Behavioral Neuroscience Summers

Yawning Behavior Evolution of Yawning Sensory Afferents to Yawn Gating the Yawn

Regulating Yawn Gating Efferent Yawn Output Neuromuscular Production of Yawns Integration of Yawn Circuitry and Behavior

norepinephrine (NE) Oxytocin (OT) ACTH & aMSH Yawning figures Yawn Circuitry end     Acronyms/Abbreviations

YAWNING

I. Yawning Behavior 

	A. a paroxysm of the respiratory cycle

		1. sudden attack/expression of inhalation
            
		2. lasts 5-10 s
            
			a. duration is not fixed
                
				i. appears to be fixed
                    
				ii. can be modulated voluntarily
                    
                    
	B. Standard cascade of movements: 3 distinct phases 

		1. Initiation:  opening the mouth widely

			a. allows for slow, deep inspiration

				i. almost entirely through the mouth

            
			b. accompanied by expansion of the pharynx / larynx & thorax

			c. & vocal cord abduction

                        
		2. Acme Phase
        
			a. thorax reaches maximum capacity

				i. followed by a brief interruption of inspiration

			b. eyes close

				i. limb stretching

					a) yawning + stretching = Pandiculation

			c. generalized stretching of respiratory tract muscles

				i. diaphragm, intercostals, face and neck

		3. Conclusion: short expiration and relaxation



II. Respiratory Cycle 

	A. Regulated by brain stem chemosensitive area
    
		1. Medulla oblongata and pons

		2. Sensitive to D in blood PCO2 or [H+]
        
	B. Chemosensory neurons excite respiratory premotor centers
    
		1. Inhalation: Nucleus of solitary tract (NST = Dorsal respiratory group)

			a. signal begins weakly, increases for 2-3 s
             
			b. NST stimulates motor neurons 

				i. Üphrenic (C3-C5) & intercostal (T1-T11) nerves
            
				ii. Üdiaphragm + intercostal muscles

				iii. Ramp signal Ü steady ñ thoracic volume 

					a) sensory feedback inhibits diaphragm excitation 

			c. elastic recoil Ü expiration

		2.  Forced Exhalation

			a. Nucleus ambiguus (Ventral respiratory group)

		3. Pontine pneumotaxic & apneustic centers

			a. rate + coordination of inhalation and exhalation
            
				i. stimulate NST

	C. Yawning caused by a transient ñ sympathetic arousal

		1. not deep inhalation 

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III. Evolution of/Purpose for Yawning

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