Pain Lecture Notes PDF

Assafa College Department of Physiology NERUROPHYSIOLOGY Dr. Rayan Khalid, MBBS, M.Sc, MD Lecture No (4) PAIN  Pain is an unpleasant subjective sensation caused by noxious stimulation of the sensory nerve endings due to actual or potential damage. Nociceptors...

Assafa College Department of Physiology NERUROPHYSIOLOGY Dr. Rayan Khalid, MBBS, M.Sc, MD Lecture No (4) PAIN  Pain is an unpleasant subjective sensation caused by noxious stimulation of the sensory nerve endings due to actual or potential damage. Nociceptors: Pain sensation arise from unmyelinated dendrites (free nerve ending). Benefits of pain sensation Pain is an important symptom, it has protective or survival benefits: Gives warning signal about the existence of a problem or threat. Prevents further damage by causing withdrawal reflex from the source of injury. Forces the person to rest or to minimize the activities thus enabling rapid healing of injured part Urges the person to take required treatment to prevent major damage. PROPERTIES OF PAIN SENSATION ▪ All pain receptors are free nerve ending ▪ Pain receptors are the most widely distributed among receptors of other modalities. ▪ Pain sensation can be produced by various type of stimuli (mechanical , chemical, thermal). ▪ Localization pain stimuli is less exact than that of other modalities (e.g. referred pain)  Pain receptor adapt very little if at all in fact the sensitivity of pain receptor increase with time (hyperalgesia) The pain thresholds higher than other modalities i.e. painful stimuli must be strong and noxious. Certain visceral area insensitive to pain e.g. include brain tissue ,liver parenchyma, and lung alveoli. EFFECT ASSOCIATED WITH PAIN SENSATION Motor reaction: Withdrawal reflex , Muscle rigidity. Autonomic reaction Mild pain : tachycardia ,rise blood pressure. Sever pain: bradycardia and decrease blood pressure. Emotional reaction : Anxiety , crying , depression. FIBER TYPES  QUALITIES OF PAIN Fast pain Slow pain (First or prinking ) (Second or burning) Delayed pain whose Acute sensation occurs intensity increase with within 0.1 S time It occur both in skin and Well localized superficial deeper tissues transmitted transmitted by A delta fiber by C fiber  PAIN PATHWAY From skin and deeper structure: Receptors: free nerve endings --- posterior nerve root ganglia --- spinal cord --- lateral spinothalamic tract --- lateral white column of the opposite side and ascend --- ventral posterolateral nucleus of thalamus --- postcentral gyrus of parietal cortex.  From face: Carried by trigeminal nerve From viscera Carried by vagus and glossopharyngeal nerves From pelvic region Conveyed by sacral parasympathetic nerves  TYPES OF PAIN ❖According to origin Acute Chronic A) Neuropathic Pain: Diabetic neuropathy, Toxin induced nerve damage, Ischemia. B) Inflammatory pain C) Idiopathic pain ❖According to site of stimulation: 1.Cutaneous pain 2.Deep somatic pain 3.Visceral pain  CUTANEOUS PAIN occurs in 2 phases of fast prinking pain then burning slow pain accurately localized due to large number of receptors Glutamate is the neurotransmitter released by type A fiber. Substance P is the neurotransmitter of type C fiber DEEP SOMATIC PAIN Pain receptor in deep tissues muscle, tendon, joint and bone. It is dull diffused, intense and prolonged Associated with autonomic symptoms ( sweating vomiting and changes in HR & BP) VISCERAL PAIN Poorly localized, unpleasant, and associated with autonomic symptoms Often radiates or referred to other areas The fibers are type C so the pain is dull aching type ???? Pain radiation vs referral  REFERRED PAIN Referred pain is the pain that is perceived at a site adjacent to or away from the site of origin. Deep pain and some visceral pain are referred to other areas. But, superficial pain is not referred pain is referred to a structure, which is developed from the same dermatome from which the pain producing structure is developed.  E.g. the heart and the arm have the same segmental origin Convergence theory: visceral and the somatic afferent fibers converge on the second order of neuron in the spinothalamic tract Facilitation theory.  ANALGESIA SYSTEM Central analgesia 1.Gate theory: The pain stimuli transmitted by afferent pain fibers are blocked by gate mechanism located at the posterior gray horn of spinal cord. If the gate is opened, pain is felt. If the gate is closed, pain is suppressed.  Opened by: Stress & low mood Closed by : Enjoyment & distraction, Tactile stimulation such as stroking, massaging an affected area closes the gate and raises the pain threshold  Electrical stimulation Transcutaneous stimulation & the implantation of dorsal column stimulators has been successful in certain painful conditions 2. Brain Opiate system: naturally occurring peptides found in brain: Enkephalins Endorphin Enkephalins Naturally occurring peptides. They induce their effects by acting on opioid receptors as those found on : Periaquaductal gray matter (could also be stimulated electrically) Dorsal horn cells Site of injury Hypothalamus limbic system  Like morphine , they modify the emotional state via there action on limbic system , thus promoting a sense of well-being.  Endorphins plentiful in hypothalamus & pituitary. They prevent withdrawal symptoms in opium addicts. Their presence in high concentration in some females during parturition. In stressful conditions they are secreted together with ACTH. Non opioid endogenous analgesics : Acetylcholine Cannabinoids Other pain modulators Stress Exercise Placebo Acupuncture Alcohol  TREATMENT Opioids. NSAID: these classes of medication act by inhibiting cyclooxygenase that prevent formation of prostaglandin and interleukin Local anesthesia that block the neural conduction in type c fibers  Electrical stimulation of the periaqueductal tract Denervation Acupuncture  ABNORMALITIES Analgesia loss of pain sensation. Hyperalgesia increased sensitivity to pain sensation. May be caused by damage to nociceptors or peripheral nerves and can cause hypersensitivity to stimulus. Paralgesia Abnormal pain sensation.