Please read the chapter assigned for this week.
(Reading Schedule: http://www.uni.edu/~maclino/hybrid/sp_book_s11.pdf)
After reading the chapter, please respond to the following questions:
Of the various aspects of Sensation & Perception presented in the chapter, which did you find the most interesting? Why? Which did you find least interesting? Why? What are three things you read about in the chapter that you think will be the most useful for you in understanding Sensation & Perception? Why? What are some topics in earlier chapters that relate or fit in with this chapter? How so?
Please make sure you use the terms, terminology and concepts you have learned so far in the class. It should be apparent from reading your post that you are a college student well underway in a course in psychology.
Make a list of key terms and concepts you used in your post.
Let me know if you have any questions.
--Dr. M
Chapter 12 is very interesting. Discussing about touching, from physilogical and psychological point of view. To me, interesting was reading about different kind of pain and different level of it. Pain might be sensory, emotional or cognitive. Pain sensation are triggered by the nociceptors. neruone are carrying the signals to the spinal cord in area called substantia gelatinosa of the dorsal horn. Acocrding to the gate control theory, the pain signals can be blocked by feedback circuit.
The least interesting was the physiological part of the touch and how does the brain respond becasue; it is a long and complicated process, yet it owuld be the most useful understanding the physiological process of touching to have a better understanding of sensations and percpetion. Earlier chapter was talked aobut hearing, seeing, and now antoher sense : touch . There are all connect to each other.
Terms:
nociceptors, substantia gelatinosa,dorsal horn,
I found chapter 12 very interesting. Before reading this chapter, I would not have considered the change in temperature, perceptions of pain, or the sensation of movement of limbs or joints to be a form of touch. Kinestesis are the internal sensations such as the sensations we fell when the positions and movements of our limbs change. Proprioception is when the sensations arise from the vestibular system. All of these senses combined together are somatosensation. The first part of the chapter discusses how important the sensation of touch really is to our daily life. The authors encourage the readers to try completing daily tasks while wearing a blindfold. I didn't try this activity, however I do have a similar experience. I work as a photo tech at Walgreens and often have to change the paper for the machine in a black bag. All of this has to be done without seeing what I am doing. At first it was a difficult experience, but after a while I got used to it and it became easier to do this task.
There were several things that I found interesting in this chapter. The first thing that I found interesting and useful to the understanding of sensation and perception are the mechanorecptors. Mechanorecptors are sensory receptors responsive to mechanical stimulation (pressure and vibration). There are four different kinds of mechanorecptors. They are meissner corpuscles, merkel cell neurite compleces, pacinian corpuscles, and Ruffini endings. Meissner corpuscle are specialized nerved endings associated with fast-adapting fibers with small receptive fields (FA 1). Merkel cell neurite complex are specialized nerve ending associated with slow-adapting fibers with small receptive fields (SA 1). Pacinian corpuscle are specialized nerve ending associated with fast-adapting fibers with large receptive fields (FA 2). Ruffini endings are specialized nerve ending associated with slow-adapting fibers with large receptive fields (SA 2). These four types of mechanorecptors are always working together to inform you about every individual object you touch. An example in the text of useing all the mechanorecptors is: "feeling the shape of your key in your pocket requires the SA 1 channel. Shaping your fingers to grasp the key involves the SA 2 channel. As you insert the key into the lock, your grip force increases so that the key does not slip, thanks to your FA 1 channel. Finally, your FA 2 channel tells you when the key has hit the end of the keyhole."
Another thing that I found interesting are the nociceptors. Nociceptors are sensory receptors that transmit information about noxious (painful) stimulation that causes damage or potential damage to the skin. Nociceptors can be divided into two types based on the nerve fibers. A-delta fibers respond primarily to strong pressure or heat and are myelinated, which allows them to conduct signals very rapidly. C fibers are unmyelinated and respond to intense stimulation of various sources: pressure, hear or cold, or noxious chemicals.
A couple other concepts that I found interesting were the concept of a phantom limb and and the gate control theory. The phantom limb is perceived sensation from a physically amputated limb of the body. The gate control theory states that pain sensations can also be blocked via a feedback circuit located in an area called the substantia gelatinosa (a jellylike region of interconnecting neurons in the dorsal forn of the spinal cord) of the dorsal horn (region at the rear of the spinal cord that receives inputs from receptors in the skin) of the spinal cord. Neurons in this area receive information from the brain and synapse with the neurons that are conveying sensory information from nociceptors to the brain. When these gate neurons send excitatory signals the sensory information is allowed to go through, but inhibitory signals from the gate neurons cancel transmission to the brain.
What I found the least interesting was the information in the text about how the sensation preceived from touch travels from the skin to the brain. There are several things in this chapter that remind me of information that we learned in previous chapters. The author made a connection between the different types of mechanoreceptors and rods and cones. both are used in perception of different aspects.
