SECTION X 

 OTHER FORMS OF CONTRACTILE TISSUE 



SMOOTH OR UNSTRIATED MUSCLE 



THE little we know about the physiology of unstriated muscle is 

 derived chiefly from experiments on the intestine, ureter, bladder, and 

 retractor penis.* This tissue differs from voluntary muscle in con- 

 taining numerous plexuses of nerve fibres (non-medullated) and 

 ganglion- cells, so that in all our researches it is difficult to be certain 

 whether the results are due to the muscle fibres themselves, or to the 

 nerves and nerve- cells which are so intimately connected with them ; 

 especially as we have as yet no convenient drug like curare, by aid 

 of which we might discriminate between action on muscle and action 

 on nerve. 



The differences between unstriated and voluntary muscle, although 

 at first sight very pronounced, on further investigation prove to be 

 in most cases differences of degree only, qualities and reactions which 

 are marked in involuntary muscle being also present in a minor degree 

 in the more highly differentiated tissue. 



The contraction of smooth muscle is so sluggish that the various 

 stages of latent period, shortening, and relaxation can be easily 

 followed with the eye. The latent period may be from 0-2 to 0-8 

 second, and the contraction may last from three seconds to three 

 minutes. 



Smooth muscle preserves many of the properties of un differentiated 

 protoplasm, especially an automatic power of contraction, which is 

 regulated by the condition of the muscle. Thus whereas the voluntary 

 muscle is intimately dependent on its connection with the central 

 nervous system, and in the absence of this is reduced to a flabby inert 

 tissue, the smooth muscle, isolated from all its nervous connections, 



* The retractor penis, which is found in the dog, cat, horse, hedgehog (but 

 not in rabbit or man), is a thin band of longitudinally arranged unstriated 

 muscle, which is inserted at the attachment of the prepuce, and is continued back- 

 wards in a sheath of connective tissue to the bulb, where it divides into two 

 slips, which pass on either side of the anus. It is innervated from two sources, 

 the motor fibres being derived from the lumbar sympathetic and running to the 

 muscle in the internal pudic nerve, while the inhibitory fibres run in the pelvic 

 visceral nerves (nervi erigentes) and are derived from the second and third 

 sacral nerve -roots. 



071 



