Lecture 3 - Pain Flashcards
Pain definition
An aversive sensory and emotional experience typically caused by actual or potential tissue injury
Nociception vs. pain
Nociception refers to the sensory signals, pain includes the emotional interpretation
Congenital insensitivity to pain (CIP)
Genetic disorder that results in the inability to experience pain, the ability to feel touch is still intact
CIP mutation
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
Leprosy and pain
Leprosy is a bacterial infection that affects nerves, respiratory tract, skin, and eyes, causes an inability to feel pain
Acute pain
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
Spinal reflex arc
- Sensory receptor is activated
- Action potential propagates through afferent sensory neuron
- Spinal cord integrates the signal, afferent neuron will stimulate a number of interneurons
- Efferent pathways stimulate muscle contraction/relaxation to remove limb from the stimulus
- The muscles are effectors which withdraw from the painful stimulus
*Any signal to the brain is beyond the reflex arc
Types of nociceptors
- Mechanical nociceptors
- Thermal nociceptors
- Chemical nociceptors
Nociceptive afferent fibre names
A-delta or C-fibre
A-delta vs. C-fibres
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.
Types of neurons in the dorsal horn
Sensory neurons
Types of neurons in the ventral horn
Motor neurons
Ascending pain pathways
- Lateral spinothalamic tract
- Spinoreticular tract
- Spinomesencephalic tract
Lateral spinothalamic tract
Projects to thalamus then sensory cortex, determines intensity & location
Spinoreticular tract
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.
Spinomesencephalic tract
Projects to midbrain. activates the periaqueductal gray which produces endogenous analgesia. involves the affective and aversive behaviours of pain, such as fear.
Where does localization of pain occur
Somatosensory cortex
Where does the perception of pain occur
Thalamus
Where do the behaviour and emotional responses to pain occur
Hypothalamus, limbic system
Which brain area causes increased alertness as a result of painful stimuli?
Reticular formation
Nociceptive receptors are
Free nerve endings
Factors that affect pain perception
- Context
- Cognition
- Mood
- Pathology
- Injury
- Genetics
Gating of pain
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.
Descending inhibitory pain pathways
- Periaqueductal grey matter (PAG)
- Locus coeruleus (LC)
- Rostral ventromedial medulla (RVM)
Periaqueductal grey matter (PAG)
Release enkephalins, mediated by opioid receptors
Locus coeruleus (LC)
Releases norepinephrine, alpha2-adrenergic receptors inhibit pre-synaptic and post-synaptic pain transmission, alpha1-adrenergic receptors release GABA from interneurons
Rostral ventromedial medulla (RVM)
Release serotonin, 5-HT is the serotonin receptor
Chronic pain
No known function, neuropathic or inflammatory, poorly defined temporal onset (the pain persists), limited treatment options
Allodynia
Sensation of pain in response to a stimulus that would not typically produce pain, a lowered pain threshold
Hyperalgesia
Increased sensitivity to pain, a stimulus that normally causes pain will feel more painful
Central sensitization
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
Peripheral sensitization
Increased responsiveness and reduced threshold of nociceptive neurons in the periphery to the stimulation of their receptive fields
Functional switching after peripheral nerve injury
Nerve responds more intensely after injury
Sex differences in pain
Women have a lower pain tolerance and have higher prevalence of chronic pain
Spontaneous pain
Pain without a stimulus, recurring pain
