Pain Pathways Comp
What nerve fiber is responsible for slow pain?
C fibers Free nerve endings Unmyelinated 0.4-1.2 mmm Diffuse pain, burning, aching, throbbing sensation Pain exceeds duration of stimulus
How does the spinal nerve root connected?
Connected to the paravertebral sympathetic ganglia by communication channels called white and gray rami communicans
What is the substantia gelatinosa?
Lamina II Lamina II and III
What spinal cord tract carries pain and temperature to the brain?
Lateral spinothalamic Component of the anterolateral sensory system
What does the descending dorsolateral tract do?
Modulates pain
What is the function of the dorsolateral tract?
Modulates pain
What is the dominating receptor of spinal analgesia?
Mu 2 Patient's perception of pain is diminished because fewer action potentials are relayed to the brain Mu1, Mu2, kappa, and delta all responsible
What is the most dominant receptor with supraspinal analgesia?
Mu1 Patient's response to pain is altered "I feel pain, but don't care" Euphoria IV
What receptors mediate supraspinal analgesia?
Mu1, kappa, delta
White rami carry what?
Myelinated sympathetic preganglionic neurons
Where does substance P bind?
Neurokinin - 1 (NK1) on the postsynaptic membrane
What is the pain pathway for slow-chronic pain?
The C fibers terminate in lamina II and III. Interneurons transmit C fiber impulses to lamina V. Neurons leave lamina V cross immediately to the contralateral lateral spinothalamic tract and ascend to the brain.
Gray rami carry what?
Unmyelinated sympathetic postganglionic neurons
What would be the cause of early ventilatory depression?
Usually use of fentanyl (lipophilic) because significant systemic uptake
What is the pain pathway?
When free nerve endings of the A delta and C fibers are stimulated Cell bodies of the A delta and C fibers are located in the dorsal root ganglion. They enter the dorsal cord, divide, and ascend or descend 1-3 segments into the Tract of Lissauer
When does supraspinal analgesia occur?
When opioids act in the brain at sites including the limbic system, hypothalamus, thalamus
Where do preganglionic sympathetic nerves arise from?
intermediolateral horn of the spinal cord
What nerve fiber is responsible for fast pain?
A delta fibers Free nerve endings Myelinated 1-4mmm Sharp, stinging, pricking pain Duration of pain coincides with duration of painful stimulus
Where does glutamate bind?
AMPA and NMDA receptors on the postsynaptic membrane
What is the pain pathway for fast-sharp pain?
After leaving the tract of Lissauer, axons of A delta fibers enter the dorsal horn and terminate in Rexed's lamina I and V. Second order neurons leave lamina I or V cross to the contralateral lateral spinothalamic tract to the brain
Where do motor nerves to skeletal muscle arise from?
Anterior horn of the spinal cord
What is the most common inhibitory NT?
GABA (brain) Glycine (spinal cord)
What NT is released from A delta fibers?
Glutamate
What is the most common central NT excitatory?
Glutamate
Where do opioid agonist/antagonist mediate their clinical effects?
Kappa and delta receptors
How do opioids work on the pain pathway?
Opioids stimulate the same receptors that are stimulated by the body's endorphins and enkephalins. Opioids diffuse into the substantia gelatinosa and unites with opioid receptors on nerve terminal. The release of substance P is reduced.
Opioids acting in the brain to produce spinal analgesia act where?
Periventricular/periaqueductal gray
Side effects of neuraxial opioids
Pruritus Neonatal morbidity nausea Sexual dysfunction Urinary retention Ocular dysfunction Depression of ventilation GI dysfunction Sedation Thermoregulatory dysfunction CNS excitation Water retention
Side effects of Naloxone
Reversal of analgesia Excitement/Dysphoria Tachycardia HTN Cardiac dysrhythmias (V. FIb) Pulmonary Edema
What would be the cause of late ventilatory depression?
Rostral spread - systemic circulation is minimal at first but then significant quantities of opioid in csf circulates to brainstem
Kappa
Spinal (Kappa 1) Supraspinal (Kappa 3) Dysphoria, Sedation Low abuse Diuresis
Mu 2
Spinal analgesia Respiratory depression Physical dependence Constipation
Mu 1
Spinal analgesia Supraspinal analgesia *** Decreased HR *** Euphoria *** Low abuse potential Urinary retention Pruritus ***
Delta
Spinal and Supraspinal (Delta 1 and 2) Respiratory depression Physical dependence Constipation
What NT is released from C fibers?
Substance P
Spinal analgesia results from action of opioids where?
Substantia gelatinosa (epidural, IT) Periventricular/Periaqueductal gray (IV)