Terms: Kinesthesis, peopriception, somatosensation, mechanorecptors, meissner corpuscle, merkel cell neurite complex, pacinian corpuscle, ruffini ending, nociceptors, phantom limb, gate control theory, substantia gelatinosa, dorsal horn,
the concept of a phantom limb and and the gate control theory. The phantom limb is perceived sensation from a physically amputated limb of the body. The gate control theory states that pain sensations can also be blocked via a feedback circuit located in an area called the substantia gelatinosa (a jellylike region of interconnecting neurons in the dorsal forn of the spinal cord) of the dorsal horn (region at the rear of the spinal cord that receives inputs from receptors in the skin) of the spinal cord. Neurons in this area receive information from the brain and synapse with the neurons that are conveying sensory information from nociceptors to the brain. When these gate neurons send excitatory signals the sensory information is allowed to go through, but inhibitory signals from the gate neurons cancel transmission to the brain.
The phantom limb and the gate control theory are crazy concepts to think about but I was wondering if teh phantom limb research done by psychologist Vilayanur Ramachandran still remains after the gate control theory? Even though it is not pain that they are feeling just a sensation, which could be pain, could that also be blocked. Ramachandran made the obsercation that amputees often report feeling sensation in their phantom arms and hands when their faces or remaining limbs are touched.
The topics from Ch. 12 Touch that I think will be the most useful to understanding sensation & perception is the discussion of touch physiology. The receptors in our skin help create the sensation of touch. There are receptors units in both the EPIDERMIS (outer layer) and the DERMIS (inner layer). The touch receptors in the skin are the basis for the processing of the sensation of touch. Touch receptors are characterized by the type of stimulation to which they respond, the size of their receptive field, and the rate of adaptation (fast or slow).
MECHANORECEPTORS are sensory tactile receptors that are responsive to mechanical stimulation such as pressure, vibration and movement. Each receptor contains a nerve fiber called A-beta fibers which have a wide receptive field and a fast rate of adaptation. There are four populations of mechanoreceptors: MEISSNER CORPUSCLE a specialized nerve ending associated with fast adapting (FA I) fibers that have small receptor fields, MERKEL CELL NEURITE COMPLEX a specialized nerve ending associated with slow-adapting (SA I) fibers that have small receptive fields, PACINIAN CORPUSCLE a specialized nerve ending with fast-adapting (FA II) fibers that have large receptive fields, and RUFFINI ENDING a specialized nerve ending with slow-adapting (SA II) fibers that have large receptive fields. SA I fibers best respond to steady downward pressure, fine spatial details and very low frequency vibrations. Its primary functions are texture perception and pattern/form detection. SA II fibers respond best to sustained downward pressure, lateral skin stretch, and temporal changes in skin deformation. Its primary function is to determine finger position or stable grasp. FA I fibers respond best to low-frequency vibrations and detection of those is its primary function. FA II fibers respond best to high-frequency vibrations and detection of those is its primary function.
KINESTHETIC RECEPTORS refer to perception involving sensory mechanoreceptors in muscles, tendons, and joints. These receptors play a role in sensing where our limbs are and what kinds of movements we make. MUSCLE SPINDLES are sensory receptors located in a muscle that senses its tension. The angle formed by a limb at a joint is perceived through these.
THERMORECEPTORS are sensory receptors that signal information about changes in skin temperature. They are located in the epidermal and dermal layers of skin. There are two types of thermoreceptors: warmth fibers (when skin temp increases) and cold fibers (when skin temp decreases).
NOCICEPTORS are sensory receptors that transmit info about noxious (painful) stimulation that causes damage or potential damage to the skin. These receptors have bare nerve endings and there are two types: A-DELTA FIBERS (intermediate-sized, myelinated fiber that transmits pain and temp signals), and C FIBER (narrow-diameter, unmyelinated fiber that transmits pain and temp signals). A-delta fibers respond mostly to strong pressure or heat and conduct signals rapidly and create a sharp pain. C fibers respond to intense stimulation and create a throbbing sensation.
The topic I found the least interesting was the pathways from the skin to the brain. Receptors that deliver touch sensations must travel a distance to reach the brain and must first move up through the spinal cord. Once in the spinal cord the info is moved up toward the brain through two major pathways: SPINOTHALAMIC PATHWAY (carries most of the info about skin temp and pain) and the DORSAL COLUMN-MEDIAL LEMINISCAL or DCML PATHWAY (carries signals from skin, muscles, tendons, and joints. Info through the DCML is used for planning and executing rapid movements for quick feeback. From the thalamus information is sent to the cortex into SOMATOSENSORY AREA 1 or S1 (primary receiving area) or the SOMATOSENSORY AREA 2 or S2 (secondary receiving area). These areas are close to the motor control system allowing for quick communication between the two. Our brain is SOMATOTOPIC (spatially mapping in the somatosensory cortex in correspondence to spatial events on the skin) and creates a HOMUNCULUS (maplike representation of regions of the body in the brain. When a person loses a limb this can often cause problems with a PHANTOM LIMB (sensation perceived from a physically amputated limb of the body.
