Introduction
The integumentary system is made up of the skin together with other accessory structures including nails, hair, as well as glands. The four major functions that are done by the integumentary system include protection, production of vitamin D, sensation, and temperature regulation (Bailey). The integumentary system offers protection of the body against ultraviolet light and abrasion while preventing dehydration as a result of water loss and entry of pathogens into the body (Seeley, Stephens and Tate).
The skin possesses numerous receptors that make it also function as a sensory organ. The receptors are usually referred to as free or encapsulated nerve endings and enable the skin to detect cold, heat, pain and pressure. There are numerous free nerve ending receptors and are involved in subserving fine touches, cold and heat and are mainly found in the basal layers belonging to the epidermis (Ross and Pawlina).
Some of these sensory receptors become activated after being squished, bent, or disturbed. Other sensory receptors are activated through mediators such as chemicals, temperature or light. The sensory receptors alter the environmental stimuli forming efferent nerve impulses that move to the brain. There are four different types of cutanoeus sensations that have been identified. These are the tactile or touch, cold, heat, and pain. The sensory receptors for these sensations are not distributed in a uniform manner, in the skin with most of them being clustered in one place. This experiment aimed to investigate the location and physiology of cutaneous receptors.
Methods
Sensitivity of the Skin to Touch
The experiment was conducted in groups of three people with the person conducting the experiment being the experimenter, the person being experimented upon being the subject and the third person acted as the recorder. The subject marked a grid or dots on the finger tip, inside the forearm and the back of the hand as the area of the body that were to be tested. The recorder drew equivalent grids or table grids in the notebooks in which the resulted were recorded. The subject closed the eyes to avoid seeing when the experimenter applied the stimulus. A blank pin was placed in the holder and used to test the sensitivity of the subject in one of the areas by touching the pin on to every the dots in the marked areas in turn, working systematically down the rows. It was strictly observed that the pin was rested on the marked area of skin so that the head of the pin was just lifted off the support, holding the handle horizontal. The pin was left in contact with the skin for a period of more than half a second and an interval of from half to one second interval between each touch was allowed. It was, however, observed that regular intervals were not made between each touch to avoid the subject from expecting to receive regular stimuli, and this may influence subject’s judgment. It was also observed that no part of the experimenter’s hand or sleeve touched the hand of the subject during the experiment.
Recording the Results
If the subjects felt the touch of the pin they were required to say yes. The recorded then indicated the responses in the grid in the notebook leaving blank squares where the subject made no responses. Each grid was recorded with the location of the area of skin that was tested and the name of the subject. The number of positive responses was converted to percentage (%) sensitivity to the pin. Testing the other areas of the body was repeated in the same way.
Recognition of Separate Stimuli
This was also conducted in a group of three individuals, the experimenter who applied the stimulus, the subject who received the stimulus and the recorder of the response to the stimulus by the subject. The subject was to determine the least distance apart to recognize two simultaneous touch stimuli as two sensations rather than one. The subjects were not expected to know in advance whether they were to receive one or two stimuli. The experimenter drew up a table and without showing the subject wrote a program of 5 single and 5 double stimuli randomly distributed. After each stimulus, the subject said one or two according to the number of stimuli felt, and the response recognized recorded. After 10 stimuli, the correct responses were added up and converted to % the correct response. If the total was 10, the gap between the wire points was reduced to 5 mm and the test repeated. If the repeated test still gave a score of 10, the gap was further reduced. The experiment was repeated until the subjected scored a score of less than 10 was achieved. If the score was 9 or less, the test was repeated with the points 15 mm apart. If the score was still less than 10, the test was repeated as the gap was increased between the points by 5 mm every time until the subject attained a score of 10 was achieved. The front wrist and finger tips were tested in the same way, and all the four fingers were treated as the test areas.
Sensitivity to Temperature
Three jars of beakers of about the same size were collected. One jar was filled with cold water (7OC), one with standard water (19OC) and the other one with hot water (42OC). The first finger on the left hand was placed in the cold water while the first finger on the right hand was placed in the hot water. Both fingers were left immersed for at least one minute. After one minute, the fingers were removed from the jars and dipped repeatedly but alternatively in the warm water for about one second at a time. The temperature sensation in each finger was noticed.
Results
Sensitivity of the Skin to Touch
The number of positive responses at different areas of the body were recorded and converted to percentage (%) sensitivity to the pin and recorded in Table 1 below. Finger tips gave the highest sensitivity followed by back of the hand with inside of the forearm showing the least sensitivity.
