Pain Flashcards
define pain
Unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage.
Journey of pain
Sensory neurones called nociceptors stimulated
Impulse transmitted through peripheral nerve into spinal cord
Continues up to thalamus and then sensory cortex
Sensory cortex perceives it as pain
Pain is physical response to injury
Females vs males
Males suffer worse pain treated by female practitioners
Women more likely to be chronic pain sufferers than men
Pain is physical and emotional experience and can be linked to social values and past experiences of pain.
Pain can be inconsistent
Sometimes pain can be inconsistent with amount of structural damage present
Pain perceived differently in people as brain makes sense of pain related to memories, fears and emotions
Types of sensory receptors
Sensory receptors relay info to our brain to sensory cortex
They can be:
SPECIAL SENSES= Vision, hearing, balance, taste and smell
SOMATORY SENSORS= Detect touch, pressure, vibration, thermal stimuli, proprioception and pain (nociceptors).
3 important nerve fibres for pain
DELTA FIBRES (nociceptors)- small diameter and myelinated. Respond to mechanical and thermal stimuli Rapid and sharp pain signals sent up delta fibres Produce initial reflex response to acute pain
C- fibres (nociceptors)- unmyelinated and smallest type of nerve fibre. Slowest conduction and respond to chemical, mechanical and thermal stimuli.
Slow burning pain.
A-beta fibres (mechanoreceptors)- highly myelinated and large diameter. Rapid signal conduction and low activation threshold.
Respond to light touch + transmit non painful info, mechanical stimuli and thermal stimuli.
Summary=
Delta and C fibres carry pain signals to brain and a-beta fibres carry non-painful signals
Classes
A fibres (alpha, beta, gamma and delta)
4-20 micrometers
Highly myelinated
Conduction is 150 m/s
B fibres
2-4 micrometers
Moderately myelinated
18 m/s
C fibres
Less than 2 micrometers
Unmyelinated
1 m/s
General rule about thickness
Thicker a fibre, more myelination it has, and faster conduction speed of the fibre
ALPHA nerve
Information about proprioception
A- beta nerve
Carries info relating to touch
A delta fibres
Carries info related to sharp, fast pain
C fibres
Carry info related to slow burning pain
What is substantia gelatinosa?
Neurones that Cary info to brain about pain and temperature in the right side of posterior norm
Corresponds to lamina rex on other posterior horn
What neurotransmitters enable pain to transfer from neurone one to two ?
Glutamate
Substance P
Signals of pain from PNS to CNS
Nociceptors stimulated
Signal sent along afferent neurone - first order neurone
The a-delta or c fibres transmit info to specific neurones in spinal cord dorsal horn called Rex lamina
The info crosses from first to second neurone via glutamate and substance P to carry sensory info over junction in posterior horn of spinal cord
PNS part was nociceptors stimulating and first order neurone
CNS part is spinal cord, second order neurone and the brain to sensory cortex where third neurone goes
Second order neurone transmits the sensory info up to thalamus and synapses with 3rd order neurone to sensory cortex
Junction between first and second neurone is where we can modulate pain
The two main ascending pain pathway are:
Lateral spinothalamic tract
Spinoreticular tract
Spinothalamic tract
Carries main pain signals
From dorsal horn via second order neurone with a projection to PAG grey matter- ends at thalamus to connect to third order neurone
Spinoreticular tract
Laterally to the spinothalamic tract
Ascends to the reticular formation in brainstem then onto thalamus to connect with third order neurone
The spinoreticular tract plays a role in MEMORY and EMOTIONAL aspects of pain
Descending pathways ?
We have some descending pathways to try and control and inhibit the pain ascending pathways
How do descending pathways work ?
