Pain and Neuropathy (Physiology) - Block 2 Flashcards
What is pain?
Unpleasant sensory and emotional experence associated with actual or potential tissue damage
* subjectively defined
How does pin initiate a stress response?
- hormonal and metabolic change
- HPA axis and sympathetic NS
- Neuroendocrine response induces catabolic state
- Increases oxygen delivery and organ perfusion
- Increased plasma glucose, proteins , and free fatty acids
- Water retention by kidnes
What are the negative effects of stress response?
- HTN and tachycadia
- Hyperglycemia, negative nitrogen, immunosuppression
- Hypercoag state
What is nociceptive pain?
Physiologic response to heat, cold, viration, stretch, or chemicals released from damaged cels that may cause tissue damage
* a protective biological response
What is the difference between somatic and visceral pain?
Somatic: aching, throbbing, dull pain from skin, muscle, and joints
Visceral: squeezing, cramping, dull, and deep pain from organ
What is neuropathic pain?
Nerve cell dysfunction in the PNS and/or CNS
What is the difference between acute and chronic pain?
Acute: hours-weeks
Chronic: occurs after resolution of an acute infury or inflammation
What is transduction?
COnversion of noxious thermal, mechanical, chemical stimulus into a nerve impulse
What is transmission?
Transfer of a noxious peripheral stimulus to the CNS
What is modulation?
Peripheral and central neurotransmitters and other substances that enhance or dampen the transduction and transmission of noxious stimulus
What is perception?
Cognitive appreciation of a noxious stimulus
What is the function of afferent neurons?
Detection of a noxious thermal, mechanical, or chemical stmulus
What is a nociceptors?
Free peripheral endings of sensory neurons
What is the difference between somatic and visceral nociceptors?
Somatic: Respond to thermal, mecanical, chemical stimulus
Visceral: Stimulated by inflammation, ischemia, dilation, stretch, and spasm
What is the function of afferent nociceptive fibers with VGSCs?
Transmission of noxious stimulus to the CNS
What are A delta fibers?
Large myelinated fibers that have a low stimulation threshold and a fast conduction velocity
Differentiate the typws of A delta fibers?
Type 1: High-threshold mechical nociceptors that respond to both chemical and mechanical stimuli (first and fast and ends when the stimulus is removed)
Type 2: Low-heat threshold and high mechanical threshold (fast for heat stimulus)
What are C fibers?
Smaller unmyelinated, polymodal, mechno-heat-responsive nociceptors that have a slow conduction velocity (second or slow pain such as throbbing, burning, aching)
What happens if a pain threshold of fibers is reached?
Action potetial is generated
How is an action potential produced by nociceptors?
- Nociceptor carries the noxious stimulus to the CNS
- Conscious percepton of pain
- Nociceptors show no adaptation and depolarize in portion to the intensity and frequency of the stimulus
- Activation of:
* VOltage gated sodium and potassium channels -> generation and conduction of action potential
* VOltage gated calcium channels -> release of neurotransmitters for transmission of pain or mediation
What is the roles of upregulation of calcium channels in C fibers?
Hyperalgesia: exaggerated and prolonged response to pain
Allodynia: perception of pain from a stimulus that doesn’t usually cause pain
Describe the structure of a-delta and c afferents?
- cell bodies from the trunk and limbs located in the dorsal root ganglion
- cell bodies from the fce are located in the trigeminal ganglion
- Both have a peripheral branch and central axonal branch
What are the layers of gray matter in the spinal cord called?
Rexed laminae
* dorsal horn contains laminae I-VI
What are the first-order neurons invlved with transmission of pain?
Aδ fibers synapse with second-order neurons.
C fibers primarily synapse with interneurons that synapse with second-order neurons.
Aβ fibers may be involved in the transmission of chronic pain.
What are the second-order neurons invlved with transmission of pain?
nociceptive-specific neurons: small receptive fields and respond only to nociceptive stimuli
Wide dynamic range (WDR) neurons: Have complex receptive fields and respond to nociceptive and tactile input.
Excitatory neurotransmitters in the dorsal horn
What are the receptors used for glutamate signalling?
AMPA
NMDA
What is the inhibitory neurotransmitter?
GABA adn glycine
What are the excitatory neurotransmitters?
GLutamate, aspartate, VIP, substance P, CCK, CGRP
What are the tracts that ascend second-order neurons to the thalamus?
- Spinothalmic tract (STT)
- Spinoreticular tract (SRT)
- Spinomesencephalic (SMT)
What are thrid order neurons?
Transmit novious impulses from the thalamus to the primary somatosensory areas of the cortex for the perception of pain
What are the primary neurotransmitters?
NE, seratonin
What stimulates the releae of supraspinal and spinal endogenous opiods?
Descending tracts
What are the peripheral influences of modulaing pain?
- injuredtissue releases substance p and glutamate which activate nociceptors
- mediators are released to tissue -> inflammation
- peripheral sensitization -> primary heperalgesia
What are the functions of glial cells?
decreases the effectiveness of the inhibitory function of te descending tracts
What is central sensitization?
Increased excitability of the dorsal horn -> amplification of the novious stimulus
Excessive or continued activation of the dorsal horn -> abnormal response to sensory input and secondary hyperalgesia
What influences the perception of pain?
- Emotional or psychological stress
- Cultural and religious beliefs
- Prior experience with pain
What is a pain threshold?
The minimum intensity of a noxious therma, mechanical, or chemical stimulus that activates nociceptors and is perceived as painful
How is the pain threshold modulated in the periphery?
Increased release of chemical mediators that increase/decrease the threshold
How is the pain threshold modulated in the central?
Exictaory/inhibitory neuortransmitters that increase/decrease the threshold in the dorsal horn and thalamus
What is an increased excitability of neurons?
Sensitization
What is central sensitization?
Increased excitability of neurons in the CNS
What responses results from central sensitization?
- Tactile allodynia
- Secondary hyperalgesia
What is pain tolerance?
Amount of pain an individual can take or tolerate
How do you increase pain tolerance?
Activation of large somatic fibers
What is the gate control theory of pain?
Nnpainful input closes a pain gate to painful input in the dorsal horn and prevents the transmission of pain to the CNS