Pain Physiology Lecture Notes PDF

# Neuro-Physiology ## LECTURE NO (3) ### PAIN PHYSIOLOGY 1 #### Abdelmuhsin Hussien Mohamed #### Faculty Of Medicine Head Dept. Of Physiology # What is Pain? ## Definition: Pain is an unpleasant sensation caused by noxious stimulation of the sensory nerve endings due to actual or potential damage....

# Neuro-Physiology ## LECTURE NO (3) ### PAIN PHYSIOLOGY 1 #### Abdelmuhsin Hussien Mohamed #### Faculty Of Medicine Head Dept. Of Physiology # What is Pain? ## Definition: Pain is an unpleasant sensation caused by noxious stimulation of the sensory nerve endings due to actual or potential damage. # Pain sensation - Pain is unpleasant sensation that is characterized by the following: - It has protective function initiate the withdrawal reflex. - Pain can be produced by mechanical, thermal or chemical stimuli that lead to tissue damage. # PAIN RECEPTORS - They are free nerve endings and their cell bodies are found in the spinal ganglia body and trigeminal nerve ganglia Face. - It is widely distributed particularly in the skin. - They respond to different types of stimuli when their intensity reach the noxious threshold the nociceptors. - Non Adapting receptors. # Mechanism of stimulation of pain receptors: - Pain receptors are stimulated chemically by certain substances released from the damaged tissues is pain producing substances PPS e.g. bradykinin, histamine, serotonin, acids, excess K+ ions, prostaglandins. # Mechanisms of stimulation of pain receptors: - A diagram of a hand is shown, representing the skin. Labels in a rectangle under the diagram include "Thermal", "Chemical", and "Mechanical". There is a match, a glass beaker with an acid liquid, a syringe and a hammer, representing the types of stimulus. - The diagram represents that a stimulus travels through the hand to the spinal cord. - The spinal cord has a label "DRG (cell body). - The signal then travels to the brain, with a label "Pain Avoidance Emotional reaction". - There is also a line coming out of the spinal cord that travels back down to the hand with a label "Withdrawal". # Mechanism of pain - A diagram of a spinal cord is shown. The spinal cord has a label "Dorsal horn" - The top of the diagram is labeled "To Brain". - Several arrows and labels showing the path of the signal are included. - Arrows to the left of the spinal cord show the path of "Aspartate, Neurotensin, Glutamate, Substance P". - To the right of the spinal cord shows the path of "lon Fluxes H+/K+". - Below the spinal cord is a label "Mast Cell" with arrows pointing to it. - An arrow pointing upwards to the right of the spinal cord is labeled "spinothalamic Tract". - To the right of the spinal cord is a label "Tissue Injury" and a label "Sensitized Nociceptor". - Arrows coming from Tissue Injury show the path of "Bradykinin", "Leukotrienes" and "Histamine". # Reactions associate with pain ## 2. Autonomic reactions: - Mild pain stimulates posterior hypothalamus - Sympathetic changes: - Tachycardia - Increase in BP - Pupillodilatation - Increase respiration - Server pain stimulates anterior hypothalamus - Parasympathetic changes : - Bradycardia - Hypotension # 2. Motor reactions: - Withdrawal reflex - Reflex contraction of overlying muscles Deep somatic & visceral pain # 3-Emotional effects: - Crying - Anxiety - Depression, etc. # Quality of pain - A table with these headers and rows is shown: "Fast pricking", "Slow burning", "Afferent", "Onset", "Duration", "Nature", "Localization", "Center", "Site of receptors", "Chemical transmitter". The table includes 2 columns. Each column includes data associated with the header at the top. - Data in the table includes A delta fibers, C fibers, Immediate, Follow fast pain, Short, Longer, Pricking, Burning, Well localized, Poorly localized, Sensory cortex, thalamus, Skin, Subcutaneous tissues& viscera, Glutamate, Substance P. # Types of Pain ## According to site of origin receptors: - Cutaneous pain. - Deep pain. - Visceral pain # Cutaneous pain - This type of pain is perceived as a result of stimulation of