Electrotherapy II Lecture 2

Electrotherapy II Lecture 2

• Lecture 2 covers mechanisms of pain and tissue repair
• Objectives include: the sensory system, pain definition, pain physiology, pain modulation, and tissue repair principles
• The sensory system provides information about internal and external environments
• Visceral sensations include blood pressure (BP) and extracellular fluid (ECF) volume
• Somatic sensations include touch, pressure, and vibration
• Sensory receptors are detectors and transducers of energy (light, sound, chemical, mechanical) into action potentials in neurons
• Anatomically, receptors are specialized structures present at the peripheral termination of afferent nerve fibers
• Receptors are classified traditionally as special, cutaneous, and visceral senses
• Receptors can also be classified according to the site of the event (Teleceptors, exteroceptors, interoceptors, proprioceptors) and the degree of adaptation (slowly adapting, rapidly adapting, non-adapting, moderately adapting)

Receptors Classification

• Receptors are also classified by the type of stimuli they respond to (energy): mechanoreceptors (pressure, stretch, sound), chemoreceptors (solute concentration), thermoreceptors (hot, cold), nociceptors (pain from tissue damage), and baroreceptors (blood pressure) (photoreceptor)
• Nociceptors have a high activation threshold, so they don't respond to everyday stimuli like sitting unless pain is severe
• Cutaneous mechanoreceptors include Meissner and Pacinian corpuscles and Merkel tactile disks
• Cutaneous thermoreceptors detect temperature changes

Pain

• IASP defines pain as an unpleasant sensory and emotional experience associated with actual or potential tissue damage, which has physiological and psychological aspects.
• Pain is the most common complaint and most prevalent symptom in rehabilitation programs
• Pain can be acute or chronic
• Acute pain is caused by injury, infection, or disease and lasts less than 12 weeks, and is often well-defined (sharp, skin, easy to locate pain), or deep-tissue pain from muscles, joints or viscera can be diffuse
  • Treatment can include pharmacology and non-pharmacological interventions (e.g., rehabilitation, surgery.)
  • Monitoring of vital signs (heart rate, blood pressure, and respiration) is helpful.
• Chronic pain persists beyond the expected time of healing (3-6 months) and has associated central nervous system changes, requiring a multidisciplinary treatment approach.
• Chronic pain is associated with physical, emotional, social, and financial disability
• Referred pain is pain that occurs at a site remote from the disease or injury source. It's often due to convergence of cutaneous, visceral, and skeletal muscle nociceptors on a common nerve root
• Example includes pain radiating to the arms, jaws, or chest during angina or myocardial infarction

Pain Process

• The pain experience has five distinct and successive physiologic phases: transduction, peripheral transmission, modulation, central transmission, and perception
• Transduction is the phase of converting energy to electrical energy affecting nociceptors
• Peripheral Transmission -the propagation or transmission of nerve impulses from nociceptors to the spinal cord; mediated by A-delta and C fibers, which are distinct, afferent sensory fibers. A-delta fibers mediate mechanical and thermal noxious stimuli; C fibers mediate mechanical, thermal, and chemical noxious stimuli
• Modulation -diminution, suppression, or amplification of pain via the spinal gating system in the dorsal horn; affected by the interaction between inhibitory neurons (substantia gelatinosa) and pain-transmitting neurons (T). GABA release inhibits glutamate and substance P production, modulating pain signaling
• Central Transmission -transmission of nociceptive nerve impulses through ascending tracts; crucial signals are communicated through the lateral spinothalamic tract (A-delta and C fibers) to the thalamus, then to the cortex.
• Perception -detection and determining the meaning of pain; somatosensory cortex is involved in pain's spatial and temporal features (location, duration), and limbic system is key for emotional and motivational aspects

Pain Modulation

• Modulation of pain involves two major mechanisms:
  • The spinal gating system: A-beta fibers and the spinal gate, influenced by GABA secretion and inhibition of glutamate & Substance P, modulates signaling pain
  • Descending endogenous opiate system (DEOS): neurons located in the periaqueductal gray matter (PAG) and the nucleus raphe magnus (NRM), release enkephalins, endorphins, and serotonin into blood and cerebrospinal fluid
  • These release suppress pain signals at the level of the spinal cord.

Soft Tissue Repair

• Soft tissue healing follows several distinct phases
  • Hemostasis: The first phase stops bleeding at the wound site. This typically takes seconds to minutes (or longer with extensive tissue damage)
  • Inflammation: Cleans up cellular debris. Characterized by recognizable signs and symptoms (erythema, hyperthermia, edema, pain, and dysfunction). Typically lasts hours/days/weeks, depending on severity.
  • Proliferation: Formation of new and immature tissue to replace damaged tissues (i.e., fibroplasia and angiogenesis)
  • Remodeling/Maturation: Immature tissue rebuilds for optimal function, with increased mechanical strength. (Lasts weeks/months or years)
• Tissue healing can be through regeneration or repair
• Regeneration: tissue restoration is identical in structure and function
• Repair: fibrous scar formation alters structure and function
• Soft tissue healing often combines regeneration and repair techniques