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 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

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

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

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 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