Pain and the Nervous System PDF

Central Nervous System Dr. Nermeen Bastawy and Dr. somia mokabel  ‫بسم هللا الرحمن الرحيم‬ ‫اللهم ال سهل إال ما جعلته سهال وأنت تجعل الحزن إن‬ ‫شئت سهال‬ Pain Sensation Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue...

Central Nervous System Dr. Nermeen Bastawy and Dr. somia mokabel  ‫بسم هللا الرحمن الرحيم‬ ‫اللهم ال سهل إال ما جعلته سهال وأنت تجعل الحزن إن‬ ‫شئت سهال‬ Pain Sensation Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage. Pain sensation is a protective mechanism for the body; it motivates the individual to withdraw from damaging situations, to protect a damaged body part while it heals, and to avoid similar experiences in the future. Pain receptors Free never ending: slowly non adapting they are excited by the following agents: Chemicals: Chemo-sensitive pain receptors. Excessive heat : Thermo-sensitive pain receptors. Mechanical stress : Mechano-sensitive pain receptors. Mechanism of stimulation of pain receptors: They are stimulated chemically by certain substances released from damaged tissues e.g. Bradykinin, substance P, histamine, Serotonin, K+ ions, Proteolytic enzymes and prostaglandins. Types of pain According to location of pain : cutaneous (skin), deep (joints and bones), visceral (body organs). According to the quality of pain: Sharp pricking Dull aching  Cutaneous pain This type of pain is perceived as a result of stimulation of pain receptors in the skin. Pain receptors are slowly-adapting receptors, which continuously inform the CNS about tissue damage.  Cutaneous Pain This may be fast well- localized pricking pain or slow diffuse burning pain. It is not referred to other areas Resulted in a serious of reactions Reactions of pain  Reactions of Pain Somatic Emotional Autonomic effects Reflexes effects: withdrawal (e.g. crying, - Sympathetic reflex restlessness effects - protective, - If severe, and anxiety) Cutaneous & prepotent Parasympatic due to hyperalgesia effects stimulation of the limbic (tenderness) system Pain pathway DRG (1st order neuron  Perception of pain signals Fast pain Thalamus & cortex (SSI,II) Slow pain Thalamus  RF & others Role of the cortex in pain perception: 1.Localization & intensity of pain 2.Emotion reactions to pain 3.Control of pain  Deep Pain Causes: (1) Trauma to the deep structures. (2) Bone fractures and inflammation, due to excitation of the periosteal pain receptors. (3) Arthritis. (4) Severe muscle spasm e.g.in tetany Ischemic pain : This occurs due to either a severe muscle spasm or an occlusive vascular disease & it occurs as follows: A certain metabolite known as Lewis P factor causes pain if it accumulates in the muscle. Visceral Pain Visceral Pain Pain is the only sensation produced from the viscera. Most viscera contain only few pain receptors, so localized damage is not painful. However, a generalized damage causes pain. If a viscus is inflamed, minor stimuli may cause sever pain  (2) Interneuronal Characters of barrages Visceral Pain (circuits) (1)It is a slow pain. (2)It is diffuse (i.e.poorly- localized). (3)It is often dull aching, but it may be spasmodic in the form of colic.  (2) Interneuronal Characters of barrages Visceral Pain (circuits) (5)It is often associated with sweating, nausea and vomiting as well as parasympathetic effects e.g. bradycardia and hypotension. (6)It often causes Referred pain SGR The gate theory of pain SGR act as a gate for pain transmission. - The gate is opened by Impulses from C fibers release substance P - The gate is closed by by spinal and supraspinal inhibition: 1) Spinal (Peripheral) gate inhibition: Stimulation of Aβ fibers  ++ enkephalins or GABA  inhibition of SGR Examples: Rubbing or massage of skin Counter irritation: e.g. heat, cold, mustard plaster Acupuncture  The gate theory of pain (2) Supraspinal (Central) Descending Analgesia System: 3 A- Hypothalamus B- Anterior pituitary gland Endogenous Opioids C- Periaqueductal gray area (PGA) Beta endorphins D- Raphe magnus nucleus Enkephalins E- Pain inhibitory complex area in the spinal cord Dynorphins These areas secrete analgesics called opioids  inhibition of SGR (prevent release of substance P)  Stress induced Analgesia Soldiers wounded in the battle Athletes wounded in the sport events Sometimes they don’t feel pain during the stress but experience pain later at the end. Stress stimulates H.th or Pituitary gland to secrete opioids