EXAM 2 will test your knowledge of: THE LEMNISCAL SYSTEM: Mechanoreceptors You should understand the anatomy and sensory physiology of the 4 kinds of mechanoreceptors emphasized in class (Basket Cells, Pacinian corpuscles, muscle spindle fibers, Golgi tendon organ) and the stimuli that activate them.1) Basket Cells- as soon as pressure comes on, it will keep on firing till it’s turned off. Slowly adapting continues firing as long as the stimulus is there. Tactile, pressure (detection)2) Pacinian Corpuscle- specialized nerve ending associated with fast adapting fibers that have large receptive fields. Responds to a vibrating (texture) stimulus. Fires at onset at pressure then stops then fires at the offset. (Compression)3) Muscle spindle fibers – stretch receptor (contracts)4) Golgi tendon organ - Tension Receptor. (Cannot contract) a) Receptors in muscles and tendons encode body position 5) Receptors can be characterized in terms ofa) Stimulation type (pressure, vibration, temp, damage)b) Size of receptive field (amount of branching)c) Rate of adaption (slow, medium, fast) You should understand the fundamental similarity between inner hair cells (sensory cells for hearing) and mechanoreceptors in the skin, muscles, and tendons. After all, each of these receptor types transduces a mechanical stimulus into neural activity.1) There are also mechanoreceptors in hairy skin, and the hair cells in the cochlea are the most sensitive mechanoreceptors, transducing air pressure waves into nerve signals sent to the brain. Both respond to pressure and basket cells react to hair movement2) Cytoskeletal strands are like the “tip links” of inner hair cells. Ion channels “pulled open” by mechanical force You should understand the different perceptual functions of different receptor types:1) Detection, Basket Cells – hair movement 2) Identification based on surface texture and shape, Pacinian corpuscles3) Kinesthesis, muscle spindle fibers and Golgi tendon organs You should be able to describe differences in the distribution of Basket Cells and Pacinian Corpuscles across the skin surface and understand how these differences relateto human detection vs. identification of tactile stimuli. 1) Detection: converging neurons= less discrimination, lower threshold. Many to one2) Identification: less convergence, more discrimination, higher threshold. Each receptive field connected to it’s own. Spinal cord organization and the lemniscal system (be able to draw the pathway) You should be able to describe how differences in the receptive field size and density of mechanoreceptors relate to 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 mechanoreceptor receptive field size and density in that animal’s skin.1) Lower face more detection because of little hairs on face. Hands and lower half of the face identify fine texture and have the greatest level of fine motor control. (Necessary for haptic perception to work). Most animals have very little motor control in the lower half of the face You should be able to describe the effects of experience on somatosensory maps in cortex – don’t forget developmental (young vs. old) differences in the effects of experience on somatosensory maps. 1) Experiences change cortical maps.2) What happens if you a lose a finger? What happens to all the neurons? They findnew receptive fields in the skin of the adjacent finger. Will be more sensitive for the inside of the side fingers because of new sensory receptors. However, whenever you stimulate those receptors, it’s now going to feel like the middle finger is being touched, like you still have a finger. Not really phantom because incortex it never went away. Cortex of adjacent fingers will start to encroach. Readjust, but always going to have phantom sensation of lost finger.3) If you lose a hand, stump will be very sensitive because all sensory receptors are trying to find sense from little stump. Cortical maps will readjust and experience alone can readjust. Example of violin training- Young vs. OldThe homunculus.a)Left hand is someone who didn’t use left hand much. Middle is one who started playing violin when older. And right started when they were young. Other cortical region had to give up some space so we could use itto process input from the left hand. What is the result of all this experience? Variation in cortical map. b) What activity would maximize all parts of the brain?1. Music is an activity that uses all of your cortical regions (playing aninstrument) You should understand what ‘Haptic Perception’ is – using all of your mechanoreceptorsat the same time to actively explore the texture and/or shape of an object in order to identify that object. Knowledge of the world that is derived from sensory receptors in skin, muscles, tendons, and joints, usually involving active exploration. See Chapter 13 and Lecture Slides (‘Skin’) THE SPINOTHALAMIC SYSTEM: Free nerve endings Here you should focus on the anatomy and sensory physiology of free nerve endings (nociceptors and thermal receptors). Why are they called ‘free’? 1) Tissue damage, pain (nociceptor) = detects. Pain is a perception: the stimulus is tissue damage. Nociceptors respond to and release chemical stimuli (the basis of inflammation) you do not perceive pain until it reaches the brain. What’s being sensed is injury, or tissue damage. Nociceptors have branches, when stimulation is placed on a single dendrite of a Nociceptors, it’s going to send a signal back out to these branches. Cause blood vessels to dilate, which causes us to get more blood into the cite of injury, causing greater stimulation, causing a strongersignal to be sent to the brain, causing more dilation of the local vasculature.a) A-delta fiber responds primarily to strong pressure or heat and are myelinated so they can conduct signals very rapidly. Sharp burst of painb) C Fibers- are unmyelinated and respond to intense stimulation of various sorts: pressure, heat or cold, or noxious chemicals. Dull throbbing2) Temperature, hot/ Cold (thermal receptor) Identificationa) Warmth fibers- fire when temp of the skin surrounding the fibers rises.b) Cold fibers – which outnumber warmth fibers by a ratio of about 30:1 fire in response to decreases in skin temp3) This pathway is gated in the spinal and there is a
View Full Document
Unlocking...