Somatosensation Touch Somatosensation What are somatosensation kinesthesis and proprioception What are the types of proprioceptive receptors Where are they and what kind of info do they convey o the sense of touch all sensory signals from the body o used when there is a mechanical interaction with your body and another object the soft touch of a cat the painful feeling of a stubbed toe or the rough feeling of sandpaper o The perception of the position and movement of our limbs in space Kinesthesis Muscle spindles Golgi tendons Proprioception o perception mediated by kinesthetic and vestibular receptors 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 Type 1 Type 2 Slow adapting pressure shape of objects o Total of action potentials evoked per second is proportional to indention force Fast adapting motion of objects against skin o Responds when the position of the stimulus changes stops firing when it comes applied to rest Located at the dermal epidermal boundary Low threshold Small Receptive Fields Meissner Corpuscle FA Type Merkel Cell SA Type steady downward pressure Both respond best to low frequency vibrations Located deep in the dermis Higher threshold Large Receptive Fields Ruffini Endings SA Type sustained downward pressure lateral skin stretch Pacinian Corpuscle FA Type fast sudden pressure high frequency vibrations Mechanoreceptors respond to pushing pulling or movement How do Pacinian corpuscles work Force neuron s membrane is deflected channels become leaky to sodium receptor potential mechanoreceptors The greater the deflection the greater the receptor potential threshold 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 BTW the other rapidly adapting receptor Meissner s corpuscle works in a similar way Pacinian corpuscles detect gross pressure changes and vibrations Any deformation in the corpuscle causes action potentials to be generated by opening pressure sensitive sodium ion channels in the axon membrane This allows sodium ions to influx in creating a receptor potential These corpuscles are especially susceptible to vibrations which they can sense even centimeters away Pacinian corpuscles cause action potentials when the skin is rapidly indented but not when the pressure is steady due to the layers of connective tissue that cover the nerve ending It is thought that they respond to high velocity changes in joint position Pacinian corpuscles have a large receptive field on the skin s surface with an especially sensitive center They only sense stimuli that occur within this field 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 Thermoreceptors A cutaneous receptor that codes absolute and relative changes in temperature o Reside in dermis and epidermal layers o Differently concentrated in different areas thermal sensitivity is irregularly distributed over the skin Warm fibers detect increases in skin temperature Cold fibers detect decreases in skin temperature more cold o 30x than warm fibers In dermis and epidermis fibers o Polkadot distribution Warmth receptors deeper than cold receptors Normal skin temp 30 36 C or 86 97 F o Most objects in our world are COOLER than that o Respond if temp is higher or lower than neutral or higher or lower than what skin is used to o So feeling temp is relative try the hand in the bucket experiment TRP channels transient receptor potential channels o Non selective cation channels in cell membrane o These channels are able to respond to various ranges of temperatures o Allows positive charged ions to go through which are depolarizing To detect such a large range of temps probably need more than 1 Turns out we have at least 6 different TRP channels for temp all tuned to specific range of temperature BTW some thermoreceptors also respond to chemicals How do some tastes lead to the sensation of warmth or hot or coolness TRP channel that are sensitive to temperature and to come chemicals like capsaicin and menthol Food that can stimulate those 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 Information from skin brain Spinothalamic ST pathway o Slower transmits information from thermoreceptors and nociceptors o Smaller diameter axons o Pathway Synapse in dorsal horn of spinal cord crosses over immediately at the Lissauer s Tract within the spinal cord Dorsal column medial lemniscus DCML pathway o Wider diameter axons fewer synapses faster o Transmit touch vibration and proprioception o Pathway synapse in dorsal column nuclei of medulla crosses over at the Medial Lemniscus of the Medulla 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 column nuclei of medulla crosses over at the Medial Lemniscus of the Medulla 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 Trigeminal nerve CN V Different fibers nuclei involved in general sensory versus pain and temp Also conveys info from stretch receptors from chewing muscles Joins medial lemniscus STT Are all axons the same What is the result of increasing the diameter and or myelination of axons Different diameter and different amounts these increase and decrease together of myelination work at different conduction velocities Increased diameter and myelination makes AP travel faster What is the difference between S1 S2 and somatosensory association cortex Somatotopic organization homunculus S1 S2 association cortex S1 gets info from medial lemniscus via thalamus Cells in Broadmamn s areas 3 1 2 respond to different type of sensory information SA cutaneous receptors FA cutaneous receptors receptors in joints respectively They all respond
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