somesthesis

Question 1

dorsal column pathway is related to:

Answer 1

• touch
• pressure
• vibration
• joint position sense
  (discriminatory, fine touch)

Question 2

the dorsal column system is tested by:

Answer 2

• running a piece of cotton on the surface of the skin

Question 3

skin receptors

Answer 3

• meissner corpuscles
• pacinian corpuscle
• ruffini’s corpuscle
• merkel’s disc

Question 4

where are meissner corpuscles located? what are they receptors for?

Answer 4

at the junction of the dermis and epidermis
- specialized encapsulated receptors of touch

Question 5

pacinian corpuscle receptors
(sense, rate, location)

Answer 5

sense: vibration
rate: very rapid
location: subcutaneous tissue

Question 6

ruffini’s corpuscle receptors (sense, rate, location)

Answer 6

sense: stretch of the skin
rate: slow
location: all skin & periodontal ligament

Question 7

Merkel discs receptors? (sense, rate, location)

Answer 7

sense: pressure
rate: slow
location: all skin

Question 8

Meissner Corpuscle (sense, rate, location)

Answer 8

sense: touch
rate: rapid
location: glabrous skin

Question 9

Hair follicle (sense, rate, location)

Answer 9

sense: touch
rate: rapid
location: hairy skin

Question 10

physiological classification of receptors:

Answer 10

• very rapidly adapting
• rapidly adapting
• slowly adapting

Question 11

very rapidly adapting receptors for:

Answer 11

sinusoidal stimulation (vibration)

Question 12

rapidly adapting receptors for:

Answer 12

velocity of movement (touch)

Question 13

slowly adapting receptors for:

Answer 13

depth of skin indentation (pressure)

Question 14

somatic sensory receptors

Answer 14

• pacinian corpuscles
• hair follicale
• meissner’s corpuscle
• Merkel’s discs
• Ruffini’s corpuscle

Question 15

hair follicle response to touch

Answer 15

• 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

Question 16

what is glabrous skin?

Answer 16

area of the skin with no hair

Question 17

Meissner corpuscles

Answer 17

• present in hairy and glabrous skin
• rapidly adapting
• sense a moving stimulus

Question 18

Merkel’s Disc

Answer 18

• nerve terminal ends in a flat disc
• slowly adapting
• senses pressure
• deeper you push, stronger the stimulus (faster firing)

Question 19

Ruffini Corpuscle

Answer 19

• slow adapting
• in skin, joint capsules, periodontal ligament
• senses the stretch of the skin

Question 20

In the orofacial region what is present and what is not?

Answer 20

present: ruffini endings in periodontal ligament
not present: pascinian corpuscles

Question 21

2-point discrimination

Answer 21

• 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

Question 22

how is 2-point discrimination tested?

Answer 22

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.

Question 23

is 2 point discrimination the same all over the body?

Answer 23

no, depends on density of receptors
ex: tongue, lips, and
hands are sensitive
back is less sensitive

Question 24

what is the basis of 2-point discrimination?

Answer 24

receptor density
- more dense = richly innervated
- less dense = receptors are further apart

Question 25

afferent fibers of fine touch

Answer 25

- receptor endings encapsulated - A-beta fibers

Question 26

classification of nerve fibers

Answer 26

Question 27

dorsal column pathway

Answer 27

- signal - DRG - DCN - decussate - ML - VPL - postcentral gyrus

Question 28

postcentral gyrus

Answer 28

main area for somatosensory sensations

Question 29

Trigeminal (Gasserian) Ganglion

Answer 29

Question 30

trigeminal nerve (V3)

Answer 30

- mandibular - innervates muscles of mastication - only motor division of trigeminal

Question 31

dermatomes

Answer 31

one nerve innervates portions of the skin and damage to one can cause loss of sensation to that whole section of skin

Question 32

trigeminal pathway

Answer 32

1. sensation comes into DRG 2. info goes to chief nucleus of V (synapse) 3. fibers cross (not distinct crossover) and go to VPM of thalamus 4. Postcentral gyrus

Question 33

primary somatosensory cortex

Answer 33

postcentral gyrus

Question 34

somatotopic organization of post central gyrus

Answer 34

- 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

Question 35

the somatotopic mapping is:

Answer 35

- disproportionate - discontinuous (finger comes before forehead) - plasticity (shrink or grow depending on stimulation to that region)

Question 36

surrounding (lateral) inhibition

Answer 36

an inhibitory interneuron inhibits neighboring neurons (like a network)

Question 37

how does surrounding inhibition work?

Answer 37

if there is a stronger signal coming through, the neighboring neurons will be inhibited - stronger signal give off stronger inhibition

Question 38

why does surrounding inhibition inhibit the neighbors?

Answer 38

- 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)

Question 39

descending (presynaptic) inhibition

Answer 39

descending pathway that goes in opposite direction of dorsal columns pathway and inhibits the synapsing at the DCN

Question 40

secondary somatosensory cortex

Answer 40

- in parietal lobe - receives input from the other side of the body - higher level analysis of sensory info

Question 41

somatosensory perception includes

Answer 41

- basic - intermediate - higher level - guide motor planning

Question 42

basic somatosensory perception includes

Answer 42

- pressure - touch - stretch - vibration - joint position

Question 43

intermediate somatosensory perception includes

Answer 43

- weight - size - shape - texture - motion (speed and direction) - 2-point discrimination - graphesthesia

Question 44

higher level somatosensory perception includes

Answer 44

- tactile object recognition - graphesthesia