Lecture 3 - Pain

Question 1

Pain definition

Answer 1

An aversive sensory and emotional experience typically caused by actual or potential tissue injury

Question 2

Nociception vs. pain

Answer 2

Nociception refers to the sensory signals, pain includes the emotional interpretation

Question 3

Congenital insensitivity to pain (CIP)

Answer 3

Genetic disorder that results in the inability to experience pain, the ability to feel touch is still intact

Question 4

CIP mutation

Answer 4

SCN9A gene, codes for the Nav1.7, mutation results in the inability to produce nociceptive action potentials, cannot sense thermal or mechanical pain as a result

Question 5

Leprosy and pain

Answer 5

Leprosy is a bacterial infection that affects nerves, respiratory tract, skin, and eyes, causes an inability to feel pain

Question 6

Acute pain

Answer 6

Has a protective function, warns of immediate or imminent tissue damage, a normal function of the PNS and CNS, well defined temporal onset, treatment options work effectively

Question 7

Spinal reflex arc

Answer 7

1. Sensory receptor is activated
2. Action potential propagates through afferent sensory neuron
3. Spinal cord integrates the signal, afferent neuron will stimulate a number of interneurons
4. Efferent pathways stimulate muscle contraction/relaxation to remove limb from the stimulus
5. The muscles are effectors which withdraw from the painful stimulus

*Any signal to the brain is beyond the reflex arc

Question 8

Types of nociceptors

Answer 8

• Mechanical nociceptors
• Thermal nociceptors
• Chemical nociceptors

Question 9

Nociceptive afferent fibre names

Answer 9

A-delta or C-fibre

Question 10

A-delta vs. C-fibres

Answer 10

A-delta: fast pain, temperature. thicker and faster than c-fibres, myelinated, muscle axons III.

C-fibres: slow pain, temperature, itch (duller pain sensation). thinner and slower than a-delta, unmyelinated, muscle axons IV.

Question 11

Types of neurons in the dorsal horn

Answer 11

Sensory neurons

Question 12

Types of neurons in the ventral horn

Answer 12

Motor neurons

Question 13

Ascending pain pathways

Answer 13

1. Lateral spinothalamic tract
2. Spinoreticular tract
3. Spinomesencephalic tract

Question 14

Lateral spinothalamic tract

Answer 14

Projects to thalamus then sensory cortex, determines intensity & location

Question 15

Spinoreticular tract

Answer 15

Projects to reticular formation, then to other brain areas such as the thalamus and hypothalamus. involves the autonomic, motor, and sensory pain responses. motivational, affective, and aversive (emotional) aspects of pain.

Question 16

Spinomesencephalic tract

Answer 16

Projects to midbrain. activates the periaqueductal gray which produces endogenous analgesia. involves the affective and aversive behaviours of pain, such as fear.

Question 17

Where does localization of pain occur

Answer 17

Somatosensory cortex

Question 18

Where does the perception of pain occur

Answer 18

Thalamus

Question 19

Where do the behaviour and emotional responses to pain occur

Answer 19

Hypothalamus, limbic system

Question 20

Which brain area causes increased alertness as a result of painful stimuli?

Answer 20

Reticular formation

Question 21

Nociceptive receptors are

Answer 21

Free nerve endings

Question 22

Factors that affect pain perception

Answer 22

• Context
• Cognition
• Mood
• Pathology
• Injury
• Genetics

Question 23

Gating of pain

Answer 23

Pain signals from periphery never reach the brain. by rubbing the injury, touch and pressure fibers are activated which causes the “gate” in the spinal cord to close. the pain signals are still being sent via pain fibers, but do not reach the brain.

Question 24

Descending inhibitory pain pathways

Answer 24

• Periaqueductal grey matter (PAG)
• Locus coeruleus (LC)
• Rostral ventromedial medulla (RVM)

Question 25

Periaqueductal grey matter (PAG)

Answer 25

Release enkephalins, mediated by opioid receptors

Question 26

Locus coeruleus (LC)

Answer 26

Releases norepinephrine, alpha2-adrenergic receptors inhibit pre-synaptic and post-synaptic pain transmission, alpha1-adrenergic receptors release GABA from interneurons

Question 27

Rostral ventromedial medulla (RVM)

Answer 27

Release serotonin, 5-HT is the serotonin receptor

Question 28

Chronic pain

Answer 28

No known function, neuropathic or inflammatory, poorly defined temporal onset (the pain persists), limited treatment options

Question 29

Allodynia

Answer 29

Sensation of pain in response to a stimulus that would not typically produce pain, a lowered pain threshold

Question 30

Hyperalgesia

Answer 30

Increased sensitivity to pain, a stimulus that normally causes pain will feel more painful

Question 31

Central sensitization

Answer 31

Increased responsiveness of nociceptive neurons in the central nervous system, the processes that inhibit and heighten pain are imbalanced which causes an exaggerated pain response

Question 32

Peripheral sensitization

Answer 32

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

Question 33

Functional switching after peripheral nerve injury

Answer 33

Nerve responds more intensely after injury

Question 34

Sex differences in pain

Answer 34

Women have a lower pain tolerance and have higher prevalence of chronic pain

Question 35

Spontaneous pain

Answer 35

Pain without a stimulus, recurring pain