Behavioral Neuroscience
Yawning Behavior
Evolution of Yawning
Sensory Afferents to Yawn
Gating the Yawn
Yawning Regulating Yawn Gating
Efferent Yawn Output
Neuromuscular Production of Yawns
Integration of Yawn Circuitry and Behavior
norepinephrine (NE)
Oxytocin (OT)
Yawning figures
Yawn Circuitry
end     Acronyms/Abbreviations

IV. Sensory Afferents producing Yawning A. Stimulation of Inspiration 1. Tissue O2 use PCO2 and H+ in the blood a. Central chemoreceptive neurons sensitive to PCO2 and H+ i. PCO2 and H+ in CSF ii. ventrolateral surface of medulla b. Chemosensitive area Inspiratory area (DRG/NST) i. Dorsal Respiratory Group (DRG) / Nucleus of the Solitary tract (NST) c. Apneustic Center neurons DRG i. promote inspiration 1) delay off signal of the inspiratory ramp 2) intensity of breathing ii. inhibited by pulmonary stretch d. NST Þ phrenic nerve Þ diaphragm i. NST Þ intercostal nerves Þ rib muscles e. Pneumotaxic center = PRG Apneustic neurons i. ... cyclically inhibits respiration ii. PRG phrenic activity 2. But... PCO2 or O2 a. do NOT Þ yawning i. Inspiration does occur during yawning 1) so, Þ NST activity is necessary a) Key component of autonomic control ii. so... what is the sensory stimulus?
B. Afferents (inputs) to the NST include facial (VII), glossopharyngial (IX) and vagus (X) nerves 1. chemoreceptors and mechanoreceptors a. carotid bodies via glossopharyngial nerve b. aortic bodies via vagus nerve 2. senory information from lungs, airways, pharynx a. vagus and glossopharyngial nerves C. NST projects to reticular formation (includes respiratory groups) 1. via phrenic/intercostal Þ diaphragm/ribs 2. hypothalamus (including PVN) 3. CeA (central nucleus of the amygdala) 4. sympathetic preganglionic neurons
D. O2 in the PVN Þ Yawning 1. PVN = paraventricular nucleus of the hypothalamus a. stimulates sympathetic output via the NST b. 1o site of CRF synthesis: begins endocrine stress cascade i. CRF Þ ACTH Þ B/F 1) ACTH = AdrenoCorticoTropic Hormone (from pituitary) 2) B/F = cortcosterone/cortisol (steroids from adrenal cortex) c. PVN produces oxytocin (OT) and vasopressin (AVP) 2. electrical stimulation of PVN Þ Yawning a. histamine Þ PVN Þ Yawning
E. Yawning is initiated by widening the mouth and pharynx 1. open the jaw: a. inferior alveolar nerve, trigeminal nerve (V), facial nerve (VII) 2. widen the pharynx: a. pharyngial branch of the vagus nerve, superior cervical ganglion, sympathetic fibers i. Yawning caused by a transient sympathetic arousal
F. Yawning is triggered by drowsiness 1. transition of arousal states 2. driven by circadian rhythms a. circadian clock is the SCN (suprachiasmatic nucleus) 1) SCN projects directly to the PVN a) stimulation of the PVN Þ yawning
G. ... Drowsiness/SCN signal Þ AVP ÞPVN 1. PVN Þ NST Þ ciliospinal center C8-T2 a. NSTÞcc C8-T2Þ superior cervical ganglion b. SCG Þ postganglionic sympathetic fibers Þ c. sympathetic NE Þ pharyngial widening
IV. Gating the Yawn
Neuroscience Group at USD                     Biology Department                     Summers' Biology Webpage                     Summers' Course Offerings                     Contact Us                     USD