Lecture 8: Mechanosensation & Pain Flashcards
Different forms of specific receptors are sensitive to pressure, stretch, vibration,
acceleration, and sound
Five types of touch receptors :
1.
2.
3.
4.
5.
Pacinian corpuscle
Meissner’s corpuscle
Merkel’s disc
Ruffini’s ending
Free nerve ending
___________: respond with a burst of activity when the stimulus is first applied, but then quickly decrease their firing rate (adapt) as the stimulus is maintained - often also exhibit an ‘off’ response
Phasic receptors
_______: produce a relatively constant rate of depolarization & firing as long as the stimulus is maintained
Tonic receptors
_____ receptors are the most common receptors in the body
Touch
_____-: An unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential
tissue damage
Pain ( nociception )
______ of painful experiences in memory helps us avoid
potentially harmful events in future
Storage
Stimulation of ______ Produces the Perception of Pain
Nociceptors
Pain receptors are generally free ______
Nerve endings
There are three categories of pain receptors
◦ ______ receptors respond to mechanical damage (cutting, crushing, pinching)
◦ _______ receptors respond to temperature extremes
◦ ______ nociceptors respond to damaging stimuli
mechanical
thermal
polymodal
Do nociceptors adapt?
NO
Nociceptors Can be sensitized:
• _______: by prostaglandins (PGs) - enhance the receptor response to the noxious stimuli
• _____-: by NMDA receptor mediated long-term potentiation
• Hyperalgesia and allodynia
Peripheral
Central
Aspirin and other NSAIDs - inhibit synthesis of PGs ————-> ________ effect
Analgesic
Pain can be characterized as either ____ or ____
Fast or slow
________– initial perception as brief, sharp sensation that is easily localized – originates from specific mechanical or thermal receptors
Fast pain
_______ pathway tends to be activated by chemicals like bradykinin or other PGs (prostaglandins)
◦ Pain can be provoked by stimulating ________receptors
◦ Also can contribute to the ________ response to tissue injury
◦ Persistence of these chemicals —> long lasting pain that continues after removal of the mechanical or thermal stimulus
Slow pain
Polymodal
Inflammatory
Pain impulses are transmitted to the CNS via one of two types of afferent fibers
◦ Distinguished by diameter and conduction _____
◦ _______ are myelinated, medium size and fast – cold, warmth, mechanical
◦ ______ are unmyelinated, smallest and slowest – heat, cold, mechanical
Aδ fibers
C fibers
Velocity
Two best-known pain neurotransmitters:
__________:
◦ Activates ascending pathways that transmit nociceptive signals to higher levels for further processing
_______:
◦ Major excitatory neurotransmitter
◦ Binding to AMPA receptors -> APs in dorsal horn neurons
◦ Binding to NMDA receptors -> increases _____ entry- activates second messenger systems that
make the neurons more excitable-> contributes to hypersensitivity/hyperalgesia in injured areas
Substance P
Glutamate
Ca2+
in Brown Sequard Syndrome, which side of the body losses pain sensation and which side losses touch sensation?
Pain sensation- opposite side
Touch sensation - same side
______- Pain is perceived due to abnormal signaling
Sensitization
________: lowered threshold to the thermal or mechanical stimulation- induced pain at the injured site
Hyperalgesia
______: normally innocuous stimulus (touch) can result in a painful sensation due to sensitization of the adjacent uninjured tissue (2nd hyperalgesia)
Allodynia
____ is the main component for sensitizing procedure of the nociceptors
PG
________ (acting on NMDA receptors) plays a role in this in terms of sensitizing dorsal horn afferents- central sensitization
Glutamate
________: Built in pain-suppressing system that involves the periacqueductal gray matter
(PAG) and the reticular formation
Endogenous analgesic
Stimulation of the PAG or reticular formation -> profound _______
Analgesia
analgesia
◦ Blocks ______ release from afferent nerve terminals (presynaptic inhibition)
Substance P
Analgesia Depends on presence of _____ receptors – endogenous opiates include endorphins,
enkephalins and dynorphin (e.g., ‘runner’s ‘high’)
◦ Released from the terminals of descending analgesic pathway and bind to the opiate receptors on the presynaptic terminal of the primary sensory ______ —> blocks further transmission of pain signal by presynaptic inhibition
Opiate
Afferent
Why does tactile stimulation can reduce pain?
Gate control theory of pain modulation
A(b) afferent fibers that carry mechanosensitive information can act to block ___________
• Ab terminals synapse on inhibitory interneurons and enhance the inhibitory activity of these interneurons, while c fibers inhibit them If simultaneous information from Ab and C fibers reaches the inhibitory interneurons, then the outcome is an integrated response that provides partial inhibition of the ascending pain pathway
• Perception of pain is lessened
Pain transmission
Gate control theory of pain modulation:
A. In absence of input from ______, topically active inhibitory inter neuron suppresses pain pathway
B. With strong pain , c fibres stops inhibition of the pathway , allowing a strong signal to be sent to the ____
C. Pain can be modulated by simultaneous _______ input
C fibres
Brain
Somatosensory
