somesthesis Flashcards
dorsal column pathway is related to:
- touch
- pressure
- vibration
- joint position sense
(discriminatory, fine touch)
the dorsal column system is tested by:
- running a piece of cotton on the surface of the skin
skin receptors
- meissner corpuscles
- pacinian corpuscle
- ruffini’s corpuscle
- merkel’s disc
where are meissner corpuscles located? what are they receptors for?
at the junction of the dermis and epidermis
- specialized encapsulated receptors of touch
pacinian corpuscle receptors
(sense, rate, location)
sense: vibration
rate: very rapid
location: subcutaneous tissue
ruffini’s corpuscle receptors (sense, rate, location)
sense: stretch of the skin
rate: slow
location: all skin & periodontal ligament
Merkel discs receptors? (sense, rate, location)
sense: pressure
rate: slow
location: all skin
Meissner Corpuscle (sense, rate, location)
sense: touch
rate: rapid
location: glabrous skin
Hair follicle (sense, rate, location)
sense: touch
rate: rapid
location: hairy skin
physiological classification of receptors:
- very rapidly adapting
- rapidly adapting
- slowly adapting
very rapidly adapting receptors for:
sinusoidal stimulation (vibration)
rapidly adapting receptors for:
velocity of movement (touch)
slowly adapting receptors for:
depth of skin indentation (pressure)
somatic sensory receptors
- pacinian corpuscles
- hair follicale
- meissner’s corpuscle
- Merkel’s discs
- Ruffini’s corpuscle
hair follicle response to touch
- very rapidly adapting
- afferent neurons that wrap around base of hair follicle that go to dorsal column
- senses touch and velocity of movement (sensation only while moving)
- does not sense steady stimuli
what is glabrous skin?
area of the skin with no hair
Meissner corpuscles
- present in hairy and glabrous skin
- rapidly adapting
- sense a moving stimulus
Merkel’s Disc
- nerve terminal ends in a flat disc
- slowly adapting
- senses pressure
- deeper you push, stronger the stimulus (faster firing)
Ruffini Corpuscle
- slow adapting
- in skin, joint capsules, periodontal ligament
- senses the stretch of the skin
In the orofacial region what is present and what is not?
present: ruffini endings in periodontal ligament
not present: pascinian corpuscles
2-point discrimination
- discrimination of stimuli at one point, two times we can sense
- discrimination of 2 stimuli and 2 points, we can sense
- cannot discriminate from 2 different points that are too close together
how is 2-point discrimination tested?
Ask the patient
whether they feel 2 points or 1 point
stimulation?
Also, bring the points closer together,
and test if the patient can still tell the
difference.
is 2 point discrimination the same all over the body?
no, depends on density of receptors
ex: tongue, lips, and
hands are sensitive
back is less sensitive
what is the basis of 2-point discrimination?
receptor density
- more dense = richly innervated
- less dense = receptors are further apart
afferent fibers of fine touch
- receptor endings encapsulated
- A-beta fibers
classification of nerve fibers
dorsal column pathway
- signal
- DRG
- DCN
- decussate
- ML
- VPL
- postcentral gyrus
postcentral gyrus
main area for somatosensory sensations
Trigeminal (Gasserian) Ganglion
trigeminal nerve (V3)
- mandibular
- innervates muscles of mastication
- only motor division of trigeminal
dermatomes
one nerve innervates portions of the skin and damage to one can cause loss of sensation to that whole section of skin
trigeminal pathway
- sensation comes into DRG
- info goes to chief nucleus of V (synapse)
- fibers cross (not distinct crossover) and go to VPM of thalamus
- Postcentral gyrus
primary somatosensory cortex
postcentral gyrus
somatotopic organization of post central gyrus
- very precise
- face, tongue, and hand are on the lateral convexity
- lips and index finger have large region
- upper arm, abdomen, and thorax have smaller regions
the somatotopic mapping is:
- disproportionate
- discontinuous (finger comes before forehead)
- plasticity (shrink or grow depending on stimulation to that region)
surrounding (lateral) inhibition
an inhibitory interneuron inhibits neighboring neurons (like a network)
how does surrounding inhibition work?
if there is a stronger signal coming through, the neighboring neurons will be inhibited
- stronger signal give off stronger inhibition
why does surrounding inhibition inhibit the neighbors?
- make a clearer signal
- if no inhibition, there will be a fog of information
- more precise identification of the location of the signal
(important in visual)
descending (presynaptic) inhibition
descending pathway that goes in opposite direction of dorsal columns pathway and inhibits the synapsing at the DCN
secondary somatosensory cortex
- in parietal lobe
- receives input from the other side of the body
- higher level analysis of sensory info
somatosensory perception includes
- basic
- intermediate
- higher level
- guide motor planning
basic somatosensory perception includes
- pressure
- touch
- stretch
- vibration
- joint position
intermediate somatosensory perception includes
- weight
- size
- shape
- texture
- motion (speed and direction)
- 2-point discrimination
- graphesthesia
higher level somatosensory perception includes
- tactile object recognition
- graphesthesia
