The Cutaneous Senses Flashcards
What are cutaneous senses?
Based on mechanoreceptors in the skin for touch/tactile perception, vibration, texture, shape, warmth, cold, itch, and pain
What is proprioception?
Sensing position of the body and limbs
What is kinesthesis?
Sensing movement of the body and limbs
What is haptic perception?
Coordination of tactile and kinesthetic sensation
What is vestibular sense?
Balance/spatial orientation due to semicircular canals and vestibular sacs
What are some characteristics of the skin?
Heaviest organ
Range of thickness
May by glabrous or hairy
Neural structures at the epi/dermal boundary are believed to be receprots
What is the outer layer of the skin called?
The epidermis
The surface is called the corneum
What is the inner layer of the skin called?
The dermis
What is specificity theory?
One mechanoreceptor type proposed for each basic sensation
What do Ruffini endings detect?
Warmth
What do Krause end bulbs detect?
Cold
What to Meissner corpuscles detect?
Touch
What do free nerve endings detect?
Pain
What touch blend leads to detection in something wet?
Even pressure, cold
What touch blend leads to the detection of something oily?
Weak pressure, warm, movement
What is punctate sensitivity?
If there is a receptor under the skin at a location, there must be sensitivity to the associated sensation
What is microneurography?
Use an electrode to find a nerve fibre that is triggered by a particular stimulus
What is histology?
Trace the fibre back to the receptor
What are the problems with determining the nature of fibers?
Self-dissection shows no correlation between structure and sensations, restest impossible
Skin transmits kinetic and thermal energy over a distance from the point of stimulation - many receptors affect by any stimulus
Cornea only has free nerve endings but all four sensations
Sensory spots changed over time
What is the thermal grill illusion?
Simultaneous presentation of separate warm and cold stimuli = painfully hot
What is pattern theory?
The pattern of neural impulses from a number of receptors corresponds to a particular sensation
Assumed that receptors differ in structure, but not in function
The same receptor can yield two different kinds of sensations, depending on the intensity of activation
What is stimulus preference?
Intermediate approach
Each sensation arises from the firing of a number of receptor types tuned to different aspects of a stimulus
What do the Pacinian corpuscles do?
The corpuscle around the nerve fibre acts to absorb sustained pressure
Fibre itself only stimulated at onset or offset of stimulus
What is the spinothalamic pathway?
Smaller nerve fibres synapse in the spinal cord
Ascends via the spinal cord and brainstem to the thalamus
Projects to the anterior cingulate cortex, and insular cortex. and primary somatosensory cortex
Carries primarily temperature and pain information
What is the medial lemniscal pathway?
Larger, longer nerve fibres synapse in the medulla
Ascends via medial lemniscus to the thalamus
Projects to the primary somatosensory cortex
Conveys touch and proprioceptive information
What is the evoked potential method?
Electrodes on the scape measure cortical activity
Different skin loci are stimulated until activity produced at electrode
Very time-consuming
What is stimulation during open brain surgery?
Stimulate the cortex at a low voltage to produce sensations in awake patients to not damage vital parts of the brain
How is the somatosensory cortex organized?
Somatotopic organization, adjacent points on the skin have adjoining cortical representations
Touch represented in somatosensory cortex as a homunculus
What is touch?
Constant pressure
What is vibration?
Changing pressure
Where does soft touch go?
To the insular cortex where emotion is processed
Plays a role in development, social cooperation, and affiliation
What is proxemics?
Zones of personal space
Distances between people depend on the nature of social interaction
What is public distance?
For public speaking
Over 3.5 m
What is social distance?
For interaction with strangers and acquaintances
1.2-3.5 m
What is personal distance?
For interactions with friends and family
45-120 cm
What is intimate distance?
For whispering, touching, or embracing intimate partners
15-45 cm
What is oxytocin?
A hormone synthesized in the hypothalamus and stored in the pituitary gland
Involved in contractions and lactation
Release at orgasm
What is the absolute touch threshold?
Hair pushed into skin until hair bends
Each bends with a different amount of force
Use stronger hairs until absolute threshold is established
What is the difference threshold for touch?
Two-point threshold
Smallest separation between two points on the skin that can be perceived
What does actively handling an object aid in?
Identification
What do exploratory procedures do?
Provide information on different stimulus features
What can we determine with lateral motion and contour following?
Texture
What can we determine with pressure?
Hardness
What can we determine with static contact?
Temperature
What two fibres are temperature encoded by?
Warm fibres = 30-48 degrees
Cold fibres = 20-45 degrees
What is paradoxical cold?
A hot stimulus produces the sensation of cold due to activation of cold fibres
What is physiological zero?
Temperature at which receptors have become adapted
Perception of temperature is relative to this point
What is pain?
An unpleasant sensory or emotional experience associated with actual or potential tissue damage
What is nociception?
The neural encoding of impending or actual tissue damage
What are nociceptors?
Receptors for noxious stimuli
Peptide substance P is released from C fibres
What do A-delta fibres transmit?
Sharp, pricking pain
What do C fibres transmit?
Burning, throbbing pain
What is double pain?
Sharp pain followed by dull pain
What is congenital insensitivity to pain with anhidrosis?
Rare congenital insensitivity disorder
Cannot feel pain
Complete absence of A-delta and C fibers; normal sensation of touch in A-beta fibres
Where is the substantia gelatinosa?
In the spinal cord
Where are transmission cells found?
In the spinothalamic pathway
What are L-fibers?
Large diameter axons from mechanoreceptors
What are S-fibers?
Small diameter axons from nociceptors
What does activity in L-fibers do?
Closes the gate
Activates the SG so that T is inhibited and there is no pain signal
What does activity in S-fibers do?
Opens the gate
Activates the SG so that T is excited and a pain signal is sent
How does rubbing reduce pain?
By activating A-beta fibers
What is TENS?
Transcutaneous Electrical Nerve Stimulation
Small electrical current activates A-beta fibers
Inhibits pain signals
How might pain signals be attenuated?
This may be due to endogenous opioids
Inhibit Substance P
What is naloxone?
Narcotic antagonist
Wipes out the effects of placebo and acupuncture, but not hypnosis
What is synesthesia?
The involuntary physical experience of a cross-modal association in which stimulation of one sensory modality reliably causes a perception in one or more different senses
What are the characteristics of synesthesia?
Responses are generic and unelaborated
One-way projections
Idiosyncratic
What are one-way projections in relation to synesthesia?
A synesthete who sees colours when hearing spoken words does not necessarily hear words when viewing colours
What are the two theories of synesthesia?
More connections
Less inhibition
What was found about colour synesthetes in an fMRI?
Their V4 activates in response to spoken words but not when viewing coloured surfaces
What might synesthesia reveal?
Aspects of top-down processing, the binding problem, sensory integration, and conscious experience
