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78 Cards in this Set
- Front
- Back
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Classifications of receptors based on microscopic structure
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Unencapsulated
Encapsulated Specialized |
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Unencapsulated Receptors
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Free nerve ending and loses its myelin sheath and is only separated from tissue by the Schwann cell and a BM. Many of these respond to NOXIOUS stimuli and HIGH THRESHOLD mechanical stimuli.
Examples: thermoreceptors, nociceptor |
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Encapsulated Receptors
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Consits of an elabortate arrangement of specialized cells that receive the peripheral endings of nerve fibers.
Examples: Pacinian corpuscle and Meissner's corpuscle |
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Specialized Receptors
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ELECTROGENIC cells that become involved in the process of SENSORY TRANSDUCTION and their response depolarizes the attached nerve ending.
Ex: cochlear hair cells and photoreceptors |
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Sherrington's Classification of Receptors
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Exteroceptors
Enteroceptors Proprioceptors |
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Exteroceptors
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detect EXTERNAL stimuli (5 senses = visual, touch, hearing, taste, smell)
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Enteroceptors
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detect INTERNAL stimuli (stomachache, visceral receptors)
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Proprioceptors
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Detect body position or movement (ex: muscle and joint mechanoreceptors, vestibular system)
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Functional classification of receptors (based on physiological function)
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mechanoreceptor
thermorecepor chemoreceptor photoreceptor nociceptor (** can respond to mechanial, thermal, or even chemical stimulation) |
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Auditory Sensory system
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Modality: hearing
Stimulus energy: sound Receptor class: mechanoreceptor Receptor cell type: hair cells (cochlea) |
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Visual sensory system
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Modality: vision
Stimulus energy: light Receptor class: photoreceptor Receptor cell type: rods, cones |
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Vestibular sensory system
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Modality: balance
Stimulus energy: gravity Receptor class: mechanoreceptor Receptor cell type: hair cells (vestibular labyrinth) |
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Gustatory sensory system
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Modality: taste
Stimulus energy: chemical Receptor class: chemoreceptor Receptor cell type: taste buds |
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Olfactory sensory system
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Modality: smell
stimulus energy: chemical Receptor class: chemoreceptor Receptor cell type: olfactory sensory neurons |
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Touch [submodality]
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stimulus energy: pressue
receptor class: mechanoreceptor receptor cell type: cutaneous mechanoreceptors |
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Proprioception [submodality]
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Stimulus energy: displacement
receptor: mechanoreceptor Receptor cell type: muscle and joint receptors |
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Temperature sense [submodality]
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stimulus energy: thermal
receptor class: themoreceptor Receptor cell types: cold and warm receptors |
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Pain [submodality]
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stimulus energy: chem, thermal, or mechanical
receptor class: chemo,thermo, mechanoreceptor |
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Itch [submodality]
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stimulus energy: chemical
receptor class: chemoreceptor Receptor cell type: chemical NOCICEPTOR |
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Rapidly adapting receptors
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application of a stimulus may result in a few or only 1 action potential even if the stimulus is maintained.
ex: pacinian corpuscle |
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slowly adapting receptors
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application of a stimulus results in a repetitive discharge in the primary afferent neuron as long as the stimulus is maintained.
ex: most nociceptors |
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Stimulus intensity
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Refers to the strength of a stimulus. It is encoded at the receptor by FREQUENCY (nerve impulse/sec) and POPULATION (# of receptors activated).
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Frequency coding
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The strength of the stimulus is directly related to the firing rate of the sensory unit -- this is true for many slow adapting receptors.
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Spatial or Population responses
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more intense stimuli activate more sensory units at the point the stimulus is applied.
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Why do large myelinated nerve fibers conduct action potentials more rapidly than smaller myelinated/unmyelinated fibers?
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- increased diamater of myeline sheath produces a LOWER INTERNAL LONGITUDINAL RESISTANCE
-Myelinated fibers propagate impulses by SALTATORY CONDUCTION--> longer internodes so conduction is more efficient. |
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Relationship between conduction velocity and fiber diamater of myelinated fibers.
