Lecture 11- Somatic Sensory System

Question 1

Give a general overview of the sensory pathway from receptor endings (dermatome)

Answer 1

stimuli–> dorsal root ganglion –> pain and temp decussates at level of entry/ mechanosensory fibres travel up through spinal cord to cuneate (upper body)/ gracile (lower body) nuclei then decussate at medial lemniscus in medulla –> up through medulla –> midbrain –> thalamus –> somatosensory cortex of cerebrum

Question 2

what is sensory transduction?

Answer 2

where the energy of a stimulus is converted to an electrical signal

Question 3

what are the 2 types of receptors?

Answer 3

rapidly adapting
slowly adapting

Question 4

what’s the difference between rapidly adapting and slowly adapting receptors?

Answer 4

rapidly adapting are transient, firing maximally in immediate response to stimulus briefly
slowly adapting are tonic and fire as long as stimulus is present

Question 5

what are the 5 receptors found in the skin for tactile stimulation?

Answer 5

• meissner corpuscle
• pacinian corpuscle
• ruffini’s corpuscle
• merkel’s disc
• free nerve endings

Question 6

describe Meissner corpuscles

Answer 6

• rapidly adapting
• most common in smooth/hairless skin
• 40% hand innervation
• detects texture moving across skin- useful in detecting object slippage/grip

Question 7

describe Pacinian corpuscles

Answer 7

• rapidly adapting
• more sensitive that Meissner- fine textures
• 15% hand innervation
• tickle/vibration sensation
• skilled tool use

Question 8

Describe Ruffini’s Corpuscles

Answer 8

• slowly adapting
• 20% receptors in hand
  -unknown function but linked to proprioception

Question 9

Describe Merkel’s Discs

Answer 9

• slowly adapting
• 25% receptors in hand
• dense in fingertips
• stimulation produces light pressure sensation
• detection of shape/edges/rough texture- braille reading

Question 10

Describe free nerve endings

Answer 10

pain and temp sensation

Question 11

Why is it useful to understand these receptors?

Answer 11

developing artificial systems and bioimplants

Question 12

name 3 areas of the body which have the greatest 2-point discrimination threshold

Answer 12

hands, face, feet

Question 13

name 3 areas of the body that have the lowest 2-point discrimination threshold

Answer 13

legs, arms, back

Question 14

what determines 2-point discrimination threshold?

Answer 14

the density of receptors and the size of their receptive field

Question 15

what are the 2 main types of proprioceptors?

Answer 15

muscle spindles
golgi tendon organs

Question 16

what do muscle spindles do?

Answer 16

signal muscle length

Question 17

what do golgi tendon organs do?

Answer 17

signal changes in muscle tension

Question 18

what does the number of muscle spindles reflect?

Answer 18

how fine the control of each muscle is

Question 19

where in the body has the highest density of muscle spindles?

Answer 19

oculomotor muscles

Question 20

what are the 2 types of muscle spindles and what do they indicate?

Answer 20

group 1- info about dynamic movement
group 2- info about static positions of limbs

Question 21

do golgi tendon organs respond to passive stretch?

Answer 21

no, only active contraction

Question 22

what are the 3 key somatic sensory pathways?

Answer 22

• dorsal column medial lemniscus
• trigeminal system
• spinothalamic

Question 23

generally what does the dorsal column medial lemniscus pathway detect?

Answer 23

upper and lower body sensation

Question 24

generally what does the trigeminal system pathway detect?

Answer 24

face sensation

Question 25

generally what does the spinothalamic tract detect?

Answer 25

pain and temp

Question 26

describe the pathway of the dorsal column medial lemniscus pathway

Answer 26

mechanosensory receptor–> dorsal root ganglion–> up spinal cord–> upper body cuneate/lower body gracile tracts in medulla–> cuneate and gracile nuclei in medulla–> decussates in medulla–> through medial lemniscus of medulla/ pons/ midbrain –> ventral posterior lateral (VPL) nucleus of thalamus –> somatosensory cortex of cerebrum

Question 27

which dermatomes have more overlap, touch or pain?

Answer 27

touch

Question 28

describe the pathway of the trigeminal tract

Answer 28

mechanosensory receptors in face–> trigeminal ganglion–> decussates at medulla to enter medial lemniscus–> up through pons and midbrain–> ventral posterior medial nucleus (VPM) –> somatosensory cortex

Question 29

describe the structure of the primary somatosensory cortex

Answer 29

it’s divided into 3a, 3b, 1 and 2 areas anterior to posterior
3a- proprioception
3b+1- cutaneous stimuli
2- proprioceptors and tactile stimuli

Question 30

describe Albrecht et al’s study into plasticity

Answer 30

focussed laser to induce stroke in forelimb cortical region, found after 90 minutes there was a redistribution of forelimb cortical sensation to hindlimb region

Question 31

Describe Frostig’s 2012 study into mechanism of rat stroke plasticity

Answer 31

MCA filament occlusion model to cause permanent stroke, if whiskers were tickled soon after stroke, cortex was restored, if tickled 3 hours after, make damage worse
thought to be ACA providing some compensatory blood to region if stimulated