The topic I found the most interesting was pain. There are multiple levels of pain: sensory, emotional, and cognitive. According GATE CONTROL THEORY the bottom-up pain signals can be blocked via a feedback circuit located in the DORSAL HORN (region at the rear of the spinal cord that receives inputs from touch receptors. The sensory info can go through but inhibitory signals from the gate neurons cancel transmission to the brain. Pain influences our cognition and is evident in the PREFRONTAL CORTEX (a region of the brain concerned with cognition and executive control. In this region a “secondary pain affect” can occur where there is an emotional response associated with long-term suffering that occurs when painful events are imagined or remembered. Pain can be moderated through various techniques. ANALGESIA is when pain sensation is decreased during a conscious experience such as through analgesic drugs. It has been shown that there are also interpersonal and social influences on the emotional component of pain that helps reduce it as well. ENDOGENOUS OPIATES are chemicals released by the body that block the release or uptake of neurotransmitters necessary to transmit pain sensations to the brain. Medical drugs such as morphine, codeine, etc. have similar chemical makeup to these. On the other hand, HYPERALGESIA is an increased or heightened response to a normally painful stimulus. This often occurs if more pain stimulus is given to an area that has already been damaged and pain has been triggered.
What are some topics in earlier chapters that relate or fit in with this chapter? How so?
It is necessary for the different sensations sections of our body have different types of receptors. Like the eyes (rods and cones) the skin has different receptors for different types of touch.
Terms: epidermis, dermis, mechanoreceptors, meissner corpuscle, merkel cell neurite complex, pacinian corpuscle, ruffini, SA I, SA II, FA I, FA II, kinesthetic receptors, muscle spindles, thermoreceptors, nociceptors, a-delta fibers, c fibers, spinothalamic pathway, DCML pathway, S1, S2, somatotopic, homunculus, phantom limb, gate control theory, dorsal horn, prefrontal cortex, analgesia, endogenous opiates, hyperalgesia
When looking through this chapter on touch I found three terms at the beginning that I found very useful. Kinesthesis or the perception of the position and movement of our limbs in space, proprioception or perception mediated by kinesthetic and vestibular receptors, and somatosensation or a collective term for the sensory signals from the body, were all very useful in understanding touch. The next topic that I found interesting was the area on touch physiology. When looking at touch physiology we have to look at what the sensory organs for touch are. The epidermis or the outer of two major layers of the skin and the dermis or the inner of two major layers of skin, consisting of nutritive and connective tissues within which lie the mechanoreceptors are the sensory organs for touch. The skin has different types of receptor for touch, but each receptor can be characterized by the type of stimulation to which the receptors responds, the size of the receptive field, and the rate of adaptation. The first kind of receptor present in our skin is tactile receptors, which are called mechanoreceptors, or sensory receptors that are responsive to mechanical stimulation. These receptors consist of a nerve fiver and an associated expanded ending. Another type of receptor is called a kinesthetic receptor or a receptor that is responsible for the perception involving sensory mechanoreceptors in muscles, tendons, and joints. These sensors are useful in sensing where our limbs are and what kinds of movements we are making. Another type of sensor is thermoreceptors, or the receptors that signal information about changes in skin temperature. These are made from warmth fibers that fire when skin temperature increases and cold fibers that fires when skin temperature decreases. The final type of receptor is the nociceptors, which are the receptors that transmit information about painful stimulation that causes damage or potential damage to the skin. Noiceptors come in two types of nerve fibers: A-delta fibers which respond primarily to strong pressure or heat and C fibers which respond to intense stimulation of various sorts of pressure, heat or cold. A-delta fibers are much faster than C fibers.
Terms: Kinesthesis, Proprioception, Somatosensation, Epidermis, Dermis, Mechanoreceptors, Kinesthetic, Thermoreceptors, Warmth Fiber, Cold Fiber, Nociceptors, A-delta Fiber, C Fiber
I thought the information about moderating pain was very interesting. One way to relieve pain is to apply pressure to another area of the body that isn’t the original source of pain. This works because the information from the new stimulation is being sent to the brain and so the brain basically forgets that there’s more pain in a different area. This is called “counter-irritation”. Another way to decrease pain is to stimulate the area around the pain source. An example I can think of is when you have an ear ache, it sometimes feels better to rub the area around the ear, like your jaw or right next to the ear. Another way is done unconsciously by endogenous opiates, which are chemicals released that block the release/uptake of neurotransmitters that transmit pain to the brain. These chemicals basically block the pain until the stress of the situation is over. The varying levels people have of this chemical may be related to people’s pain thresholds. The last way pain may be reduced is by using emotions. The book explains how research has showed that women who hold their husbands hand while receiving a shock rated the experience as being less unpleasant than holding a strangers hand or no hand at all. This shows that there is a social influence on pain. I think all of this is very interesting because I tend to think of pain as something stable and not influenced by so many different things.
One thing I found least interesting is the four different populations of tactile fibers – Meissner corpuscle, Merkel cell neurite complex, Pacinian corpuscle, and Ruffini ending. Each group of fibers has different sensitivities and work together to tell us information about objects we feel. Although these fibers are important in understanding the physiology of touch, I’m more interested in the psychophysics of touch rather than the physiology.
