The cremaster muscle is a paired structure made of thin layers of striated and smooth muscle that covers the testicles and the spermatic cords in human males. It consists of the lateral and medial parts. Cremaster is an involuntary muscle, responsible for the cremasteric reflex; a protective and physiologic superficial reflex of the testicles. The reflex raises and lowers the testicles in order to keep them protected. Along with the dartos muscle of the scrotum, it regulates testicular temperature, thus aiding the process of spermatogenesis.

Function

Retraction

The cremaster muscle's function is to raise and lower the testes in order to regulate scrotal temperature for optimal spermatogenesis and survival of the resultant spermatozoa. The ideal temperature for human sperm development is around 34.5-35 degrees Celsius, which is about 2-2.5 degrees Celsius below body temperature. Temperature is regulated by increasing or decreasing the exposed surface area of the surrounding tissue, allowing faster or slower dissipation of body heat. The amount of retraction or relaxation is directly related to how far the environmental temperatures are from the ideal.

The cremaster muscle is an involuntary muscle and contraction can occur during arousal which can prevent injury to the testicles during sexual intercourse. The muscle may contract during moments of extreme fear, possibly to help avoid injuring the testes while dealing with a fight or flight situation.

Clinically, a reflex arc termed the cremasteric reflex can be demonstrated by lightly stroking the skin of the inner thigh downwards from the hip towards the knee. This stimulates the sensory fibers of the ilioinguinal nerve, which enters the spinal cord at L1. The sensory fibers stimulate the motor fibers of the genital branch of the genitofemoral nerve (also at spinal level L1), which provides innervation to the cremaster muscles causing the contraction of the muscle and elevation of the testes. This causes the cremaster muscle on the same side to rapidly contract, raising the testicle.

The cremaster can also be contracted voluntarily, by performing Kegels (which somehow contracts the cremaster), or by flexing and tightening the abdominal muscles.

Etymology

The name of the cremaster muscle is derived from the Ancient Greek noun (kremastḗr), meaning "suspender"; its plural, (kremastēres), was used by Galen in the sense of "cremaster muscle".

Additional images

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File:Musculus cremaster.png|The scrotum

File:Gray1148.png|The right testis, exposed by laying open the tunica vaginalis

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References

  • - "Inguinal Region, Scrotum and Testes: Layers of the Spermatic Cord"