Recognition of Separate Stimuli
The number of times that the subject was correct on the number of stimuli received was counted and recorded in Table 2 below. Other than for a gap of 20 mm that did not have any correct response, the other gap distances, showed an increased number of recognized stimuli as the distance increased.
Sensitivity to Temperature
The first finger on the left hand that was placed in the cold water for one minute indicated that the warm water was cold. Similarly, the first finger on the right hand that was placed in the hot water indicated that the warm water was hot.
Discussion
This experiment was conducted with an aim of understanding where cutaneous receptors and their physiology. In the experiment to study the sensitivity of the skin to touch, the sensitivity of skin to touch increased as the size of the pin increased. This may have resulted due to the fact that heavy pins inserts more pressure to the skin than small pins and thus increasing the chances of sensory receptors being stimulated. The sensory receptors found in the skin are usually distributed in an irregular manner around the body. Some places in the body such as in the fingers and lips, have more touch receptors compared to other places such as inside the forearm. This explains why the finger tips were more sensitive to touch compared to the back of the hand and inside the forearm. Rubbing increased the area of the skin that is in contact with the pin and, therefore, greater chances of encountering a sensory receptor that is then triggered to cause a response.
Cooling the skin below the normal temperatures may result to a number of thermal effects on the sensitivity of the skin to touch. Specifically, temperatures that are lower than normal have been associated with sensitivity impairment. (Dehnhardt, Mauck and Hyvärinen). An advantage of this cooling is that, in case of illness, pain can be reduced by impairing skin sensitivity and hence poor signaling of pain stimuli (Kenny). On the other hand, such cooling may be harmful since the skin may be injured without the one realizing the intensity of the injury (Net Industries). Adding alcohol on the skin may also result in the destruction of the skin and eventually destroying or inactivating the sensory receptors. This results in a reduced sensitivity of the skin.
Two-point discrimination refers to the ability to distinguish that the two objects that are felt touching the skin are truly two different points (WSU). The tongues, as well as the fingers, are some of the body parts that have the best resolution while other areas such as the back have the poorest. This poor resolution increases the distance at which these parts are able to detect two points as separate. From the results, as the gap increased the percentage sensitivity in differentiating the touch as a single touch or double also increased. This is an indication that as the area of the skin is increased there is also an increase in the number of sensory receptors enabling the two points to stimulate different sensory receptors and thus the distinction of the two points. Failure to detect the two points as separate may also be contributed by the fact that some sensory receptors are innervated by a single nerve and thus the two stimuli although collected by different sensory receptors end up as a single signal to the brain.
Placing the left hand finger in cold water for one minute caused the thermoreceptors to get used to the cold water. This caused the finger to still detect the warm water as cold since the receptors were used to the cold water. Similarly, placing the right hand finger in hot water for one minute caused the thermoreceptors to get used to the hot water. This caused the finger to still detect the warm water as hot since the receptors were used to the hot water. After moving the finger to the warm water, there was a delay in sending the right message to the brain resulting in different hands perceiving different temperatures.
This difference in perception is created by the exposure of the sensory receptors to the same temperature for a long time. This causes the receptors to adapt to this temperature making them reluctant to change to the new temperature. This is not an indication of the skin of the fingers being incapable of judging whether an object is hot or cold but an adaptation feature that enable the body to withstand changes in temperature.
In conclusion, the experiment facilitated an understanding on the locations of cutaneous receptors and their physiology. It was clear that areas such as the finger tip are more sensitive to touch than others due to high level of sensory receptors.
Works Cited
Bailey, Regina. Integumentary System. 2013. Online. 7 February 2014. <http://biology.about.com/od/organsystems/ss/integumentary_system.htm>.
Dehnhardt, G., B. Mauck and H. Hyvärinen. "Ambient temperature does not affect the tactile sensitivity of mystacial vibrissae in harbour seals." Journal of experimental biology 201.22 (1998): 3023-3029. Print.
Kenny, Tim. Postherpetic Neuralgia. 2013. Online. 7 February 2014. <http://www.patient.co.uk/health/postherpetic-neuralgia>.
Net Industries. Touch. 2014. Online. 8 February 2014. <http://psychology.jrank.org/pages/634/Touch.html>.
Ross, Michael H. and Wojciech Pawlina. Histology. Philadelphia: Lippincott Williams & Wilkins, 2006. Print.
Seeley, R., T. D. Stephens and P. Tate. Anatomy and Physiology. 6th. New York: The McGraw Hill Companies, 2004. Print.
WSU. Two-point discrimination. 2014. 8 January 2014. <http://healthcaresciencesocw.wayne.edu/sensory/6_1.htm>.