Three things I think are most important in understanding sensation and perception are nociceptors, thermoreceptors, and haptic perception. Nociceptors are the pain receptors. They transmit information about damage (or potential damage) to the brain. There are two types of nerve fibers that make up nociceptors: A-delta fibers and C fibers. A-delta fibers mostly respond to strong pressure or heat. They conduct signals very fast. C fibers conduct signals slower than A-delta fibers and respond to intense stimulations. When someone feels pain, the A-delta fibers fire first and then the C fibers. Thermoreceptors are the receptors that send information to the brain about changes in skin temperature. There are two types of thermoreceptors: warmth fibers and cold fibers. As their names state, each fiber responds to warm and cold stimulations. The warmth fibers fire if our body temperature rises above 96 degrees F and the cold fibers fire if our body temperature falls below 86 degrees F. Thermoreceptors also tell us information about objects we touch by detecting its temperature. Depend on the temperature, thermoreceptors will tell us if something is cold or hot. Haptic perception is knowledge of the world that we extract from sensory receptors, gained by our own exploration of things. It’s how we learn to perceive certain objects and their properties. I think these three concepts are most important because I think they’re fundamentals for understanding other processes of touch.
Some topics from this chapter that relate to previous chapters are things like the four populations of tactile fibers, which the book described as being very similar to rods and cones because both are parts of each system that relay important information to the brain. Another topic is object localization. In vision and hearing, there is an exact point, called the egocenter, that is the center of the system used to define locations in space. In hearing, it’s in the middle of the head. In vision, it’s the bridge of the nose. What’s interesting about touch is that there isn’t an exact egocenter. It depends on which arm is reaching.
Terms: pain, "counter-irritation", endogenous opiates, tactile fibers, meissner corpuscle, merkel cell neurite complex, pacinian corpuscle, ruffini ending, nociceptors, thermoreceptors, haptic perception, A-delta fibers, C fibers, warmth fibers, cold fibers, rods, cones, object localization, egocenter
I think touch is an interesting topic. Touch is defined as the sensations caused by mechanical displacements of the skin. Tactile is the term used to refer to these mechanical interactions. Pain, however, occurs when our body tissues are damaged in some way. There are also temperature changes, itchiness, and internal sensations that can inform us of our limbs. The term kinesthesis is the perception of the position and movement of our limb whereas proprioception is perception mediated by kinesthetic and vestibular receptors. All of these senses put together is called somatosensation. I had no idea that touch was this complicated! Touch can tell us when something is wrong or dangerous, may cause pleasure, and can even be a means of communication. We can use it to manipulate objects as well.
I thought pain was another interesting topic in this chapter. There are different levels of pain- sensory, emotional, and cognitive, which all interact together. Pain sensations are triggered by nociceptors, which are sensory receptors that transmit information about painful stimulation that causes damage to the skin. Neurons carry nocioceptive signals to the spinal cord in a certain area called substantia gelatinosa (a jelly like region of interconnecting neurons) of the dorsal horn 9a region at the rear of the spinal cord that receives inputs from the receptors in the skin). Neurons then receive information from the brain and forms synapses with neurons that are conveing sensory information from the nociceptors. The gate control theory is a description of the system that transmits pain that incorporates modulating signals from the brain. When the gate neurons send excitatory signals, this sensory information is allowed to go through. However, the inhibitory signals from the gate neurons cancel transmission to the brain. It gets kind of complicated, but it amazes me that that many things in our bodies work together to do something as simple as making us feel pain.
The physiology of touch was very uninteresting to me because it was very complicated and had a lot of terms along with it. For example, epidermis is the outer of two major layers of skin. The dermis is the inner of two major layers of skin which consists of nutritive and connective tissues. Tactile sensitivity and acuity was also uninteresting to me as well. There are different amounts of pressure exerted by different objects depending on the size and force. The two-point touch threshold is the minimum distance at which two stimuli are just perceptible as separate. I did this experiment in Biology Lab and it was kind of interesting to see at what point we can decipher whether it is two separate objects or not.
