The cremaster muscle is a paired structure made of thin layers of striated and

smooth muscle Smooth muscle is an involuntary non-striated muscle, so-called because it has no sarcomeres and therefore no striations (''bands'' or ''stripes''). It is divided into two subgroups, single-unit and multiunit smooth muscle. Within single-unit mus ...

that covers the

testis A testicle or testis (plural testes) is the male reproductive gland or gonad in all bilaterians, including humans. It is homologous to the female ovary. The functions of the testes are to produce both sperm and androgens, primarily testostero ...

and the

spermatic cord The spermatic cord is the cord-like structure in males formed by the vas deferens (''ductus deferens'') and surrounding tissue that runs from the deep inguinal ring down to each testicle. Its serosal covering, the tunica vaginalis, is an exten ...

in human males. It consists of the lateral and medial parts. Cremaster is an

involuntary muscle Involuntary muscle may refer to: * Smooth muscle tissue * Cardiac muscle Cardiac muscle (also called heart muscle, myocardium, cardiomyocytes and cardiac myocytes) is one of three types of vertebrate muscle tissues, with the other two being ...

, responsible for the

cremasteric reflex The cremasteric reflex is a superficial (i.e., close to the skin's surface) reflex observed in human males. This reflex is elicited by lightly stroking or poking the superior and medial (inner) part of the thigh—regardless of the direction of ...

; 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 The dartos fascia or simply dartos is a layer of connective tissue found in the penile shaft, foreskin, scrotum and labia. The penile portion is referred to as the superficial fascia of penis or the subcutaneous tissue of penis, while the scrotal ...

of the

scrotum The scrotum or scrotal sac is an anatomical male reproductive structure located at the base of the penis that consists of a suspended dual-chambered sac of skin and smooth muscle. It is present in most terrestrial male mammals. The scrotum cont ...

, it regulates testicular temperature, thus aiding the process of

spermatogenesis Spermatogenesis is the process by which haploid spermatozoa develop from germ cells in the seminiferous tubules of the testis. This process starts with the mitotic division of the stem cells located close to the basement membrane of the tubule ...

Structure

human Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, culture, ...

male Male (symbol: ♂) is the sex of an organism that produces the gamete (sex cell) known as sperm, which fuses with the larger female gamete, or ovum, in the process of fertilization. A male organism cannot reproduce sexually without access to ...

s, the cremaster muscle is a thin layer of striated

muscle Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscl ...

found in the

inguinal canal The inguinal canals are the two passages in the anterior abdominal wall of humans and animals which in males convey the spermatic cords and in females the round ligament of the uterus. The inguinal canals are larger and more prominent in males. ...

and

between the external and internal layers of spermatic fascia, surrounding the testis and

. The cremaster muscle is a paired structure, there being one on each side of the body. Anatomically, the lateral cremaster muscle originates from the

internal oblique The abdominal internal oblique muscle, also internal oblique muscle or interior oblique, is an abdominal muscle in the abdominal wall that lies below the external oblique muscle and just above the transverse abdominal muscle. Structure Its fibe ...

muscle, just superior to the

, and the middle of the inguinal ligament. The medial cremaster muscle, which sometimes is absent, originates from the pubic tubercle and sometimes the lateral pubic crest. Both insert into the

tunica vaginalis The tunica vaginalis is the pouch of serous membrane that covers the testes. It is derived from the vaginal process of the peritoneum, which in the fetus precedes the descent of the testes from the abdomen into the scrotum. After its descent, ...

underneath the testis.

Blood supply

The cremaster muscle is supplied by the

cremasteric artery The cremasteric artery (external spermatic artery) is a branch of the inferior epigastric artery which accompanies the spermatic cord to supply the cremaster muscle as well as other coverings of the spermatic cord in the male (whereas in the fema ...

, a branch of the

inferior epigastric artery In human anatomy, inferior epigastric artery refers to the artery that arises from the external iliac artery. It anastomoses with the superior epigastric artery. Along its course, it is accompanied by a similarly named vein, the inferior epig ...

, along with

anastomotic An anastomosis (, plural anastomoses) is a connection or opening between two things (especially cavities or passages) that are normally diverging or branching, such as between blood vessels, leaf veins, or streams. Such a connection may be normal ...

flow from the other arteries supplying the scrotum.

Nerve supply

The cremaster muscle is innervated from the sensory and motor fibers of the

genitofemoral nerve The genitofemoral nerve refers to a nerve that is found in the abdomen. Its branches, the genital branch and femoral branch supply sensation to the upper anterior thigh, as well as the skin of the anterior scrotum in males and mons pubis in fema ...

that originates from the L1 and L2

spinal nerve A spinal nerve is a mixed nerve, which carries motor, sensory, and autonomic signals between the spinal cord and the body. In the human body there are 31 pairs of spinal nerves, one on each side of the vertebral column. These are grouped into th ...

nuclei. It receives distinctly different innervation and vascular supply in comparison to the

Development

The cremaster muscle develops to its full extent only in male human bodies; in females, the muscle is smaller and is found on the round ligament, where it is represented by only a few muscle loops. In rats, it has been shown that cremaster muscles developed from the gubernacular bulb.

