Pain
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
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
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
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 •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:6-8μ m in diameter eC fiber: 2-4um 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 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: 2~4m 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 Dorsal Root Ganglion Peripheral Nerve Spinal Cord AS C OD Sympathetic Sympathetic Preganglionic Postganglionic
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 (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
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
Nociceptor-induced inflammation • Afferent nociceptors have a neuroeffector function • Most nociceptors containing polypeptide mediators released from their peripheral terminals when are activated Substance P
