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Type 1 (A alpha) fibers; Morphology; Modality
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Type 2 (A beta) fibers; Morphology; Modality
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Sensory Receptors
Lecture 7 Vernino
| Question | Answer |
|---|---|
| Type 1 (A alpha) fibers; Morphology; Modality | Large myelinated; Motor axons and muscle spindles, golgi tendon organ |
| Type 2 (A beta) fibers; Morphology; Modality | large myelinated; vibration, pressure, stretch, touch |
| Type 3 (A delta) fibers; Morphology; Modality | large myelinated; touch, temperature, and FAST pain |
| B fibers; Morpholy; Modality | small, myelinated; autonomic |
| Type 4 (C) fibers; Morphology; Modality | small UNMYELINATED; thermal pain and SLOW pain |
| What is an example of a large fiber disorder? | Tabes dorsalis (syphilis)- presents with sensory ataxia and areflexia (no reflexes) |
| What is an example of a small fiber disorder? | Diabetes- neuropathic pain, loss of pinprick and thermal sensation, reflexes normal |
| What type of fibers do hair receptors contain? These receptors are "fast adapting"; what does that mean? | A beta and A delta. Fast adapting receptors have a brief strong response to stimulus and then rapidly desensitizes. |
| Pascinian corpuscles; Fiber type; Structure; Function; Distribution | A beta fibers; central naked axon (looks like sliced onion); Sensitive to HIGH FREQUENCY vibrations (500Hz). FAST ADAPTING; Widely distributed |
| Meissner's corpuscles; Fiber type; Structure; Function; Distribution | A beta fibers; Intertwined nerve fibers; Sensitive to LOW FREQUENCY vibrations including including 2-point discrimination. FAST ADAPTING; Finger tips, palms |
| Merkel cells; Fiber type; Structure; Function; Distribution | A beta fibers; sensitive to PRESSURE, important for discriminating edges, shapes, and textures; SLOW ADAPTING; fingertips, hairless skin |
| Are muscle spindle proprioceptors excitatory/inhibitory to agonist muscles? | Excitatory |
| Are golgi tendon organ excitatory/inhibitory to agonist muscles? | Inhibitory |
| Are muscle spindle proprioceptors excitatory/inhibitory to antagonist muscles? | Inhibitory |
| Are golgi tendon organ excitatory/inhibitory to antagonist muscles? | Excitatory |
| What are the characteristics of fast pain? | Carried by a-delta fibers, short duration, and well localized |
| What are the characteristics of slow pain? | Carried by c fibers, long duration, latency before being activated, and diffuse localization |
| What type of nociceptors are prone to sensitization? | Polymodal nociceptors |
| Define adaptation | The decline in the generator potential (for action potentials) given the same stimulus |
| Define nociceptive pain | Activation of peripheral nociceptors (described as sharp. stabbing, or achy) |
| Define neuropathic pain | Perception of pain without activation of nociceptors (described as itching, burning, prickling, electric shocks) |
| Define allodynia | Perception of pain with non-painful stimuli |
| Define hyperalgesia | Perception of a mild nociceptive stimulus as very painful |
| Define paresthesia | Spontaneous sensation without stimulus (pins and needles) |
| Define dysesthesia | Painful or unpleasant paresthesia |
| Define anesthesia | absence of sensation |
| Define hypesthesia | Abnormally diminished sensation |
| Causalgia | Neuropathic pain that persists after a peripheral nerve injury |
| What are the three major classes of nociceptors in the skin? | A delta mechanosensitive nociceptors, A delta mechanothermal nociceptors, and C FIBERS polymodal nociceptors |
| Describe the VR-1 receptor | Carries information about medium heat and capsaicin via A delta and C fibers |
| Describe the arousal response to pain | Signals travel from the spinothalamic tract up to the reticular formation |
| Describe the somatosensory response to pain (localing the pain) | Signals travles in the spinothalamic tract to the VPL (for body) or VPM (for face) of the thalamus, which then projects to the somatosensory cortex |
| Describe the association and limbic response to pain (defining the pain) | Signals travel from EITHER the spinothalamic tract or the reticulothalamic projections to the dorsal medial nucleus of the thalamus, which the projects to the prefontal cortex, association cortex, and limbic system. |
| Describe the visceral pain pathway | Travels in the dorsal columns to the nucleus gracilis, which projects to the ventral thalamus (VPM or VPL) and the insular cortex. |
| What rexed laminae do first order pain fibers synapse in? | Laminae 2 (in the substantia gelatinosa and nucleus propius) |
| Describe the structure and function of wide dynamic range neurons | WDR neurons represent the neurons of the posterior horn (aka lamina 2 spinal horn) that receives input from all of the pain fibers AS WELL as alpha beta fibers of low threshold mechanoreceptors. These fibers act on inhibitory interneurons and mediate pain |
| What is the function of a beta fibers to WDR neurons? | Activate inhibitory neurons that synapse on WDR neurons (these are LOW THRESHOLD mechanoreceptors) |
| How do descending inputs modulate pain? | They activate inhibitory interneurons that mediate the synaptic terminals of C FIBERS |
| Where do we find opioid receptors? | On the synaptic terminals of inhibitory interneurons of the spinal column that synapse with descending fibers of the CNS |
| Describe how peripheral sensitization works when there is damage to C fibers | C fibers normally carry pain to the WDR neurons. In the absence of C fiber input, WDR neurons will begin to send pain signals in response to non-painful stimuli (from A fiber inputs) --> allodynia |
| Describe how central disinhibition of pain works when there is damage to A beta fibers | Loss of inhibitory input to WDR neurons = enhanced WDR neuron excitation |
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