CHAPTE
R 35
Nociception: ability to feel pain
TRANSDUCTION: the activation of pain receptors
o It involves conversion of painful stimuli into electrical impulses that travel from
the periphery to the spinal cord at the dorsal horn.
o The nociceptors, or peripheral receptors, respond selectively to mechanical,
thermal, and chemical stimuli that are noxious
Other substances that stimulate nociceptors:
Bradykinin, a powerful vasodilator that increases capillary
permeability and constricts smooth muscle, plays an important
role in the chemistry of pain at the site of an injury even before
the pain message gets to the brain.
o Triggers the release of histamine and, in combination with
it, produces the redness, swelling, and pain typically
observed when an inflammation is present.
Prostaglandins are important hormone-like substances that send
additional pain stimuli to the CNS.
Substance P sensitizes receptors on nerves to feel pain and also
increases the rate of firing of nerves.
o Neurotransmitters: substances that either excite or inhibit target nerve cells
Prostaglandins
Substance P
Serotonin: a hormone that can act to stimulate smooth muscles, inhibit
gastric secretion, and produce vasoconstriction
o Mechanical stimulants: Friction from bed linens and pressure from a cast
o thermal stimulants: sunburn and cold water on a tooth with carries
o chemical stimulant: an acid burn
o electrical stimulant: the jolt of a static charge
TRANSMISSION: The conduction of pain sensations from the site of an injury or
inflammation along pathways to the spinal cord and then on to higher centers
o Afferent receptors: Fibers carrying impulses from the pain receptors towards the
brain
A-delta-fibers: fast-conducting; transmit acute, well-localized pain that is
typically elicited by mechanical or thermal stimuli
Sensory impulses travel over A-fibers through the dorsal root
ganglion to the dorsal horn of the spinal cord.
o At this point, the sensory nerve impulse synapses with a
motor neuron, and the impulse is carried along efferent
nerve pathways back to the site of the painful stimulus in a
reflex arc.
This results in an immediate muscle contraction
intended to withdraw/remove the injured body
part from the source of the pain.
, CHAPTE
R 35
C-fibers: slow-conducting; convey diffuse, longer-lasting pain that is
triggered by chemical stimuli or persistent mechanical or thermal stimuli
PERCEPTION of pain involves the sensory process that occurs when a stimulus for pain is
present. (the person’s interpretation of the pain)
o Pain threshold: the minimum intensity of a stimulus that is perceived as painful
Adaption may affect this perception of pain
MODULATION: The process by which the sensation of pain is inhibited or modified
o Neuromodulators: Substances that regulate or modify the sensation of pain
Endogenous opioid compounds, meaning they are naturally present,
morphine-like chemical regulators in the spinal cord and brain.
They appear to have analgesic activity and alter the perception of pain
produced by binding to specific opioid receptor sites throughout the CNS,
blocking the release of production of pain-transmitting substances
Activated by both pain and stress
Endorphin and enkephalins are opioid neuromodulators:
Endorphins are produced at neural synapses at various points
along the CNS pathway. They are powerful pain-blocking
chemicals that have prolonged analgesic effects and produce
euphoria.
o may be released when certain measures are used to
relieve pain, such as skin stimulation and relaxation
techniques, and when certain pain-relieving drugs are
used.
o The endorphin, dynorphin, has the most potent analgesic
effect.
Enkephalins are thought to reduce pain sensation by inhibiting
the release of substance P from the terminals of afferent neurons.
GATE CONTROL THEORY OF PAIN
o Describes the transmission of painful stimuli and recognizes a relation between
pain and the projection of pain information to the brain
o Small nerve fibers conduct excitatory pain stimuli toward the brain, exaggerating
the effect of the arriving impulses through a positive feedback mechanism
o Large nerve fibers Appear to inhibit the transmission of pain impulses from the
spinal cord to the brain through a negative feedback system
o When too much sensory information is sent through, certain cells in the spinal
column send a signal as if closing a gate
Past experiences, the cultural and social environment, personal
expectations, beliefs about pain, the emphasis placed on pain , and
emotions also have an impact on opening and closing of the gate
TYPES OF PAIN
o Duration of pain:
o Acute pain: generally rapid in onset and varies in intensity from mild to severe. It
is protective in nature.