Terms: kinesthesis, proprioception, somatosensation, epidermis, dermis, nociceptors, substantia gelatinosa, dorsal horn, gate control theory, two-point touch threshold
Proprioception includes kinesthetic and vestibular receptors. Kinesthesis is the perception of where our limbs are where somatosensations are sensory signals from the body. Our sense of touch happens within our largest organ in the skin. The receptor units for touch are in both the epidermis (outer layer) and the dermis (layer under the epidermis). Each type of receptor is characterized by one of three attributes: what type of stimulation it responds to, size of its receptive field, rate of adaptation. We have mechanoreceptors for tactile sensation. The expanded endings of tactile fibers of mechanoreceptors are Meissner corpuscles ( fast adapting I and small receptive field), Merkel cell Neurite complexes (slow adapting I and small receptive fields), Pacinian corpuscle (Fast adapting II with large receptive fields) and Ruffini ending (slow adapting II and large receptive fields). I found it very interesting that each one of these fast acting/slow acting types were subdivided by the size of their receptive field and this dictates their primary function. Slow acting I (small receptive field) detect long periods of pressure at low intensity and specialize in texture perception. Fast acting I detects temporal changes in skin deformation and its primary function is detecting low frequency vibration . Fast acting II also detects temporal changes in skin but functions with high sensitivity detection. There are also kinesthetic receptors which I found more interesting. These are in muscles tendons and joints and sense where our limps are and what kind of movements they are making. The angle formed by a limb is detected by receptors called muscle spindles. I thought the story about the man who lost his kinesthetic senses was very interesting. This individual had a viral infection that destroyed cutaneous nerves that connected kinesthetic receptors to other mechanoreceptors and he became completely reliant on his vision to know the location of his limbs. Thermoreceptors are receptors in the epidermis and dermis that detect changes in temperature. The two types of thermorecetors are warmth fibers which fire in response to increase in temperature and cold fibers which respond to decrease in tempearature. Nociceptors are pain receptors that are divided into A delta fibers which respond to strong pressure and heat. These fibers are myelinated so that the conductions occur very quickly with A delta fibers. The second type of fibers are C-fibers that are unmyelinated and transmit pain/ temperature more slowly. I thought it was really interesting that they think the fact that most pain sensations occur in a quick sharp burst of pain followed by a throbbing sensation because A –delta fibers are stimulated followed by C-fibers. I thought nocirecetors were particularly important in understanding from an evolutionarily perspective because if an individual were to lack these they would suffer a lot of damages to tissues because the pain sensation helps to prevent this occurrence. From the area of stimulation the sensory information goes into two major pathways. I think further studying of the spinothalamic pathway (from spinal cord to rain that carries skin temp and pain) and the dorsal column-medial lemniscal pathway (spinal cord to brain that carries signals from the skin ,muscles and joints would be very helpful. I found it interesting that the spinothalamic pathway provides a mechanism for pain inhibition and the dorsal column-medial lemnisical pathway is used for executing rapid movements and regarding sensations that require immediate feedback. I would also like to study more about the gate-control theory of pain which says that the bottom up pain signals from the nocireceptors can be inhibited through a feedback circuit in the dorsal horn. The specialized nature of different receptors with slightly different responsibilities has been an underlying theme with all of the physiology we have studied and continues to be the case with touch. There has also been a theme of certain sensations providing an evolutionary survival advantage and this also holds true with touch especially in the case of pain receptors.
Terms: Proprioception, spinothalamic pathway, nocireceptors, column-medial lemniscal pathway, kinesthesis, Meissneers corpuscles, Pacinian corpuscles.
Chapter 12 is about touch. Touch or somatosensation is the last sense that the book covers. The book states how important our sense of touch is to us. We perceptive touch though our skin, starting with the epidermis and then to the dermis. Similar to photoreceptors there are channels in which information is gathered. Furthermore, there are three types of these receptive channels; ones that respond to pressure, vibration, or temperature. There are different size ones, and there are different rates of adaptation. They are known as tactile receptors are; mechanorepcetors, meissner corpuscle, merkel cell neurite complex, pacinian corusle, riffini endings. In addition to reception that lay within the skin, there are ones that lay within our muscles.
Thermoreceptors are also located within the epidermal and dermal layers of the skin and inform our body about temp. changes. Warmth fiber fires when skin temp increase, and cold fiber when the skin temp decreases. Nocicpetors are pain signals. What I think is interesting about these are the lack of them. We would be injury all the time exteriorly and interiorly.
Like the pathways between our eye and our brain there are pathways for our touch. Our receptors and our brain can be around 2 meters away. Therefore we use our spinal cord. Route from the spinal cord to the brain is the spinothalamic pathway, this carries most of our information about skin temp and pain. Our dorsal-column-medial lemniscal pathway carries the signals from skin, muscles, tendons, and joints. First stop in our brain is the thalamus. Then to the cortex into our somatosensory areas. Areas in the somatosensory areas in the brain are linked/ mapped to areas in the body. This is called the sensory homunculus, “showing the brain regions that respond to stimulation of different part of the body”. The tight areas within the brain can have side effects, states the book. Sporadic activity can continue and lead to a “phantom limb”. This to be is interesting. When their face or remaining limb is touched, amputees feel sensation and activity in their phantom limb. Area responding to the face is close to the area responding to the arm. I think the book is trying to say that it could be that the lack of information from the missing limb could cause an over-activity of the close area and those “invade” the area that was once linked to the missing limb.
The book also mentions interesting situations that happen with pain. That it is common for pain not to be experienced during “conscious experience” This is called analgesia. Similar to this is endogenous opiates, on battlefield soldier do not feel pain until the stressful event is over is probably due to chemicals being released by the body that are blocking the uptake of neurotransmitters necessary to transmit pain sensations to the brain. However once a site has been felt, it becomes more sensitive. Pain is a subjective state. The area of our brain associated with the perceived unpleasantness of the sensation of pain is our anterior cingulate cortex. Our prefrontal cortex is responsible for the emotional side of pain.
A major topic of study within psychology seems to be two-point threshold. How far does it take for us to feel two different sensations of being touched? On our finger, it is closer than our hand.
