Chapter 47: Pain Flashcards
Define Pain
Symptom of an underlying problem
Define and explain the pathophysiology of the first stage of pain
- How does tissue injury occur?
Transduction: the stimulus
- Converting painful stimulis to neuronal action potentials at sensory level via nociceptors
- Chemical mediators alter membrane potential of pain receptor
Tissue injury:
- Results in the release of prostaglandins from the breakdown of phospholipids in cell membranes. Nonsteroidal anti-inflammatory drugs (NSAIDs) inhibit the cyclooxygenase enzyme and block the production of prostaglandins.
Define and explain the pathophysiology of the second stage of pain
- What are the specialized sensory fibers used?
- Explain the process transmission
Transmission: the AP transmitted through spinal cord to brain by specialized sensory fibers
Specialized Fibers
- A-beta Fibers: myelinated, 10%, fast, sharp/stinging sensation
- C Fibers: unmyelinated, 90%, slow, dull/aching sensation
Process of Transmission:
- Aδ and C fibers enter the dorsal horn
- Synapse on interneurons
- Cross to the opposite side (travel through 1-8 laminae)
- Travel to the brain in the anterolateral tract
Define and explain the pathophysiology of the third stage of pain
Perception: interpreting the pain - result of neural processing of the pain sensation in the brain
- Influenced by parameters: awareness, emotions, previous experiences, expectations, culture, physical status, etc.
Define and explain the pathophysiology of the fourth stage of pain
- Where does it occur?
Modulation: negative feedback; mechanism whereby synaptic transmission of pain signals are altered by endogenous opioids
- Descending pathways from raphe magnus release neurotransmitters that can inhibit synaptic transmission of pain signals (occurs in substantia gelatinosa by release of norepinephrine)
Define Nociceptors
Free nerve endings that transduce noxious stimuli into AP
What type of fiber is used the initial stage of an injury?
A-beta Fiber
- Acute pain
- Ex. Breaking a bone
What type of fiber is used after the initial stage of an injury
C Fiber
- Healing process
- Not as intense
Explain the gate control theory
- 3 Close / Open Factors
- Importance?
The idea that there is a gate in the back of the spinal cord that will modulate afferent nerve impulses; non-painful stimulus blocks painful stimulus
Factors
1) Activity in pain fiber = opens
2) Activity in sensory nerves = closes
3) Messages from brain = concentrate on pain or not thinking about it
Importance
- Prevents pain stimulus from reaching CNS
What are the first-order neurons?
- Nociceptive signals are transmitted from the periphery by nociceptive sensory neurons (first-order primary afferent neurons
- The peripheral terminals are clustered with ion channels
- The transduction of external noxious stimuli is initiated by membrane depolarization due to the activation of these ion channels
What are secondary-order neurons?
- Action potentials are conducted along the axons of nociceptive A- and C-fibres, through the cell body in the dorsal root ganglion to the axonal terminals, which form the presynaptic element of central synapses of the sensory pathway in the spinal dorsal horn or hindbrain
- The central terminals of A- and C-fibres synapse with interneurons and second-order nociceptive projection neurons, primarily within the superficial laminae of the spinal dorsal horn
- The axons of second-order nociceptive projection neurons decussate at the spinal cord level, joining the ascending fibres of the anterolateral system, and project to brainstem and thalamic nuclei, transferring information about the intensity and duration of peripheral noxious stimuli
What are the third-order neurons?
- No single brain region is essential for pain, but rather pain results from the activation of a distributed group of structures
- Third-order neurons from the thalamus project to several cortical and subcortical regions that encode sensory-discriminative, emotional, and cognitive aspects of pain
What are the segments of laminae in the dorsal horn?
- 1-3 (substantia gelatinosa) important because where transmission may be interrupted through modulation
- 5 lamina receives info on pain from body surface and internal organs (brain cannot distinguish between the two - referred pain)
- 6-8 laminae receives info originating from internal structure
How does the brain localize pain sensation?
