chapter 15: cutaneous senses Flashcards
the somatosensory system is broken down into 3 subcategories what are they?
- cutaneous senses
- proprioception
- kinesthesis
what is the heaviest and the largest organ of the body
skin
name the functions of the skin
- warning
- prevents bodily fluid from escaping and protects body from bacteria, chemical agents and dirt
- provides info about various stimuli that comes into contact with it
name the layers of the skin
- epidermis
- dermis
- hypodermis
mechanoreceptors are …
receptors that respond to mechanical stimulation such as pressure, stretching and vibration
name the 2 mechanoreceptors that are located near the epidermis
- Merkel receptor
- Meissner corpuscle
receptors located near the surface of the skin have … receptive fields, whereas receptors located deep within the skin have … receptive fields
small; large
why are Merkel receptors called slowly adapting (SA1) fiber, and Meissner corpuscles called rapidly adapting (RA1) fiber
- Merkel: fires continuously, as long as stimulus is on
- Meissner: fires only when stimulus is first applied and removed
what are the types of perception associated with Merkel receptors and Meissner corpuscles
Merkel: details, shape, texture
Meissner: controlling handgrip, and perceiving motion across the skin
Ruffini cylinders are to … as Pacinian corpuscles are to …
Merkel receptors; Meissner corpuscles
slowly adapting vs rapidly adapting
name the 2 pathways from somatosensory receptors to the brain
- medial lemniscal pathway
- spinothalamic pathway
what functions do each pathway carry
lemniscal: proprioception and perception of touch
spinothalamic: temperature and pain
in which part of the brain does both pathway synapse
ventrolateral nucleus of the thalamus
which brain region is important in sensing light touch
insula
which brain region is important in feeling pain
anterior cingulate cortex
what are the two regions that receive signals from the thalamus
primary somatosensory cortex (S1)
secondary somatosensory cortex (S2)
true or false? there is no communication between S1 and S2
false
what is the Jacksonian march
seizures progress over the body in an orderly way; seizure in one body part is followed by seizure in neighboring body part
- spread of neural activity across maps in motor area of brain
Penfield stimulated points in different part of the S1 causing participants to report sensations (touch and tingling) on various part of their bodies. in which part of their body did they perceive sensations if these regions were stimulated:
a. ventral
b. higher section
c. dorsal
a. lips and face
b. hands and fingers
c. legs and feet
how do we call the body map
homunculus
define tactile acuity
capacity to detect details of stimuli presented to the skin
explain the two-point threshold procedure that is used to measure tactile acuity
minimum separation between 2 points on the skin that when stimulated is perceived as 2 points
explain the procedure used to measure grating acuity
- grooved stimulus pressed onto skin
- Ps asked to indicate orientation of grating
- acuity measured by determining narrowest spacing for which orientation can be judged
explain why when a grooved stimulus is applied to the skin, the Merkel receptor’s firing reflects the pattern of the grooved stimulus, but the Pacinian corpuscles does not
- Merkel: small RF + fires continuously = can detect details
- Pacinian: large RF + fires when stimulus applied and removed = not sensitive to details
where is there a high density of Merkel receptors
fingertips
why are regions of high acuity represented by larger areas on the cortex
to provide extra neural processing to accurately sense fine details
which mechanoreceptors are primarily responsible for sensing vibrations
Pacinian corpuscles
why do Pacinian corpuscles respond poorly to slow and constant pushing
- corpuscle made of series of layer with fluid in between
- transmit rapidly repeated pressure to nerve fiber
- fiber received rapid changes in pressure
what happens if the corpuscle is removed and constant pressure is applied directly to the fiber
- fiber fires
- properties of corpuscle cause fiber to respond poorly to continuous stimulation
what is the duplex theory of texture perception
perception of texture depends on both spatial cues and temporal cues
differentiate spatial and temporal cues
- spatial: surface elements that can be felt both when the skin moves across surface and when pressed onto elements
- temporal: texture can’t be detected unless fingers move across surface
what are the two cortical responses to surface texture
- different textures cause different firing patterns
- different neurons respond differently to same texture
neurons that fire to coarse textures receive input from which receptors and neurons that fire to fine texture receive input from which receptors
coarse: SA1 neurons (Merkel)
fine: pacinian corpuscle receptors
differentiate between active touch and passive touch
active: touch in which person actively explores an object
passive: touch stimulus is applied to the skin
define haptic perception
perception in which three-dimensional objects are explored with the fingers and hands
what are the 3 systems used when identifying objects
- sensory system
- motor system
- cognitive system
for passive touch, you experience …, and for active touch, you experience …
- stimulation of the skin
- objects that you are touching
what are exploratory procedures (EPs) and name 4 examples
distinctive movements used to identify an object (depend on object qualities)
- lateral motion, pressure, enclosure, contour following
true or false? all neurons responsible for tactile object perception are specialized
false, neurons in ventral posterior nucleus have center-surround receptive fields
how can attention influence cortical response to tactile object identification
size of response is affected by attention, thinking, etc
- ↓ attention = ↓ response
define interpersonal touching (social touch)
one person touching another person
where can we find CT afferent nerve fibers (C-tactile)
on hairy skin
what is the difference between CT afferent fibers and other receptors found on non-hairy skin
CT are unmyelinated fibers = nerve impulse more slowly
explain the technique called microneurography
activity recorded by inserting a metal electrode with a very fine tip just under the skin
which brain region is activated by CT afferents
insula
what is the social touch hypothesis
CT afferents and their central projections are responsible for social touch
the CT system was recognized as a new touch system different from previously known touch systems. name the functions associated with each
affective function of touch (CT system): sensing, pleasure, positive emotions
discriminative function of touch (old): details, texture, vibration, objects
describe the experiment that showed CT afferents were specialized for slow stroking
- response of SA1/SA2 increased up to 30cm/sec
- response of CT afferents peaked at 3-10cm/sec and decreased
slow stroking creates connections between which part of the insula. name the functional connection too
back of insula (sensory info) + front of insula (emotional area) = pleasurable response to social touch
how does top-down processes affect social touch
people’s thoughts about who/what is touching them can influence their perception of pleasantness
name and explain the 3 types of pain
- inflammatory: damage to tissue/inflammation of joints/tumor cells
- neuropathic pain: lesion or other damage to NS
- nociceptive pain: activation of nociceptors (specialized to respond to tissue damage/potential damage
name two things that could not be explained by the direct pathway model of pain
- not feeling pain from extensive wounds
- phantom limbs
explain the gate control model
pain signals → spinal cord → brain
additional pathways that close/open gates in spinal cord determines signal strength
explain the three pathways through which the gate control system occurs
- nociceptors: excitatory synapses send excitatory signals to transmission cells → open gate = ↑ firing = more pain
- mechanoreceptors: nonpainful tactile stimulation: inhibitory signals → close gate = ↓ pain
- central control: expectation, attention, distraction = ↓ pain
what is the difference between a placebo and a nocebo effect
placebo: decrease in pain
nocebo: increase in pain
describe the experiment that showed the effect of expectation on pain ratings (Bingel 2011)
- no expectation (given drug but told its still saline no change): pain slightly reduced bc effect of drug
- positive expectation (presented w drugs): pain greatly reduced bc both drug+expectation
- negative expectation (were given drugs but now removed): pain increased bc expectation
the placebo and the nocebo effect are associated with increased activity in which brain area
placebo: areas associated with pain perception
nocebo: hippocampus
how can attention affect pain perception
shift attention = pain ↓
how can emotions affect pain perception
positive emotions ↓ pain
