Powerpoint 1 Flashcards
What is the neuronal circuit organization in the dorsal column pathway?
Divergence at each synaptic stage; stronger stimuli activate more neurons, especially in the central cortical field.
two-point discrimination, fine vs poor
Fine discrimination: 1-2 mm on fingertips;
Poorer discrimination: 30-70 mm on the back due to fewer tactile receptors.
What is lateral inhibition?
Enhances contrast by blocking lateral spread of excitatory signals.
Occurs at multiple levels: dorsal column nuclei, thalamus, and cortex
How are high frequency vibratory signals detected?
High-frequency vibrations (up to 700 cycles/sec) detected by Pacinian corpuscles
What encodes intensity in signal transmission?
Intensity is encoded by increased number of activated fibers and higher impulse rate in each fiber.
• Enables sensory systems to handle a wide range of stimulus intensities
What kinds of fibers make up the anterolateral system?
Composed of smaller myelinated (Aδ) and unmyelinated (C) fibers
What sensations does the anterolateral system transmit?
Transmits pain, temperature, and crude touch sensations.
Velocity of the anterolateral system
Slower conduction velocities (up to 40 m/sec)
Where are pain receptors located?
Free nerve endings are present in skin, periosteum, arterial walls, joint surfaces, and cranial vault.
Sparse in deep tissues. widespread damage can cause chronic, aching pain
What are the types of painful stimuli?
Mechanical, thermal, and chemical stimuli.
What is the role of bradykinin in pain sensitivity?
Bradykinin is particularly potent in eliciting pain.
How does pain receptor adaptation occur?
Minimal adaptation, often with hyperalgesia (increased sensitivity over time).
What causes pain from ischemia?
Pain from anaerobic byproducts like lactic acid.
What characterizes fast pain?
Felt within 0.1 seconds of stimulus; Sharp, pricking, acute, or electric pain.
Common stimuli: Needle prick, skin cut, acute burn.
Also limited to superficial tissues
What characterizes slow pain?
Begins 1 second or more after stimulus, increasing gradually; Burning, aching, throbbing, or chronic pain.
Associated with tissue destruction
Occurs in both superficial and deep tissues/ organs
What is referred pain?
Pain perceived in a location distant from the actual source of pain, often in a superficial area while the source is deep or visceral.
Why is referred pain clinically important?
Vital in diagnosing visceral ailments where referred pain may be the only symptom.
What is the mechanism behind referred pain?
Visceral pain fibers synapse on the same second-order neurons in the spinal cord that receive pain signals from the skin.
What are the challenges in localizing visceral pain?
Lack of direct experience with internal organs leads to poor localization; Dual pain pathways from visceral organs complicate localization.
What is the true visceral pathway?
Pain signals travel via autonomic nerves and are referred to surface areas far from the origin, based on embryonic origin.
What is the parietal pathway?
Pain signals from parietal peritoneum, pleura, or pericardium travel via local spinal nerves, localized directly over the affected area.
How is appendix pain referred?
Visceral pain is referred to the umbilical region (T10-T11) as aching/cramping; Parietal pain is sharp over the right lower quadrant.
Where does lateral inhibition of the dorsal column pathway occur?
Occurs at multiple levels: dorsal column nuclei, thalamus, and cortex.
How are lower frequency vibratory signals transmitted?
Lower frequencies (below 200 cycles/sec) detected by Meissner’s corpuscles.
How are lower frequency vibratory signals transmitted?
Lower frequencies (below 200 cycles/sec) detected by Meissner’s corpuscles.
What is an important test for dorsal column integrity in neuro exams?
Vibratory signal transmission
Where do anterolateral system fibers synapse, where do they cross, and how do they ascend?
Fibers synapse in the dorsal horns of the spinal cord and cross to the opposite side. Ascend in the anterolateral columns to the brain.
Anterolateral system is important for the perception of ________ and ______
Nociceptive signals and thermal stimuli
Anterolateral system provides _______ precise localization compared to the dorsal column system
less
Painful stimuli: Mechanical
Physical damage or pressure
Painful stimuli: Thermal
Heat, especially above 45°C, which also damages tissues
Painful stimuli: Chemical
Involves chemicals like bradykinin, serotonin, histamine, and potassium ions
How do potassium ions and proteolytic enzymes affect pain sensitivity?