The last part of the chapter talks about how important our sense of touch is to the world. Haptic perception is the knowledge of the world that is derived from sensory
Key Terms:
somatosensation epidermis dermis mechanoreceptors nociceptors thermoreceptors spinothalamic pathway somatosensory area phantom limb two-point touch threshold haptic perception
Chapter 12 starts out by defining touch. It states that the most narrow definition is "the sensations caused by mechanical displacements of the skin". This could be many things such as holding hands, getting poked, a kiss, or holding an object. The book uses the term tactile to refer to these. They expand the definition of touch to include several other things such as temperature change (thermal sensation) and pain. These internal sensations inform us of the position and movement of our limbs in space and are known as kinesthesis when they come from muscles, tendons, and joints and are part of the system called proprioception which also includes the vestibular system. If you put all of these signals together it can be referred to as somatosensation.
I found the information on the physiology of touch interesting. Like all our senses the sensory equipment for touch is located in a sensory organ. Touch is housed in the largest of sense organs, the skin. Our skin has receptor units for touch in both the outer (epidermis) and inner (dermis) layer of the skin. The skins has multiple types of touch receptors which can be characterized by 3 attributes; type of stimulation to which it responds, size of receptive field, and rate of adaptation. One type of touch receptor is tactile receptors also known as mechanoreceptors because they respond to mechanical stimulation or pressure. Tactile receptors are made up of a nerve fiber and associated expanded ending. These nerve fibers fall into the A-beta fibers class and have wide diameters that permit fast neural conduction. There are multiple types of tactile receptors. Our palms alone consist of 4 different types. The next type of receptor is kinesthetic receptors. Unlike tactile receptors these are located in the muscles, tendons and joints. These receptors have the job of sensing where are limbs are and what they are doing. Muscle spindles are a type of receptor that perceives what angle is formed by a limb at the joint. The tendons house receptors that give information about the tension in the muscles attached to the tendons. The receptors in the joint are particularly important when a joint is bent at an extreme angle. Next is the thermoreceptors. Like the tactile receptors these are located in the epidermal and dermal layers of the skin. The thermoreceptors give information about the changes in skin temperature. There are 2 types of thermoreceptors; warmth fibers which fire when the skin is heated and cold fibers which fire when the skin temperature decreases. Cold fibers outnumber warmth fibers by about 30:1. Thermoreceptors are also activated when we touch an object that is a different temperature from our skin. The last type of receptor is nociceptors. Nociceptors have bare nerve endings that transmit signals about painful stimulation that is or could be damaging to the skin. There are 2 types of nociceptors A-delta fibers and C fibers. A-delta fibers are myelinated fibers which allow them to conduct signals rapidly. These respond primarily to strong pressure and heat. C fibers are unmylinated and respond to intense stimulation such as pressure, heat/cold, or noxious chemicals.
The information on how the signals move through the body and to the brain wasn't very interesting to me but it is still important to know. Besides touch all of our sensory organs are located in the skull so the information can be quickly transmitted to the brain. Touch is different because it's sensory organ covers our entire body and must travel from every point to our brain. The visual and auditory pathways have 2 nerves that move to the brain (2 optic nerves, 2 auditory nerves). Touch on the other hand has several somatosensory nerve trunks which arise in the hands, arms, feet and other areas. The axons in these nerve trunks first go to the spinal cord. Once in the spinal cord the information moves towards the brain by 2 pathways: the spinothalamic and the dorsal column-medial lemniscal (DCML) pathway. The spinothalamic pathways is slower and carries most of the information from the thermoreceptors and nociceptors. This pathway includes synapses within the spinal cord which slows conduction while also providing a mechanism for inhibiting pain perception when necessary. The neurons that carry the signals from these receptors first go to an area in the spinal cord called the substantia gelatinosa of the dorsal horn. The neurons in the substantia gelatinosa both receives information from the brain and transmits information to the brain. The information then is sent to somatosensory areas S1 (located in the parietal lobe) and S2 (located in the upper bank of the lateral sulcus). The DCML pathway carries tactile and kinestetic information which is used for planning and executing rapid movement so quick feedback if necessary. The neurons in the DCML pathway first go to the cuneate and gracile nuclei which is near the base of the brain. The signals are then sent to the neurons in the ventral posterior nucleus of the thalamus. Then most of the information is carried to the cortex to somatosensory area 1. The neurons in S1 communicate with S2.
Another interesting topic is tactile agnosia. Tactile agnosia is the inability to identify objects by touch. If a person has lesions in the left inferior parietal region of the brain they can have tactile agnosia in the right hand but it would not affect the left hand. With tactile agnosia other capabilities seems to be normal in both hands such as sensory threshold levels. One other interesting topic was on phantom limbs. This is not new information to me but I've always found it extremely interesting. The area in our brain known as S1 is organized into a spatial map of the layout of the skin which is often called the homunculus. We all have twin homunculus one on each side of the brain. Just as with the other senses the left hemisphere receives information from the right side of the body and vice versa. With phantom limbs, even though the limb is not there, sporadic activity can continue in the area of S1 that corresponds to the arm. This activity can cause people to feel pain or feel as if they are in an uncomfortable position.
