Nociception: Physiologic process that communicates tissue damage to the CNS
Involves 4 processes:
Transduction – occurs when there is release of chemical mediators
Noxious stimuli cause cell damage with the release of sensitizing chemicals
Prostaglandins
Bradykinin
Serotonin
Substance P
Histamine
These substances activate nociceptors and lead to generation of action potential
Transmission – involves the conduct of the action potential from the periphery (injury site) to the spinal cord and then to the brainstem, thalamus, and cerebral cortex
Action potential continues from
Site of injury to spinal cord
Spinal cord to brainstem and thalamus
Thalamus to cortex for processing
Perception – conscious awareness of pain
Conscious experience of pain
Modulation – involves signals from the brain going back down the spinal cord to modify incoming impulses
Neurons originating in the brainstem descend to the spinal cord and release substances (e.g., endogenous opioids) that inhibit nociceptive impulses
Classification of Pain
By underlying pathology
Nociceptive: Somatic or Visceral
Neuropathic: CNS or PNS Damage
By durationĀ
Acute
Chronic
Acute Pain
Sudden onset
Less than 3-month for normal healing to occur
Mild to severeĀ
Generally a precipitating event or illness can be identified
Manifestations reflect sympathetic nervous system activation:
Increased heart rate
Increased respiratory rate
Increased blood pressure
Chronic pain
Persistent pain and causes may be unknown
Gradual or sudden onset
More than 3-month duration; may start acute but continues past normal recovery time
Does not go away; characterized by periods of waxing and waning
Behavioral manifestations
Decreased physical movement/activity
Fatigue
Withdrawal from others and social interaction
Can be disabling and accompanied by anxiety and depression