AUTONOMIC NEUROEFFECTOR TRANSMISSION 



223 



FIG. 8. Frequency-response curves of sympathetic effectors. .-1: abscissae, frequencies of stimulation 

 of tlie lumbar sympathetics; ordinates, angles of erection of a hair in the tail of a cat. B: abscissae, 

 frequencies of stimulation of the cervical sympathetic; ordinates, heights of the records of isotonic 

 contractions of the nictitating membrane 15 sec. after the beginning of stimulation. C: as in B, but 

 isometric contractions of the nictitating membrane. D : abscissae, frequencies of stimulation of the 

 right cardioaccelerator nerves; ordinates, maximal increases of heart rate per 15 sec. [From Rosen- 

 blueth (112).] 



Even after cutting a considerable portion of the 

 nerve the maximal effect may be approached, pro- 

 vided the frequency of stimulation is increased suffi- 

 ciently. The effect of low frequencies on a partially 

 severed nerve is smaller than in the intact nerve, 

 however, which might be expected. 



The conclusion drawn from these experiments is 

 that the neurotransmitter diffuses to the neighboring 

 cells as its concentration is raised by increasing the 

 stimulation frequency. The principle of activation of 

 smooth muscle cells may therefore be a general re- 

 lease of transmitter within the mass of these cells, 

 rnaking individual innervation as for the skeletal 

 muscle fibers unnecessary. 



T.'VBLE 3. Frequencies of Preganglionic Stimulation, 

 Giving Maximal Response of Effectors (20) 



Effectors 

 Sympathetic 



Pilomotors 



Nictitating membrane 



Pregnant uterus 



Intestine 



Adrenal medulla 



Heart (postgangl.) 

 Parasympathetic 



Heart 



Submaxillary gland 



Stomach 



Frequency 

 Stim. per sec. 



■5 

 20 

 20 

 20 

 25 

 25 



30 

 35 

 25 



