QUIZ 2 Somatosensation STUDY GUIDE Will consist of multiple choice fill in the blank true false matching and short answer questions 1 What is somatosensation Know the types of skin glabrous hairy dermis epidermis Somatosensation sense of touch Types of skin Glabrous Hairy Dermis Epidermis 2 Know the three types of cutaneous receptors Mechano Thermo and Nociceptive and where their cell bodies reside Know the three ways mechanoreceptors are classified Touch receptors the nerve cells that tell your brain about tactile sensations Mechanoreceptors detect sensations of pushing pulling or movement Thermoreceptors detect temperature Nociceptiors bare nerve endings that respond to tissue damage painful stimuli Mechanoreceptors are classified by 1 Type of stimulation pressure vibration 2 Size of receptive field body area that elicits a response 3 Rate of adaptation to stimulus 3 What is nociception What are the two types of nociceptors and how do they differ Nociception pain Two types 1 A delta fibers respond primarily to strong pressure or heat Thin axon diameter Myelinated allows the to relay information quickly Sharp burst of pain 2 C fibers respond to intense pressure heat or cold and noxious chemicals Thicker axon diameter Unmyelinated relays information more slowly than A delta fibers Dull throbbing 4 Know the different mechanoreceptors what fast adapting vs slow adapting means which receptors are fast vs slow adapting which have small Type I vs large Type II receptive fields Know the chart from Lab 3 powerpoint slide 9 Different mechanoreceptors Pacinian corpuscle Ruffini s endings Meissner s corpuscle Merkel s disks Slow adapting receptors signal the pressure and shape of objects The total number of action potentials evoked per second is proportional to the indentation force applied to the receptor Fast adapting receptors sense motion of objects on the skin Respond during the period when the position of a stimulus changes AND stops firing when it comes to rest Mechano receptor population Adaptation rate Receptive field size Mechano receptor Merkel complexes Ruffini endings Meissner corpuscle Pascinian corpuscle SAI SAII FAI FAII Slow adapting Slow adapting Fast adapting Fast adapting Small Large Small Large 5 Know what thermoreceptors are and they can be separated into warm vs cold Know the relative distribution of cold vs warm receptors Thermoreceptors transduce temperature cutaneous receptor codes absolute and relative changes in temperature Dermis and epidermis Differentially concentrated in different areas thermal sensitivity irregularly distributed over the skin Maximum feature sensitivity Sustained pressure and spatial deformation Sustained pressure lateral skin stretch Temporal changes in skin deformation Temporal changes in skin deformation Primary functions Texture pattern form detection Finger position stable grasp Low frequency vibration detection High frequency vibration detection Warm fibers detect increases in skin temperature Cold fibers fire in response to decreases in skin temperature 30x more cold fibers than warm fibers 6 What is two point threshold Point localization Method of limits Two point threshold the smallest separation of 2 separate but adjacent points of stimulation on the skin that produces 2 distinct impressions of touch Point localization the ability to localize sensations on a stimulated region of skin Method of limits 7 Know what happens to the sensitivity of thermoreceptors when there is prolonged increases vs decreases in temperature Prolonged exposure to warm hot temperatures decreases sensitivity of warm receptors and increases sensitivity of cold receptors Prolonged exposure to cold temperatures increases sensitivity of warm receptors and decreases sensitivity of cold receptors 8 What information is sent by the Spinothalamic pathway vs the Dorsal Column Medial Lemniscus pathway Which of these systems evolved first Also know that they both cross and end up on the contralateral opposite side of the cortex Spinothalamic pathway Evolutionarily older Transmits information from thermoreceptors and nociceptors pain and Sower temperature Dorsal Column Medial Lemniscus pathway Wider diameter axons and fewer synapses Responsible for transmitting information from mechanoreceptors touch vibrations and proprioception Both cross over to the contralateral side of the brain but different crossover location Spinothalamic Pathway Synapse in dorsal horn of spinal cord crosses over immediately at the Lissauer s Tract within the spinal cord Information from each pathway ends up in the somatosensory area 1 S1 in parietal cortex contralateral to the sensory receptor DCML pathway synapse in dorsal collumn nuclei of medulla crosses over at the Medial Lemniscus of the Medulla 9 Be able to explain the homunculus and topographical arrangement of the cortex Know that more cortical tissue devoted to an area of the body greater sensitivity Homunculus reflects the relative space that our body parts occupy on the somatosensation The homunculus is also commonly used to describe the distorted human figure drawn to reflect the relative space our body parts occupy on the somatosensory cortex sensory homunculus and the motor cortex motor homunculus The lips hands feet and sex organs have more sensory neurons than other parts of the body so the homunculus has correspondingly distortedly large lips hands feet and genitals Well known in the field of neurology this is also commonly called the little man woman inside the brain
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