Increase pain by enhancing nerve membrane permeability
What causes pain from muscle spasm?
Causes pain through direct stimulation and induced ischemia
“Perceived origin” of referred pain:
Pain from internal organs is “referred” to the skin because both signals share common neurons, leading the brain to perceive the sensation as originating from the skin
What are the two pathways for referred pain?
• True Visceral Pathway:
• Parietal Pathway:
Diagnostic importance of Visceral pain:
• Visceral pain is often the only indicator of visceral inflammation, infection, or disease
Two key differences of visceral pain from surface pain:
• Localized damage to viscera typically does not cause severe pain (e.g., gut incision)
• Diffuse stimulation of pain fibers, such as from ischemia, causes intense pain
What are the parietal surfaces?
• Include parietal peritoneum, pleura, and pericardium
• Supplied with extensive pain innervation similar to the skin
How is fast-sharp pain elicited?
Mechanical or thermal stimuli
What fibers transmit fast-sharp pain and what is their speed?
• Transmitted via type Aδ fibers at 6-30 m/sec
How is slow-chronic pain elicited?
• Primarily elicited by chemical stimuli (sometimes mechanical/thermal)
What fibers transmit slow-chronic pain, and at what speed?
• Transmitted via type C fibers at 0.5-2 m/sec
What is a cordotomy?
Cutting pain-conducting tracts (anterolateral quadrant) in the spinal cord to relieve intractable pain, typically for lower body pain
Pain insensitive areas include:
Liver parenchyma, lung alveoli
Pain sensitive areas include:
Liver capsule, bile ducts, bronchi, and parietal pleura
What are the four causes of visceral pain?
Ischemia, Chemical damage, spasm of smooth muscle, and overdistension
How does ischemia cause visceral pain?
Reduced blood supply leads to accumulation of acidic metabolic products
How does chemical damage cause visceral pain?
Leakage of substances (e.g., gastric juice) causing severe peritoneal pain
How does spasm of smooth muscle cause visceral pain?
Causes intermittent, cramping pain (e.g., in appendicitis, gallbladder disease)
How does spasm of smooth muscle cause pain?
Causes intermittent, cramping pain (e.g., in appendicitis, gallbladder disease)
How does overdistention cause visceral pain?
Overfilling of hollow organs may stretch tissues and collapse blood vessels, leading to pain
How does overdistention cause visceral pain?
Overfilling of hollow organs may stretch tissues and collapse blood vessels, leading to pain
Sharp Pain in Visceral Disease:
• When disease affects a viscus and spreads to the parietal surfaces, pain is felt more sharply
• Parietal pain is often well-localized over the affected area, unlike diffuse visceral pain
What fibers make up the Neospinothalamic Tract?
o Composed of Aδ fibers
Where do the fibers of the Neospinothalamic Tract synapse?
primarily in lamina I of the dorsal horns
Where do fibers of Neospinothalamic Tract cross, ascend, and terminate?
In dorsal horn, fibers cross to the opposite side and ascend through the anterolateral columns to the thalamus
Two functions of the Neospinothalamic Tract
o Transmits fast pain sensations (sharp, localized pain)
o Informs about the immediate presence and location of painful stimuli
Neospinothalamic Tract velocities are fast or slow?
Fast—. 6 or 30 m/sec
Rapid reflexive responses to painful stimuli
Transmission of thermal signals: (pathway)
• Upon entering the spinal cord, they travel a few segments in Lissauer’s tract and terminate in laminae I, II, and III
• Ascend in the anterolateral tract to the reticular formation and ventrobasal complex of the thalamus
• Some signals reach the somatic sensory cortex, though cortical removal reduces but doesn’t abolish temperature discrimination
Thermal receptors likely respond to ____________ changes that affect intracellular chemical reactions
temperature-driven metabolic rate changes
• Temperature change rather than direct effect on nerve endings likely causes stimulation
What are the two pathways for pain transmission?
