NeurobiologySpring 2000click here for text onlyacronyms |
text:
Fundamental Neuroscience - Zigmond, et al.,: Read pages 863-909 for this lecture end |
XXX. Neuromuscular Function back to XXIX. Perception and Movement A. ACh secreted from motor neuron B. ACh binds to Nicotinic receptors at a neuromuscular synapse 1. stumulates action potential (= end-plate potential or EPP) by opening transmitter-gated Na+ and K+ channel (even Ca++ passes; a large diameter channel) a. along sarcolemma and into transverse tubules i. opens voltage gated Ca++ channels in sarcoplasmic reticulum (1) binds to troponin (a) conformational change in tropomyosin uncovers binding site for myosin on actin (i) myosin binds to actin (ii) conformational change (muscle contracts) (iii) ATP allows unbinding of actin ii. Ca++ATPase returns Ca++ to cisternae of sarcoplasmic reticulum C. Useful Movement 1. Contractile force summates for each muscle cell a. requires repeated EPP's (before fiber relaxes) i. \requires Ca++ restoration to cisternae ii. \contractile force depends on initial length 2. the Nervous System Grades the force of muscle contraction a. single motor axon innervates a single muscle fiber (cell) b. one motor neuron (many axons) innervates a number of muscle fibers = Motor Unit i. smallest functional unit (1) magnitude of contractile function depends on innervation ratio (fibers/neuron) c. graded force is dependent upon motor unit recruitment d. motor units are recruited in a fixed order i. weakest to strongest (1) allows fine motor actions e. firing rate force i. more effective summation (see C 1)
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