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 A spermatozoon (; also spelled spermatozoön; ; ) is a motile sperm cell, or moving form of the haploid cell that is the male gamete. A spermatozoon joins an ovum to form a zygote. (A zygote is a single cell, with a complete set of chromosomes, ...

. The ideal temperature for human sperm development is around 34 degrees Celsius, which is about 4 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. Cremaster works alongside the

dartos The dartos fascia or simply dartos is a layer of connective tissue found in the penile shaft, foreskin, scrotum and labia. The penile portion is referred to as the superficial fascia of penis or the subcutaneous tissue of penis, while the scrotal ...

muscle in order to maintain

homeostasis In biology, homeostasis (British English, British also homoeostasis) Help:IPA/English, (/hɒmɪə(ʊ)ˈsteɪsɪs/) is the state of steady internal, physics, physical, and chemistry, chemical conditions maintained by organism, living systems. Thi ...

for the reproductive organs and protect them from physical damage. When a man is cold or

sexually stimulated Sexual stimulation is any stimulus (including bodily contact) that leads to, enhances and maintains sexual arousal, and may lead to orgasm. Although sexual arousal may arise without physical stimulation, achieving orgasm usually requires physica ...

, the dartos muscle causes the scrotum to become more wrinkled and smaller as it is retracted closer to the body. In warmer conditions, the dartos allows for less wrinkling and the scrotum becomes looser. The cremaster muscle is an

and contraction can occur during

arousal Arousal is the physiological and psychological state of being awoken or of sense organs stimulated to a point of perception. It involves activation of the ascending reticular activating system (ARAS) in the brain, which mediates wakefulness, th ...

which can prevent injury to the testicles during

sexual intercourse Sexual intercourse (or coitus or copulation) is a sexual activity typically involving the insertion and thrusting of the penis into the vagina for sexual pleasure or reproduction.Sexual intercourse most commonly means penile–vaginal penetrat ...

. Contraction also occurs during orgasm and

ejaculation Ejaculation is the discharge of semen (the ''ejaculate''; normally containing sperm) from the male reproductory tract as a result of an orgasm. It is the final stage and natural objective of male sexual stimulation, and an essential componen ...

. The muscle may contract during moments of extreme fear, possibly to help avoid injuring the testes while dealing with a fight or flight situation. The reflex can also occur when a man breathes in deeply or contracts his abdomen. Clinically, a

reflex In biology, a reflex, or reflex action, is an involuntary, unplanned sequence or action and nearly instantaneous response to a stimulus. Reflexes are found with varying levels of complexity in organisms with a nervous system. A reflex occurs ...

arc termed the

can be demonstrated by lightly stroking the skin of the inner

thigh In human anatomy, the thigh is the area between the hip (pelvis) and the knee. Anatomically, it is part of the lower limb. The single bone in the thigh is called the femur. This bone is very thick and strong (due to the high proportion of bone ...

downwards from the hip towards the knee. This stimulates the sensory fibers of the

ilioinguinal nerve The ilioinguinal nerve is a branch of the first lumbar nerve (L1). It separates from the first lumbar nerve along with the larger iliohypogastric nerve. It emerges from the lateral border of the psoas major just inferior to the iliohypogastric, a ...

, which enters the spinal cord at L1. The sensory fibers stimulate the

motor fibers A motor neuron (or motoneuron or efferent neuron) is a neuron whose cell body is located in the motor cortex, brainstem or the spinal cord, and whose axon (fiber) projects to the spinal cord or outside of the spinal cord to directly or indirectl ...

of the genital branch of the

(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 Kegel exercise, also known as pelvic-floor exercise, involves repeatedly contracting and relaxing the muscles that form part of the pelvic floor, now sometimes colloquially referred to as the "Kegel muscles". The exercise can be performed many t ...

(which somehow contracts the cremaster), or by flexing and tightening the abdominal muscles.

Clinical significance

The cremaster muscle occasionally experiences painful spasms or cramps in adult males which can be chronic and debilitating. Treatment for these spasms ranges from minor surgery to injection with Botulinum A toxin to the regular application of heat to relax the muscle. Surgery, including the excision of the cremaster muscle, has apparently been able to provide complete relief from this condition without significant side effects.

Etymology

The name of the cremaster muscle is derived from the

Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages (), the Archaic peri ...

noun (''kremastḗr''), meaning "suspender"; its plural, (''kremastēres''), was used by

Galen Aelius Galenus or Claudius Galenus ( el, Κλαύδιος Γαληνός; September 129 – c. AD 216), often Anglicized as Galen () or Galen of Pergamon, was a Greek physician, surgeon and philosopher in the Roman Empire. Considered to be one of ...

in the sense of "cremaster muscle".
in Liddell & Scott (1940), ''

A Greek–English Lexicon ''A Greek–English Lexicon'', often referred to as ''Liddell & Scott'' () or ''Liddell–Scott–Jones'' (''LSJ''), is a standard lexicographical work of the Ancient Greek language originally edited by Henry George Liddell Henry George L ...

'', Oxford: Clarendon Press.

Additional images

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

References

External links

* - "Inguinal Region, Scrotum and Testes: Layers of the Spermatic Cord" {{Authority control Muscles of the torso Scrotum