week 3 (touch + pain)

Question 1

define: primary somatosensory cortex (where, what)

Answer 1

• receives input from thalamus via internal capsule
• postcentral gyrus
• parietal lobe

Question 2

define: secondary somatosensory cortex (where, what)

Answer 2

• receives info from S1 (primaary somatosensory cortex)
• bottom part near S1
  ⤷ more towards middle of brain but still parietal lobe

Question 3

question: where are the motor areas of the cortex?

Answer 3

• ## precentral gyrus

Question 4

name + explain: types of body representation in S1 (2)

Answer 4

1. somatotopic organization
- orderly representation of body
- adjacent areas on skin connect to adjacent areas in brain
- contralateral

nonlinear representation
- sensory homunculus
- RF size dep. on location in somatotopic map
- smaller RF have larger areas in S1

Question 5

explain: columnar organization of cerebral cortex
question: what layer does somatosensory input arrive at?

Answer 5

• 6 layers
• (info from thalamus) somatosensory arrives at layer 4

**1, 2, 3a, 3b are areas of the S1, not layers (they span all 6 layers of cortex)

Question 6

define: neural plasticity

Answer 6

• changes in cortical map can occur in resp. to physiological changes in sensory and motor function
• ex. remapping after practicing, exp., injury

Question 7

define: cross-modal plasticity

Answer 7

• 1 sensory system taken over by another
• if the sys. is inhibited/unable to work

Question 8

explain: phantom limbs

Answer 8

• illusion that missing limb is still present
• functional remapping changes somatotopic map
  ⤷ S1neurons that lose input get innervated by receptors for a diff. area
• ex. amputate arm -> S1 neurons that lost input are innervated by face receptors

Question 9

question: does a higher threshold mean that part of the body is more or less sensitive?

Answer 9

• higher threshold = less sensitive
• need more stim to reach threshold ->more stim to be detected -> less sensitive

Question 10

define: two-point limen/touch threshold

Answer 10

• smallest separation of 2 points applied simultaneously to the skin that an still be discriminated
• 2 point pain threshold = separation of 2 painful stim.

Question 11

question: overall trend in detection threshold for body sensitivity?

Answer 11

• most sensitive in face
• less sensitive in leg and arms

Question 12

question: over trend in discrimination threshold for body?

Answer 12

• similar pattern to detection
• less sensitive in legs
• most sensitive in face
• sensitive at fingertips

Question 13

question: what factors influence two-point discrimination?

Answer 13

• smaller mechanoreceptor field size
• higher density of mechanoreceptors
• want brain to receive 2 separate signals so need no overlap in recep. fields

Question 14

question: what factors affect tactile sensitivity?

Answer 14

• sex
  ⤷ fem. more sensitive
• age
  ⤷ older = less sensitive (in general)
  ⤷ in blind = braille could be close together and older people could still recog.
• genetics
  ⤷ identical twins = more similar tactile sensitive than fraternal
• autism can -> hypersensitivity

Question 15

question: what can promote touch adaptation?

Answer 15

• larger stim. area
• weaker intensity force
• stim. less sensitive areas of body

Question 16

explain: pathway for nociceptive signals

Answer 16

• follows spinothalamic pathway
• signals arrive at dorsal horn of spinal cord
• interneurons in dorsal horn receive info from brain
  ⤷ cog. info (ex. emo.)
• interneurons form synapses on neurons that convey nociceptive info to brain

Question 17

explain: gate control theory

Answer 17

• pain signals can be blocked through feedback circuit in dorsal horn
• inhibitory interneuron = gate
  ⤷ can reduce feeling of pain
  ⤷ A-alpha or A-delta fiber
• relaxing beha. -> activating inhibitory interneuron -> blocks pain

Question 18

question: what areas process the discriminative vs emotional aspects of pain?

Answer 18

• discriminative = thalamus, S1, S2
• emotional
  ⤷ anterior cingulate cortex (reward anticipation, decision making. emo.)
  ⤷ insula (self awareness, emo., homeostatic emo.)
  ⤷ prefrontal cortex (cog. and executive control)
  ⤷ amygdala (emo. memory, fear)

Question 19

define: referred pain

Answer 19

• pain arises in deeper structure of body is actually felt elsewhere
• bc convergence of afferent fibers on spinal cord from diff. body parts
• ex. heart attack
  ⤷ pain in arms/shoulders but actually from heart

Question 20

question: how is pain measured? (2)

Answer 20

1. univariate approach
- group all dimensions of pain together
- measure with standard psychophysical techniques (threshold)

2. multivariate approach
- separately asses different dimensions of pain
⤷ quality, intensity, location
- harder to gauge some bc feelings are subjective

Question 21

question: why do people have different pain thresholds?

Answer 21

• biological factors
  ⤷ genetics
• psychological factors
  ⤷ mood
• social factors
  ⤷ economic

Question 22

question: what causes pain sensitization (increased sensitivity)?

Answer 22

• peripheral and central changes
• peripheral = interaction of recep. and inflammatory substances released after tissue damage
• central = increased excitability of neurons at dorsal horn

Question 23

name + categorize: types of pain sensitization (3)

Answer 23

PERIPHERAL
- hyperalgesia
⤷ increased pain to normally painful stim.
- allodynia
⤷ normally innocuous (not harmful) stim. cause pain

CENTRAL
- neuropathic pain
⤷ chronic, intense pain hard to treat
⤷ nerve fibers are damaged and pain thresholds do not return to pre-injury lvls

Question 24

explain: phantom pain

Answer 24

• lingering painful sensation in missing limb
• pain pathways are still active without peripheral stim.
  ⤷ neurons where still stim. when amputated -> still painful

Question 25

name: ways to treat and moderate pain (3)

Answer 25

**1. pharmalogical** - analgesics = dampen pain - anti-inflammatory = block inflammatory molecules that activate pain recep. - opiates = activate opiod recep. -> blocks pain sig. to brain **2. surgical and neurostimulatory** - removingparts or spinal cord or frontal lobe - TENS unit activates A-beta fibers ⤷ counterstimulation ⤷ activating tactile recep. -> activates inhibitory interneurons **3. psychological** - counterstim. or counterirritation - placebo effect ⤷ give drug w/ no actual effect but patients still claim it helps ⤷ may be due to endogenous opioids - relaxation, hypnosis, etc.

Question 26

explain: itch receptors

Answer 26

- pruiriceptors - C fibers - spinothalamic system - activated by prurigenic chemicals like histamines - diff. from pain - sometimes itch also resp. to pain stim. bc interact in cord - pain can activate inhibitory > no itch

Question 27

question: can scratching reduce itchiness?

Answer 27

- provides tactile stim. -> activates A-alpha or A-beta - at lvl of cord and/or brain - older people may strach more bc less merkel cells ⤷ less possibility to distract by scrating