8. Physiology of Somatosensation Flashcards
Somatosensory System
____
Proprioception
____
Temperature
* Touch can mean many things * Pain - \_\_\_\_ * Temperature is integrally related to \_\_\_\_; works in both directions
touch
pain
noxious
pain
Functions of the Somatosensory System
• ____ the organism.
• Innocuous sensations from innocuous stimuli- ____, ____.
• Noxious sensations from noxious stimuli- ____ conditions or ____insult that is either real or potential damage.
protect thermal tactile internal external
Somatosensory Receptors
Know this table, my boy!
* Proprioception can be both in \_\_\_\_ and \_\_\_\_ * A lot of overlap between \_\_\_\_ and \_\_\_\_
dynamic
static
nociceptors
thermoreceptors
Mechanoreceptors of the Skin
* Hairy and glabur skin (non-hairy) * Glabur > \_\_\_\_, and soles of feet * Lips - transition of epithelium (wet pink tissue) and dermis - \_\_\_\_ border * Hairy skin > nerve that goes to hair root and wraps itself around it; sensitive to deflection of the hair; weight of mosquito on hair will make you aware that it's there (it's that \_\_\_\_) * How do you figure out where the bug is that lands on you? Have to know \_\_\_\_, and \_\_\_\_ it is (map inside brain)
palms vermillion sensitive sensation where
• Receptors coding: superficial vs. deep
○ Important impact on sensitivity
○ Closer to surface > ____ their receptive field; it’s defined the same no matter where it is
§ The stimulation that acts on neuron that activates it
○ Spot that’s as small as spot on thumb, may be sufficient for it to excite the neuron (small receptive); comes from fact that they’re more sensitive bc they’re more ____
§ The deeper it is, the harder it is to get to > less sensitive; when it’s deeper it can be impacted by things going from further afield
• Fast adapting vs slow adapting
○ FA > in presence in cont stim, it responds at ____, but then eventually stops responding
○ SA > the opposite, initially responds when contacted, but in presence of ongoing stimulation, it does not ____ > enable you to know that’s something there without seeing it
• FAI > ____ corpuscles
○ ____ detector - particularly sensitive to on/off but not during - good ____ detector; feeling textures, “you’re not moving, but the world is”
○ Two ways to activate > you’re holding still, or the world is holding still and you’re moving
• SAI > ____ disc
smaller superficial beginning adapt meissner change vibration merkel
- Pacinian corpuscle > ____, large receptive field, ____, deep tissue ____ detector > hotspot of max sensitivity up to first joint of ____ and push hard, other areas will know it; ____ receptive field is a property of it being deep
- Also in fingertips; all the way along the finger, if you press in one area, you can activate a neuron somewhere else
- Rafini ending > ____, responds as long as it’s stimulated; good at tugging on the skin (sensitive to ____)
deep FA vibration pinky large SA stretch
Mechanoreceptors in the skin vary in the size and structure of their receptive fields
* Top: Type I; bottom: Type I; L SA, R FA * \_\_\_\_ receptive fields for superficial, and \_\_\_\_ fields for deep ones
smaller
larger
- Superficial have small RF, ____/lips/____ > most sensitive spots in whole body; tongue and lips are more sensitive than your ____ at detecting small sized bumps
- Not nerve specific, more specific to the ____ of the area of the body; the more sensitive, the more ____ populated it is > more info processed
face tongue fingertips region densely
- Top row: as it ramps on, the neuron responds, as continues to indent doesn’t ____ much, as lets go there’s another ____
- Bottom row: responds ____ before stimulation, as long as you indent, never stops responding
adapt
response
spontaneously
Mechanoreceptors in the skin vary in their distribution and density
* Dots depict mechanoreceptors' density and distribution throughout the skin * Superficial (left 2 on the figure): \_\_\_\_ and \_\_\_\_ are the more sensitive mechanoreceptors. Especially dense in the regions (e.g. tip of your \_\_\_\_) where sensitivity is important * Deep (right 2 on the figure): \_\_\_\_ and \_\_\_\_ are more \_\_\_\_ distributed except at the tips. * Ruffini's corpuscle makes \_\_\_\_ for sensitive superficial receptors. * These receptors are more numerous on the \_\_\_\_ than the back of your hand
merkel's disk meissner's corpuscle fingers ruffini's pacinian corpuscles evenly room palm
Two-point Discrimination
* 2 point discrimination > take two sharp pencils, and touch body simultaneously on body, and if you're touching with 1/2 > if they're far enough, you'll be able to say you're touching two pencils, when get close enough > cannot tell whether two or one > threshold * More \_\_\_\_, the closer you can bring the pencils together and you can tell that there's two there * Fingers have a low 2PD (2-3mm); \_\_\_\_ and \_\_\_\_, and everything else is insensitive * \_\_\_\_ arm higher 2PD (4cm) * Problem with 2PD > involves guess whether there are two/one guessing > \_\_\_\_ issue with the guessing
sensitive face toes upper statistical
Grading Orientation Thresholds
- 2AFC procedure used to estimate the finest grating for which two orthogonal orientations of the ridges can be discriminated.
