Somatosensory System

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Taught by W. von der Behrens

Somatosensory System

Constists of - touch - Active Touch - Proprioception - Pain

Acitve Touche

USed by Rodents for Navigation (Whiskers) Nervending, and in the Membrane of the Nerve Ending there is a machanical Transduction channel. Sodium Influx, the Cell gives the Signal down the Axon as AP's

In the colsed State we have an Inactivation particle and a Gating spring (the Inactivation Particle could pex be a Protein. When it's open the inactivation Particle moves into the Gap, after extended Periods he Particle closes the flow, if the Force is released the Receprtor moves into the "closed" Position Core mechanism from Physical to Biologicel

Different Curves for different Celltypes (Rapid adapting, intermediately adapting, slowly adapting and ultraslowly adapting. Different Timescales in graphics!

RA gives onset and end of stimulus as Signals, SA gives a Oattern as long as the Stimulus is "on"

Different distances and spatial acuity over different Bodyparts

Merkel Cell (SA)

Around the Hair follicle, they have many nerve Endings in one touch dome. Very Elaborate Stucture, between 30/40% of our Cells in the Skin are Merkel Cells. It Responds immediately and then adapts pretty slowly they are Sensitive against inentation, Very high spatial acuity

Ruffini corpuscles

Are Responsive for Stretching withihn the Skin (for example the moving of a joint Mostili found in Joints dura Mater and epidermis

Meissner curpuscules (RA)

Are most responsive for dynamic deformation They are Adapting very rapidly, only stimuly that are not constantly there are transformed int signals

Pacini corpuscles

Are sensitive for Vibration , they are als RA

Free nerve endings sit in upper layers of epidermis they are mainly for the feeling of Pain, because they don't have a defined structure aroud them. THerese Are slowly adapting receptors

Central Pathways

Brodman Areas in the Slides Brodman 1,2,3,5 Are where somatosensory action happens. Brodman found these areas just by histological differences. Auditory brodman area 41/42 Mostly 1 and 3b are for Tactile sensations

Homunvculus good Graphics in Slides

Regions that are amputated are taken over by neighbouring regions most likely the reason für phanom pain, beacuse the higher areas interpret the input wring. Same with phantom sounds (Tinitus)

Barrel Cortex

Rodents have a Cortex in their coronal Brain section, you can see the Pattern from the Whiskers The single Barrels in the Barrel cortex usually have a 1:1 Corespondence to the Whiskers. A very specialized system. Very good to study plasticity, experimetns with rats with plucked out whiskers

Star Nosed Mole

Specialist of somatic sensory cortex, The Nose of those Moles are extremely sensitive, they are covered with Eimer Organs

Mountcastle

Nuerons have similar responses to same Stimulus in Cats, so mountcastle sain whole cortex is made of vertical colums very important concept which still counts as accurate today The good thing in the Barrelcortex is, that ne barrel can bee looked at as one of those vertical colums. Most of the Thalamic Proejctions in Layer4

Research from v. de Behrens

Training a Rat so that it can discriminate simuli uand answer to them, Whiskers are stimulated, the Rat receives a reward. Th Rat has to discriminate 2 Frequencies and has to "tell" on which side the frequency was, if it licke on the correct side it will receive a reward. Animals do this for extended periods. The more similar the Stimuli become the more the results are by chance. Does the adaptation help the Rat or does it make it mor difficult? Introduce a protein in the Neurons from an algae, al neurons cary the protein, if you shine light on the Cells the Channels open.. You get it in by injectin a virus, until all neurons have protein in their membrane. Generodopisn? You can get a system where cortical sytem does not react at all. , now you stimulate a single barrel with a light stimulus. only artificial cortical Input ANimal can make sense of the stimuli, in optical stimulus the rat is way better than with just sensory input. Explanation: no adaptation and much better temporal precision light pulse is extremely sharp, while whiskers give a less sharp signal. Adaptation is a problem for the animal to discriminate ongoing stimuli, whole system is tuned to reacting to changes (if its running along a wall it doesnt have to discriminate the ongoing sti,muli, but just the changes)