Pain
Definition of pain
? A signal of disease
? Unpleasant sensation localized to a part of the body
? Penetrating or tissue destructive process
stabbing burning twisting tearing squeezing
? Bodily or emotional reaction
terrifying nauseating sickening
? Accompanied by anxiety
? Urging to escape or terminating the feeling
? Both sensation and emotion
Pathophysiology
?Irritating substances
bradykinins serotonin acetylchonie histamine
5-hydroxytypamine prostaglandins acid metabolites
?Sensation of nerve endings,
sending through posterior root of spinal cord
cross to the other side
through spinothalamic tract,lateral medulla pons,internal
capsule,spread into parietal and frontal lobe
?Segmental distribution of sensation
The pain sensory system
The primary afferent nociceptor,
(初级传入伤害感受器 )
?A peripheral nerve (外周神经 )consists of axons (轴索 )of
three different types of neurons (神经元 ),
primary sensory afferents(初级感觉传入 )
motor neurons(运动神经元 )
sympathetic postganglionic neurons(交感神经节后神经元 )
?The cell bodies of primary afferents,located in the dorsal
root ganglia in the vertebral formina
Primary afferent nociceptor
?Primary afferent axon bifurcates to send one
process into the spinal cord and the other to
innervate bodily tissue
?Primary afferents are classified by their diameter,
degree of myelination,and conduction velocity
A-beta
A-delta
C fiber
Primary afferent nociceptor
?A-beta fiber,largest-diameter fiber,respond maximally in nerves
that innervate the skin,Normally,it does not produce pain,
?A-delta fiber,6~8 ?m in diameter
?C fiber,2~4?m in diameter,unmyelinated
Most A-delta and C afferents respond maximally only to
intense (painful) stimuli and produce pain when they are
electrically stimulated; this defines them as primary afferent
nociceptors (pain receptors)
Primary afferent Components of a
typical cutaneous nerve
Sensitization (1)
? When intense,repeated or prolonged stimuli are applied
if tissue is damaged or if inflammation is present
? The threshold for activating primary afferent nociceptors
is lowed and the frequency of firing is higher for all
stimulus intensities,This process is called sensitization,
?Deep tissues are relatively insensitive to noxious
mechanical or thermal stimuli
? When inflammation exist,deep tissues become exquisitely
sensitive to mechanical stimulation
Sensitization (2)
?Inflammatory mediators (bradykinin,prostaglands,
leukotrienes) can activate or sensitize primary afferents
?Most A-delta and C afferents innervating viscera
insensitive in normal tissue,become sensitive in the
case of inflammation
Nociceptor-induced inflammation
? Afferent nociceptors have a neuroeffector function
? Most nociceptors containing polypeptide mediators
released from their peripheral terminals when are
activated
Substance P
Substance P
? An 11- amino acid peptide
? Released from primary afferent nociceptors
? Biological activities,
Potent vasodilator
Degranulates mast cell
Chemoattractant for leukocytes
Inflammatory mediator
Central pathways for pain
The axons of primary afferent nociceptors
?Entering the spinal cord via the dorsal root
?Terminating in the dorsal horn of the spinal gray
matter
?Contacting spinal neurons that transmit the pain
signal to brain sites involved in pain perception
Central pathways for pain
?The axon of each primary afferent contacts many
spinal neurons
?Each spinal neuron receives convergent inputs
from many primary afferents
Central pathway for pain
The convergence of many sensory inputs to a
single spinal pain-transmission neuron is of great
importance because it underlines the phenomenon
of referred pain
All spinal neurons that receive input from the visera and
deep musculoskeletal structures also receive input from
the skin
Referred pain
The diseased internal organ sends pain impulse
through spinal cord,which reflects the impulse
to corresponding segment of integument
Referred pain
?The afferents supply the central diaphragm are derived
from the third and forth cervical dorsal root ganglia,
?Primary afferents with cell bodies in these same ganglia
supply the skin of the shoulder and low neck,
?Thus sensory inputs from both the shoulder skin and the
central diaphragm converge on pain-transmission
neurons in the third and forth cervical spinal segments,
? Because of this convergence and the fact that the spinal
neurons are most often activated by inputs from the skin,
activity evoked in spinal neurons by input from deep
structures is mislocalized by the patient to a place that is
roughly coextensive with the region of skin innervated by
the same spinal segment
? Coronary ischemic pain usually radiates to medial side
of arm and fingers,which were supplied by 6th~8th
cervical (or T1~T2) over the left side
Referred pain
