Everyone has had the “racing heart” experience which occurs immediately after a scary loud noise, a narrowly – avoided accident or a brush with death. Real or imagined, these “fight or flight” incidents trigger a number of sympathetic nervous system responses which affect cells, tissues and organs throughout the body – certainly one of the most immediate and powerful feelings is the dramatic increase in heart rate and heart strength which people describe so graphically – “my heart leapt up into my throat” or “my heart pounded so hard I thought it would break out of my chest.”
The heart can react so vigorously whether the threat is real or imaginary – just visualizing a life-threatening, scary event will trigger the same changes in heart status. These immediate changes are strong evidence that the heart can respond to nervous stimulation from the autonomic centers in the thalamus, hypothalamus and brainstem. In fact, the entire process by which the heart rate (beats per minute) and stroke volume (the amount of blood pumped per beat, related to the internal volume of the heart and the strength of a heart contraction) are regulated by the nervous system is a fascinating story which is often referred to as a “classical case of homeostasis”.
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