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Chapter 34 Disorders of Somatosensory Function and Pain

Three Levels of Neurons Involved in Somatic Sensation

Sensory Impulses

Second-order Neurons Carry Sensory Impulses to the Brain

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Third-order Neurons Carry Sensory Impulses to the Cortex

Primary somatosensory cortex identifies sensation • Association cortex relates sensation to memories, other sensations, etc.

Question

Which level of neuron carries sensory impulses to the brain?

First-order b.

Second-order c.

Third-order d.

Answer

Second-order Rationale: Second-order neurons travel from the spinal nerve root to the medulla oblongata (brain stem or hindbrain), and cross over to the thalamus on the opposite side of the brain.

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?

Pathway of Pain Impulses

• Anterolateral pathway –

Paleospinothalamic

Pathway of Pain Impulses (cont.)

• Anterolateral pathway –

Neospinothalamic

Question

Tell whether the following statement is true or false.

The paleospinothalamic tract allows you to identify the location of your pain.

Answer

False Rationale: The neospinothalamic tract 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).

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 © 2009 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, nonmyelinated – – Impulses slower; “slow pain” Release glutamate and substance P Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins

Periaqueductal Gray Region

Kinds of Pain

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 non-noxious stimulus Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins

Question

Your patient has been given morphine following minor surgery. What effect will the morphine have?

Parasthesia b.

Dysesthesia c.

Analgesia d.

Answer

Analgesia Rationale: Morphine is the prototype opioid. CNS depressants/narcotics are commonly used to relieve the sensation of pain (analgesia = absence of pain).

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

Causes of Neuropathic Pain

Neuropathic Pain Syndromes

Types of Headaches

Airgas template - Morgan Community College

Transcript Airgas template - Morgan Community College

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