The contraction produced can be described as a twitch, summation, or tetanus, depending on the frequency of action potentials. In skeletal muscles, muscle tension is at its greatest when the muscle is stretched to an intermediate length as described by the length-tension relationship. Smooth and cardiac muscle contractions are myogenic and can be modulated by the autonomic nervous system.
sex-linked disorder - any disease or abnormality that is determined by the sex hormones; hemophilia is determined by a gene defect on an X chromosome. bleeder's disease, haemophilia, hemophilia - congenital tendency to uncontrolled bleeding; usually affects males and is transmitted from mother to son.
Sexually transmitted diseases (STDs) are infections that you can get by having sex or skin-to-skin contact between genitals with someone who has an STD. STDs are also sometimes called sexually transmitted infections or STIs. Whatever you call them, they can cause serious health problems. And they happen a lot to young people: About half of all new infections happen to people ages 15 to 24. There are more than 25 STDs caused by many different bacteria and viruses.