Behavioral Neuroscience Summers

Turtle Eyeblink Behavior Sensory Stimulation of Eyeblink Eyeblink Motor Output Neuromuscular Function In vitro Conditioning

text:Kandel pages 659 - 693 Glu ACh BDNF Turtles and Ecology Eyeblink Circuitry end     Acronyms/Abbreviations     Syllabus

Eyeblink Conditioning
VI. Neuromuscular Function  		

	A. ACh secreted from motor neuron projecting from the accessory  
	   principle abduscens to the pyramidalis, rectus, 
	   and retractor bulbi muscles 

	   
	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: retraction of the eyes 
	     by the retractor bulbi muscles 

		1. Contractile force summates for each muscle cell

			a. requires repeated EPP's (before fiber relaxes)

				i. for eyeblink this is R1 + R2
				
				ii. \requires Ca++ restoration to cisternae


				iii. \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
			
				i. R1 + R2

			d. motor units are recruited in a fixed order

				i. weakest to strongest

					(1) allows fine motor actions

					(2) like eyeblinks

			e. ñ firing rate (like R1 + R2) ñ force

				i. more effective summation       (see C 1)