touch Flashcards

Question

Types of Kinesthetic Receptors (all motor neurons):

Answer 1

1. Muscle Spindles: convey rate at which muscle fibers are changing in length (ie: angles formed by a limb and joint) 2. Golgi Tendon Organs: provide signals about the tension in the muscles attached to the tendons 3. Joint Receptors: are activated when a joint is bent at an extreme angle (connection bone-to-bone) Provide info to the motor system: tell us where our limbs are and what kind of movements were making Case of Ian Waterman: at 19 destroyed proprioceptors (couldn't feel where his limbs were in space) Cant walk/clap without light. Needs a visual system to move.

Answer 2

cell bodies of somatosensory neurons lie here -axons of various somatosensory receptors converge into a single spinal nerve -Cell bodies lie in the DRG, right next to the spinal cord -AP’s travel from the peripheral end all along the axon to the central end, where they enter the spinal cord at the dorsal horn

Answer 3

1. Signals enter the dorsal horn, organised into laminae (multiple layers) 2. Inputs organised somatotopically: adjacent areas of the skin are connected to adjacent areas within a region of the cord 3. Spinal cord is the only channel for transmission of somatosensory (and motor) info from the body to and from the brain

Answer 4

reas of skin that connect to a specific nerve root on your spine Ex: Shingles (varicella-zoster): Maps/dermatomes are good clinical tools in the event of injury or infection of a particular spinal nerve. Viral infection that causes a painful rash that most often appears as a stripe of blisters, shingles are reactivated chicken pox viruses that travel along nerve pathways to the skin.

Answer 5

Parallel Processing: of different touch qualities

Answer 6

Aα (proprio) and Aβ (tactile) 1. first order DRG neurons send axons up white matter of spinal cord 2. central terminals of DRG neurons synapse on dorsal column nuclei of medulla 3. axons of second-order neurons arch over midline (decussate) to the other side of the brain and ascend to thalamus 4. thalamic relay (third order) neurons project directly to the cerebral cortex (SI) - primary somatosensory

Answer 7

Aδ and C (pain, temp) 1. first order DRG neurons synapse on neurons in dorsal horn 2. axons of second-order dorsal horn neurons cross the midline in the spinal cord and ascend via spinothalamic tract 3. most of the axons terminate on relay nuclei in the medulla, midbrain, thalamus 4. these neurons project to the cortex in a diffuse manner

Answer 8

primary somatosensory cortex: primary cortical area that receives inputs from the thalamus via the internal capsule -Located in the postcentral gyrus (posterior to central sulcus) -Parietal lobe Secondary Somatosensory Cortex (S2): receives convergent projections from all areas of S1

Answer 9

areas of the cortex that control body parts, just in front of the central sulcus Adjacency enhances communication between somatosensory & motor control systems

Answer 10

complete, orderly representation of the body. Adjacent areas on the skin have connection to adjacent areas in the brain Contralateral mapping (all neurons in left brain, respond to right side of body)

Answer 11

cortical neurons also have receptive fields based on connected neurons. Receptive field size depends on location in somatotopic map: Varies within an area (eg. finger vs trunk) Varies across an area (eg. 3 vs 1) *Wilder Penfield: discovered somatosensory neural system. Electrically stimulated parts of somatosensory cortex w/electrode & asked where patient could feel

Answer 12

changes in the cortical map (neural circuits) can occur in response to physiological changes in sensory and motor function (ie. experience) Ex: monkey trained to use digits (fingers) 2 and 3 heavily for several months: after practise, a larger part of the cortex responds to stimulation of digits 2 and 3 (functional remapping) Ex: Found that smartphone users have an enhanced thumb sensory representation in the brain. Used EEG to measure cortical potentials in response to mechanical touch on the thumb, index, and middle fingertips of touchscreen users vs. non-users Ex: normal, sighted volunteers who are blindfolded for 5 days show increased activity in brain areas associated with vision during somatosensory/touch tasks (discriminating braille patterns) = Cross Modal Plasticity: 1 sensory system taken over by another Young brains have more neuroplasticity

Answer 13

illusion that a missing limb (eg:after amputation) is still present. Happens because neurons are still firing w/o input Usually diminishes over time Phantom sensations are often felt when the face is touched: functional reorganization of the somatotopic map after amputation. S1 neurons that lost their input are innervated by tactile receptors from the face.