They come from the PAG, down to the nucleus raphe magnus and synapse withsecond and first neurones
Junction between first and second neurones = descending Pathway communicates with interneurones and stops messages being sent from first to second neurone
Pain transmission + descend tracts
Normally ;
Pain stimulus from receptors
Alon first order neurone to junction to second
Pain transmits over the gap via substance P and glutamate
Second neurone crosses over at spinal cord
Ascends to thalamus
Synapses with third at thalamus and goes to sensory cortex
NEURONE FROM DESCENDING PATHWAY
Comes from PAG
Connects with junction
Inhibits substance P so pain signal does not cross
Also stimulates interneurone in substantia gelatinosa to release opioid
Stops signals being transmitted along second order neurone
Nociceptors
Free nerve endings
Detect thermal, mechanical and chemical, stimuli
Found in muscles, skin, joint capsule and internal organs
PAIN PATHWAY
Nociceptors stimulated by painful stimulus
Action potential formed + a delta and c fibres send pain signal along first neurone to dorsal horn
Info transmitted across junction to second order neurone via neurotransmitters glutamate and substance P
Second neurone crosses spinal cord up to thalamus
Synapses and third order neurone up to sensory cortex
Descending pain pathway comes from PAG of midbrain and nucleus raphe magnus of medulla
They inhibit substance P
Stimulate interneurone in substantia gelatinosa so opioid released
Registering pain in brain
Dull ache pain is slow
Sharp pain travels fast
Pain messages at thalamus - transferred to limbic system and sensory cortex
Located : source of injury, assess damage and course of action
Sensory cortex activates automatic response systems
Eg, increase blood flow to tissue damage
Release pain suppressing chemicals to stop pain messages transmitting over junction in spinal cord
Limbic system and pain
Associated emotions of pain like sadness, frustration, anxiety and fear. That can make pain more or less intense
Reflex
Rapid automatic response , no conscious thought
Immediate response to harmful scenarios
Spinal reflex occurs in grey matter of spinal cord and initiated reflex arc
How does reflex work?
Sensory neurones in tissue stimulated
Info passed down first neurone
Goes through interneurone from post to ant horn
Motor info directly sends the info to effect organ
Automatic response initiated at the effectors eg, moving limb out of fire
Pain gate
Rub it better - means activating a beta fibres to inhibit pain signals to brain (BETA makes it BETTER)
C fibres would slowly transmit pain across junction to second neurone, but if we rub it better we activate a beta fibres that travel faster.
They arrive faster and close the pain gate
If no stimulus = pain gate closed
If we activate a beta fibres by pressure, inhibitory inyerneuron inhibits substance P (stops pain signal transmission).
Substantia gelatinosa excited and closes pain gate, no passage of pain up to brain
If we activate a delta and C fibres, pain transmits from first to second neurone and up to brain
Inhibitory interneuron is inhibited so pain gate is open
Unmodulated pain
C fibres transmit slow dull pain to junction between first and second neurones, crosses due to neurotransmitters and then goes up to brain perceived as pain in CNS
Modulated pain.
C fibres send signals to junction BUT we have activated a beta fibres too
A beta fibres travel faster
Cross at junction UP TO BRAIN
reduces transmission of c fibres, causing modulation of pain
TREATMENTS TO CLOSE PAIN GATE
SEC
State of mind = anxiety opens pain gate, more pain to brain
If we relax, we can activate substantia gelatinosa and close the pain gate
Encephalins and endorphins - opioid release closes pain gate (from interneuron in SG)
Levels of this increased in exercise
Central control- brain can affect pain gate as it controls memories, past experiences and response strategies to the pain,
Types of pain
Always call neighbours nosy please
ACUTE pain- lasts less than 3 months
CHRONIC PAIN- persistent pain lasting more than 3 months
NOCICEPTORS PAIN- pain caused by stimulating nociceptors in soft tissue, eg bump your elbow
NEUROPATHIC PAIN- damage to nervous system by burning pain or altered sensations. Disorders of peripheral neuropathic or central neuropathic pain
PSYCHOGENIC PAIN- pain brought by psychological factors
CHRONIC PAIN
10% of patients have chronic persistent pain
Beyond time of healing
Unknown
Maybe pathology , eg cancer damaging tissues or arthritis
Also DYSFUNCTIONAL NOCICEPTIVE SYSTEM.
Modifies CNS so patient more sensitive and more pain
Peripheral sensitisation - increased sensitivity to afferent nerve stimulation
Also may spread to other parts of body with no pathology - central sensitisation , constant state of high reactivity
Can cause
Central sensitisation can cause
Widespread hyperalgesia= enhanced sensitivity to pain
Allodynia= pain from stimuli that aren’t usually painful
Chronic pain state
A healthy person can have descending inhibition but in central sensitisation, malfunction to descending pathways so they experience more pain in painful stimuli and pain in non-painful stimuli
Example
Patient with knee osteoarthritis pain
Peripheral sensitisation
Changes to CNS
Central sensitisation
Widespread pain, hyperalgesia and allodynia
Nociceptors pain
Visceral pain - activates receptors in abdominal, pelvic and thoracic organs
Somatic pain- receptors in skin, joints and muscles activated
