Lecture 8: Mechanosensation & Pain

Question 1

Different forms of specific receptors are sensitive to pressure, stretch, vibration,
acceleration, and sound
Five types of touch receptors :
1.
2.
3.
4.
5.

Answer 1

Pacinian corpuscle
Meissner’s corpuscle
Merkel’s disc
Ruffini’s ending
Free nerve ending

Question 2

___________: 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

Answer 2

Phasic receptors

Question 3

_______: produce a relatively constant rate of depolarization & firing as long as the stimulus is maintained

Answer 3

Tonic receptors

Question 4

_____ receptors are the most common receptors in the body

Answer 4

Touch

Question 5

_____-: An unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential
tissue damage

Answer 5

Pain ( nociception )

Question 6

______ of painful experiences in memory helps us avoid
potentially harmful events in future

Answer 6

Storage

Question 7

Stimulation of ______ Produces the Perception of Pain

Answer 7

Nociceptors

Question 8

Pain receptors are generally free ______

Answer 8

Nerve endings

Question 9

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

Answer 9

mechanical

thermal

polymodal

Question 10

Do nociceptors adapt?

Answer 10

NO

Question 11

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

Answer 11

Peripheral
Central

Question 12

Aspirin and other NSAIDs - inhibit synthesis of PGs ————-> ________ effect

Answer 12

Analgesic

Question 13

Pain can be characterized as either ____ or ____

Answer 13

Fast or slow

Question 14

________– initial perception as brief, sharp sensation that is easily localized – originates from specific mechanical or thermal receptors

Answer 14

Fast pain

Question 15

_______ 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

Answer 15

Slow pain
Polymodal
Inflammatory

Question 16

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

Answer 16

Aδ fibers
C fibers
Velocity

Question 17

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

Answer 17

Substance P
Glutamate
Ca2+

Question 18

in Brown Sequard Syndrome, which side of the body losses pain sensation and which side losses touch sensation?

Answer 18

Pain sensation- opposite side
Touch sensation - same side

Question 19

______- Pain is perceived due to abnormal signaling

Answer 19

Sensitization

Question 20

________: lowered threshold to the thermal or mechanical stimulation- induced pain at the injured site

Answer 20

Hyperalgesia

Question 21

______: normally innocuous stimulus (touch) can result in a painful sensation due to sensitization of the adjacent uninjured tissue (2nd hyperalgesia)

Answer 21

Allodynia

Question 22

____ is the main component for sensitizing procedure of the nociceptors

Answer 22

PG

Question 23

________ (acting on NMDA receptors) plays a role in this in terms of sensitizing dorsal horn afferents- central sensitization

Answer 23

Glutamate

Question 24

________: Built in pain-suppressing system that involves the periacqueductal gray matter
(PAG) and the reticular formation

Answer 24

Endogenous analgesic

Question 25

Stimulation of the PAG or reticular formation -> profound _______

Answer 25

Analgesia

Question 26

analgesia
◦ Blocks ______ release from afferent nerve terminals (presynaptic inhibition)

Answer 26

Substance P

Question 27

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

Answer 27

Opiate
Afferent

Question 28

Why does tactile stimulation can reduce pain?

Answer 28

Gate control theory of pain modulation

Question 29

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

Answer 29

Pain transmission

Question 30

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

Answer 30

C fibres
Brain
Somatosensory