Musculus Cremaster: Structure, Function & Diseases

The cremaster muscle is also known as the cremaster muscle or testicular lifter and surrounds the spermatic cord and testicles. It contracts reflexively in response to external stimuli such as cold, pulling the testicles toward the trunk. In testicular malpositions such as pendulous testis, exaggerated reflex movement causes abnormal testicular positions.

What is the cremaster muscle?

The cremaster muscle or musculus cremaster is a loop-shaped muscle made of muscle fibers from the abdominal muscles. Specifically, the fibers of the obliquus internus abdominis muscle and the transversus abdominis muscle are involved in the cremaster muscle. These are muscle cords of the lower abdomen that meet in a loop in the cremaster muscle. The cremaster muscle belongs to the striated musculature and thus to the skeletal musculature. Like any other skeletal muscle, the cremaster muscle can contract and thus moves the testicles towards the head. Because of this function, the muscle is also popularly called the testicle-lifting muscle. Unlike most skeletal muscles, contraction of the cremaster muscle is relatively involuntary and tied to specific environmental stimuli. The cranial movement of the testes is thought to ensure sperm production in the face of counterproductive stimuli such as cold.

Anatomy and structure

The muscle fibers of the two lower abdominal muscles form fiber bundles in the cremaster muscle. These bundles follow the spermatic cord in their course. They run in loops of increasing length that accompany the fascia of the testis and the spermatic cord. They insert the tunica vaginalis and are innervated by the ramus genitalis. This nerve is a section of the genitofemoral nerve that connects the anatomical structure of the kermaster muscle to the nervous system and enables it to respond to stimuli. Unlike the testes, the spermatic cord is completely sheathed by the muscle fibers. The striated muscles of the body are composed of sarcomeres. The myofilaments myosin and actin make up these sarcomeres and partially overlap within them. Light I bands of actin alternate with dark A bands of myosin bundles in the muscles.

Function and roles

Elevation of the testis toward the abdominal wall is the function of the cremaster muscle. For example, when the skin on the inner thigh is exposed to temperature stimuli, contraction of the muscle pulls the testes upward, placing them in a more protected environment. This process corresponds to a reflex and is also called the cremasteric reflex. This is an innate external reflex, which, like all other motor reflexes of the skeletal muscles, is interconnected via the spinal cord. Thanks to this circuitry, the muscle is capable of a particularly rapid contraction response to certain stimuli. The responsible spinal cord segments for the external reflex are segments L1 and L2. The cremasteric muscle reflex can also be observed in animals. Some animals even retract the testes completely into the abdominal cavity in response to certain stimuli. Since the cremasteric reflex is triggered primarily by cold stimuli, there was long talk in this context of a separate thermoregulation of the testes. The general assumption at that time was that the reflex movement aims to establish an ideally tempered level for sperm production by regulating the supply of heat in the milieu of the testes. Thus, the function of the cremaster muscle was not insignificantly associated with reproduction. However, because the cremasteric reflex causes the testes to draw closer to the body even during strong arousal, the connection with thermoregulation is now considered controversial. During arousal, the reflex presumably merely indicates an imminent orgasm. However, the original thermoregulation thesis is not completely ruled out even after this observation.

Diseases

The cremasteric reflex of the cremasteric muscle may behave abnormally and, for example, may be too strong or too light. In some circumstances, the reflex movement may stop completely. Abnormal reflex behavior of this type may refer to both peripheral and central nerve damage. For example, the spinal cord segments L2 and L3 may be affected by lesions that are usually due to either spinal infarction or degenerative and inflammatory diseases of the central nervous system. In this context, in addition to the autoimmune disease multiple sclerosis, the degenerative nervous system disease ALS should be mentioned among others.However, excessive reflex responses of the cremasteric muscle may also occur in the context of testicular dystopias such as pendulous testis. Testicular dystopias are unilateral or bilateral malformations of the testes, as they may occur in the context of mutations and various hereditary diseases. In this context, pendulous testicles are testicles that are normally located in the scrotum but react to external stimuli with an enormously lively cremasteric reflex. This lively reaction makes them momentarily change to an aberrant localization, such as a high-scrotal or an inguinal location. This testicular dystopia belongs to the retractile malpositions and does not necessarily have to be treated as long as the affected person does not suffer from it. However, if a pendulous testicle is not in scrotal position most of the time, corrective surgery may make sense. The cremaster muscle can also be affected by disease itself. However, typical muscle diseases such as muscle fiber tear or muscle inflammation occur rather rarely in this region. Peripheral nerve damage occurs more frequently. For example, neuropathy can affect this muscle, as triggered by malnutrition, various infectious diseases, or poisoning.