Skin Senses Pressure, Temperature & Pain Touch • Touch receptors are on the skin • Skin is the largest & heaviest organ (20 sq. ft. & 6 lbs.) • Four basic skin senses are – Pain, warmth, cold, and pressure • All skin sensations are a combination of these four basic senses Pressure • Only pressure has identifiable neural receptors – Pacinian Corpusle – located beneath the skin, it converts pressure stimulation into neural messages it sends to the brain. • Constant pressure causes sensory adaptation and it either reduces the number of signals or quits sending them all together. (like the clothes on your body) • Sensory receptors are located unevenly on the body so certain areas are more sensitive than others. Temperature • Temperature is sensed by specific spots that produce either cold or warm sensations. • Cold spots can be triggered by cold or a hot stimulus. • Warm spots only respond to warm stimulus of about 105 degree Fahrenheit. • If both warm and cold spots are stimulated at the same time you will feel hot. • Various combinations of skin sensations produce different results • Check out the Amazing Hypothermia Man (2 min) Cold + Warm Receptors = HOT!!! What purpose does pain serve? • Pain is your body’s way of telling you something is wrong. It tells you to change your behavior immediately. • Any external stimulus that can produce tissue damage can cause pain. • Internal stimuli like disease or infection can also cause pain. • Certain areas of the body are more sensitive than others • Itch is caused by "itchsensitive" neurons that respond to histamines. Gate-control Theory of Pain • Pain is registered by free nerve endings • Pain messages travel on one set of nerve fibers containing pain gates. • The gates are open when pain is felt. • Other sensory messages go through another set of fibers. • The nonpain fibers can close the pain gates to stop the sense of pain. The Process of Gate-Control Theory • Intense stimulus activates small-diameter sensory fibers called free nerve endings. • Free nerve endings carry their messages to the spinal cord, releasing a neurotransmitter called substance P that activates other neurons to send their messages through the open spinal gates to the thalamus. • Thalamus sends pain signals to parietal, frontal lobes and limbic system. • Brain interprets pain and sends messages to the spinal cord to either close or open gates. If more gates open, pain gets worse. If gates close, less pain experienced. • Endorphins can be released which inhibit the release of substance P thus lessening pain. Acupuncture may work in this way. • Muscle Tension, psychological arousal and rapid heart beat can all produce or intensify pain. The Pain Process 2. Free Nerve Endings Activates (located in skin, muscles, & internal organs) Carries Message To… 3. Spinal Cord 1. Intense Stimulus (which releases substance P) (too much pressure, heat, tissue damge) causes Pain is reduced Pain is intensified Closes the Gates Leaves Gates Open 4. Other Neurons to activate & send pain message to the Thalamus through open Spinal Gates. Brain then… Biopsychosocial Perspective • Our experience of pain is much more than neural messages sent to the brain. Can we distract ourselves from the pain? YES! • An athlete who is injured doesn’t realize it until after the game. • Emotions and cultural differences can influence the brain's decisions on opening or closing gates. • Person's mental state can influence one's experience of pain. – – – – Distraction – focus on a nonpainful stimulus Imagery – create a vivid mental image can help control pain. Positive Self Talk – "It hurts, but I'm OK." Or redefine pain. Counter irritation – create a strong competing sensations that's mildly stimulating or irritating. Rubbing a sore area. Stimulating the “gateclosing” nerve fibers can help lessen pain. Rubbing a stubbed toe creates a competing stimulation that will block some of the pain messages. Putting ice on a bruise sends cold messages to the brain which lessen the pain messages. – Relaxation – Deep breaths and relaxing deeply Virtual Reality Pain Control • For burn victims undergoing painful skin repair, an illusory virtual reality can powerfully distract attention, thus reducing pain and the brain's response to painful stimulation Virtual Reality Distracts the Brain • The burn victim’s brain is less responsive to painful stimulation, as shown by these MRI scans An Acupuncturist's Nightmare Watch Video Clip Pain and Phantom Pain • The brain comes prepared to anticipate that it will be getting information from the limbs of the body. This is why amputees may experience sensations in a phantom limb. • Phantom limb sensations – the brain is misinterpreting central nervous system activity that occurs in absence of the normal sensory input from that limb. This can be true of the other senses as well. • Play “Phantom Limb Pain: Fooling the Mind” (4:29) Segment #20 from The Mind: Psychology Teaching Modules (2nd edition).