- expressed in ____, the threshold grove width = ____ width.
- ____ movement prohibited to assure that subject’s response reflects oriented, spatial modulation in the population of MRAs activated.
- Plastic chip that has grooves sticking out of surface
- Ask if the grid is ____ or ____ (2-alternative force test)
- The ____ the ridge, the easier it is to accomplish
mm
ridge
lateral
horizontally
vertically
bigger
Letter Recognition Thresholds
- tracking procedure used to estimate the ____ letters whose identity can be discerned.
- ____ movement encouraged to maximize information obtained about letter identify.
- 48 stimuli used: A, I, J, L, O, T, U, and W at heights 3, 4, 5, 6, 7, and 8 mm.
- ____ male and ____ female subjects, each tested once.• Used for mapping sensitivities inside the mouth
○ People can “read” with their tongue, not just braille
• Use only certain letters
• ____mm tall letter > can easily figure it out
○ The smaller, the more difficult
shortest lateral 10 10 10
- ____ papillae and ____ makes the sensitivity
- Dye tongue blue, and press plastic on top > the papillae are pink, the tissue in between stain dark
- Two different people’s histological tongues over the same area (cm^2) are shown here . Notice that the tongue on the right has smaller but more numerous papillae, thus more ____ to stimuli because each papillae is innervated by a nerve.
- Each papillae has ____, and they run up inside and loop around and come back down again > with low-mag can see the capillaries
fungiform
filliform
sensitive
capillary loops
• X-axis: density of ____ papillae (the larger the number, the more sensitive your tongue to mechanical stimuli)
• Y-axis: threshold height for letter recognition (the larger the number, less sensitive your tongue)
• For people with a lot of papillae, ____ threshold height
• Superimposed on top of this is the sensitivity to ____ compound
◦ Back from taste lecture, T2R38 responsible for detecting anti-thyroid drugs, PTC or PROP (some of us might have experienced bitter strips of small PTC papers - some people can taste them, some can’t depending on what alleles you have for the T2R38 receptors)
◦ If you have 2 copies of sensitive alleles from mom and dad, you’ll be very sensitive to ____; if you have 2 copies of insensitive alleles, not very sensitive to PTC.