Definition of pain
? A signal of disease
? Unpleasant sensation localized to a part of the body
? Penetrating or tissue destructive process
stabbing burning twisting tearing squeezing
? Bodily or emotional reaction
terrifying nauseating sickening
? Accompanied by anxiety
? Urging to escape or terminating the feeling
? Both sensation and emotion
Pathophysiology
?Irritating substances
bradykinins serotonin acetylchonie histamine
5-hydroxytypamine prostaglandins acid metabolites
?Sensation of nerve endings,
sending through posterior root of spinal cord
cross to the other side
through spinothalamic tract,lateral medulla pons,internal
capsule,spread into parietal and frontal lobe
?Segmental distribution of sensation
The pain sensory system
The primary afferent nociceptor,
(初级传入伤害感受器 )
?A peripheral nerve (外周神经 )consists of axons (轴索 )of
three different types of neurons (神经元 ),
primary sensory afferents(初级感觉传入 )
motor neurons(运动神经元 )
sympathetic postganglionic neurons(交感神经节后神经元 )
?The cell bodies of primary afferents,located in the dorsal
root ganglia in the vertebral formina
Primary afferent nociceptor
?Primary afferent axon bifurcates to send one
process into the spinal cord and the other to
innervate bodily tissue
?Primary afferents are classified by their diameter,
degree of myelination,and conduction velocity
A-beta
A-delta
C fiber
Primary afferent nociceptor
?A-beta fiber,largest-diameter fiber,respond maximally in nerves
that innervate the skin,Normally,it does not produce pain,
?A-delta fiber,6~8 ?m in diameter
?C fiber,2~4?m in diameter,unmyelinated
Most A-delta and C afferents respond maximally only to
intense (painful) stimuli and produce pain when they are
electrically stimulated; this defines them as primary afferent
nociceptors (pain receptors)
Primary afferent Components of a
typical cutaneous nerve
Sensitization (1)
? When intense,repeated or prolonged stimuli are applied
if tissue is damaged or if inflammation is present
? The threshold for activating primary afferent nociceptors
is lowed and the frequency of firing is higher for all
stimulus intensities,This process is called sensitization,
?Deep tissues are relatively insensitive to noxious
mechanical or thermal stimuli
? When inflammation exist,deep tissues become exquisitely
sensitive to mechanical stimulation
Sensitization (2)
?Inflammatory mediators (bradykinin,prostaglands,
leukotrienes) can activate or sensitize primary afferents
?Most A-delta and C afferents innervating viscera
insensitive in normal tissue,become sensitive in the
case of inflammation
Nociceptor-induced inflammation
? Afferent nociceptors have a neuroeffector function
? Most nociceptors containing polypeptide mediators
released from their peripheral terminals when are
activated
Substance P
Substance P
? An 11- amino acid peptide
? Released from primary afferent nociceptors
? Biological activities,
Potent vasodilator
Degranulates mast cell
Chemoattractant for leukocytes
Inflammatory mediator
Central pathways for pain
The axons of primary afferent nociceptors
?Entering the spinal cord via the dorsal root
?Terminating in the dorsal horn of the spinal gray
matter
?Contacting spinal neurons that transmit the pain
signal to brain sites involved in pain perception
Central pathways for pain
?The axon of each primary afferent contacts many
spinal neurons
?Each spinal neuron receives convergent inputs
from many primary afferents
Central pathway for pain
The convergence of many sensory inputs to a
single spinal pain-transmission neuron is of great
importance because it underlines the phenomenon
of referred pain
All spinal neurons that receive input from the visera and
deep musculoskeletal structures also receive input from
the skin
Referred pain
The diseased internal organ sends pain impulse
through spinal cord,which reflects the impulse
to corresponding segment of integument
Referred pain
?The afferents supply the central diaphragm are derived
from the third and forth cervical dorsal root ganglia,
?Primary afferents with cell bodies in these same ganglia
supply the skin of the shoulder and low neck,
?Thus sensory inputs from both the shoulder skin and the
central diaphragm converge on pain-transmission
neurons in the third and forth cervical spinal segments,
? Because of this convergence and the fact that the spinal
neurons are most often activated by inputs from the skin,
activity evoked in spinal neurons by input from deep
structures is mislocalized by the patient to a place that is
roughly coextensive with the region of skin innervated by
the same spinal segment
? Coronary ischemic pain usually radiates to medial side
of arm and fingers,which were supplied by 6th~8th
cervical (or T1~T2) over the left side
Referred pain
