Pain and Headaches Flashcards
What is pain?
unpleasant sensory component that is influenced by previous experience, emotions, gender, culture, and physical, cognitive, and spiritual factors
Recall the two types of pain scales often used to assess the subjective nature of pain.
numeric scale and visual analog scale
What is pain threshold and pain tolerance?
- pain threshold: point at which a stimulus is perceived as pain
- pain tolerance: duration of time or the intensity of pain that a person will endure before removal from the stimulus
What are nociceptors?
pain receptors that are free nerve endings capable of responding to several different noxious stimuli including chemical, mechanical, and thermal energy
What are the four main phases of nociception?
- Transduction: painful stimulus is turned into action potential energy
- Transmission: electrical signal is transmitted to areas of the brain and CNS that will perceive it
- Perception: subject becomes consciously aware that they are in pain
- Modulation: body attempts to modulate the symptoms of pain
pain transduction
opens sodium and calcium channels and allow nociceptors to reach threshold and create an action potential.
Explain what Capsaicin is and how it works.
- activates ligand-gated ion (Ca2+ and Na+) channels by binding to vallanoid (VR-1) receptors
- desensitizes pain fibers and prevents substance P from being released
Describe the role of Substance P/ CGRP, bradykinin, ATP, H+, K+, histamine, serotonin, and prostaglandins in the transduction of pain.
- Substance P/CGRP: intracellular products that can cause depolarization. inflammation and hyperalgesia
- Bradykinin: proteases breakdown extracellular peptide kininogen into bradykinin= depolarization
- ATP: causes depolarization and binds directly to ATP-gated K+ ion channels
- H+: activate acid-sensing ion channels (ASICs) in nociceptors resulting in depolarization
- K+: when released it has a depolarizing effect
- Histamine: binds to its receptor on nociceptors=making it more painful
- Serotonin: binds to its receptor on nociceptors=making it more painful
- Prostaglandin: increase the cAMP levels inside nociceptors. also reduce the threshold
Explain peripheral sensitization and hyperalgesia
- increased sensitivity to an afferent nerve stimulus
- abnormally heightened sensitivity to pain
Difference between allodynia and
hyperalgesia
Allodynia: pain due to a stimulus that does not usually provoke pain. (light touch to sunburn)
Hyperalgesia: exaggerated pain and from a stimulus that usually does provoke some pain (slap to
sunburn)
-“postherpetic neuralgia”: damage to neurons by the herpes zoster virus
Describe the type of sensory nerve fibers (A-alpha, A-beta, A-delta, and C). Compare their size, speed and type of sensation they carry
- A-delta: lightly myelinated and transmit pain signals quite quickly (fast pain; localized)
- C: unmyelinated fibers that transmit action potentials relatively slowly (slow wave pain; less localized)
- A-alpha: thickly myelinated and have a rapid conduction rate
- A-beta: myelinated (though not quite as thick) and have also have a quick conduction rate
Explain the primary, secondary and tertiary order neurons involved in ascending sensory information
- Substance P, norepinephrine, and glutamate released
- project to the thalamus and also have collateral axons that innervate the reticular activating system (RAS) of the brainstem, which helps regulate the attention and alertness we give to the pain
- transmit pain signals to the somatosensory cortex
Explain the DCML and ALS pathways and what types of sensations are conducted by both
-Dorsal Column Medial Lemniscus (DCML): larger, myelinated and faster variety (A-alpha and A-beta). Sensations include textures, fine touch, vibration, two point
discrimination, and proprioception
-Anterior Lateral Spinothalamic Pathway (ALS): second order neurons synapse in the thalamus where third order neurons leave the thalamus and carry the signal to the cerebral cortex. Sensations include pressure, tickle, itch, pain and temperature
What things contribute to the perception of pain?
- limbic system for emoting
- neurological system for modulating the amount of pain experienced for a given nociceptive stimulus
- anxiety and depression can make pain worse
- pain is mental
How does the central nervous system (PAG, nucleus raphe magnus, and spinal cord interneurons) work to modulate pain signal input
- Periaqueductal gray (PAG): has a lot of opiate receptors
- Nucleus raphe magnus: release serotonin and sends projections to the dorsal horn of the spinal cord to directly inhibit pain
- Spinal cord interneurons: causes inhibition of the nociceptive pain transmission onto second order neurons
Describe where opioid receptors are found and where opioid like molecules are released in the areas mentioned just above
Describe how the enkephalin releasing neurons in the spinal cord work to modulate pain signals
Interneurons receive excitatory signals (serotonin) from efferent neurons of the medulla. Then release enkephalin and bind to opioid receptors and reduce intracellular calcium.
Describe the DNIC modulation of pain.
describes how afferent pain signals coming from different areas of the body can be inhibited by one another
Explain the Gate-Control Theory of Pain. Explain how A-alpha and A-beta neurons can conduct signals that mitigate the pain experience
- Proposes a mechanism for how pain is reduced by activating a non painful sensation.
- primary neurons (a-delta) send signals to secondary neuron and ultimately cause a decrease in the frequency of pain signals that reach the brain.