measures on the localization of the evoked mono-filament touch. The application of the stimuli was at interstimulus intervals (ISAs) ranging from 1 to 9s to establish discrimination occurring between successive sites of the stimuli of the skin. The threshold for localization was about twice for the heat pain than the touch. With the prolongation of interstimulus intervals, the threshold for localization decreased from 1 to 6-8s. As the ISI increased so did the discriminative capacity. Geldard & Sherrick Carl, (1986} The study was on the localization errors on the three various body parts of the subject. The stimulation of the skin was done at three different anatomical sites through the means of the pressure by felt-tip pen. The subject was given the instructions to locate the position by touching the part nearer to the point where the stimulation was initiated. The average error of localization showed variations at the different parts of the body but only the forehand recorded the most accurate and the least or the highest error was at the forearm. Highly intense stimuli recorded less accuracy while the light touch stimuli had the high levels of accuracy. When there is sight there is only a projection but not localization. Borg, G. (1982). Part C: Thermoreceptors Methodology. 1. Using two temperature probes (refer to Figure 1.1), fill one syringe with ice water and chopped ice, the other with hot water and plug both with a rubber stopper. Figure 1.1 Temperature Probe 2. On the forearm, mark off a square of 1 x 1 cm with a black felt-tip pen. 3. The partner touches the skin lightly in the square. If the subject reports it as cold, a blue dot is made (using a blue pen). If only a touch is felt, make no mark. Find as many cold receptors as possible in the square. 4. Repeat with the hot probe and find as many heat receptors as possible (using a red pen). 5. Tally the cold and heat receptors. Which are the more common in the marked-off area? 6. Mark off a square of 1 x 1 cm on the forefinger, and repeat (steps 3 - 5). Results: The results are shown in the table below. PART OF BODY COLD RECEPTORS HEAT RECEPTORS Forearm 1.25per cm2 3.5per cm2 Forefinger 0.5per cm2 2.5per cm2 Discussion. Warmth was recorded on the finger that was subjected to cold water while the finger that was originally put on hot water recorded coldness. This sensational variance would be attributed to the temperature differences on the finger and the forearm after one minute of immersion. The alternative explanation is that the receptors responsible for the warmth that were subjected to warmth progressively became adapted for example after long warmth; they do not transmit impulses to the brain. When they were subjected to cold, some impulses were sent to the brain. Holmes, O. (1993) Conclusion. The results show that the forearm and fingers detect when they are loosing or gaining heat despite the real temperature of the object. At room temperatures, metal objects are normally felt cold due to the fact that heat is being conducted from the forearms and the fingers. From the results we can conclude that the thermoreceptors respond to temperature change not any given temperature. Its true that there is steady transmission of impulses from cold and warmth in every temperature within range limits References: Borg, G. (1982). Psychosocial bases of perceived exertion. Medicine and Science in Sports and Exercise. 14(5):377-381 Borg, G. (1988). Borg’s perceived exertion and pain scales. Geldard, Frank A. & Sherrick, Carl E., (1986) Space, Time and Touch, Scientific American, 255 (1): 84-89. July 1986. Gronberg, P.O. (1992). Human physiology under cold exposure. Arctic Medical Research, 53, (S7), 23-28 Nolar, M.F., (1987) Two-point discrimination assessment in the upper limb in young adult men and women, Physical Therapy, 62, pp965-969. Schmidt, R.F., (1981) Fundamentals of Sensory Physiology, Springer-Verlag, Weinstein, S., (1968) Intensive and extensive aspects of tactile sensibility as a function of body part, sex and laterality, in Kenshalo, T., the Skin Senses, pp195-222. Holmes, O. (1993). Human Neurophysiology 2nd ed., London, Chapman Hall (5 copies in Library) Laboratory report manual Read More