Neuroanatomic Pathway
pain is highly complex and subjective experience that originates from CNS or PNS or both; has nociceptors
Nociceptors
specialized nerve endings that are designed to detect painful sensations from periphery and transmit them to CNS; located within skin, connective tissue, muscle, and thoracic, abdominal and pelvic viscera; can be stimulated directly by trauma or injury or
How do Nociceptors carry pain?
carry signal to CNS by 2 primary sensory (or afferent) fibers: A(gamma) and C fibers
A (gamma) fibers
myelinated and larger in diameter so transmit pain signal rapidly to CNS; sensation is very localized, short-term and sharp in nature because of A(g) fiber stimulation
C fibers
unmyelinated and small and they transmit signal more slowly; "secondary" sensations are diffuse and aching, they last longer after initial injury;
Where do fibers enter spinal cord?
by posterior nerve roots within dorsal horn by tract of Lissauer; fibers synapse with interneurons located in specific areas of cord (substantia gelatinosa); gray matter of spinal cord divided into series of consecutively numbered laminae; pain signals cr
What happens when pain is poorly controlled?
when poorly controlled over extended period, cells within dorsal horn become altered in size and function and this damage ultimately turns future pain signals into more exaggerated or hypersensitive processing
Nociceptive processing of Pain
develops when neve fibers in periphery and in CNS are functioning and intact; nociceptive pain starts outside NS fro actual or potential tissue damage; has 4 phases: 1) transduction, 2) transmission, 3) perception, 4) modulation; processing is protective;
Nocioceptive Processing - Transduction
occurs when noxious stimulus in form of traumatic or chemical injury, burn, incision, or tumor takes place in periphery (includes skin, somatic and visceral structures); tissue then releases variety of chemicals: substance P, histamine, prostaglandins, se
Nocioceptive Processing - Transmission
pain impulse moves from leel of spinal cord to brain; at synaptic cleft, there are opiod receptors that can block pain signaling w/our own endogenous opiods or with exogenous opiods if they are adminstered; if not stopped, pain impulse moves to brain via
Nocioceptive Processing - Perception
indicates the conscious awareness of painful sensation; coritical structures like limbic system account for emotional response to pain, and somatosensory areas can characterized sensation; only when noxious stimuli are interpreted in higer cortical struct
Nocioceptive Processing - Modulation
pain message is inhibited through modulation; our bodies have built-in system that will eventually slow down or stop the processing of a painful stimulus; if not, we would continue to experience pain from childhood injuries and beyond; Descending pathways
Neuropathic Processing of Pain
pain that does not adhere to typical and rather predictable phases in nociceptive pain; implies abnormal processing of pain message from injury to nerve fibers; often perceieved long after site of injury heals (can start 2-3 yrs later); can cnage into neu
How do you test for Nuropathic Pain
pain is sustained on neurochemical level. Identify by electromyography and nerve-conduction studies
Abnormal processing of neuropathic pain
impules can be continued by PNS or CNS; proposed mechanism is that injury to peripheral neurons can result in spontaneous and repetitive firing of nerve fiber (almost seizure like) and sustained centrally in phenomenon known as neuronal 'wind-up'; in dors
Source of Pain
based on origin; viceral, deep somatic, cutaneous, mental, referred
Source of Pain - Viceral
pain originates from larger interior organs (kidney, stomach, intestine, gallbladder, pancreas); can stem from direct injury to organ or from stretching of organ from tumor, ischemia, distention, or severe contraction; pain impulse transmitted by ascendin
Source of Pain - Deep Somatic Pain
comes from sources such as blood vessels, joints, tendons, muscles, and bone; injury may result from pressure, trauma, or ischemia
Source of Pain - Cutaneous
derived from skin surface and subcutaneous tissues; injury is superficial, w/sharp, burning sensation
Source of Pain - Mental
outdated and derogatory; psychogenic pain or psychogentic; linking pain to mental disorder negates pts pain report; lack of awareness and understanding of neuropathic pain may contribute to mislabeling
Source of Pain - Referred
pain felt at a particular site but originates from other location; both sites are innervated by same spinal nerve, and is difficutl for brain to differentiate point of origin; may originate from visceral or somatic structure; ex - inflamed appendix in rig
Types of Pain
can be classified by its duration into acute or chronic (persistent - carries less negative, malingering connotation) categories; duration provides information on possible underlying mechanisms and teatment decisions;
Types of Pain - Acute
short-term and self-limiting, often follows predictable trajectory, and dissipates after injury heals; serves a self-protective purpose; warns individual of actual or potential tissue damage; ex - surgery, trauma, kidney stones
Types of Pain - Acute Incident Pain
acute type that happens predictably when certain movements take place; ex - lower back upon standing or shoulder pain when arms raised
Types of Pain - Persistent (chronic)
diagnosed when pain continues for 6 mo or longer; can last 5, 15, 20 yrs or more; can be divided into malignant and nonmalignant; does not stop when injury heals and persists after predicted trajectory; many pts are not believed and often are labeled as m
Types of Pain - Chronic Malignant Pain
cancer-related; often parallels the pahtology created by tumer cells; is induced by tusse necrosis or stretching of organ by growing tumor; pain fluctuates w/disease
Types of Pain - Chronic Nonmalignant Pain
often associated w/musculoskeletal conditions such as lower back pain, arthritis, fibromyalgia
Types of Pain - Breakthrough Pain
pain that starts again or excalates before next scheduled analgesic dose; pain breaks through when is is expected to be controlled by pain meds