• Neospinothalamic Tract: Transmits fast-sharp pain signals
• Paleospinothalamic Tract: Transmits slow-chronic pain signals
Where do slow pain signals terminate?
• Slow pain signals terminate in the reticular areas of the brain stem and intralaminar nuclei of the thalamus
Pain signals have a _______ effect
• Strong arousal effect, keeping the brain alert – explains difficulty sleeping during severe pain
Lower brain centers (brain stem and thalamus) are essential for__________
Conscious pain perception
The cortex helps in ________ pain quality
interpreting
Paleospinothalamic Tract is made of what kind of fibers?
C fibers
Where does the Paleospinothalamic Tract synapse?
lamina II and III of the dorsal horns
Where do the Paleospinothalamic Tract fibers cross, ascend, and terminate?
synapse in lamina II and III of the dorsal horns
o Fibers cross to the opposite side and ascend through the anterolateral columns to the various brain areas, primarily the brainstem
Two functions of the Paleospinothalamic Tract
o Transmits slow pain sensations (dull, aching pain)
o Contributes to emotional and autonomic responses to pain
Is Paleospinothalamic Tract slow or fast?
o Slower conduction velocities (0.5-2 m/sec)
Paleospinothalamic Tract localization/ pain perception
o Less precise localization, contributing to diffuse pain perception
Cold receptors fiber type and velocity
• Type Aδ fibers, thinly myelinated, transmit signals at 20 m/sec
• Some type C fibers may also function as cold receptors, suggesting a role for free nerve endings
Warmth receptors fiber type and velocity
• Likely free nerve endings, transmit signals via unmyelinated type C fibers at 0.4 to 2 m/sec
Pain receptors re. temperature?
• Activated by extreme cold and heat
• Thermal Receptor Adaptation:
• Cold receptors adapt significantly but not fully, responding more strongly to temperature changes than to constant exposure
Double Pain Sensation:
• Immediate fast-sharp pain via Aδ fibers prompts quick reaction
• Delayed slow pain via C fibers grows over time, reinforcing need for relief
• Pain Signal Processing in the Spinal Cord: Where does it enter?
• Entry: Pain fibers enter the spinal cord via dorsal spinal roots
• Dual Processing Systems:
• Fast-sharp and slow-chronic pain signals are processed separately, with relay neurons in the dorsal horns
• Analgesia System Components:
• Periaqueductal gray and periventricular areas in the mesencephalon and pons
• Raphe magnus nucleus and nucleus reticularis paragigantocellularis in the medulla
• Dorsal horn inhibitory complex in the spinal cord
• Analgesia System Components:
• Periaqueductal gray and periventricular areas in the mesencephalon and pons
• Raphe magnus nucleus and nucleus reticularis paragigantocellularis in the medulla
• Dorsal horn inhibitory complex in the spinal cord
Pain inhibition pathway
• Signals from periaqueductal gray → raphe magnus nucleus → dorsal horns of spinal cord
Pain inhibition pathway
• Signals from periaqueductal gray → raphe magnus nucleus → dorsal horns of spinal cord
RE. the pain inhibition pathway: Release of _____ in the spinal cord stimulates secretion of ________, which inhibits pain signals
• Serotonin release in the spinal cord stimulates enkephalin secretion, inhibiting pain signals
The two key neurotransmitters for pain suppression
• Enkephalin and Serotonin
• Natural opiate-like substances
β-endorphin, met-enkephalin, leu-enkephalin, and dynorphin
• Peripheral Tactile Stimulation
Rubbing skin near painful areas activates Aβ fibers, providing pain relief through lateral inhibition
• Electrical Stimulation Techniques
Electrodes on the skin, spinal cord, or brain regions (e.g., thalamus, periventricular, periaqueductal areas) for pain control
• Thermal Sensations: gradations
• Gradations: Freezing cold, cold, cool, indifferent, warm, hot, burning hot
• Extreme temperatures can stimulate pain receptors, creating sensations of freezing cold or burning hot
