Behavioral Neuroscience Summers

C-Start Behavior Fundamentals of Neurocircuitry Senstory Stimulus for Startle Mauthner Cells - Response Gating Mauthner Efferent output Neuromuscular Function Integration of C-Start Circuitry and Behavior

text:Kandel pages 180 Glu DA ACh Transmitter Figures Figures of C-Start Behavior C-Start Circuitry end   Acronyms/Abbreviations

Escape Behavior
VIII. Efferent Mauthner + Motor Output 		

	A. Single Action Potential from Mauthner Neuron
	
		1. 1 ms duration
	
		
		2. neurotransmitter is excitatory = ACh
		
			a. vesicular ACh transporters (vAChT) 
			   found in Mauthner cells
	
			b. Nicotinic receptors? likely
	
			
		3. very fast depolarization of motor neurons
	
			a. Mauthner giant axons projecting through reticulospinal tract
			
				i. lateral column white matter of spinal cord 
				
				ii. just lateral to the ventral horn
			   
			b. to ventral horn motor neurons
			
				i. 10's of thousands of syaptic terminals


	B. Spinal Motor Neurons
	
		1. Mauthner cells activate Stage 1 = C-start
		
			a. never Stage 2 = Forward propulsion
	
			
		2. 2 ms delay from Mauthner AP to depolarization of muscle
		
			a. Mauthner-motor synapse, motor AP, neuromuscular synapse
			
				i. very fast
	
				
		3. ACh released at neuromotor junction
			
			a. ACh binds Nicotinic receptor Þ end-plate potential
				
				i. Ca++ released Þ binds troponin
					
				ii. muscles contract
			
		
	C. Massive Activation of nearly the entire motor system
	
		1. Opposite trunk musculature
		
			a. ventral horn motor neurons project 
			   via the ventral root to myomeres
			
				i. sheet-like muscle masses
			   
			b. at precaudal & caudal vertebrae 
			
			c. commissural inhibitory interneurons
			
				i. stimulated by Mauthner AP
				
				ii. cross midline
				
					(1) inhibits contralateral motor neurons
					
					(2) inhibits contralateral commissural neurons
	
		
		2. musculature of the fins
		
			a. via caudal fin vertebrae
			
			b. pectoral fin: first 4 spinal motor neurons
			
				i. precaudal vertebrae
	
		
		3. Oculomotor system
		
			a. oculomotor, trochlear and abduscens cranial nerves
	
		
		4. Jaw and operculum
		
			a. trigeminal and facial cranial nerves
	
		
		5. approximately 100 ms duration
	
		
	D. Feedback
	
		1. shortly after emergence from axon cap
		
			a. Mauthner giant axon sends out small collateral branch
			
		2. back toward axon hillock/cap
			
			a. recurrent branch
				
		3. terminates on small inhibitory interneuron
		
			a. recurrent inhibition
			
				i. large size of Mauthner spreads inhibitory signal fast
				
					(1) inhibitory transmitters = Gly & GABA
				
				ii. results in disrete pulses of muscle stimulation
				
					(1) 1st pusle = initial bending
					
		
	E. Intial Bending - starting the C
	
		1. very consistent initial bending component
		
			a. speed and shape of C from trial to trial
			
			b. 'stereotypic' for 20-30 ms  = stage 1
	
		
		2. variability comes in stage 2