R 35
Nociception: ability to feel pain
TRANSDUCTION: the activation of pain receptors
o It involves conversion of painful stimuli into electrical impulses that travel from
the periphery to the spinal cord at the dorsal horn.
o The nociceptors, or peripheral receptors, respond selectively to mechanical,
thermal, and chemical stimuli that are noxious
Other substances that stimulate nociceptors:
Bradykinin, a powerful vasodilator that increases capillary
permeability and constricts smooth muscle, plays an important
role in the chemistry of pain at the site of an injury even before
the pain message gets to the brain.
o Triggers the release of histamine and, in combination with
it, produces the redness, swelling, and pain typically
observed when an inflammation is present.
Prostaglandins are important hormone-like substances that send
additional pain stimuli to the CNS.
Substance P sensitizes receptors on nerves to feel pain and also
increases the rate of firing of nerves.
o Neurotransmitters: substances that either excite or inhibit target nerve cells
Prostaglandins
Substance P
Serotonin: a hormone that can act to stimulate smooth muscles, inhibit
gastric secretion, and produce vasoconstriction
o Mechanical stimulants: Friction from bed linens and pressure from a cast
o thermal stimulants: sunburn and cold water on a tooth with carries
o chemical stimulant: an acid burn
o electrical stimulant: the jolt of a static charge
TRANSMISSION: The conduction of pain sensations from the site of an injury or
inflammation along pathways to the spinal cord and then on to higher centers
o Afferent receptors: Fibers carrying impulses from the pain receptors towards the
brain
A-delta-fibers: fast-conducting; transmit acute, well-localized pain that is
typically elicited by mechanical or thermal stimuli
Sensory impulses travel over A-fibers through the dorsal root
ganglion to the dorsal horn of the spinal cord.
o At this point, the sensory nerve impulse synapses with a
motor neuron, and the impulse is carried along efferent
nerve pathways back to the site of the painful stimulus in a
reflex arc.
This results in an immediate muscle contraction
intended to withdraw/remove the injured body
part from the source of the pain.
, CHAPTE
R 35
C-fibers: slow-conducting; convey diffuse, longer-lasting pain that is
triggered by chemical stimuli or persistent mechanical or thermal stimuli
PERCEPTION of pain involves the sensory process that occurs when a stimulus for pain is
present. (the person’s interpretation of the pain)
o Pain threshold: the minimum intensity of a stimulus that is perceived as painful
Adaption may affect this perception of pain
MODULATION: The process by which the sensation of pain is inhibited or modified
o Neuromodulators: Substances that regulate or modify the sensation of pain
Endogenous opioid compounds, meaning they are naturally present,
morphine-like chemical regulators in the spinal cord and brain.
They appear to have analgesic activity and alter the perception of pain
produced by binding to specific opioid receptor sites throughout the CNS,
blocking the release of production of pain-transmitting substances
Activated by both pain and stress
Endorphin and enkephalins are opioid neuromodulators:
Endorphins are produced at neural synapses at various points
along the CNS pathway. They are powerful pain-blocking
chemicals that have prolonged analgesic effects and produce
euphoria.
o may be released when certain measures are used to
relieve pain, such as skin stimulation and relaxation
techniques, and when certain pain-relieving drugs are
used.
o The endorphin, dynorphin, has the most potent analgesic
effect.
Enkephalins are thought to reduce pain sensation by inhibiting
the release of substance P from the terminals of afferent neurons.
GATE CONTROL THEORY OF PAIN
o Describes the transmission of painful stimuli and recognizes a relation between
pain and the projection of pain information to the brain
o Small nerve fibers conduct excitatory pain stimuli toward the brain, exaggerating
the effect of the arriving impulses through a positive feedback mechanism
o Large nerve fibers Appear to inhibit the transmission of pain impulses from the
spinal cord to the brain through a negative feedback system
o When too much sensory information is sent through, certain cells in the spinal
column send a signal as if closing a gate
Past experiences, the cultural and social environment, personal
expectations, beliefs about pain, the emphasis placed on pain , and
emotions also have an impact on opening and closing of the gate
TYPES OF PAIN
o Duration of pain:
o Acute pain: generally rapid in onset and varies in intensity from mild to severe. It
is protective in nature.
