Lecture 6-Pain Flashcards
What is the role of somatosensory afferents?
Somatosensory afferents convey information from the skin’s surface to the central nervous system.
What type of neurons are typically found in the dorsal root ganglia associated with somatosensory afferents?
Pseudounipolar neurons are commonly found in the dorsal root ganglia of somatosensory afferents.
What’s the difference between mechanoreceptor afferents and those carrying pain and temperature information when it comes to their peripheral processes?
Mechanoreceptor afferents have protective receptor cells around their peripheral processes, while afferents for pain and temperature just end freely in the periphery.
Which nerve endings are found in the epidermis and what sensation do they transmit?
Free nerve endings are located in the epidermis, and they transmit sensations of pain and temperature (not specialized for any specific type of mechanical stimulus)
Where are Meissner’s corpuscles located, and what do they detect?
Meissner’s corpuscles are located just below the epidermis in the dermal folds (areas in the body where there is no hair); detect fine, discriminative touch and vibration.
Three Layers of Skin
Epidermis, dermis, subcunaneous
Where are Ruffini and Pacinian corpuscles found, and what sensations do they detect?
Ruffini corpuscles are found in the dermis and detect skin stretch, while Pacinian corpuscles are located in the subcutaneous layer and are sensitive to deep pressure and vibration.
Why does the epidermis have a folded structure?
The epidermis is folded to increase its surface area, which enhances its capacity for mechanosensation
How are slowly and rapidly adapting receptors different in how they react to things?
Slowly adapting receptors maintain their response to a stimulus over time, while rapidly adapting receptors only respond at the onset and sometimes the offset of a stimulus, allowing us to perceive both the steady and changing aspects of the stimulus.
What are nociceptors, and when do they start firing intensely?
Nociceptors are pain receptors. They start firing intensely when the temperature reaches a threshold of around 45 degrees.
What distinguishes non-nociceptive thermoreceptors from nociceptors in their response to the stimulus?
Non-nociceptive thermoreceptors activate earlier as the stimulus increases but plateau in their response beyond a certain threshold, while nociceptors continue to fire more intensely.
What happens to the firing of nociceptors as the stimulus intensity increases?
As the stimulus intensity increases, the firing of nociceptors (pain receptors) increases in terms of both the number and frequency of action potentials.
Describe “first pain” and “second pain” in terms of their characteristics.
“First pain” is immediate, sharp pain experienced right after an injury, while “second pain” is a lingering, long-lasting pain with a dull, burning quality.
What type of nerve fibers carry the sensation of “first pain”?
“First pain” is carried by myelinated (faster) nerve fibers (a-deltafibers)
How is “second pain” different from “first pain” in terms of the nerve fibers involved?
“Second pain” is carried by non-myelinated (slower) nerve fibers (C fibers)
Which receptors use C afferent axons and what sensations do they transmit?
Free nerve endings use C afferent axons, which are unmyelinated, to transmit sensations of pain, temperature, and itch.
What happens when capsaicin binds to VR-1 receptor channels?
When capsaicin binds to VR-1 receptor channels, the channels open and allow calcium and sodium ions to enter the cell, leading to the sensation of heat.
What do TRAP1 channels detect?
TRPA1 channels detect a variety of sensations, including chemical exposure, mechanical stress, and temperature changes.
TRP (Transient Receptor Potential) channels:
Large family of ion channels that are broadly involved in the detection and transduction of sensory signals.
What role do TRP channels located near glands have?
TRP channels near glands can be involved in lipid synthesis, cell proliferation, differentiation, and cell death.
What types of stimuli can activate TRPV1 channels?
TRPV1 channels can be activated by capsaicin, heat, and acidic conditions.
What is the role of agonists and antagonists in the function of TRPV1 channels?
Agonists activate TRPV1 channels, causing an action potential that leads to sensations like pain or heat, while antagonists block these channels, preventing their activation.
How does the activation of TRPV1 channels lead to the perception of sensations such as burning or itching?
The activation of TRPV1 channels initiates an action potential that travels to the spinal cord and then to the brain, where it is interpreted as burning, itching, or stinging sensations.
What are the potential cellular consequences of prolonged TRPV1 channel activation?
Prolonged TRPV1 channel activation may lead to calcium overload, mitochondrial dysfunction, and neuronal damage, affecting synaptic plasticity and potentially causing cell death.
Inflammatory response to tissue damage (6)
- Injury: ATP released, signaling pain and activating nerve endings.
2) Stimulation of Nerve Endings: ATP stimulates free nerve endings, initiating a molecular cascade that drives the inflammatory response.
3) Immune cells such as macrophages and neutrophils are drawn to the injury site
4) Substance P Role: Cell death and substance P increase the inflammatory signal intensity.
5)Sensory information travels from the dorsal root ganglion to the spinal cord.
6) Signal Ascension: Pain signals cross the spinal cord and ascend to the brain via the anterolateral system
Anterolateral System Steps
- Sensory input via dorsal root ganglia.
- Fibers may briefly travel in Lissauer’s tract.
- First-order neurons synapse with second-order in dorsal horn.
- Crossed second-order neurons form spinothalamic tract.
- Spinothalamic tract ascends to thalamus.
- Second-order neurons synapse with third-order.
- Third-order neurons project to cortex for sensation perception.