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Conduction velocity increases by about 6 m/s per 1 micrometer increase in fiber diameter.
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Fiber Type I
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Aalpha
diameter: 12-20 microns conduction velocity: 72-120 m/s receptor associations: mechanoreceptors: muscle spindles; golgi tendon organs |
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Fiber Type II
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Abeta
diameter: 6-12 microns conduction velocity: 36-72 m/s receptor associations: mechanoreceptors: muscle spindles; Meissner, Pacinian, etc. |
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Fiber Type III
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Agamma and Adelta
diameter: 1-6 microns cond. velocity: 6-36 m/s receptor associations: thermoreceptors (COOL); nociceptors |
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Fiber Type IV
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C fibers
diameter: 0.4-1.2 microns cond. velocity: 0.5-2.0 m/s receptor associations: thermoreceptors (WARM); nociceptors |
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FAI
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Fast-adapting Type I
Only on non-hairy part of hand Small, sharp borders 43% meissner corpuscle; edge sensitive |
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SAI
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Slow-adapting Type I
Irregular discharge Edge sensitive 25% merkel cells Found in hairy skin Small, sharp borders |
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FAII
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Fast-adapting Type II
Large, obscure borders 13% Paccini (Golgi-Mazzoni) Large receptive field (deep in skin) |
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SAII
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Slow-adapting Type II
Large receptive field Deep in skin Regular discharge Sensitive to lateral skin stretch 19% Ruffini |
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Pacinian Corpuscles
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Most sensitive to vibration, particularly in the 100-400Hz range. At 250 Hz vibration, PC can detect skin displacement of 0.10 micrometers.
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Types of receptors found in the PDL
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several types of modified Ruffini nerve endings and a variety of free nerve endings.
Ruffini: slowly adapting mechanoreceptors |
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Threshold sensitivity
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Often tested with monofilaments; varies across body; determined by sensitivity of RAPIDLY adapting mechanoreceptors (although perception of PRESSURE is mediated by slowly adapting mechanoreceptors).
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Types of input of DC-ML system
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MECHANORECEPTIVE
slowly and rapidly adapting cutaneous mechanoreceptors as well as muscle and joint mechanoreceptors |
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Which encapsulated mechanoreceptor is the FAST-adapting one(s)?
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Pacinian corpuscle, then Meissner.
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Which encapsulated mechanoreceptor is found on GLABROUS skin?
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Meissner's corpuscle
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Which encapsulated mechanoreceptor functions for the stretching of skin?
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Ruffini's corpuscle
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DC-ML pathway: where are the second order neurons?
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gracile nucleus: MEDIAL; fibers that convey infromation from LOWER limbs
cuneate nucleus: LATERAL: fibers that convey information from UPPER limbs, trunk, neck. |
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Internal arcuate tract
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Right after contacting the 2nd order neurons; axons project in the dorsal portion of each side of the lower branstem; subsequently cross the midline.
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Medial Lemniscus
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Elongated dorsoventrally (after the internal arcuate axons cross the midline).
Info. from lower limbs located ventrally; info. from upper limbs located dorsally. |
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When does hte medial lemniscus rotate 90 degrees laterally?
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when it ascends through the pons and midbrain.
Upper body: medial Lower body: lateral |
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DC-ML pathway: 3rd order neurons
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cells of ventral posterior lateral (VPL) nucleus of thalamus.
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TRIGEMINAL SOMATIC SENSORY SYSTEM
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-these are mechanosensory receptors from FACE
-trigeminal ganglion -principal nucleus (2nd order) -medial lemniscus -trigeminal lemniscus (trigeminothalamic tract) -VPM (ventral posterior medial) nucleus of thalamus |
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Primary somatic sensory cortex
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aka SI
Located in the postcentral gyrus of the parietal lobe and comprises 4 regions: Broadmann's areas 3a, 3b, 1, and 2. |
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Which laminae do the Adelta fibers and C fibers synapse in?
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Adelta: laminae 1 and 5
C: laminae 1 and 2 |
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The MAJOR ascending pathway for information abotu pain and temperature (for below face)
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Spinothalamic tract
aka anterolateral system |
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At what level of the brainstem does the first-order axons enter? This is for noxious and thermal stimulation of the FACE.
