PhysioBio Psych - 11 (1) PDF

Hi Students! Thank you for joining our session today. We'll start in a while PLMun Psychology Department physiological & biological psychology  Chapter 6: other sensory system Mechanical Senses The mechanical senses respond to pressure, bending, or other distortions of a receptor. They inc...

Hi Students! Thank you for joining our session today. We'll start in a while PLMun Psychology Department physiological & biological psychology  Chapter 6: other sensory system Mechanical Senses The mechanical senses respond to pressure, bending, or other distortions of a receptor. They include touch, pain, and other body sensations, as well as vestibular sensation, which detects the position and movement of the head. VESTIBULAR SENSATION When you move your head, the vestibular organ adjacent to the cochlea monitors movements and directs compensatory movements of your eyes. When your head moves left, your eyes move right; when your head moves right, your eyes move left. Effortlessly, you keep your eyes focused on what you want to see. Sensations from the vestibular organ detect the direction of tilt and the amount of acceleration of the head. You use that information automatically for guiding eye movements and maintaining balance. VESTIBULAR SENSATION The three semicircular canals, oriented in perpendicular planes, are filled with a fluid and lined with hair cells. Acceleration of the head at any angle causes the fluid in one of these canals to move, just as the water in a bucket will splash if you jerk the bucket from side to side. SOMATONSENSATION Consider the Pacinian corpuscle, which detects vibrations or sudden displacements on the skin At the center is the neuron membrane. The onion-like outer structure provides mechanical support that resists gradual or constant pressure. It thereby insulates the neuron against most touch stimuli. However, a sudden or vibrating stimulus bends the membrane, enabling sodium ions to enter, depolarizing the membrane SOMATONSENSATION SOMATONSENSATION The body has specialized receptors to detect temperature, a critical variable to monitor, given that overheating or overcooling the body can be fatal. The systems for cooling and heating show an interesting asymmetry: Cold-sensitive neurons in the spinal cord respond to a drop in temperature. For example, a cell that responds to a drop from 39° C to 33° C would also respond to a drop from 33° C to 27° C. SOMATONSENSATION Heat-sensitive neurons in the spinal cord respond to the absolute temperature, and they do not adapt. A cell that responds to 44° C will respond the same way regardless of whether the skin was hotter, cooler, or the same temperature a minute or two ago TICKLE Why can’t you tickle yourself? It is for the same reason that you cannot surprise yourself. When you touch yourself, your brain compares the resulting stimulation to the “expected” stimulation and generates a weaker somatosensory response than you would experience from an unexpected touch. SOMATOSENSATION IN THE CNS SOMATOSENSATION IN THE CNS The primary somatosensory cortex is essential for touch experiences. When weak, brief stimuli are applied to the fingers, people are conscious of only those that produce a certain level of arousal in the primary somatosensory cortex. Damage to the somatosensory cortex impairs body perceptions. A patient who had damage in the somatosensory cortex hadtrouble putting her clothes on correctly. Also she could not point correctly in response to such directions as “show me your elbow,” although she pointed correctly to objects in the room. PAIN Many sensations sometimes evoke strong emotions, but pain is unique among senses because it always evokes an emotion, an unpleasant one. People who are depressed become more sensitive to pain. Economic insecurity leads to depression and makes a pain feel worse. Some languages do not have a separate word for depressed; they describe a depressed state of mind as “sick” or “pained.” Also, pain and depression are both sensitive to placebo effects. STIMULI AND SPINAL CORD PATHS Pain sensation begins with the least specialized of all receptors, a bare nerve ending. Because the axons carrying pain information have little or no myelin, they conduct impulses relatively slowly, in the range of 2 to 20 meters per second (m/s). EMOTIONAL PAIN EMOTIONAL PAIN If you watch someone—especially someone you care about—experiencing pain, you experience sympathetic pain that shows up as activity in your cingulate cortex and other cortical areas. Hurt feelings do resemble physical pain in several regards. EMOTIONAL PAIN What happens with more intense hurt feelings? Experimenters measured brain activity while young adults remembered a recent romantic breakup, made more intense by looking at a photo of the ex- boyfriend or ex-girlfriend. In this case, the hurt feelings showed up as activity in both the emotional areas (especially the cingulate cortex) and the sensory areas responsive to physical pain EMOTIONAL PAIN What happens with more intense hurt feelings? Experimenters measured brain activity while young adults remembered a recent romantic breakup, made more intense by looking at a photo of the ex- boyfriend or ex-girlfriend. In this case, the hurt feelings showed up as activity in both the emotional areas (especially the cingulate cortex) and the sensory areas responsive to physical pain WAYS OF RELIEVING PAIN Opioids and Endorphines Cannabinoids and Capsaicin Placebos SENSITIZATION OF PAIN To prevent chronic pain, it helps to limit pain from the start. Suppose you are about to undergo major surgery. Which approach is best? 1. Take medication to relieve pain before the surgery. 2. Begin medication soon after awakening from surgery. 