Nociceptors are kept in specific anatomic order in the cord (sensory dermatomes) and somatosensory cortex
- Note: Pain located in the pattern of a dermatome occurs with spinal nerve injury and is referred to as radiculopathy
Define Pain threshold
Level of pain stimulation required to be perceived
- Without this = no pain
Define Pain Tolerance
Degree of pain an individual is willing to bear before seeking relief
- Varies amongst individuals
Define Pain Expression
Way in which pain experience is communicated to others
- Varies amongst individuals
Why do some individuals not experience/feel pain?
Pathological problem
- Tolerate pain until they perceive the pain as a threat and need to relieve it; they have a high pain tolerance
- Ex. Carrying weights with body parts that are not built to support these actions
Name the 2 types of Pain
1) Physiological Pain: Tissue injury has occurred; caused by injury of tissue; goes away after healing process
2) Pathological Pain: occurs after tissue injury, but long-term changes occur both within peripheral and CNS; changes occur along somatosensory pathways from the periphery to the cortex
- Hyperalgesia: pain can be significantly enhanced
- Allodynia: Non-noxious stimuli may cause pain
- Can have no beneficial purpose
Classification of Pain: Duration
- Acute: serves as a protective function (assists repair of tissue)
- Chronic: Usually more than 6 months of healing time, increased peripheral sensitivity, increased gain of nociceptive inputs
- Can result in depression
- Pain clinic with multi-modal therapies for treatment
What classification does a headache/migraine fall under?
- What causes them?
Acute episodes and person may be healthy but may have chronic headaches (reoccur)
- They result from dysfunction of brainstem area involved with modulation of craniovascular afferent fibers
- Treatment: anti-epileptic drugs
What classification does FMS fall under
Chronic duration
- Etiology unknown
- Risk factors (abuse, stress)
- Women > men
- Hyperalgesia affecting all 4 extremities
Describe cancer related pain
- Pain may result from infiltration of organs, compression from expanding tutor, or cancer treatment
- Pressure on nerve fibers (a-beta, and C-fibers are continuously stimulated)
- Clinical manifestation: SNS and behavioural changes
- Treatment: potent medication and multi-faceted approach (destroys tutor and neighbouring tissues)
Describe cancer related pain
- Pain may result from infiltration of organs, compression from expanding tutor, or cancer treatment
- Pressure on nerve fibers (a-beta, and C-fibers are continuously stimulated)
- Clinical manifestation: SNS and behavioural changes
- Treatment: potent medication and multi-faceted approach (destroys tutor and neighbouring tissues)
Define Radiculopathy
Pain due to spinal nerve injury - follows dermatomal distribution
Define Sensory Dermatome and dermatomal maps
- particular area of the body surface innervated by a spinal nerve with its nociceptor fibres
- useful for locating a source of neurologic pain
Define peripheral neuropathies
- do not follow a dermatomal pattern
- ex. carpal tunnel syndrome
Define trigeminal neuralgia
Sudden momentary but excruciating pains along second/third division of trigeminal nerve
- Women > men
- May result from compression of the trigeminal nerve but other structures = demyelination or irritation
- Clinical manifestations: sharp, shooting pains (electric)
- Treatment: anti-convulsants, surgical nerve decompression, gamma radiosurgery
What is referred pain?
Percieved in an area other than the site of an injury
- Referred to a structure within the same sensory dermatome
- Result of a convergence of visceral nociceptor activity with primary somatic afferents in the posterior horn of the cord
What is referred pain?
Percieved in an area other than the site of an injury
- Referred to a structure within the same sensory dermatome
- Result of a convergence of visceral nociceptor activity with primary somatic afferents in the posterior horn of the cord
What are physiological responses to pain?
Sympathetic NS
- Increase HR or BP, dilated pupils, perspiration, etc.
- Helpful short term; deleterious in long term
Explain pain in young to elderly beings?
- Both receive inadequate pain management
- Infants do have pain perception - if left untreated = behaviour changes and physical changes in CNS
- Pain does no decrease with aging just the communication/expression of pain may vary
3 Treatment Modalities Include
Pain Management
1) Interrupting peripheral transmission
2) Modulating pain transmission at spinal cord level
2) Altering perception & integration of nociceptive impulses in the brain
