Somatosensation II

Question 1

What are the two major pathways of the somatosensory system?

Answer 1

→ Dorsal column

→ spinothalamic tract

Question 2

What does the dorsal column receive inputs from?

Answer 2

→ Large diameter myelinated afferents : tactile

Question 3

What does the spinothalamic tract receive inputs from?

Answer 3

→ small diameter
→ thinly myelinated
→ coarse touch, nociception and temperature sensitivity

Question 4

What happens if there is a cut on one half of the spinal cord?

Answer 4

→ You interrupt all the ascending axons on one side

Question 5

What are the two types of pain?

Answer 5

→ Sensory discriminative

→ Affective motivational

Question 6

What are nociceptors?

Answer 6

→ Neurons specialized for the detection of painful stimuli

Question 7

What are the 3 types of nociceptors?

Answer 7

→ Mechanical
→ Chemosensory
→ Thermal

Question 8

When does temperature become painful?

Answer 8

→ 45 degrees or higher

Question 9

What is the difference between non nociceptive and nociceptive thermal receptors?

Answer 9

→ non nociceptive plateau above a certain range

→ nociceptors don’t response until the temperature approaches the range that is deemed painful

Question 10

What is the TRPV1 receptor involved in?

Answer 10

→ Transduction of noxious heat

Question 11

What kind of a receptor is TRPV1?

Answer 11

→ Ion channel that allows both Na+ and Ca2+ to pass

Question 12

What can activate TRPV1 and why?

Answer 12

→ Capsaicin

→ it is lipid soluble

Question 13

What does capsaicin binding to TRPV1 cause?

Answer 13

→ Activation of thermal nociceptor

Question 14

What is the conduction of the A delta fibres like?

Answer 14

→ Slowest of the myelinated fibres

→ Conduct moderately compared to C fibres

Question 15

How do C fibres conduct?

Answer 15

→ Unmyelinated

→ Slowly

Question 16

What pain does the A delta fibre mediate?

Answer 16

→ Mediates the sharp first pain

Question 17

What pain does the C fibre mediate?

Answer 17

→ second dull burning pain

Question 18

What blocks the smallest fibres?

Answer 18

→ low dose anaesthetic

Question 19

What blocks larger axons?

Answer 19

→ Pressure

Question 20

What maintains the sensitivity of the C fibres after the original stimulus?

Answer 20

→ Prostaglandins
→ Cytokines
→ Signaling molecules

Question 21

Why is there inflammation?

Answer 21

→ Tissue damage

Question 22

What is hyperalgesia?

Answer 22

→ Increased sensitivity to pain

Question 23

What is allodynia?

Answer 23

→ Something painless like gentle touch will be painful

Question 24

What do peripheral neurons release?

Answer 24

→ Substance P which reinforces the release of inflammatory molecules

Question 25

Describe the pathway from an injured right hand to the somatosensory cortex

Answer 25

→ Cells are damaged and release PGE → Sensory nerve fibres send the impulse to the dorsal horn (1ST ORDER NEURONS) → The 1st order neurons synapse with 2nd order neurons in the dorsal horn → The 2nd order neuron crosses over contralaterally and enters the spinothalamic tract → 2nd order neuron continues moving up to the thalamus where it synapses with a 3rd order neuron → 3rd order neuron sends impulse to somatosensory cortex

Question 26

Where do C fibres terminate?

Answer 26

→ Exclusively in superficial layers

Question 27

Where do A delta fibres terminate?

Answer 27

→ in both superficial and deep

Question 28

Why is angina not felt in the heart?

Answer 28

→ Afferents from cardiac muscle are converging on dorsal horn interneurons on the cervical segments

Question 29

What are the pathways of the spinothalamic and the dorsal column like in relation to each other?

Answer 29

→ Parallel

Question 30

What is necessary for the localisation of pain?

Answer 30

→ primary somatosensory cortex

Question 31

Where do the lateral and the medial systems of the anterolateral system diverge?

Answer 31

→Diverge at the level of the thalamus

Question 32

Where is the cingulate gyrus?

Answer 32

→ Just above the corpus callosum

Question 33

Where do the lateral system 2nd order neurons project to?

Answer 33

→ ventral posterior nucleus of the thalamus | → primary and secondary somatosensory cortex

Question 34

Where do the medial system 2nd order neurons project to?

Answer 34

→ Midline nuclei of the thalamus | → Anterior cingulate and insular cortex

Question 35

What type of pain does the lateral system mediate?

Answer 35

→ Sensory discriminative

Question 36

What type of pain does the medial system mediate?

Answer 36

→ Affective motivational

Question 37

What are the effects of a lobotomy?

Answer 37

→ Behaviour is more docile | → loss of sensitivity to pain

Question 38

What procedure is done for intractable pain?

Answer 38

→ Anterior cingulotomy

Question 39

What are 2 endogenous opioids?

Answer 39

→ Enkephalins | → Endorphins

Question 40

Describe how the descending pathways modulate pain

Answer 40

→ 5-HT neurons project to the place where the 1st order neurons synapse with 2nd order neurons → they release NA and 5-HT which inhibits the release of substance P from the 1st order neuron → They stimulate interneurons → Interneurons inhibit the 2nd order neurons and release enkephalins

Question 41

Why does phantom limb pain occur?

Answer 41

→ The somatosensory part of the cortex that corresponds to the limb is still there

Question 42

What is chronic pain defined as?

Answer 42

→ >3 months

Question 43

What is neuropathic pain attributable to?

Answer 43

→ Nerve damage