Terms: touch, tactile, thermal sensation, kinesthesis, proprioception, vestibular system, somatosensation, epidermis, dermis, mechanoreceptors, A-beta fibers, kinesthetic receptors, muscle spindles, thermoreceptors, warmth fibers, cold fibers, nociceptors, A-Delta fibers, C-dibers, mylinated, nerve trunks, spinal cord, spinothalamic pathway, dorsal colum-medial lemniscal pathways, substantia gelatinosa, dorsal horn, S1, S2, cuneate nuclei, gracile nuclei, ventral posterior nuclues, thalamus, cortex, tactile agnosia, phantom limb, homunculus
Chapter 12 first defines touch as kinesthesis which is the percetption of the postion and movement of our limbs in space. this is part of the proprioception systyem--the perception mediated by kinestheic and vestibular receptors. Both form somatosensation that is a collective term for sensory signals from the body. Touch is a way for us to gain knowledge about our environment that we use for warnings or pleasure that is a survival tatic.
What I thought was interesting in this chapter was the different receptors for touch. The first is a tactile receptor called mechanoreceptors. These are sensory receptors that are responsive to mechanical stimulation(pressure, vibration, and movement). There are four different kinds of tactile receptors or mechanoreceptors which include meissner corpuscles( a specialized nerve ending associated wth fast-adapting fibers that have small receptive fields-FAI.), merkel cell neurite complexes(a specialzed nerve ending associated with slow adapting fibers that have small receptive fields-SAI.), pacinian corpuscles(a specialized nerve ending associated with fast-adapting fibers that have large receptive fields-FAII), an ruffini endings(a specialized nerve ending associated with slow-adapting fibers that have large receptive fields-SAII). These are found on the hairless skin on the hand. We classify these by their adaption rates and sizes of receptive fields. SA1 fibers respond best to steady downward pressure, fine spatial detail, and low frequency vibrations. Used for texture and patteren perception. SA11 are fibers that are used when we grasp objects. They will determine when are fingers are shaped properly for picking up the given object. FAI are fibers that would help us correct the grip of an object. If the object was heavier then we expected or we were wobbly with the object, these fibers would correct our grip and stop us from dropping the object. FA II fibers let us know when something touches our skin or the object in hand would touch something else. IF a bug lands on us or we tap our pencil on a desk, these fibers let us know and at what magnitude.
Another receptor is a kinesthetic receptor( referring to peception involving sensory mechanorecptors in muscles, tendons, and joints). These receptors help us in sensing where our limbs are and what kinds of movements we're making with them. A muscle spindle is a receptor located in a muscle that senses tension. I thought the story about Ian Waterman was very interesting and gave you an idea about just how important our kinesthetic receptors are.
Thermoreceptors are sensory receptors that signal information about changes in skin temperature. The two different types or thermoreceptors are warmth fibers and cold fibers. These nerve fibers fire whenever your skin temp increases or decreases.
Lastly Nociceptors are sensory receptors that transmit info about noxious or painful stimulation that causes damage or potential damage to the skin. Basically these receptors tell us if we are in pain. Nociceptors can be broken down into two types, A-delta fibers and C fibers. A-Delta fibers are an intermediate-sized myelinated sensory nerve fiber taht transmits pain and temperature signals. C fibers are a narrow-diameter, unmyelinated snesory nerve fiber that transmits pain and temperature signals. When we feel pain it usually starts with a sharp burst of pain and then a throbbing sensation which we think is signals from the A-delta fibers and then the c fibers. I think these are all really intersting because you never think about how complex something is and how much is at work by just touching or holding and object.
The thing in this chapter that i found to be not so intersting was the information on the skin to brain. The two pathways that carry touch information to the brain are the spinothalamic pathway and the dorsal column-medial lemniscal pathway. The first is the routefrom the spinal cord to the brain that carries most of the information about skin temperature and pain. The second is the route from the spinal cord to the brain that carries signals from skin, muscles, tendons, and joints. The two areas that receiving areas are somatosensory area 1 and somatosensory area 2. I thought this was kind of intersting but not as much as the rest of the chapter.
This would relate to motion and attention because we it would help us to be aware of our surroundings and where we are in our environment along with our movements. Like Ian Waterman, He had to rely on his eye sight to get around. He couldnt walk up stairs or tie his shoes because he lacked kinesthetic receptors. If lights were turned off he couldnt move at all. He had to physically see his movements.
kinesthesis, proprioception, somatosensation, mechanoreceptors, meissner corpuscles, merkel cell neurite complexes, pacinian corpuscles, ruffini endings, SAI, SAII, FAI, FAII, kinesthetic receptors, muscle spindles, thermoreceptors, warmth fibers, cold fibers, nocireceptors, A-delta fibers, C fibers
Chapter twelve explains touch. all of the internal sensations that we percieve is called kinesthesis. These sensations come from the movement of muscles tendons and joints. The system as a whole is somatosensation. The chapter describes the anatomical way in which we sense touch. Mechanoreceptors respond to mechanical stimulation or pressure. Kinesthetic receptors sense where our limbs are, and thermoreceptors inform us of changes in temperature. Together these are all called mechanoreceptors. The spinothalamic pathway carries the message from the specific receptor to the brain stem. I found the Somatosensory map very interesting because we have a much higher density of sensation receptors in our fingers hands and arms than we do in our legs. I also find the phantom limb symptoms very interesting. Apparently if an area is stimulated that is adjacent in the humonucleas it can trigger them both to be excited.
