Somatosensory System

Question 1

what are the 4 main somatosensory receptors in the skin

Answer 1

pacinian corpuscles
meissner’s corpuscles
Merkel’s disks
Ruffini’s endings

Question 2

what are somatosensory receptors called

Answer 2

mechanoreceptors

Question 3

what are 2 types of skin

Answer 3

hairy skin and glabrous skin (smooth)

Question 4

what are the 2 layers of skin

Answer 4

epidermis and dermis (thicker layer underneath)

Question 5

which mechanoreceptors are near the top of the dermis

Answer 5

merkels disk and meissner’s corpuscle

Question 6

which mechanoreceptors are deep in the dermis

Answer 6

Pacinian corpuscle and Ruffini’s ending

Question 7

sensory axons

Answer 7

unmyelinated axon branches inside of mechanoreceptors that contain ion channels sensitive to mechanical force

Question 8

how do different mechanoreceptors differ to detect a large rage of stimuli

Answer 8

• different size receptive fields
  -different response to pressure (adaptation)
• preferred stimulus frequencies

Question 9

3 different types of mechanosenstve ion channels

Answer 9

• membrane stretch -> ap
• force applied to extracellular protein -> ap
  -force applied to intracellular protein -> ap

Question 10

Meissner’s corpuscle: adaptation, receptive field size, frequency detection

Answer 10

rapid adaptation, small receptive field, detects low frequencies (ex. hand over rough surface)

Question 11

Pacinian corpuscle: adaptation, receptive field size, frequency detection

Answer 11

rapid adaptation, large receptive field, detects high frequency (ex. vibrations hand on speaker)

Question 12

Merkel’s disk: adaptation, receptive field size, frequency detection

Answer 12

slow adaptation, small receptive field, detects very low frequencies (ex. hand over a smooth surface).

Question 13

Ruffini’s ending: adaptation, receptive field size, frequency detection

Answer 13

slow adaptation, large receptive field, detects very low frequencies (ex. hand over a smooth surface).

Question 14

mechanoreceptor adaptation

Answer 14

reduced response to physical stimuli over time

Question 15

mechanoreceptor capsule

Answer 15

20-70 layers filled with fluid surrounding sensory axon

Question 16

mechanoreceptor adaptation mechanism

Answer 16

probe presses on site, indentation of sensory axon, generate action potential -> adaptation (capsule layers move so no more indentation to sensory axon, back to resting membrane potential

Question 17

mechanoreceptor adaptation: what happens when stimuli/ pressure removed from mechanoreceptor

Answer 17

receptor action potential due to disruption to the sensory neuron.

Question 18

2 point discrimination

Answer 18

minimum distance necessary to differentiate between 2 simultaneous stimuli; point where you can no longer differentiation between 2 separate stimulus points

Question 19

what is sensitivity of an area determined by

Answer 19

density of mechanoreceptors and size of receptive fields

Question 20

qualities of more sensitive areas of the body

Answer 20

more mechanoreceptors (higher density) and smaller RF

Question 21

how does a sensory receptor send signals to spinal cord

Answer 21

through doral root

Question 22

dorsal root ganglion

Answer 22

collection of cell bodies in dorsal root

Question 23

4 main afferent axons

Answer 23

A alpha, A beta, A delta, C

Question 24

axons with largest diameter and most meylin ranked from most -> least

Answer 24

A alpha, A beta, A delta, C

Question 25

A alpha axon sensory receptors

Answer 25

proprioceptors (skeletal muscles)

Question 26

A beta axon sensory receptors

Answer 26

mechanoreceptors (skin)

Question 27

A delta axon sensory receptors

Answer 27

pain and temp

Question 28

C axon sensory receptors

Answer 28

temp, pain, itch

Question 29

how many segments are in the spinal cord

Answer 29

30

Question 30

what are the 4 groups of the spinal cord

Answer 30

cervical, thoracic, lumbar, sacral

Question 31

A beta axon pathway through spinal cord

Answer 31

dorsal root -> branches off into gray matter (spinal reflexes) and white matter pathway to brain

Question 32

dorsal column-medial lemniscal pathway

Answer 32

sensory neuron -> A beta axon -> doral root of spinal cord -> dorsal column nuclei (medulla) -> VP nucleus (thalamus) -> primary somatosensory cortex (S1)

Question 33

medial lemniscus pathway

Answer 33

pathway of sensory info from dorsal column in the medulla to the VP nucleus in the thalamus

Question 34

where does sensory info cross midline and processing goes from ipsilateral to contralateral: dorsal column-medial lemniscal pathway

Answer 34

medial lemniscus pathway (medulla)

Question 35

where does sensory info cross midline and processing goes from ipsilateral to contralateral: trigeminal touch pathway

Answer 35

pons

Question 36

trigeminal touch pathway

Answer 36

tactial/ sensory information from above the neck/ face to S1

Question 37

trigeminal touch pathway mechanism

Answer 37

trigeminal nerve -> principal sensory trigeminal nucleus in the pons -> contralateral shift in the VP nucleus (thalamus) -> S1

Question 38

what area of the somatosensory cortex receives input

Answer 38

Area 3b (from thalmus)

Question 39

proprioception

Answer 39

sense of limb position in space

Question 40

where does area 3b send info

Answer 40

area 1, area 2 and areas 5 and 7

Question 41

what info does area 1 recive

Answer 41

texture infow

Question 42

what info does area 2 recive

Answer 42

shape and size information

Question 43

what info does area 3a recive

Answer 43

input from muscle spindles from proprioception (limb position in space)

Question 44

what area if the primary somatosensory cortex (S1)

Answer 44

area 3b

Question 45

S1 orginization

Answer 45

cortical columns and digit representation

Question 46

S1 digit representation

Answer 46

the little finger (D5) represented most medially and the thumb (D1) most laterally; each digt contains slow and fast adapting neurons

Question 47

somatotopic map

Answer 47

a spatial arrangement of neurons that corresponds to body parts (larger body part, more neurons dedicating to information processing)

Question 48

where does vestibular information cross the midline -> contralateral:

Answer 48

medial lemniscus (medulla)

Question 49

main vestibular pathway

Answer 49

vestibular nerve, medial vestibular nucleus, VP nucleus (thalamus), vestibular cortex