Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Chapter 35 Somatosensory Function, Pain, and Headache

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins First-order: detect the sensation Second-order: in the spinal cord; transmit message to brain Third-order: in the brain Three Levels of Neurons Involved in Somatic Sensation

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Sensory Impulses Sensory impulses travel up spinal nerves to the spinal cord

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Discriminative pathway From spinal nerve root to medulla Crosses over to thalamus on other side of brain Second-Order Neurons Carry Sensory Impulse to the Brain

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Primary somatosensory cortex identifies sensation Association cortex relates sensation to memories, other sensations, etc. Third-Order Neurons Carry Sensory Impulse to the Cortex

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Question Which level of neuron carries sensory impulses to the brain? a.First-order b.Second-order c.Third-order d.Association

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer b.Second-order Second-order neurons travel from the spinal nerve root to the medulla oblongata (brainstem or hindbrain), and cross over to the thalamus on the opposite side of the brain.

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Discussion How does an “itch” sensation reach the brain and how is it interpreted? What was the: –Receptor type? –First-degree neuron type? –Spinal nerve? –Pathway to the brain?

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Pathway of Pain Impulses Anterolateral pathway –Paleospinothalamic tract ºTo reticular activating system ºAffects arousal, mood, attention

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Pathway of Pain Impulses (cont.) Anterolateral pathway –Neospinothalamic tract ºTo thalamus and parietal cortex ºAllows localization, identification of pain

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Question Tell whether the following statement is true or false: The paleospinothalamic tract allows you to identify the location of your pain.

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer False. The neospinothalamic allows you to tell where your pain is (helpful when you describe symptoms to a health care provider); the paleospinothalamic tract activates the reticular activating system (controls sleep/wake cycles and allows you to maintain a state of consciousness).

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins What Makes Pain Different? Specificity theory –Special pain receptors detect pain (nociceptors) Pattern theory –Sensory receptors create pain signals when stimuli are too strong Gate control theory –Pain is carried by distinct fibers in the spinal cord Neuromatrix theory –The brain identifies pain

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Nerve Fibers that Carry Pain Impulses A-delta fibers –Large, myelinated fibers –Impulses travel quickly; “fast pain” –Release glutamate at the synapse with the spinal neurons C fibers –Small, non-myelinated –Impulses slower; “slow pain” –Release glutamate and substance P

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Periaqueductal Gray Region Endogenous analgesic center Stimulated by opioids Can send nerve impulses to inhibit other neurons in the pain pathway

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Kinds of Pain Cutaneous Deep somatic Visceral Referred

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Altered Pain Sensitivity Hyperpathia: continued stimulation causes pain Paresthesias: spontaneous, unpleasant sensations Dysesthesia: distortions of somesthetic sensation Hypalgesia: reduced pain sensation Analgesia: absence of pain Allodynia: pain after nonnoxious stimulus

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Question Your patient has been given morphine following minor surgery. What effect will the morphine have? a.Parasthesia b.Dysesthesia c.Analgesia d.All of the above

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer c.Analgesia Morphine is the prototype opioid, CNS depressants/narcotics that are commonly used to relieve the sensation of pain (analgesia = absence of pain).

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Neurogenic Inflammation tissue damage inflammatory mediators stimulate nociceptors impulses run up C fibers dorsal nerve root reflex inflammatory mediators move back down and are released into tissues

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Causes of Neuropathic Pain Pressure on nerve Physical injury to neuron Chemical injury to neuron Infection of neuron Ischemia Inflammation

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Neuropathic Pain Syndromes Trigeminal neuralgia (tic douloureux) Postherpetic neuralgia Complex regional pain syndrome Phantom limb pain

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Types of Headaches Migraine Cluster Tension-type Temporomandibular joint pain