In chapter 12 I chose the topic of Tacoma. I chose Tacoma because it is so interesting to read about a concept that I could never fathom. The Tacoma method for conveying speech to the blind and deaf uses the hands. The haptic listener spreads the fingers of one hand across the speaker’s lips, jaw, and throat. Movements and vibrations of the speaker’s speech apparatus provide inputs to the cutaneous and kinesthetic components of the recipient’s haptic system, and these signals can be translated by a skilled recipient into spoken words. This technique used by the deaf and blind tracks speech in real time and is named after Tad Chapman and Oma Simpson.
This was interesting but not as interesting as Tacoma. So as my least favorite I chose thermoreceptors. Thermoreceptors are sensory receptors that signal information about changes in skin temperature. The two types of thermoreceptors are warmth fibers and cold fibers. Warmth fibers are sensory nerves that fire when skin temperature increases, and cold fibers are sensory nerves that fire when skin temperature decreases. I chose this because it is black and white hot and cold. But what is interesting are the people who cannot sense hot and cold.
The three things I read about in chapter 12 that I think will be the most useful for me in understanding sensation and perception is somatosensation, mechanoreceptors, and the skin to brain. Somatosensation is a collective term for sensory signals from the body. Somatosensation can be broken up into parts that can better explain the sensory system. To understand the sensory system would better help you understand sensation and perception of what you touch. Mechanoreceptors are sensory receptors that are responsive to mechanical stimulation such as pressure, vibration, and movement. Last but not least is the skin to brain or the spinothalamic pathway which is the route from the spinal cord to the brain that carries most of the information about skin temperature and pain.
Touch is an important chapter that should go hand-in-hand with the auditory and hearing chapters. Touch can be utilized in both sensation and perceptions of hearing and seeing.
TERMS: Tacoma, kinesthetic, cutaneous, haptic system, thermoreceptors, warmth fibers, cold fibers, sensory nerves, somatosensation, mechanoreceptors, spinothalamic pathway
Our ability to perceive tactile information is dependent on receptors located within our skin, muscles, tendons, and ligaments. Mechanical changes in position of the skin or motor tissues trigger a response in the receptor cells. Receptors are either fast-adapting and send signals when a tactile information is applied or removed from the receptor but do not register a signal if the stimulus is continuously applied. Slow-adapting receptors relay a sensation signal the whole time they are being stimulated by tactile sensation. Tactile receptors are known as mechanoreceptors because they respond to stimulation that is called mechanical, rather than chemical. Meissner corpuscles are fast adapting receptors with small receptive fields located on the edge of the dermis and the epidermis. Meissner cells sense low frequency vibrations such as your skin moving over your inner tissue (skin is like a suit there is movement and sliding constantly occuring). Merkel cell neurite complexes are slow adapting receptors with small receptive fields located near Meissner cells between the dermis and epidermis. Merkel cells sense fine detail and difference in tactile information. Merkel cells allow the blind to read braile and allow us to sense very small fine tactile differences kind of like cones in the visual system. Pacinian corpuscles are fast adapting, large receptive field receptors that are located near the subcutis. Pacinian receptors detect high frequency vibrations that occur whenever an object comes into contact with our skin. The book uses the example of a mosquito landing on our arm. Rufini endings are slow adapting large receptive field receptors that responds to continuous downward pressure, like gravity, and are sensitive to skin stretch which occurs nearly every time we move.
Kinesthetic receptors are located in muscles tendons and ligaments and respond to internal movement and are heavily involved with our perception of the position of our body and limbs. Spindles are receptor bundles that relay to the brain the rate at which muscle fibers change in length.
Thermoreceptors sense change in temperature. Warmth fibers are activated and fire when the skin associated with its receptive area increases in temperature. Cold fibers fire when the skin corresponding to their receptive fields decreases in temperature.
Nociceptors are receptors that carry the message of pain to the brain. These receptors have bare endings and respond to tissue damage or to stimuli that are associated with tissue damage. A-delta fibers respond to strong pressure or high heat and are myelinated allowing them to send their signal to the brain very rapidly. C receptors relay information from intense pressure, temperature or presence of damaging stimuli. Pain seems to occur in two stages, the initial pain stimulus and a throbbing that continues afterward. The book suggests these two stages are caused by the two types of receptors and the temporal separation is caused by the fact that a-delta cells are myelinated and c cells are not.
Skin receptors are some of the only receptors we've studied that have to travel through the spinal chord before reaching the brain. The spinothalamic pathway is the "old" route information takes from receptors up the spinal chord and into the thalamus. Humans have apparently developed a new pathway known as the dorsal-column-medial-lemniscal pathway which operates in wider diameter axons and with fewer synapes allowing information to get the brain much faster. Quick feedback is the goal here and this route is used to gauge tactile information and produce a very fast behavioral response.