Chapter 35 Somatosensory Function, Pain, and Headache

1. Chapter 35Somatosensory Function, Pain, and Headache

2. Three Levels ofNeurons Involved inSomatic Sensation • First-order: detect the sensation • Second-order: in the spinal cord; transmit message to brain • Third-order: in the brain

3. Sensory Impulses Sensory impulses travel up spinal nerves to the spinal cord

4. Second-Order Neurons Carry Sensory Impulse to the Brain • Discriminative pathway • From spinal nerve root to medulla • Crosses over to thalamus on other side of brain

5. Third-Order Neurons Carry Sensory Impulse to the Cortex • Primary somatosensory cortex identifies sensation • Association cortex relates sensation to memories, other sensations, etc.

6. Question Which level of neuron carries sensory impulses to the brain? • First-order • Second-order • Third-order • Association

7. Answer • 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.

8. 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?

9. Pathway of Pain Impulses • Anterolateral pathway • Paleospinothalamic tract • To reticular activating system • Affects arousal, mood, attention

10. Pathway of Pain Impulses (cont.) • Anterolateral pathway • Neospinothalamic tract • To thalamus and parietal cortex • Allows localization, identification of pain

11. Question Tell whether the following statement is true or false: The paleospinothalamic tract allows you to identify the location of your pain.

12. 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).

13. 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

14. 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

15. Periaqueductal Gray Region • Endogenous analgesic center • Stimulated by opioids • Can send nerve impulses to inhibit other neurons in the pain pathway

16. Kinds of Pain • Cutaneous • Deep somatic • Visceral • Referred

17. 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

18. Question Your patient has been given morphine following minor surgery. What effect will the morphine have? • Parasthesia • Dysesthesia • Analgesia • All of the above

19. Answer • Analgesia Morphine is the prototype opioid, CNS depressants/narcotics that are commonly used to relieve the sensation of pain (analgesia = absence of pain).

20. tissue damage Neurogenic Inflammation inflammatory mediators stimulate nociceptors impulses run up C fibers dorsal nerve root reflex inflammatory mediators move back down and are released into tissues

21. Causes of Neuropathic Pain • Pressure on nerve • Physical injury to neuron • Chemical injury to neuron • Infection of neuron • Ischemia • Inflammation

22. Neuropathic Pain Syndromes • Trigeminal neuralgia (tic douloureux) • Postherpetic neuralgia • Complex regional pain syndrome • Phantom limb pain

23. Types of Headaches • Migraine • Cluster • Tension-type • Temporomandibular joint pain