pain receptors in the skin. - Afferents: - Thin myelinated A delta fibers # Deep pain - Origin: pain receptors in the deep structures as muscles, ligaments and joints. - Afferent: non myelinated C- fibers - Nature: dull aching. - Localization: poorly localized. # Visceral Pain - Origin: from internal viscera. - Nature: dull aching. - Afferent: non myelinated C fibers pass mainly with autonomic fibers. - Localization: poorly localized. # Types of Pain - A table is shown with the following headers: "Superficial Somatic Pain", "Deep Somatic Pain", "Visceral Pain". - The table includes 6 rows with data associated with each header. - Row 1 includes: "Arise from the skin and subcutaneous tissue", "Arise from muscles, ligaments, joints, tendons and peri-osteum of bones", "Arise from the viscera". - Row 2 includes: "Well localized", "Poorly localized", "Poody localized". - Row 3 includes: "Usually not associated with autonomic disturbances", "Often associated with autonomic disturbances", "Often associated with autonomic disturbances". - Row 4 includes: " - ", "May be referred or radiate to other sites", "Often referred or radiates to other sites". - Row 5 includes: " - ", "Causes reflex contraction of the overlying muscles → Ischaemia->more pain", "Causes reflex contraction of the overlying muscle → rigidity guarding reflex". - Row 6 includes: "Transmitted by Somatic nerves", "Transmitted by somatic nerves", "Transmitted by autonomic nerves". # PAIN PATHWAY - An image showing the nerves from the hand traveling to the brain is shown. - The brain is divided into an anterior and posterior part. - The image has several labels, including "Nociceptor", "Spinothalamic-tract", "Spinoreticular-tract", "Reticular formation", "Midbrain", "Pons", "Medulla", "Reticulospinal tract". - Labels on the posterior section of the brain include "Primary somatosensory cortex (postcentral gyrus)", "Somatosensory association area", "Thalamus", "Hypothalamus", "Limbic system". - Labels that go across the image include ")"interpretation of pain quality & topognosis", "Perception of pain", "Alertness", "Behavioral & emotional response". # Referred pain - Pain is referred to the dermatome supplied by the same dorsal nerve roots as the diseased structure. - Referred pain is explained by two theories: - Convergence projection theory. - Facilitation theory. # Important examples of referred pain - Organ and Site of referral are listed in a table. - Organs listed include: "Heart", "Appendix", "Small intestine", "Central part of diaphragm", "Pleura", "Kidney", "Ureter", "Trigone of bladder", "Tongue", "Teeth", "Hip", "Uterus". - Sites of referral include: "Precordium; inner aspect of left arm; epigastrium", "Umbilicus", "Tip of shoulder", "Abdomen", "Costovertebral angle (Loin)", etc. # Mechanism of referred pain ## I-Convergence projection theory: - Afferent pain fibers from the skin area and the diseased viscera converge on the same second order neuron and finally stimulate the same cortical neuron. - Cortex will feel pain as if it is coming from the skin because the sensory cortex is accustomed to receive pain from the skin. # Convergence projection theory: - A diagram depicts the pain receptors in the left arm traveling along the same nerves from the heart to the spinal cord for interpretation by the brain. - The brain interprets the pain as left arm pain. - Labels on the diagram include: - Brain interprets source of pain as left arm - Pain pathway to brain - Spinal cord convergence - Sensory fibers - Pain in heart - Skin of left arm # 2-Facilitation theory - Visceral pain afferent fibers send collaterals to facilitate the second order neuron of pain pathway from the skin area of reference facilitating the pain sensation from this area. - Minor activity in the pain pathway from this area leads to pain sensation. # Facilitate theory - A diagram of the spinal cord and nerves traveling from the skin and viscus is shown. - The location where the nerves connect is labeled "threshold". # ANY QUESTION - An image of a brain held by a gloved hand is shown..