PAIN Dr Ghulam Mustafa

LO’s of the class Define pain Properties of pain Stimuli for pain Receptors for Pain Causes of pain Types of pain w.r.t., Site Fast vs Slow pain Pain pathways Body response to pain

Unpleasant sensory experience that is elicited by Noxious or nociceptive stimuli

Properties of pain Pain is a protective reflex Pain receptors are widely distributed Commonest symptom Earliest sign of Morbidity Non adaptive receptors Certain viscera insensitive to pain –Brain –Liver parenchyma –Alveoli

Stimuli for pain Mechanical Thermal –More than 45°C Chemical –Bradykinin –Serotonin –Histamine –Potassium ions –Proteolytic enzymes

Receptors for Pain 1.Superficial skin layers 2.Internal tissues Periostium Joint surfaces Arterial walls Falx and tentorium

Causes of pain 1.Tissue damage Bradykinin Increased Potassium Increased Proteolytic enzymes Rate of tissue damage α Pain intensity 2.Tissue Ischemia Lactic acid by Anerobic metabolism Bradykinin and proteolytic enzymes

Causes of pain 3Muscle spasm Stimulate mechanosensitive pain receptors –Compress the blood vessels and cause ischemia –Increases the rate of metabolism

Types of pain w.r.t., Site 1.Cutaneous pain Skin and subcutaneous tissues Accurately localized 2.Deep somatic pain Muscles, Tendons, Joints, Ligaments Mechanical forces, Ischemia, Chemicals 3.Visceral pain Poorly localize, radiates or refers Associated with ANS dysfunction Rigidity & tenderness nearby skeletal muscles

Fast pain –Sharp pain –Pricking pain –Acute pain –Electric pain Stimuli –Mechanical –Thermal –Electrical Transmission –A Delta Fibres Slow Pain –Burning pain –Ache –Throbbing pain –Chronic pain Stimuli –Chemical Transmission –Type C fibres

Transmission velocity –6 to 30 m/s Perception time –0.1 sec after stimulation Body parts involved –Usually skin Duration –Short Neurotransmitter –Glutamate Transmission velocity –0.5 to 2 m/s Perception time –1 sec or more Body parts involved –Skin and deep tissues Duration –Long Neurotransmitter –Substance P

Localized Examples of stimuli Needle prick Skin cut Burn Electric shock Neo spino thalamic tract Diffuse Tissue destruction Paleo spino thalamic tract

A Delta fibres Terminate in Lamina I Lamina Marginalis Excite 2 nd order neurons Cross to opp side thru Ant commissure Pass upward in Anterolateral pathway Type C fibres Terminate in Lamina II & III substantia gelatinosa Signals thru short fibre neurons Reach Lamina V Last neuron give rise to long axons Cross to opp side thru Ant commissure Pass upward in Anterolateral pathway

Neospinothalamic Few –Reticular areas of brain stem Most –Thalamus –Ventro basal complex –Post nuclear gp Somatosensory cortex

Paleo spino thalamic –Reticular areas of medulla and pons –Tectal area of mesencephalon –Peri aqueductal gray region From brain stem –Intra laminar nuclei –V/L Nuclei of thalamus –Hypothalamus

Body response to pain Motor reaction: –Withdrawl reflex –Muscle rigidity Autonomic reaction –Mild pain Posterior hypothalamic nuclei –Increased sympathetic discharge –Tachycardia –Increased Blood pressure

Severe pain Anterior hypothalamic nuclei –Increased Para sympathetic discharge –Bradycardia –Decreased Blood pressure Emotional reactions –Anxiety –Depression –Crying

LO’s were Define pain Properties of pain Stimuli for pain Receptors for Pain Causes of pain Types of pain w.r.t., Site Fast vs Slow pain Pain pathways Body response to pain