QUIZ 2 Somatosensation STUDY GUIDE Will consist of multiple choice fill in the blank true false and short answer questions NOTE If a question asks What is you must be able to define that term not describe what happened in the lab What is nociception What is somatosensation What is thermoreception What is proprioception Nociception pain respond to tissue damage Somatosensation collective term for sensory signals from the body touch pain temperature proprioception kinesthesis Thermoreception respond to changes in temperature Proprioception perception mediated by kinesthetic and vestibular receptors Know the types of skin Glabrous skin hairless skin such as the palms of the hands Hairy skin skin with hair Dermis the lower layer of skin Epidermis the topmost layer of skin Know the three types of cutaneous receptors and how they are classified o Mechanoreceptors respond to mechanical stimulation or pressure much like hair cells deflecting side to side respond to pushing pulling or movement o Thermoreceptors warm fibers cold fibers respond to changes in temperature codes absolute and relative changes in temperature reside in dermis and epidermis differently concentrated in different areas o nociceptive receptors a delta fibers c fibers respond to tissue damage pain respond to noxious stimuli bare nerve endings and high threshold Classification 1 Type of stimulation pressure vibration 2 Size of receptive field area that elicits a response 3 Rate of adaption slow adapting pressure and shape of objects Total of action potentials evoked per second is proportional to indention force applied Fast adapting motion of objects against skin responds when the position of the stimulus changes stops firing when it comes to rest Know the different mechanoreceptors what fast adapting versus slow adapting means which receptors are fast versus slow adapting which have small Type I versus large Type II receptive fields what type of information do they convey E g vibration etc 1 Merkel Complexes Slow adaption rate SAI small receptive field texture and pattern perception sustained pressure and spatial deformation 2 Ruffini Endings Slow adaption rate SAII large receptive field sustained pressure skin slip or stretch stable grasp finger position 3 Meissner s Corpuscles Fast adaption rate FAI small receptive field low frequency vibration movement across skin temporal changes in skin deformation 4 Pacinian Corpuscles Fast adaption rate FAII large receptive field high frequency vibration initial touch or change in pressure temporal changes in skin deformation Receptors with small receptive fields work together for tactile discrimination are the closest to the surface of skin and both start with M Of those 1 is rapidly adapting and the other is slowly adapting Corpuscles Meissner and Pacinian are always rapidly adapting large receptive fields have deeper receptors What is two point threshold Why do different areas of the body have different two point thresholds Two point threshold the smallest separation of two separate but adjacent point of stimulation on the skin that produces two distinct impressions of touch sensitive areas with the highest density of receptors and fine muscle control will have the smallest two point thresholds i e mouth face hands due to having smaller receptive fields Know the relative distribution of cold versus warm receptors Warm fibers detect increases in skin temperature deeper than cold fibers Cold fibers detect decreases in temperature 30x more cold fibers than warm fibers Normal skin temp 30 36C most objects in our world are cooler than that These receptors are also chemically activated Capsaicin heat and Menthol cold What type of pain fibers do we have and what do they convey Are they myelinated or not Bimodal polymodal pain occurs in 2 stages a sharp burst of pain A delta fibers and dull throbbing pain C fibers A delta fibers respond to strong pressure or high temperatures thin diameter and myelinated relays pain quickly well localized C fibers intense pressure heat or cold noxious chemicals thick diameter and unmyelinated info travels slowly poorly localized Know what happens to the sensitivity of thermoreceptors when there is a prolonged increase or decrease in temperature Prolonged exposure to warm temperatures decreases the sensitivity of warm receptors and increases the sensitivity to cold rushing to campus in the middle of August then walking into your 60 degree classroom Works both ways prolonged exposure to cold sensitizes warm receptors and desensitizes cold receptors What type information is sent by the spinothalamic pathway Does the information ascend ipsilaterally or contralaterally from the side of stimulation Where does it cross Spinothalamic pathway slower transmits info from thermoreceptors and nociceptors smaller diameter axons Synapse in substantia gelatinosa crosses over and ascends into medulla branches off throughout Lissauer s Tract caudal medulla BOTH pathways synapse in VPL Ventral Posterolateral Nucleus of the thalamus info from each pathway ends up in the somatosensory area 1 S1 in parietal cortex contralateral to the sensory receptor What information is sent via the dorsal column medial lemniscus pathway Does the information ascend ipsilaterally or contralaterally from the side of stimulation Where does it cross DMCL Wider diameter axons fewer synapses faster transmit touch vibration and proprioception Synapse in dorsal column nuclei of medulla crosses over in medulla pathway after this is called Medial lemniscus BOTH pathways synapse in VPL Ventral Posterolateral Nucleus of the thalamus info from each pathway ends up in the somatosensory area 1 S1 in parietal cortex contralateral to the sensory receptor Be able to define dermatomes and understand what they represent Dermatomes area of the skin innervated by a particular portion of the spinal cord shoulders and up Cervical torso Thoracic front part of legs and feet Lumbar back part of legs and feet Sacral What does the homunculus represent in its topographical depiction of the cortex The homunculus reflects the relative space that our body parts occupy on the somatosensory and motor cortices The neighboring areas of the skin are represented in neighboring regions on the somatosensory cortex the homunculus is a topographic representation of the brain areas devoted to various parts of the body
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