Behavioral Neuroscience, lecture on neuromuscular function
USD Department of Biology
Behavioral Neuroscience
Summers
Sexual Behavior
Reflexes
Sensory Reception - Tactile Receptors
Spinal Synapses
Ruffini Endings Afferent Spinal Pathways Hypothalamic Gating
Efferent Motor Cascade
Neuromuscular Production of Lordosis
Integrated Story of Lordosis
VIP
Substance P
Estrogens
5-HT
GnRH
ACh
Lordosis figures
Sensory Receptors
Spinal Cord
Lordosis Circuitry
end     Acronyms/Abbreviations
LORDOSIS
XIV. Neuromuscular Function  	

	A. ACh secreted from motor neuron projecting from the ventral horn 
	
		1. Lumbosacral spinal cord 
		
			a. to lateral longissimus and transversospinalis muscles 

		2. may be inhibited by spinal GABA interneurons
		
			a. acting on GABAA receptors

	B. ACh binds to Nicotinic receptors at a neuromuscular synapse

		1. stumulates action potential (= end-plate potential or EPP) 
		
		2. Opening transmitter-gated Na+, Ca++ and K+ channel 
		   (a large diameter channel)


			a. EPP passes 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: bilateral dorsiflexion of entire vertebral 
	    column by lateral longissimus and transversospinalis muscles 

		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

				ii. not necessary for Lordosis
				
					(1) deep back muscles contract with maximum
					    force to support male
						
					(2) termination of descending axons across
					    a wide range of lumbosacral spinal cord levels
						produce a ballistic muscular ressponse

			e.  firing rate  force


				i. more effective summation       (see C 1)

XV. Integrated Systems producing Lordosis