Somatosensation Physiology What are somatosensation kinesthesis and proprioception What are the types of proprioceptive receptors Where are they and what kind of info do they convey Somatosensation a collective term for sensory signals from the body touch pain temperature proprioception kinesthesis Kinesthesis The perception of the position and movement of our limbs in space Proprioception perception mediated by kinesthetic and vestibular receptors Cutaneous receptors nerve cells that tell your brain about tactile sensations 1 Mechanoreceptors respond to pushing pulling or movement 2 Thermoreceptors respond to changes in temperature 3 Nociceptors respond to tissue damage pain What are the 4 main types of touch receptors How do they differ in terms of adaptation and receptive field size What tactile functions do they subserve What does it mean that they are mechanoreceptors 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 Mechanoreceptors respond to mechanical stimulation or pressure much like hair cells deflecting side to side How do Pacinian corpuscles work Force deflects neuron s membrane channels become leaky to sodium receptor potential mechanorecptors The greater the deflection the greater the receptor potential threshold leads to AP Only sudden or vibrating force can deflect membrane Onion like outer membrane provides mechanical support so it is resistant to gradual or constant pressure so rapidly adapting Meissner s corpuscles work in a similar way What are thermoreceptors and what kinds are there What type of channel do they use Understand that these are free nerve endings know what that means with TRP receptors in the membrane Warm fibers and cold fibers free nerve endings like nociceptors located in dermis and epidermis polka dot distribution warmth receptors deeper than cold receptors 30x more cold receptors than warm receptors Respond to changes in skin temperature normal is 30 36 C neither type of fiber fires much in this range Respond if temp is higher or lower than neutral or higher or lower than what skin is used to so feeling temp is relative TRP channels transient receptor potential channels non selective cation channels in cell membrane To detect such a large range of temps probably need more than 1 turns out we have to have at least 6 different TRP channels for temp all tuned to specific range of temp How do some tastes lead to the sensation of warmth or hot or coolness Some thermoceptors also respond to chemicals Capsaicin heat can activate warm fibers and menthol cold can activate cold fibers What is the pathway names and all the stops along the way for touch info to get to the brain What part of the spinal cord does it enter When where does it cross to the other side of the brain What part of thalamus does it use If that touch is on the face or head what cranial nerve is involved DMCL TOUCH INFO 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 Are all axons the same What is the result of increasing the diameter and or myelination of axons Wider diameter axons speed up action potentials Myelination of axons speed up action potentials What is the difference between S1 S2 and somatosensory association cortex S1 Primary Somatosensory Cortex gets info from medial lemniscus via thalamus and spinothalamic tract stimulated by contralateral tingling numbness S2 Association cortex responds to complicated stimuli but dorsal where pathway ventral what pathway receives its info from S1 responds to sensory stimuli bilaterally Both in close proximity to motor cortex for quick relay and action based on perception How is S1 organized What does the homunculus tell us Besides cortex what else is somatotopically organized What is somatotopy S1 is organized somatotopically spatially mapped in the somatosensory cortex in correspondence to spatial events on the skin Homunculus is a maplike representation of regions of the body in the brain tells us what areas of the body occupy more area on the somato sensory 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 What sensations are lost if there is damage to the dorsal columns or S1 Position sense tactile localization two point discrimination stereognosis graphesthesia weight discrimination perception of simultaneous stimuli perception of texture How do phantom sensations arise Sporadic activity in S1 can cause perception of missing limb in homunculus face area and hand area are adjacent Missing arm hand area of cortex no longer gets direct stimulation fibers that normally go to face cortex sprout collaterals to hand cortex stimulation of these hand cortex cells makes amputee perceive hand stimulation Give an example of cortical plasticity in the touch system Subjects blindfolded for 5 days each day braille and fMRI 1st day braille only activated S1 Throughout other days activity in S1 decreased while activity in V1 primary visual cortex increased Deprived of visual info visual cortex started processing somatosensory info returned to normal after blindfold was removed PLASTICITY What is haptic
View Full Document
Unlocking...