ANATOMY&PHYSIOLOGY FOR NURSES

Cardiac muscle is found  only in the muscle of the heart . It is striated like voluntary muscle. But it differs in that its fibres branch and anastomose with each other: they are arranged longitudinally as in striated muscle, are characteristically red in colour and not controlled by the will. Cardiac muscle possesses the special property of automatic rhythmical contraction independent of its nerve supply. This function is described as myogenic as distinct from neurogenic. Normally the action of the heart is controlled by its nerve supply Muscular Contraction When a muscle is stimulated a short latent period follows, during which it is taking up the stimulus. It then contracts, when it becomes short and thick, and finally it relax and elongates.  In the case of a striped  (voluntary) muscle fibre the contraction lasts only a fraction of a second and each contraction occurs in response to a single nerve impulse. Each single occurs in response to a single nerve impulse. Each single contraction is of the same force. The force with which a whole muscle contracts is adjusted by varying the number of fibres contracting and the frequency with which each fibre contracts. When contracting vigorously the individual fibres may contract more than 50 times each second. Certain things influence the force with which a muscle fibre contracts. It contracts more forcibly when it is stretched and when it is warm. Fatigue and cold weaken the power to contract. Un striped muscle fibres contract much more slowly and are not dependent on nervous impulses, although these alter the force of their contraction. Muscle tone. Muscle is never completely at rest; it may appear to be, but it is always in a condition of muscle tone, which means ready to respond to stimuli. For instance, the knee-jerk obtained by sharply tapping the patellar tendon results in contraction of the quadriceps extension of the thigh and slight extension of the nerves.

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