pain and nociception Flashcards
define pain
pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage
describe physiological responses to pain
- increased HR
- increased BP
- increased RR
- decreased gastric motility
- decreased BF to viscera, skin and kidneys
- nausea
- pallor
- dilated pupils
define pain threshold
the point at which a stimulus is perceived as pain
define pain tolerance
duration or intensity of pain that an individual will tolerate before initiation of overt pain response
situations that decrease ones tolerance to pain
- repeated exposure
- fatigue
- anger
- sleep deprivation
- boredom
situations that increase ones tolerance to pain
- alcohol consumption
- medication
- hypnosis
- warmth
- distracting activities
age and perception of pain
newborns = less sensitive to pain
children= lower threshold than adults
adults = threshold tends to increase with ageing
define analgesia
absence of pain in response to stimulation that would normally be painful
define anaesthesia
absence of ALL sensory modalities
define hyperalgesia
an increased response to a stimulus that is normally painful
define allodynia
pain due to a stimulus that is not normally painful
define nociception
the sensory process of detecting tissue damage
define noxious stimulus
a noxious stimulus is one that is due to an event potentially or actually damaging to body tissue
what are the four basic processes involved in nociception (the sensory process for detecting tissue damage)
- transduction
- transmission
- perception
- modulation
define nociceptors and 3 categories of noxious stimuli
nociceptors are the peripheral free nerve endings of primary sensory neurons reactive to noxious stimuli (high threshold)
stimuli
- mechanical (pressure, swelling)
- thermal (burn, scald)
- chemical (excitatory NT, toxic substance)
characteristics of C pain fibres and receptor type
- primary afferent fibres
- small diameter
- unmyelinated
- slow conducting
receptor type = polymodal
-respond to more than one type of noxious stimuli
characteristics of A-delta fibres and receptor type
- primary afferent fibres
- medium diameter
- myelinated
- fast conducting
receptor type =
- responds to noxious mechano-thermal stimuli over a certain intensity
difference in pain quality between C fibres and A-delta fibres
C fibres
- diffuse
- dull
- burning
- aching
- referred to as slow or second pain
A-delta fibres
- well-localised
- sharp
- stinging
- pricking
- referred to as fast or first pain
describe the process of transduction
sensory cells convert external painful stimuli into electrical signals (AP)
describe the process/pathway of transmission
primary afferents -> DH -> brain stem -> thalamus -> sensory cortex
nociceptor excitation is conducted to the sensopry cortex via a combination of electrical (AP) and chemical (NT)
what are the 2 main classes of dorsal horn cells (secondary order neurons)
- nociceptive specific (rexed lamina 1 & 2)
- respond to only noxious stimuli: C & A-delta fibers - wide dynamic range (rexed lamina 5)
- respond to both painful & non-painful fibers
describe endogenous opioids
substances produced in the body that can activate opioid receptors
e.g. endorphins
perception of pain
is multi-dimensional
reticular system:
-autonomic & motor response to pain
limbic system:
-emotional & behavioral responses
somatosensory cortex
-perception & interpretation of sensations
modulation of perception of pain
there is a difference between objective reality and subjective response to pain. Explaining that there is a mechanism in the body that MODULATES pain perception
pain dampening
down-regulation
- segmental inhibition
- descending inhibitory nerve system
gate control theory
based on the premise that a gate, located in the dorsal horn of the spinal cord, modulates the afferent nerve impulses
implies that a non-painful stimulus can block the transmission of a noxious stimuli
3 input variables that affect the gate control theory
- A-delta and C fibers - open gate
- A-beta fibers that carry messages of light touch - close gate
- messages from the brain - open/close
the mechanism involved in keeping the ‘gate’ closed
there are special inhibitory interneurons in the spinal cord which keep the gate closed.
these neurons make a pain-blocking endogenous opioid called enkephalin
this is an opioid-like which blocks NT release from C and A-delta fibers and this keeps the gate closed
give examples that open and close the ‘gate’
open
- extend of injury
- anxiety
- boredom
close
- medication
- relaxation
- distraction
- positive emotions
describe the process and different fibers involved in bumping your head
- initial trauma activates A-delta fibres
- eventually C fibres
- rubbing area stimulates A-beta fibres which activates the DH to close gate
define the term windup
increased AP output from the DH cells in response to sustained low Hz input from nociceptive afferents via C fibres to the DH neurones
mechanism of windup
receptor on DH neurons are stimulated by C fibres due to a continuous stimuli for an extended period of time. causing increased Ca2+ influx into DH neurons. This leads to pathophysiologic changes by lowering threshold of receptors. thus becoming more sensitive to inputs resulting in hyperalgesia or allodynia
types of pain
- nociceptive (tissue damage)
- neuropathic (damage to nerve fibers)
- inflammatory
- referred
nociceptive pain pathway
- tissue damage causes release of mediators e.g. OG, serotonin, ACh
- mediators stimulate pain receptors
- process of transduction, transmission, perception and modulation takes place
describe the 2 types of inflammation
non-neurogenic
- release of inflammatory substances from BVs & CTs
- e.g. histamine, PG, cytokines
neurogenic
- release of neuropeptides from C-fibre terminals - e.g. noradrenaline, substance P
describe the non-neurogenic inflammatory pathway
- tissue damage
- inflammatory mediators (e.g. mast cell, macrophages) release substances
- substances sensitive receptors and lower threshold
- more pain felt
= peripheral sensitisation
-primary hyperalgesia
neuronal plasticity
changes to the neuronal anatomy & physiology in DR
due to prolonged pain with no treatment
Very difficult to treat
enkephalin
is an endogenous opioid - inhibitory interneuron
blocks neurotransmitter release from C and A-delta fibers
-keeps gate closed
