The cremaster muscle is the thin muscle that covers the testis. Its main function is to lower and raise the scrotum, which helps to control the temperature of the testis and avoids overheating. The muscle also often contracts when a man is sexually aroused in order to protect the testis during intercourse. A cremaster muscle only develops fully in males — female cremaster muscles 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. It’s made up of a layer of muscle that encloses the testis. There are actually two cremaster muscles on a normal human body — one on either side of the scrotum. The muscle originates from the internal oblique muscle and inserts beneath the testis.

Primarily, the function of the cremaster muscle is to regulate the temperature of the testis. This means that if a man is in a cold situation the muscle will contract in order to bring the testis closer to the body and hence keep them warm. If the person is in a warm situation then the muscle will relax allowing the testis to move further away from the body. This allows them to stay cool and is an effective way of controlling the temperature of the testis.

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. Often, the muscle will also contract during sexual intercourse. This is so that even during a particularly vigorous sexual experience the testis will not be damaged. It’s also possible for a man to manually contract the muscle by pulling in the abdomen.

The cremasteric reflex is a demonstration of the reflex arc associated with the muscle. To perform this reflex test 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 cremaster 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.