Lecture 10 Flashcards
Area of skin
1.8 m^2
Weight of skin
5kg
What is skin?
Largest sense organ in the body
Two types of skin
Glabrous and hairy
Where is glabrous skin found?
Palms of hands and feet
Where is hairy skin found?
Everywhere but hands and feet
Physiology of skin senses
4 stages
1) stimulus contacts skin
2) receptor in skin fires
3) signal travels to the brain via spinal cord
4) signal reached somatosensory cortex on opposite side of the body
What 4 senses do skin receptors give sense to
Touch (mechanical stimuli)
Pain
Body sense (proprioception)
Temperature
4 types of tactile receptor
Merkel’s disc
Meissner corpuscle
Ruffini organ
Paccinian corpuscle
Merkel’s disc responds to
Fine details (e.g., braille)
Meissner corpuscle responds to
Flutter (like an object slipping through fingers)
Ruffini organ responds to
Stretching
Paccinian corpuscle responds to
Vibration, fine texture (like using a tool)
Why do we have multiple receptor types
Many receptors allows us to detect many types of information
A single stimulus can activate many different receptor systems
Receptive fields
The area of skin that a particular cell receives information about
Do meissener’s or Paccinian corpuscles have larger receptive fields?
Paccinian
Two point threshold
The smallest separation of 2 separate but adjacent points that just produces two distinct impressions of touch
fingertip 2 point threshold
2 mm
arm 2 point threshold
3.5 cm
what stops two points from being discriminated|?
both points of pressure are within the same receptive field
where are we most sensitive?
lips, hands and face
fovea of the skin, why is it named this?
fingertip
most receptors
what happens to fingertip with experience
acuity can change
active touch
active exploration of environment
passive touch
body is stationary
advantages of active touch
more parts of your body are in contact with the object
you can search for the most diagnostic parts of objects to feel
kinaesthetic senses are also engaged
cues in perceiving texture
spatial
temporal
spatial cues in perceiving texture
bumps and grooves when finger is stationary or moving
temporal cues when perceiving texture
only when moving finger across a surface
paccinian corpuscles: adaption to high frequencies impairs performance
can perceive texture via a tool
tactile agnosia
cannot identify objects by touch but have no problems with spatial processing (WHERE not what)
tactile extinction
the. failure to detect a stimulus only in the presence of. another stimulus to certain parts of the body
no problems in object recognition (WHAT not where)
activity when determining what object was
activity in primary and secondary somatosensory cortex
activity when determining where object was
activity in superior parietal areas
top down influences on touch
must update as move body position
emotional effect of touch- same sensation may be pleasurable or unpleasant
expectation vs surprise (tickling)
illusions of touch
Aristotle’s illusion
cutaneous rabbit illusion
affect of the cutaneous rabbit illusion
activity in the primary somatosensory cortex as if more points than physically touched had actually been stimulated
why cant you tickle yourself ?
can predict your own actions
same touch rates as more ticklish when produced by an experimenter rather than self
nociceptor
receptors for pain
two types of pain
A delta fibres- fast sharp pain
C fibres - slow dull pain
a delta fibre pain examples
pin prick, pinches, extreme temperature
C fibres pain examples
many types of pain
mild stimulation can be pleasurable
can one stimulus activate both pain systems
yes
what can pain be affected by?
a persons mental state
attention
an example of pain in the absence of stimulation
phantom limb pain
gating of pain in the spinal cord influences…
the degree to which painful information reaches the brain
what can pain be reduced by?
non-painful tactile inputs (massage, rubbing)
top down input (expectations etc.)
what is a phantom limb?
after a limb is amputated and a patient feels a phantom limb in its place
there is no external stimulus but the patient still perceives the limb
many patients feel phantom arms/ hands when touched on the face: missing hand is still represented in the brain
what is proprioception?
where your body is in space
what is proprioception reliant on?
signals from muscles
vestibular system, tactile receptors…
kinesthesis`
kinesthesis
movement of limbs in space
IW case study
lost proprioception, kinesthesis and touch age 19 from viral infection
learned to compensate using visual system, unable to move if its dark
physiological changes in IW
lost fast myelinated fibres, retained slow C fibres
C tactile
pain, temperature, enjoy being cuddled
