Behavioral Neuroscience Summers

Crayfish Escape Behavior Crayfish Neuroanatomy Fundamentals of Neurocircuitry Sensory Afferent input for Tail Flip

Gating the Full Flip Gating the Tail Flip for Upward Thrust Parallel Gating of Crayfish Escape Motor Neuron output for Crayfish Escape Integration: Crayfish Escape

Acetylcholine ACh GABA 5-HT

Crayfish figures Crayfish Escape Neurocircuitry end     Acronyms/Abbreviations

Escape - Crayfish
III. Crayfish Neuroanatomy  

	A. Nervous system consists of a chain of ganglia
    
		1. similar to the spinal cord it is medially located
        
		2. in contrast to the spinal cord it is ventrally located
        
			a. except the brain
    
		3.  Chain of 13 ganglia (neural cell body groups)

			a. connected by projection axons
            
			b. in a linear chain

		4. Chain begins rostrally (anterior) with the brain

			a. brain is dorsal

				i. serves rostral sensory organs
                
				ii. eyes, antannae

			b. 5 thoracic ganglia

				i. serve legs 
                
				ii. ganglion 2 serves gullet (food tube)
                
				iii. ganglion 6 serves sternal artery

			c. 6 abdominal ganglia

				i. serves swimmerets
                
				ii. serves the tail
            
			d. therefore, each ganglion serves local physiology and anatomy

	B. All of the nervous system is contained in this chain

		1. unlike vertebrates with Brain and Spinal cord = Central Nervous System (CNS)

			a. and Peripheral Nervous System (PNS)

	C. Inputs and Outputs
    
		1. Defined by postion on the ganglion
    
			a. 1st root is the largest, lateral root    
    
				i. root contains sensory dendrite inputs
                
					1) to cell bodies in the ganglion
    
				ii. and motor axon outputs

					1) from cell bodies in the ganglion

					2) cell bodies = soma, perikarya

			b. 2nd root is posterior to 1st root                   
                
			c. 3rd roots are posterior

				i. along the connective

					1) between ganglia

	D. Identified Neurons

		1. Each and every ganglion includes a very similar set of neuronal soma

			a. All of the neurons are known

			b. All of the functions of each neuron can be known
            
				i. the function of many neurons in each ganglion are known                                

		2. 3 important neuron types

			a. Medial Giant Neurons (MG) 

				i. MG = pair of neurons 
                
				ii. dorsally located

					1) in brain, thoracic and abdominal ganglia
                
				iii. excited by an attack to front of the animal

				iv. induce quick curling of abdomen and throws animal backward

				v. activated by rostral stimuli and cause all abdominal segments to bend

			b.  Lateral Giant Neurons (LG)

				i. also a pair of neurons

				ii. ventral and lateral to MG

					1) in abdominal ganglia
                    
					2) all LG are electrically interactive
                    
				iii. LG excited by strong, sudden stimulus to tail

				iv.	Cause only bending in rostral abdominal segments
                
				v.	Trigger sudden sharp flip of abdomen to throw crayfish upward 
                
					1) hind end rotates forward away from stimulus

			c. non-Giant Neurons (NG)		

				i. many neurons

				ii. ventral to LG

				iii. Excited by more gradual stimuli

				iv. trigger directed tail flip escape 
   
	E.  Coordination of these 3 systems results in adaptive responses to real and potential threat