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11 Cards in this Set
- Front
- Back
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Fiber types by diameter/conduction velocity |
Motor: Aα, Aγ, B, C [Erlanger-Gasser classification] Sensory: Ia, Ib, II, III, IV [Lloyd classification] |
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Motor n. distribution in spinal cord |
Interneurons (IN's): intermediate gray -> activate α motor n.'s (MN's) - cluster in ventral horn: motor pools -> all these MN's go to 1 muscle - spread over several spinal segments - distal mm. ~ lateral ventral horn [x proximal] - extensor mm. ~ anterior ventral horn [x flexor] |
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Motor unit |
= 1 MN -> branches -> multiple m. fibers => synchronized contraction (Motor unit = all of the muscle fibers innervated by a single motor neuron) - contraction -> successive ↑ in firing rate & motor unit recruitment |
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Muscle fiber classification |
Type I (myoglobin -> red) - small, slow, weak; high aerobic metabolism; endurance [Intermediate, white, fast, fatigue-resistant] Type II (white) - large, fast, strong; anaerobic metabolism; fast fatigue -- Type phenotype is determined by innervation! |
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Classic spinal cord reflexes |
Myotatic/deep tendon: muscle stretch -> contraction (reflex hammer) Inverse myotatic (Golgi tendon organ reflex): muscle stretch (to pt of dmg) -> relaxation Flexion reflex: pain stimulus -> withdrawal |
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Muscle receptors |
Muscle spindle: Annulo-spiral endings around intrafusal muscle fibers (in capsule, sensory) -> Spindle afferent 1A <- γ MN Golgi tendon organ: Capsule b/w m. fibers/tendon -> Afferent n. (1B) <- |
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Stretch reflex circuitry & gamma loop |
Passive m. stretch / γ MN-activated stretch -> intrafusal fibers (sensory fxn, contractile terminal elements to keep tension) stretched -> annulospiral endings activated -> spindle afferent (1A) -> dorsal root, SC -> - flexor m. MN (extrafusal fibers) - IN --| antagonist m. MN |
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Golgi tendon organs |
- in CT b/w m. fiber & tendon - contraction -> tension -> 1B afferent fiber activation - most activation when the CT is about to tear => IN's -> relaxation (protective) [+ antagonist activation] |
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Spasticity |
- overactivity of γ MN's -> excessively sensitive stretch reflex => resistance to passive movement (greater w/ faster movement) (- usually due to dmg to descending inhibitory projections from brainstem) - also excessively active GTO's ("clasp-knife") |
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Withdrawal reflex circuitry |
Polysynaptic physiological flexion: - flexion in the limb (ipsilateral to pain) - extension in the contralateral limb - reciprocal connections in other limbs - Babinski response = overactive withdrawal r. |
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Complex IN reflexes |
- IN's responsible for complex pattern-generating movements - some are larger networks of IN's in brain stem (reticular formation) or intermediate gray matter of SC - ex.: gait, cough, sneeze, bling/corneal |
