SomatoSensation II

Question 1

List the two major central pathways of the somatosensory system

Answer 1

• Dorsal column medial lemciscal system
• Spinothalamic tract (Anterolateral system) (Left side of brain)

Question 2

What mediates sensory aspects for the body?

Answer 2

Ascending pathways mediate sensory aspects of pain for the body and the face

Question 3

How is this pain mediated?

Answer 3

2nd order neurons decussate and project to ventral posterior nuclear complex of thalamus
- VPL: Body
-VPM: Face

Question 4

Where does the DCML and STT cross in the body?

Answer 4

• They both cross the midline of the body at different points
• Differential loss of temperature/pain vs fine tactile discrimination

Question 5

What is dual aspect model of pain?

Answer 5

Sensory discriminative
- Location
- Intensity
- Duration
- Quality

Question 6

What is the affective motivational model of pain?

Answer 6

• Unpleasantness: The painful mess of pain
• Effects on arousal, mood (affect), behaviour

Question 7

What are nociceptors?

Answer 7

Neurons specialized for detection of painful stimuli

Question 8

What are A-delta fibres and C fibres?

Answer 8

Both contribute to different aspects of pain sensation
- The first pain sensation is picked up by A delta fibres
- The second pain sensation is picked up by C fibres
- As time goes on, you can only feel pain by A delta fibres

Question 9

What receptor is involved in the transaction of noxious heat?

Answer 9

• TRPV 1 receptors
• Originally called vanilloid receptor
• Present in A delta and C fibres

Question 10

How is nociceptor activity maintained after injury?

Answer 10

• An inflammatory soup containing cytokines, prostaglandins and small signalling molecules
• Maintain depolarisation and sensitivity of C fibre terminals after original stimulus
• Leads to:
• Hyperalgaesia
• Allodynia

Question 11

Where is the anterolateral system (STT) located?

Answer 11

They are dorsal horn interneurons
- Located in superficial and deep layers of dorsal horn

Question 12

What is the function of The anterolateral system (STT)?

Answer 12

• Synaptic input from C and A delta fibres
• axons cross and ascend in anterolateral white matter
• Some are multi modal (receive convergent nociceptive and non nociceptive inputs)
• Some receive convergent input from visceral afferents

Question 13

Describe the cortical representation of pain

Answer 13

Cortical representation of pain is complex
- STT projects to S1 via VP nuclei of thalamus (like DCML system)
- However, STT and DCML axons do not converge on same thalamic neurons: pathways are parallel
- S1 is necessary for localisation of pain but stimulation of S1 gives rise to referred tactile, not painful sensations
- Additional areas are involved in pain sensations

Question 14

Name the 2 systems in central pain processing

Answer 14

• Lateral system (Dont confuse with the anterolateral system)
• Medial system
• Both diverge at the level of the thalamus

Question 15

Describe the lateral system

Answer 15

• VP nuclei of thalamus is in parallel with the DCML system
• Primary and secondary somatosensory cortex (SI and SII)
• Sensory discrimination
• Project nuclei via specific somatosensory thalamic nuclei

Question 16

Describe the medial system

Answer 16

• Midline nuclei of thalamus (intralaminar)
• Anterior cingulate and insular cortex
• affective motivational
• Project to different cortical areas via (non specific) midline thalamic nuclei

Question 17

Describe the pathway of pain for the anterolateral system via the sensory discriminative way

Answer 17

Anterolateral system -> Ventral posterior nucleus -> Somatosensory cortex

Question 18

Describe the pathway of pain for the anterolateral system via the affective motivational approach

Answer 18

Anterolateral system -> either
- Reticular formation -> Superior colliculus -> Periaquiductal grey -> Hypothalamus -> Amygdala
Or
- Midline thalamic nuclei -> Anterior cingulate cortex or Insular cortex

Question 19

List the 2 types of Pains

Answer 19

Acute pain
Chronic pain

Question 20

Describe acute pain

Answer 20

• Nociceptive response to tissue damage
• Mechanisms are well understood
• Resolves with healing process
• Treatment relatively successful

Question 21

List some treatments for acute pain

Answer 21

• NSAID
• Opiate drugs
• Successful at treating pain as neurophysiological response to tissue damage

Question 22

Describe chronic pain

Answer 22

• Persists beyond tissue damage or may be due to CNS damage
• Poorly understood mechanisms
• Treatment relatively ineffective

Question 23

What are some treatments for chronic pain?

Answer 23

• Antidepressants (e.g. Amitryptyline, Duloxetime)
• At lower dosage and in absence of diagnosis of clinical depression
• Experimental/rare/anecdotal: Neurosurgery, deep brain stimulation

Question 24

Describe Chronic pain in more detail

Answer 24

• > 3 months
• Alarmingly high prevalence
• May be due to nerve damage from prior injury: neuropathic pain
• May occur in absence of nerve damage e.g. Stroke
• Neuroplasticity: sensitisation at level of DH imterneurons or higher in the pathway
• Cortical reorganisation

Question 25

What type of pain dissociate form tissue damage?**

Answer 25

• Phantom limb pain
• Central pain

Question 26

What is intractable pain?

Answer 26

Intractable pain, also called intractable pain disease (IPD), is a severe, constant, relentless, and debilitating pain that is not curable by any known means and which causes a house-bound or bed-bound state and early death if not adequately treated

Question 27

How is anterior cingulotomy used for intractable pain

Answer 27

• Targeted lesion to discomfort anterior cingulate cortex on both sides
• Used for decades as a last resort