The cremaster muscle is the thin muscle that covers the testes. Its main function is to lower and raise the scrotum, which helps to control the temperature of the testicles and avoids overheating. The muscle also often contracts when a man is sexually aroused in order to protect the area during intercourse. These muscles only develop fully in males — in females, they are much smaller and only contain a few loops of muscle.
The structure of the cremaster muscle is different from many others found in the human body, and is only made up of a layer of tissue. There are actually two of these muscles on a normal human body — one on either side of the scrotum. They originate from the internal oblique muscles and insert beneath the testes.
Primarily, the function of this muscle is to regulate the temperature of the testicles. This means that, if a man is in a cold situation, the muscle will contract in order to bring the testicles closer to the body and keep them warm. If the person is in a warm situation, then it will relax allowing them to move further away from the body. This allows the testicles to stay cool.
It’s also possible for the cremaster to be contracted for other reasons. For example, in some situations, the muscle will contract during a frightening experience. It typically contracts during sexual intercourse as well, so that even during a particularly vigorous sexual experience, the testicles will not be damaged. It’s also possible for a man to manually contract the muscle by pulling in the abdomen.
This muscle also contracts as a reflex when the inner thigh is stroked downwards along the length of the leg to the knee. If the reflex arc is working correctly, then a contraction of the muscle on the same side should be observed and the testicle will be raised. It’s often the case that this reflex is stronger in the young, although it can still be observed for men.
The innervation of the cremaster muscle is from the genitofemoral nerve. This is interesting as it’s a different nerve to that which supplies the internal oblique — the muscle to which the cremaster originates. The cremasteric artery provides the muscles supply.