The Nociceptive System and Pain Perception The Peripheral Nervous System

Question 1

feeling

Answer 1

What we feel is usually a very good measure of what is occurring at the tissues.
Assumes that perception (what we feel) accurately represents the stimulus - but we often try to measure the stimulus by our perception (what we feel).

Question 2

What is a brain and how plastic is neuronal function?

Answer 2

A single interneuron adaptively modulates activity in 50,000 neurons, enabling consistently sparse codes for odors.
• ~100,000,000 neurones
• Each can make 1000s of synapses
• Dendrites move 30% of their length to find new connections.
• Millions of synapeses are linking up and unlinking every second

Question 3

A Neurotag associated with pain

Answer 3

1. Spinal cord input
2. Hippocampus: memory, spatial recognition, fear conditioning
3. Hypothalamus/Thalamus: stress responses, autonomic regulation, motivation
4. Sensory cortex: discrimination of symptoms region
5. Cingulate cortex: concentration/focus, surrounds corpus callosum
6. Amygdala: fear, fear conditioning, addiction
7. Prefrontal cortex: problem solving, memory
8. Cerebellum: movement and cognition
9. Premotor/motor cortex: organise and prepare movements / muscle activation

Question 4

Pain is the opposite of pleasure

Answer 4

grouped with emotions and appetites not sensation. Motivation for avoidance behaviour.

Question 5

Is acute pain different to chronic pain?

Answer 5

l. Sensory-discriminative dimension
II. Cognitive-evaluative dimension
III. Motivational-affective dimension
3 all link together to cause
Intensity, location, quality & behaviour of pain.
Anticipation, attention and influence of previous experiences

Question 6

Is acute pain different to chronic pain?

Answer 6

• Acute pain has an inherent biological function;
  it is a warning for actual or potential physiological harm.
• Acute pain or nociceptive pain occurs when a strong, noxious stimulus impacts the skin or deep tissues.
• Acute pain stops quickly after the noxious stimulus is removed, often long before the healing is completed, a process that may take a few days or weeks.
  even before healing is completed.

Question 7

Acute Pain

Answer 7

The characteristics of acute pain are a combination of tissue damage, pain and anxiety.
…There is anxiety about the future consequences of the injury…
The assessment of this threat and therefore the degree of anxiety will depend on factors such as personality and experience.
Acute pain, then, encompasses he unpleasantness of past injury and the hope of future recovery

Question 8

IASP and NHMRC definitions of Acute Pain

Answer 8

pain of recent onset and probable limited duration. It usually has an identifiable temporal and causal association with injury or disease.

• Increased understanding of the mechanisms of acute pain has led to improvements in clinical management and in the future it may be possible to more directly target the pathophysiological processes associated with specific pain syndromes.
  It entirely possible to generally impact a range of pathophysiological / nociceptive / perceptive processes associated with pain syndromes.

Question 9

IASP and NHMRC definitions of Chronic Pain

Answer 9

Commonly persists tissue healing and there may not be any identifiable cause

• clinical benchmark is 3 months
• Acute and chronic pain may represent a continuum rather than distinct entities.

Question 10

Important terms = Noxious stimulus

Answer 10

A stimulus that is damaging or threatens damage to normal tissues.

Question 11

Important terms - nociceptor

Answer 11

Nociceptor: A high-threshold sensory receptor of the peripheral somatosensory nervous system that is capable of transducing and encoding noxious stimuli. Note:

i) Avoid use of terms like pain receptor, pain pathway, etc.
ii) With sensitisation, the ‘nociceptor’ can respond to non-noxious stimuli.
- unmylennated

Question 12

Important terms - Nociception

Answer 12

The neural process of encoding noxious stimuli (not perception).

Question 13

Important terms - Pain threshold

Answer 13

The minimum intensity of a stimulus that is perceived as painful (variable within and between individuals).

Question 14

Important terms - Sensitization

Answer 14

Increased responsiveness of nociceptive neurons to their normal input, and/or recruitment of a response to normally subthreshold inputs.

• Sensitization can include a drop in threshold and an increase in suprathreshold response. Spontaneous discharges and increases in receptive field size may also occu

Question 15

Important terms - Hyperesthesia:

Answer 15

Increased sensitivity to cutaneous stimulation including touch and thermal sensation without pain, as well as to pain i.e. Diminished threshold to any stimulus and an increased response to stimuli that are normally recognized. Note: The stimulus and locus should be specified.

Question 16

Important terms - Hyperalgesia

Answer 16

An increased response to a stimulus which is normally perceived to be painful. Note: Hyperalgesia
i) reflects increased pain on suprathreshold stimulation.
ii) is a consequence of perturbation of the nociceptive system with peripheral or central sensitization, or both
Primary hyperalgesia: at the site of injury
Secondary hyperalgesia: at uninjured skin surrounding the site of injury.

Question 17

Important terms - Allodynia

Answer 17

Lowered threshold for pain perception, so that pain is perceived with a stimulus which does not normally provoke pain. Touch, light pressure, or moderate cold or warmth evoke pain when applied to apparently normal skin. Seen in patients with lesions of the nervous system.

Question 18

Important terms - Central sensitization

Answer 18

Increased responsiveness of nociceptive neurons in the central nervous system to their normal or subthreshold afferent input. This may include increased responsiveness due to dysfunction of endogenous pain control systems.

• either amplifyign whats coming in or not doing enough

Question 19

Important terms - Peripheral sensitization

Answer 19

Increased responsiveness and reduced threshold of nociceptive neurons in the periphery to the stimulation of their receptive fields.

Question 20

Important terms - Peripheral neuropathic pain

Answer 20

Pain caused by a lesion or disease of the peripheral somatosensory nervous system.