Define pain
An unpleasant sensory and emotional experience that is associated with potential or actual tissue damage
Explain characteristics of pain
Multidimensional phenomenon
Unobservable and defies objective measure
Personal experience
Subtle issues of definition have significant clinical implications
Cultural impacts
Describe the sensory experience of pain
The sensory-discriminative process is the ability to locate painful stimuli and describe the intensity and quality
The sensations are controlled through the afferent nerve fibres, spinal cord, brainstem and higher brain centre which results in prompt withdrawal from painful stimuli
Describe the emotional experience of pain
The unpleasantness of experiencing pain produces an emotional response which produced changes in both mental state (affect) and behaviour (motivation) which is referred to as the affective-motivational aspect of pain
The degree of response depends on the intensity and duration of the pain, past experience and treatment option/availability
The intensity of the pain experience can be modified by behaviour, cognitive and clinical interventions
What are the 3 types of pain
- Nociceptive
- Neuropathic
- Psychogenic
What is nociceptive pain
Most common type of pain
Produced by nociceptive stimuli which may cause peripheral tissue damage
Can have Noxious stimuli (mechanical (breaking bone, bruises, bumps), chemical (mediators, inflammation, etc.) and thermal (burns))
Linked more with acute pain
Is internal or external
Explain internal nociceptive pain
Less common, more severe and longer duration. Associated with disease. Treatment involves removing the cause of tissue damage. Pain relief achieved with the use of narcotic analgesia
Explain external nociceptive pain
Usually mild and duration is short in time. Involves trauma to the skin and underlying tissue. Treatment is simple- to assist in the healing process mild analgesia may be required
Explain neuropathic pain
Caused by disease or injury to the nervous system
Can be both severe and persistent (last years)
Linked more with chronic pain
Treatment may be challenging due to complex aetiology
A combination of pharmacological interventions are often required
Example: phantom limb pain in an amputee
Explain psychogenic pain
May be severe and persistent but despite investigations no underlying pathology can be found
Assumed the pain is the result of a psychological disorder
Can be debilitating and interfere with the patient’s ability to function normally
Describe acute pain
Accompanies tissue damage and inflammation (actual or potential damage)
Can lead to chronic pain if untreated
Usually lasts 3-6 months
Sharp, localized pain that may radiate
Involves fight-or-flight ANS response including tachycardia, rapid and shallow respirations, increased BP, dilated pupils, sweating, pallor and altered BGL
3 types - somatic, visceral and referred
Describe somatic acute pain
Nerve receptors in the skin and close to body surface
Describe visceral acute pain
From body organs and is commonly dull and poorly localised due to small number of nociceptors
Describe referred acute pain
Pain felt in an area different from the site of stimuli and commonly occurs with visceral pain
Describe chronic pain
Lasts longer than 3-6 months
Not always associated with an identifiable cause
Can be treated with non-pharmacological treatments
Patients may experience muscle deconditioning, alterations in appetite and weight, sleep disturbances, other psychological behaviours such as drug dependence, distorted beliefs, anxiety, anger, frustration, depression and hopelessness
Examples: arthritis, lupus, back pain
Explain breakthrough pain
Occurs between doses of analgesia
Can be prevented by increasing the frequency of analgesia, increasing the dose or commencement of controlled (slow) release analgesia
There are two types:
1. Hyperalgesia: increased pain in response to a stimulus that is normally painful
2. Allodynia: pain that results from a stimulus that does not normally produce pain
Explain the pathway of how pain is perceived
Pain is perceived in the cerebral cortex by a 3-order neuronal pain pathway
PNS consists of sensory and motor neurons
Nociceptors are the nerve receptors of pain
They only respond to a stimulus of sufficient intensity to threaten the integrity of the tissue they innervate
What are the two types of cutaneous (skin) nociceptors
- High Threshold Mechanoreceptors: responsible for initial feeling of sharp, stabbing-like pain
- Polymodal Nociceptors: responsible for the duller, aching sensation felt a few seconds after the initial sharp pain
List the steps of pain pathway
- A noxious stimulus (mechanical, chemical or thermal) creates the activation of the cascade of chemical mediators to be released such as:
- TRANSDUCTION: Chemical mediators bind to nociceptors and initiate pain impulses (if reach threshold) which are generated along first order neurons (nociceptors/sensory neurons- high threshold and polymodal) towards the dorsal horn of the spinal cord (dorsal is the back of the spinal cord)
- TRANSMISSION: sensory neurons enter through dorsal horn of spinal cord where they cross over and synapse with second order neurons (spinothalamic neurons) (substance P released during synapse, this is what is contained in the vesicles)
- PERCEPTION: Impulse ascends along spinothalamic tract towards the thalamus of the brain so information can be relayed to other parts of brain
- In thalamus, spinothalamic neurons synapse with thalamocortical neurons (third order neurons) which are responsible for taking the information to the somatosensory cortex (parts of the cerebral cortex which correspond with different parts of the body e.g. part for the hand, the leg, the trunk, etc., which are on both LH and RH sides)
- Once reaching somatosensory cortex, a response to that pain will be generated
- MODULATION: Impulse sent down descending pathway through periaqueductal grey matter of spinal cord. Continues to descend until it comes to the nucleus raphe magnus of the spinal cord where it synapses with another descending neuron. This neuron travels towards the dorsal horn of the spinal cord where it will try to inhibit/control the synapse between the first and second neurons of the ascending pathway
- The neuron from the descending pathway contains serotonin and noradrenaline which bind to receptors of pre-synaptic neuron to inhibit release of substance P. Also stimulate opioid interneuron in the Substantia Gelatinosa which releases opioid that inhibits release substance P and inhibits post-synaptic neuron from becoming depolarised - this stops the transmission of the nerve impulse
What is the main role of the descending pathway
To get rid of the pain (inhibits ascending pathway)
What is the specific area of the dorsal horn where sensory neurons enter
Substantia Gelatinosa
Where does info from right side of body go to in the brain
The Left side (crosses over in spinal cord) - always the opposite
What is a chemical inhibitory mechanism
Endorphins are naturally occurring opioid peptides
Are present in neurons in the brain, spinal cord and GI tract
Endorphins attach to the opiate receptors and inhibit the transmission of pain impulses
What is neuropathic pain
When the NS is affected by injury or disease there is an inability to perceive pain and as a consequence neuropathic pain results
Peripheral neuropathic pain results from damage to the peripheral NS and can result from physical injury, disease, infection and toxicity