◦ Trend observed from the graph above: the more sensitive they are to bitter compound, the more ____ they have per given area; this is an ____ (not a ____ relationship)
fungiform low bitter PTC papillae association causal
Proprioceptors
• Joint and capsule of joint tell you the ____ of the limb
• Muscle, when ____, tells you when the muscle is being shortened/lengthened
○ When using > shortening (gets fatter) and there’s nerves that get in and wrap around
• Receptors that go to tendons > ____ organs (tells you when there’s tension on ligament or organ) > ____ or ____ motion
○ Prosopagnocia
• Patellar tendon reflex > not an active movement, it’s a ____ movement
○ Leg reacts as if someone grabs on and pulls it back, you will resist
position stretched golgi tendon active passive
passive
PROPRIOCEPTORS
•Muscle spindles– specialized stretch receptors in muscle that provide information about muscle ____ and ____
•Golgi tendon organs– located at the junction between muscle and ____ that provide information about changes in muscle ____
•Joint receptors– located in joint capsules that provide information about joint ____ and limb ____
•Stereognosia
length thickening tendons tension movement position
• As increase of weight, gravity pulls mug downward > feeling in ligament is ____ stretching > maintain the angle, so return back to lock on angle and increase tension in muscle
passive
Innocuous and Noxious Thermal Sensations
Body temperature = 36-37 deg C
• Past the ends of this scale we perceive as hot/cold and painful; inside the scale that’s shown here we perceive
as ____
• Historically, it was thought that we had cold and warm receptors in our body which get maximally stimulated at 2 specific temperatures (one below and one above our normal body temperature) as shown by the 2 peaks on this graph. As we fall away from these peaks either above or below it, these receptors get stimulated less.
But this can’t really be the case since we experience cool and warm as continuous range of variation; how do we account for that if activity falls off as we go to higher/lower temperatures (away from the peaks)? It turns out that we have dozens of receptors that are ____ stimulated at every ____ that cover this whole range. This yields a more accurate measure of what temperature we’re experiencing
innocuous
maximally
couple degrees
• What is sensitive to temperature? Molecular channel
• Free nerve endings > unmyelinated ____ fibers > responsible for noxious and thermal sensations
• Large family > M, C, V, etc, marker of ____ taste cells (polysystic), and ____
• Bite into red hot chili pepper > you feel warmth > not changing temp of mouth, but the receptors (____, V class, ____, normally for thermal sensation), and being changed by a chemical instead of thermal
○ ____ > looks like vanilla
○ Causes the illusion of ____ (bright red > thermally sensitive, and different ranges
• ____ > response to menthol > same mechanism as capsaicin for TRP channels, but here acting on cool channels
○ Causing the illusion of cold, feels cold even though temp isn’t changing
• This is all ionotropic!
• ____ > horse radish/wasabi/irritating compounds > no thermal sensation, just irritation and pain, associated with “extreme cold”
C sour TRPa1 vanillioid TRPV1 capsaicinoids heat TRPM8 ANK (TRPa1)
- Not a 7 TM, not GPCR; ____ channels!
* Sometimes have extra loops, EC as well, or huge IC loops > has to do with binding and what gates them open
ion
• ____ > normal threshold of anything over 43 (close to BT); maximum response is higher
• ____ > doesn’t start until 52 (near to threshold for pain)
• Switch from red to blue > ____ (below BT) > innocuous cooling (not painful)
• Circular > some of the TRP channels can be activated by extreme cold; low T > you can activate the red ones as well
○ When you refer to holding to ice > hand starts to burn (“ice-burn”) > gives rise to ____
• When you get extreme T > injure tissue > will actually burn it
• Bruise > sensitive to ____ (innocuous things become painful) > good thing > doesn’t want you to reinjure an injury
○ Radiotherapy > give fractionated a little bit of a time, transformation of tissue from reinjury that makes it difficult to heal
○ If you continue to burn > will have tough time to healing properly
• Neurogenic inflammation, neurons participating in pain (____ etc.) > acted upon > mere stimulation > tissue inflamed
○ Capsaicin > ____ > area will be raised inflamed and red > may eventually go away (but hot shower will make it red again)
• ____ can be driven by tissue damage, or it can go straight to activating receptors (even in absence of tissue damage > neurogenic inflammation)
• ____ > ion channel that is sens to horse radish
• Whole family of receptors from fruit flies > similar ion channel > offer fruit fly horse radish it won’t go near
○ Flies without receptor > painless > load it with horse radish they will still eat it, and they have some thermal differences
○ Everything we know about TRP comes from fruit fly
TRPV1 TRPV2 TRPM8 extreme pain touch TRPa1 lipophilic inflammation TRPa1
