Behavioral Neuroscience, lecture on Turtle Efferent Eyeblink Pathway
USD Department of Biology
Behavioral Neuroscience
C. picta Turtle Eyeblink Behavior
Sensory Stimulation of Eyeblink
Eyeblink Motor Output
Neuromuscular Function
In vitro Conditioning
text:Kandel pages 1243 & 849
Turtles and Ecology
Eyeblink Circuitry
end     Acronyms/Abbreviations
Eyeblink Conditioning
IV. Turtle Eyeblink motor output  		

	A. Early blink R1
		1. 3 ms latency : 100 ms duration
		2. direct sensory (premotor) Glu synapses on 
		    accessory abduscens motor neurons
			a. similar to mammals 
			b. AMPA receptors stimulate depolarization 
			    (via Na+ influx) and Action Potenital
			c. ACh released at neuromotor junction
				i. binds Nicotinic receptor Þ end-plate potential
					(1) Ca++ released Þ binds troponin
					(2) retractor bulbi, lateral rectus
					     and pyramidalis muscles contract
			d. controls orbit retraction and blinking
				i. influenced by auditory input
		3. also direct sensory Glu synapses on principle abduscens motor neurons
			a. controls eye movements
				i. influenced by vestibular system
		4. plus indirect premotor Glu synapses on
		    accessory & principle abduscens motor neurons
			a. via interneurons in the rostral trigeminal nuclear complex (pV)
				i. sensory trigeminal neurons also the more caudal
				    spinal trigeminal nucleus (see R2)
		5. early blink can be blocked by AMPA antagonists
	B. Later blink R2
		1. 15 ms latency : several s duration
		2. interneurons from spinal trigeminal nucleus in medulla
			a. receive signals directly from trigeminal sensory neurons
			b. and indirectly via the rostral sensory trigeminal nuclei
		3. medullary Glu interneurons synapse on Glu interneurons
		    in principal sensory trigeminal nucleus in the pons
			a. binds both AMPA and NMDA receptors
			b. R2 blocked by AMPA and NMDA antagonists
		4. feedback loop between principal sensory and spinal
		    nuclear groups of trigeminal complex
			a. transection of medulla eliminates
			    R2 discharge in abduscens nerves
	C. Auditory input
		1. accessory and principal abduscens also have interneuron input
		   from cochlear and vestibular nuclei
			a. can contribute to neuromuscular discharge 
		2. auditory sensory neurons (VIII or auditory nerve) also innervate
		    principal sensory trigeminal nucleus (pV)
			a. along with trigeminal sensosry neurons
			b. can drive motor output via sensory trigeminal,
			    cochlear or vestibular interneurons
		3. classical conditioning of eyeblinks with sound (CS) uses this circuit

V. Acetylcholine = ACh