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Enter at the PONS, then descend to the MEDULLA forming the spinal trigeminal tract.
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First-order axons for pain/thermal stimulation for FACE originate where?
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trigeminal ganglion cells and from ganglia associated with VII, IX, X
[geniculate gang, sup/inf gang, sup/inf gang] |
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What are 2 subdivions of the spinal [descending] nucleus of V?
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Pars interpolaris
Pars caudalis |
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What is the major ascending pathway for inforamtion about pain/temp from the FACE?
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trigeminothalamic tract
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Neurons in the parabrachial nucleus project where?
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Hypothalamus & amygdala --> motivation and affect; also sends projections to the periaqueductal gray matter which has to do with descending modulation of the pain circuits.
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Where do projections of affective-motival pain pathway NOT in the parabrachial nucleus go?
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Other projections go to older parts of the thalamus such as the INTRALAMINAR nad MEDIAL THALAMIC NUCLEI (medial to ventral posterior nucleus)
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Projections from the anterolateral system to the medial thalamic nuclei provide nociceptive signals to which areas?
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Frontal lobe, insula, and cingulate cortex
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Nociception vs. pain
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Sensibility is the ability to detect noxious stimuli. Sensation is how the brain interprets that sensory information. Generally, sensation has two components: recognition of the location, form and intensity of the stimulus and the affective-emotional responses to the noxious stimulus.
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how does capsaicin create pain?
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capsaicin activates responses in a subset of nociceptive polymodal C fibers by opening ligand-gated ion channels (like VR-1) that permit the entry to Na+ and Ca2+.
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dysesthesias
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abnormal unpleasant sensations
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characteristics of persistent pain (7):
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hyperalgesia
allodynia referred pain trigger zones pain in the absence of detectable tissue damage pain in a region of sensory deficit summation and after-reaction with repetitive stimuli |
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The analgesic effects of stimulating the periaqueductal gray are mediated through which brainstem sites?
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parabrachial nucleus, medullary reticular formation, locus coeruleus, raphe nuclei
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Referred pain: anginal pain (pain arising from heart muscle that is not adequately perfused with blood)
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upper chest wall, radiation into left arm and hand.
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referred pain: gallbladder pain
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scapular region
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referred pain: esophogeal pain
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chest wall
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referred pain: ureteral pain
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lower abdominal wall
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referred pain: bladder pain
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perineum
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referred pain: inflamed appendix
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anterior abdominal wall around the umbilicus
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Gate control theory: activation of the small fibers
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leads to inhibition of SG (substantia gelatinosa) fibers which are inhibitory interneurons and this leads to increased activation of teh transmission cells and opening of the gate.
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Gate control theory: activation of the large fibers along with the small fibers
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leads to excitation of SG neurons and more inhibition of the T cells and closing of the gate.
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3 families of endogenous peptides and their receptors
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endorphin: mu
enkephalin: delta dynorphin: Kappa |
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Serotonin pathways of descending control originate where?
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medulla: mainly the nucleus raphe
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Norepinephrine pathways of descending control originate where?
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in the pons locus coeruleus and subcoeruleus regions.
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Chemical mediators of CENTRAL sensitization
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excitatory amino acids
opioid peptides substance P CGRP (calcitonin gene-related peptide) |
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Management of hyperalgesia and pain following TISSUE injury (peripheral + central)
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This is INFLAMMATORY hyperalgesia.
Peripheral: local anesthetics & NSAIDS Central: opioids & NMDA receptor antagonises |
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Management of hyperalgesia and pain following NERVE injuery (peripheral + central)
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This is NEUROPATHIC hyperalgesia.
Peripheral: Local anesthetics & capsaicin analogs Central: Opioids, NMDA receptor antagonists, and tricyclic antidepressants. |
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Chemical mediators for descending control (3)
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5-HT (serotonin)
NE opioids |
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What are the EAA (excitatory amino acid) receptors of central sensitization?
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NMDA - Ca++ influx
AMPA - Ca++ influx (?) Kainate Metabotropic glutamate |
