Lecture 12 (Cut off for Exam 3) Flashcards
Pain
Pain Physiological Steps (4)
- Transduction
- Transmission
- Perception
- Modulation
Transduction
- Nociceptors - free nerve ending at surface of skin that convert physical stimuli into action potentials
- Physical Stimuli - pressure, tension, heat, and cold
- Chemical Stimuli - K+, lactate, histamine, bradykines, prostaglandins (alter membrane potentials to cause an action potential)
Prostaglandin Inhibitors
- Aspirin, Ibuprofen, other NSAIDs, corticosteroids
- Prostaglandins are produced by COX-1 to protect gastric mucosa from damage by acids
- By blocking COX-1, you inhibit release of prostaglandins
Transmission
- Signalling of peripheral nervous system to the central nervous system via the spinal cord
- Done with Ad fibers and C fibers
Ad Fibers
- Large and myelinated
- 10% of fibers
- Fast
- Mechanical pain
- Sharp, stinging, cutting, pinching, localized pain
C Fibers
- Unmyelinated
- Slower
- 90% of fibers
- Mechanical, chemical, and thermal pain
- Dull, throbbing, burning, aching, unlocalized pain
Transmission to Spinal Cord
- Glutamate carries impulse from primary afferent fibers to secondary neurons
- NMDA receptor binding can induce memory from repeated or excessive action of C-fibers by glutamate sensitization (mild stimulation becomes painful)
- Other neurotransmitters - Substance P, GABA, endorphins, and serotonin
Tract of Lissauer
- First step upon reaching spine in transmission
- Fibers branch and form collaterals that go up and down the spinal cord for a few segments
- Helps maintain posture during withdrawal reflex
Lamina 1
- Second step of spine transmission
- Ad and C fibers carry impulse to this region which then send them across the spinal cord and activates neurons in anterolateral tract
Substantic Gelantinosa
- Multiple synaptic area that contains afferent sensory, interneurons, and anterolateral neurons
- Strategic location to target for modulating of pain
Lamina V
- Area where somatic and visceral (organ) fibers converge
- Leads to referred pain sensations
Referred Pain
- Pain perceived in area other than the injury
- Can be far from actual site of injury
- Caused by nociceptors convergence in the dorsal horn
- Brain can’t differentiate between two sources of pain so it attributes visceral pain to the surface
- Certain patterns of reffered pain can be used to identify the region of concern or pathology occuring in the body
Lamina VI-VIII
Sensory input from joints, muscles, and organs
Transmission to Brain
- Ad fiber signals are transmitted through neospinothalmic division. Rapid transfer to thalmus/somatosensory cortex
- C fiber signals are transmitted through pateospinothalmic division. Slower bit more widespread travel throughout the brain
Brain Areas Associated with Pain
Stimuli»_space; Thalmus»_space; Other areas of Brain
- Primary Sensory Cortex - perceive and localize pain
- Cortical Association Area - Integration of pain with other sensory inputs
- Limbic forebrian - adds emotion to pain response
Pain Perception and Tolerance
- Perception of pain involves neural processing of pain (awareness, interpretations of area, severity, etc.)
- Influenced by other factors like attention, fear, anxiety, fatigue, expectations, etc.
- Combination of pain tolerance and threshold
Pain Threshold
Level at which pain is perceived. Similar for different people.
Pain Tolerance
Pain level when you seek relief from pain. Varies greatly between people and within one person depending on what factors are influencing them.
Modulation of Pain - Spinal Cord
- Modulation in spinal cord is the most understood
- Pain perception initiates descending pain and inhibits signals to dorsal horn
- Norepinephrine and serotonin stimulate interneurons to release endogenous opioids that provide presynaptic inhibition of neurotransmitter release from Ad and C fibers
Endorphins
- ENDOgenous moRPHINe
- Refers to enkephalins and (alpha, beta, gamma) endorphins which are the body’s endogenous pain killers
Opioid Modulation
- Bind presynaptically to prevent transmission of signals and the release of Substance P to block pain
- Mechanoreceptor activation also triggers opioid release from dorsal horn interneurons (deep tissue massage or acupuncture)
Pain Treatments - Inhibiting Transduction/Transmission
- NSAIDs and steroids
- Local anesthetics (lidocaine and novacaine) block sodium influx and action potentials
Pain Treatments - Alter Spinal Cord Transmission/Modulation
- Cutaneous stimulation (opioid release) - massage and acupuncture
- Spinal analgesia (opioids)
- Dorsal Column stimulation - implant an electrode and stimulate dorsal horn interneurons to release opioids
Pain Treatments - Perception/Integration Alterations
- Systemic Opioids - impacts brain perception and integration as well as spinal cord modulation. Affects many other receptors in the body so many side effects
- Distraction (imagery, hypnosis) - Force brain to attend to multiple stimuli and not just pain
- Relaxation and biofeedback - increase blood flow to that area, dilute pain-inducing chemicals, and increase endorphin release