Answer 14

set of calibrated fibers with different diameters, each producing a different force when applied to the skin. Used to determine touch thresholds. Smaller diameter = less force Finding detection threshold: start w/least stiff/thinnest fiber and work your way up to thicker. Use the method of limits to see when they feel the stimulus. Larger threshold = body is less sensitive, need to apply more force to detect it

Answer 15

change in pressure (short, repetitive) over time Maximal sensitivity occurs at ~200 Hz Overall curve reflects the contributions of different mechanoreceptor populations (SAI, FAI, FAII) at different levels of vibration Absolute vibratory threshold: the minimum amount that a vibrating stimulus displaced the skin for it to be detected

Answer 16

smallest separation of 2 points applied simultaneously to the skin that can still be discriminated (measured by compass test: start at large separation and keep moving closer to see how long until participant can detect 2 points) Two point pain threshold: smallest separation of 2 painful stimuli applied simultaneously that can be differentiated (measured by applied small pulses of radiant heat heat using lasers) How these values compare to detection threshold: similar, here the finger tips are more sensitive than the face *separate mechanoreceptors are needed to detect 2 point touch. Stay separate when arriving at the brain. Determination of 2 closely spaced points instead of just 1 requires that the brain receives 2 separate signals.

Answer 17

Smaller mechanoreceptor field size Higher density of mechanoreceptors

Answer 18

Sex (women tend to have better sense of touch due to smaller finger size) Age (depends on experience/doesn't disappear. Can be maintained across a lifetime with daily attention to tactile stimulation on the fingers - daily attention to stimulation is important to retain this. Ex: old blind ppl retained the same sensitivity compared to sighted people whose sensitivity decreased. Same with painists) Genetics (autism spectrum disorder diagnosis, those with ASD have altered tactile discrimination and hypersensitivity to gentle touch)

Answer 19

occurs in response to prolonged, steady stimulation Promoted by: larger stimulus area, weaker intensity force, stimulating less-sensitive areas of the body *adaptation cannot solely be explained by reduced mechanoreceptor discharge (consider SA fibers). Related to lack of stimulus movement?

Answer 20

the perceptual consequence of nociception Important survival value: warning signal to withdraw from stimulus. People who lack nociception are vulnerable to self-harm or death. (can be congenital, ex: congenital insensitivity to pain, or acquired - leprosy) Highly subjective state: sensory, emotional, and cognitive influences together interact to create our conscious experience of pain

Answer 21

Nociceptive signals arrive at the dorsal horn of the spinal cord Interneurons in the dorsal horn receive info from the brain (aka: descending inputs) Interneurons form synapses in neurons that convey nociceptive info to the brain

Answer 22

theory describes how various influences integrate to form pain perception. Bottom-up (pain) signals can be blocked via a feedback circuit in the dorsal horn Projection neuron is like gate, if excited than pain info goes to brain and vice versa

Answer 23

Discriminative Aspects: location, intensity, and quality of the noxious stimulus Emotional Aspects: unpleasant feeling, fear, anxiety, autonomic system activations that accompanies exposure to noxious stimuli) Anterior Cingulate Cortex (ACC): attention allocation, reward anticipation, decision making, emotion Insula: self-awareness, emotion, homeostatic emotions Prefrontal Cortex: cognition and executive function Amygdala: emotional memory, fear

Answer 24

pain that arises in deeper structures of the body is actually felt elsewhere (due to convergence of afferent fibers onto the spinal cord from different parts of the body) Ex: pain in “arms or shoulders” due to heart attack - actually due to pain arising from heart muscle

Answer 25

Univariate Approach: group all dimensions of pain together, measure using standard psychological techniques Multivariate Approach: separately assesses different dimensions of pain (location, intensity, quality)

Answer 26

Peripheral: results from interaction of nociceptors w/inflammatory substances released after tissue damage Central: due to increased excitability of neurons at the dorsal horn (neuropathic): ex: activity in nociceptive afferents that was previously subthreshold now generates APs in dorsal horn neuron

Answer 27

increased/heightened pain to a normally painful stimulus (due to peripheral or central mechanisms) mast + immune cells come to heal (ex: cut on skin)

Answer 28

stimuli that are normally innocuous (eg: brushing on skin) causes pain (ex: sunburn), this is called: Neuropathic pain: chronic, intensely painful experience that is difficult to treat (occurs when afferent nerve fibers or central pathways are damaged due to injury or disease and pain thresholds do not return to pre-injury levels)

Answer 29

a lingering painful sensation (tingling, burning) in the missing limb Example of central pain → nociceptive signals arise in the brain or spinal cord (Central pain pathways are still active without peripheral stimulation) Initial damage causes overactive nociceptors, leads to heightened sensitivity in dorsal horn - you still feel pain

Answer 30

1. Pharmacological Analgesics: dampen pain sensation (orajel) Anti-Inflammatory Drugs: block pro-inflamattory molecules that activate pain reception (tylenol) Opiates: activate opioid receptors, helps with pain tolerance 2. Surgical & -neurostimulatory approaches *serious cases Remove part of spinal cord (cordotomy) or part of frontal lobe (lobotomy) TENS (transcutaneous electrical nerve stimulation) → activates Aβ fibres (benign counter stimulation) - noninvasive, can self-administer reduction in pain only when machine is on 3. Psychological approaches Counterstimulation (ex:hot water bottle) or counterirritation (direct pain elsewhere, pinch arm when toothache) Placebo effect → patients proclaim beneficial effects of drugs that contain no medicinal ingredients (May actually be due to action of endogenous opioids) Relaxation training, distraction techniques, hypnosis, physical contact with a loved one

