Neurobiology, lecture on neuromuscular function

Summers
USD Department of Biology

Neurobiology

Spring 2000

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acronyms
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)

	 

XXXI. Reflexes



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