EXAM 2 EX3202 SKIN THE LEMNISCAL SYSTEM 1 Anatomy and sensory physiology of the 4 kinds of mechanoreceptors and the stimuli that activate them a Basket Cells Neuron connected to hair on the skin relatively few used for detection b Pacinian corpuscles activated by even the finest stimuli identification stimulated by rough stimuli because it is deep in the skin are relaxed c muscle spindle fibers d Golgi tendon organ Stretch Receptor Tension Receptor info about which muscles are contracted and which a type of receptor connected to sensory neurons used for 2 The different perceptual functions of different receptor types a Detection Basket Cells b Texture and Shape Identification Pacinian corpuscles c Kinesthesis muscle spindle fibers and Golgi tendon organs 3 Differences in the distribution of Basket Cells and Pacinian Corpuscles across the skin surface and how these differences relate to detection vs identification of tactile stimuli Relatively few basket cells which are connected to the hairs on the skin of the body Due to how close they are to the skin surface they are used mainly for detection of even the smallest stimuli Pacininian Corpuscles located deep in the skin and used mainly for identification of stimuli through yes no signaling 4 Spinal cord organization and the lemniscal system be able to draw the pathway Lemniscal Pathway used by mechanoreceptors carries tactile pressure stimuli information basket cells carries tactile vibrations texture information pacinian corpuscle Right half of the body somatosensory information goes to the hind brain then goes to the left side of the thalamus and ends up in the left parietal lobe Left parietal lobe controls the right side of the body Lower Body region information enters at the bottom of the spinal cord Upper body region information enters higher up on the spinal cord 5 You should be able to describe the relationship between tactile sensory neuron receptive field size and density and the distortions present in somatosensory maps in cortex You should be able to look at a homunculus from any animal species and make accurate predictions about tactile sensory neuron receptive field size and density in that animal s skin Distortions on the homunculus reflect density of receptor neurons in each body part body parts which appears abnormally large have the greatest of sensory neurons Degrees of freedom of possible movements you can generate with a specific body part For humans the face and hands have the highest degrees of movement depicts sensation threshold on the human body most sensitive parts hands fingers lip face have the lowest thresholds 6 You should be able to describe the effects of experience on somatosensory maps in cortex don t forget developmental differences in the effects of experience Experience has a lot to do with the way our somatosensory cortex gets mapped out The more we use a certain sense body part or region of the brain the more connections will form in the corresponding part of the cortex EX When body parts go missing neurons re route cortical maps readjust and other neighboring body parts may become extra sensitive Also some one that is blind will have re adjusted cortical area that makes them more kean to sound and other senses 7 You should understand what Haptic Perception is using all of your mechanoreceptors at the same time to actively explore the texture and or shape of an object BODY SURFACE INFO BODY POSITION INFO HAPTIC PERCEPTION Humans can get info of objects through the surface of the skin via haptic perception See Chapter 13 and Lecture Slides Skin SKIN THE SPINOTHALAMIC SYSTEM 1 Here you should focus on the anatomy and sensory physiology of free nerve endings nociceptors and thermal receptors Why are they called free Free Nerve Endings a bare neuron sitting in the skin not attached to any apparatus why they are called free very dense especially in skin surfaces without hair heavily myelinated Thermoreceptors detect temperature o Warm fibers detect increases in skin temperature o Cold Fibers fire in response to decreases in skin temperature Nociceptors bare nerve endings that respond to tissue damage pain o A delta fibers respond primarily to strong pressure or heat Myelinated allows them to relay information quickly chemicals Unmyelinated Relays information more slowly than A delta fibers respond to intense pressure heat or cold and noxious o C fibers o Pain seems to occur in two stages a sharp burst of pain carried by A delta fibers and a dull throbbing carried by C fibers 2 Why are there so many of free nerve endings in human skin and how does their distribution differ across the skin surface Having a dense and numerous counts of free nerve endings is important because they play a key role in detecting pain injury Nociceptors also plays a key role in initiating a process known as inflammation crucial to attempt to put up a defense perimeter around the region of skin that has been breached and therefore initiate the 1st step of the immune defense People without nociceptors usually die due to infection not the injury itself Non hairy regions of the body use a many to one signaling convergent excitation to relay information about pain This produces a lower threshold Lower threshold lower identification rate Pain in hairless regions is therefore perceived as being diffused ex Feeling pain in your arm when it is really coming from your chest region during a heart attack 3 How are nociceptors activated How do nociceptors amplify weak signals You should understand the role of nociceptors in the process known as inflammation Nociceptors both respond to and release chemical stimuli They get activated in the presence of blood serum released due to tissue damage and they release chemicals CGRP Substance P which are the basis of inflammation These substances increase blood flow act as chemical amplification Therefore they increase levels of the very signal that activated the nociceptors in the first place This process occurs in order to increase the odds of bringing white blood cells to the site of injury 1st step of the immune system 4 Generally speaking what is the role of nociceptors in healing and what does this tell us about the function of pain Nociceptors activate the inflammation process and act to bring while blood cells to the site of injury in order to begin defense and healing Therefor pain is necessary in order to prevent infection and not only identify injury but begin to heal it 5 Spinal
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