Answer 31

Itch-sensitive touch receptors C-fibers (thinnest, unmyelinated); convey info via the spinothalamic (antro/ventrolateral pathway/system). Activated by prurigenic (itch-inducing) chemicals like histamine produced by mast cells - due to allergic rxn Interaction between itch and pain are closely related Some itch receptors also respond to painful stimuli (reduce itch) Pain and itch interact in the spinal cord

Answer 32

Scratching may reduce itchiness! ( Effect may be at the level of spinal cord and/or the brain) Another stimulus activates mechanoreceptors Older people may itch/scratch more due to age-related loss of Merkel cells

Answer 33

Rate of change (if gradual its harder to detect) Size of skin area being stimulated (spatial summation, larger area = easier to detect) Body location where stimulation is made (sensitivity is like that for pressure) *Adaptation: prominent feature of thermal sensation (temps closer to physiological zero are better adapted to, we get used to temperatures and may not notice over time

Answer 34

physiological zero can be shifted -> the intermediate temperature (30 degrees) now evokes thermal sensations due to prior adaptation (if one hand in 10 degree and other in 40 degree water and you wait 20 mins your body adapts, then when you put both hands in 30 degree water the 10 degree hand feels warm and 40 degree feels cool) warm and cool receptors are activated Adaptation: prominent feature of thermal sensation (temps closer to physiological zero are better adapted to, we get used to temperatures and may not notice over time)

Answer 35

Pathways initially follow spinothalamic tract but then diverges at the level of the cortex CT fibers synapse in lamina II of the dorsal horn - > second order neurons decussate and synapse in the thalamus -> thalamic neurons project to the insula (links sensory to emotional systems) Cats Love Tuna, Tasty & Irresistible Ie: diff pathways for discriminative touch vs. affective touch

Answer 36

Used fMRI to measure brain activity during fast and slow stroking Participants rated the pleasantness and intensity of stroking Pleasantness rating was related to the activity in the anterior cingulate cortex (ACC) and was independent of activity in S1 (primary somatosensory cortex) or insula

Answer 37

Mother rats that lick and groom their pups produce offspring that lick and groom their own pups. But, if pups from attentive and remote moms are switched at birth, pumps inherit the behaviour of their adoptive parents. Experience turns licking-and-grooming genes on or off (epigenetics) McGowan, P.O. et al. (2009) - Examined epigenetic differences in a glucocorticoid receptor (neuroendocrine receptor) between postmortem hippocampus from suicide victims with a history of childhood abuse and those from suicide victims with no history of childhood abuse or controls Decreased levels of glucocorticoid receptor mRNA in suicide victims with a history of childhood abuse, Also found increased modification of the promoter region of glucocorticoid receptor Thus, parental care influences the epigenetic regulation of hippocampal neuroendocrine receptor expression.

Answer 38

perceptual processing of inputs from multiple sensory subsystems, including those in skin, muscles, tendons, and joints. Active and information seeking

Answer 39

Static contact (temp) Contour following (global/exact shape) Enclosure (global shape, volume) Unsupported holding (weight)

Answer 40

using hands to actively explore the world of surfaces and objects outside our bodies (ex: using exploratory procedures) Freely and actively touching object: allows to better identify an object as it is willful and engages mind in purposeful exploration - problem solving, recruits proprioceptors to provide kinesthetic info Each exploratory procedure is linked to a specific object property because different procedures activate different mechanoreceptors (ex: FAII afferent fire in synchrony when skin rubs a fabric texture - move hand back and forth to activate correct receptors , FAII afferent fire in synchrony with a vibrating stimulus applied to the skin)

Answer 41

we are very good at, and can usually detect common objects in less than 5 seconds. Texture and temperature are usually easier to perceive with our sense of touch Hard to recognize some objects by touch (braille), easier to see - geometry info provided from visual system

Answer 42

Perceived as curved surface: slant changes, height doesn't change Perceived as flat surface: height of fingers changes, not slant

Answer 43

First requires that we establish a frame of reference (the coordinate system used to define locations in space) Haptic egocentre: tends to change, get top and bottom to line up and not overshoot (above and below table demo) Localizing stimuli is a complex process that we can do from a very young age (Leed, Chinn, and Lockman (2019) used vibrating patches to test childrens’ ability to locate stimuli on the skin - can easily locate mouth from young (7 months), and become good at other body parts as they get older)

Answer 44

inability to identify objects by touch. Caused by lesions of the parietal lobe (Patient E.C.: lesion to the left inferior parietal lobe. Patient could not recognize objects haptically with right hand! Could recognize objects with left hand or visually - discriminative features were not connected to persons memory, issue with perceptual binding) Disorder of touch perception requires you to first rule out: that tactile receptors still work (loose touch sensation), don't have cognitive deficit (memory deficit)