3. Postpone the medication as long as possible and take as little as possible. chemical senses TASTE Vision, hearing, and touch provide information useful for many purposes, but taste is useful for just one function, telling us whether to swallow something or spit it out. Taste results from stimulation of the taste buds, the receptors on the tongue. When we talk about the taste of food, we generally mean flavor, which is a combination of taste and smell. Whereas other senses remain separate throughout the cortex, taste and smell axons converge onto many of the same cells in an area called the endopiriform cortex TASTE RECEPTORS Mammalian taste receptors are in taste buds located in papillae on the surface of the tongue HOW MANY TYPES OF RECEPTORS? Jalapeños and other hot peppers produce a hot mouth sensation that is not considered a taste. The evolution of hot peppers is an interesting story. Most plants produce chemicals that discourage animals from eating them. The capsaicin in hot peppers discourages mammals, but not birds, because birds’ heat receptor does not respond to capsaicin. MECHANISM OF TASTE RECEPTORS Sweetness, bitterness, and umami receptors resemble the metabotropic synapses. After a molecule binds to one of these receptors, it activates a G- protein that releases a second messenger within the cell. People have two types of sweetness receptors and two types of umami receptors, each with somewhat different sensitivities MECHANISM OF TASTE RECEPTORS Bitter taste used to be a puzzle because bitter substances include a long list of dissimilar chemicals. Their only common factor is that they are to some degree toxic. One consequence of having so many bitter receptors is that we detect a great variety of dangerous chemicals. The other is that because each type of bitter receptor is present in small numbers, we don’t detect very low concentrations of bitter substances. TASTE CODING IN THE BRAIN The taste nerves project to the nucleus of the tractus solitarius (NTS), a structure in the medulla From the NTS, information branches out, reaching the pons, the lateral hypothalamus, the amygdala, the ventral-posterior thalamus, and two areas of the cerebral cortex One of these areas, the somatosensory cortex, responds to the touch aspects of tongue stimulation. The other area, known as the insula, is the primary taste cortex. VARIATION IN TASTE SENISITIVITY Some people have three times as many taste buds as other people do on the fungiform papillae near the tip of the tongue. That anatomical difference depends partly on genetics but also on age, hormones, and other influences. Women’s taste sensitivity varies with their hormones and reaches its maximum during early pregnancy, when estradiol levels are high VARIATION IN TASTE SENISITIVITY People with more taste buds, known as supertasters, tend to dislike strongly flavored foods, especially foods that taste very bitter to them, but only mildly bitter to other people. People at the opposite end, having the fewest taste buds, tolerate many somewhat bitter foods. OLFACTION OLFACTION Olfaction, the sense of smell, is the response to chemicals that contact the membranes inside the nose. For most mammals, olfaction is critical for finding food and mates and for avoiding dangers. Researchers blindfolded 32 young adults, made them wear gloves, and then asked them to try to follow a scent trail across a field. The scent was chocolate oil. (They decided to use something that people care about.) Most of the participants succeeded and improved their performance with practice. OLFACTORY RECEPTORS The neurons responsible for smell are the olfactory cells that line the olfactory epithelium in the rear of the nasal air passages. In mammals, each olfactory cell has cilia (threadlike dendrites) that extend from the cell body into the mucous surface of the nasal passage. Olfactory receptors are located on the cilia. OLFACTORY RECEPTORS Each of these proteins traverses the cell membrane seven times and responds to a chemical outside the cell (here an odorant molecule instead of a neurotransmitter) by triggering changes in a G protein inside the cell. OLFACTORY RECEPTORS The G protein then provokes chemical activities that lead to an action potential. The best estimate is that humans have several hundred olfactory receptor proteins, whereas rats and mice have about a thousand types MESSAGES TO THE BRAIN When an olfactory receptor is stimulated, its axon carries an impulse to the olfactory bulb. Although the receptors sensitive to a particular chemical are scattered haphazardly in the nose, their axons find their way to the same target cells in the olfactory bulb, such that chemicals of similar smell excite neighboring areas, and chemicals of different smell excite more separated areas INDIVIDUAL DIFFERENCES PHEROMONES The vomeronasal organ (VNO) is a set of receptors located near, but separate from, the olfactory receptors. Unlike olfactory receptors, the VNO receptors respond only to pheromones, chemicals released by an animal that affect the behavior of other members of the same species. PHEROMONES The behavioral effects of pheromones apparently occur unconsciously. That is, people react to certain chemicals in human skin even when they describe them as odorless. The smell of a sweaty woman increases a man’s testosterone secretions, especially if the woman was near her time of ovulation PHEROMONES This effect is stronger for heterosexual men than for homosexual men The smell of a sweaty man does not increase sexual arousal in women. Instead, it increases release of cortisol, a stress hormone Evidently a man reacts to a sweaty woman as a sex signal, and a woman reacts to a sweaty man as a potential danger signal. PHEROMONES Another study dealt with the phenomenon that a woman in an intimate relationship with a man tends to have more regular menstrual periods than women not in an intimate relationship. In the study, young women who were not sexually active were exposed daily to a man’s underarm secretions. (Getting women to volunteer for this study wasn’t easy.) Gradually, over 14 weeks, most of these women’s menstrual periods became more regular than before SYNTHESIA Synesthesia is the experience some people have in which stimulation of one sense evokes a perception of that sense and another one also. For example, someone might perceive the letter J as green or say that each taste feels like a particular shape on the tongue That’s it! Time for some Q&A, any question?