Nociceptions & somatosensation (systems)

Question 1

What is pain?

Answer 1

An unpleasant sensroy & emotional experience associated with actual or potential tissue damage

Question 2

What are the 3 branches of pain?

Answer 2

• Acute
• Subchronic
• Chronic or clincal

Question 3

Acute pain:

• Duration
• Characteristics
• Adaptive?

Answer 3

• Duration = seconds
• Characteristics = e.g. contact w a hot surface
• Adaptive? = high - prevents or reduces damage

Question 4

Subchronic pain

• Duration
• Characteristics
• Adaptive?

Answer 4

• Duration = hours to days
• Characteristics = resolves on recovery e.g. inflamed wound
• Adaptive? = protective

Question 5

Chronic or clinical:

• Duration
• Characteristics
• Adaptive?

Answer 5

• Duration = months to years
• Characteristics = exceeds resolution of damage - oftern profound psychological components
• Adaptive? = none - maladaptive

Question 6

What are the 4 types of pain?

Answer 6

• Hyperalgesia
• Causalgia
• Allodynia
• Dysaesthesia

Question 7

What is hyperalgesia?

Answer 7

An enhanced perception of pain in response to noxious stimuli

Question 8

What is causalgia?

Answer 8

A chronic burning pain that persists in the absence of an obvious noxious stimulus

Question 9

What is allodynia?

Answer 9

Abnormal painful responses to innocuous or tactile stimuli that do not usually cause pain

(e.g. touching sunburned skin)

Question 10

What is dysaethesia?

Answer 10

Unpleasant abnormal sensations

(e.g. pins and needles)

Question 11

Why is it important that we feel pain?

Answer 11

Important to protect ourselves from stimuli that will harm us

People who suffer from genetic pain disorders can end up with serious injuries as their body does not know when to stop

Question 12

What gene mutation causes genetic pain disorders & why?

Answer 12

The gene SCN9A (sodium channel protein type 9 subunit alpha)

It codes for the alpha subunit of NaV1.7 channels = associated w a spectrum of pain disorders

Question 13

How can genetic pain disorders differ from one another?

Answer 13

Slightly different mutation of the same alpha subunit can cause a different pain disorder:

• PEPD effects the Na+ channels but causes the opposite effect to other disorders = heightenes pain response in the eyes and rectum
• Other ones affect feet & hands

Question 14

What sort of receptors do primary afferent fibres have?

Answer 14

• Mechanosensitive = low threshold
• Also have nociceptors = high threshold reponse

Question 15

What are DCRASIC channels & ASIC activated by?

Answer 15

Can be activated by blunt force trauma

Question 16

What is TRPM8 activated by?

Answer 16

By cold

Question 17

What response do ion channels have to burning?

Answer 17

Allow an influx of sodium ions into the channel as a response to burning

Question 18

What can nociceptors detect?

Answer 18

Changes in pH

The channels are not very specific to one type of stimulus

Question 19

Where do pain reflexes miss out?

Answer 19

They don’t travel to the brain

Makes the response much faster

Question 20

What are the 3 types of primary afferent fibres?

Answer 20

• Abeta fibres
• Adelta fibres
• C fibres

(These are classified by axon diameter)

Question 21

What are Abeta fibres like?

Answer 21

They are larger & usually myelinated so transmit APs very fast

30-70m/s

Question 22

What are Adelta fibres like?

Answer 22

Can be involved in touch perception & sometimes in pain too

Smaller but also myelinated, will send APs quickly to the spinal cord

2-10 m/s

Question 23

What are C fibres like?

Answer 23

Are nociceptors

Very small & unmyelinated - much slower response

1 m/s

Question 24

Where do sensory afferent nerve fibres project to?

Answer 24

The spinal cord

Question 25

What theory did Melzak & Wall, 1965 come up with?

Answer 25

The Substantia Gelatinosa & the Gate Theory of Pain

Question 26

What does the substantia gelatinosa contain?

Answer 26

Inhibitory interneurones - these have a gate keeper function

Question 27

Why do we rub an area when we hurt it?

Answer 27

Rub the area to modulate the amt of pain signals reaching the brain by doing this Dampens the signal

Question 28

Why does rubbing an area when we hurt it help to reduce the pain we feel?

Answer 28

- Pain signals are sent to sc, glutamate etc are relased on the secondary neurone to trigger a response - When rubbing the area - touch receptors around this are activated --> touch receptors are mainly Abeta = signals are sent faster than C fibres - So touch receptors synapse w an area close to C fibres & activate the inter neurons which the C fibres try to inhibit so the pain signal can be sent to the brain --> by rubbing around the area we dampen the signal that goes to the brain

Question 29

Where do most signals we recieve synapse at first and where do they move onto?

Answer 29

The thalamus They move on from there to the primary somatosensory cortex

Question 30

What is the role of the somatosensory cortex?

Answer 30

This is the area that maps our body in the brain based on the size & sensisivity of the body area More sensitive = larger area

Question 31

What do ascending fibres do?

Answer 31

Connect brainstem & midbrain

Question 32

What does the anterior cingulate cortex do?

Answer 32

Very important in concious perception e.g. we can pretend not to feel the pain, this is shutting this area off

Question 33

What are the descending pain pathways for?

Answer 33

Send signals from the brain to the SC & other parts of the body to control movement & regulate sensory input

Question 34

Where do ascending nociceptice nerves transmit signals to?

Answer 34

Not only to the higher centres in the brain, but also make connections to the brainstem & midbrain e.g. the periaqueductal grey matter (PAG) & nucleus raphe magnus (NRM)

Question 35

Where do the PAG & NRM return efferent signals to?

Answer 35

Return them downwards to various levels of the spinal cord, where, with help of inhibitory interneurones they produce a diffuse inhibition

Question 36

Summarise the Central Gate Control of Pain:

Answer 36

- PAG & NRM = important areas - Primary afferent fibres innovate skin, sent up the spinal cord, switches to the other side & then ascends up the spinal cord - Some of these synapse in NRM or PAG but most synapse in the thalamus

Question 37

Finish from descending inhibitory controls

Answer 37

:)