Cremaster muscle

The cremaster muscle is a muscle that covers the testis and the spermatic cord.

Cremaster muscle
The cremaster muscle appears as a thin layer just superficial to the tunica vaginalis.
Details
OriginInternal Oblique
InsertionTunica vaginalis
ArteryCremasteric artery
NerveGenital branch of genitofemoral nerve
Actionsraise and lower the scrotum
Identifiers
Latinmusculus cremaster
TA98A04.5.01.018M
A09.3.04.003
TA22374, 3617
FMA21531
Anatomical terms of muscle

Structure

In human males, the cremaster muscle is a thin layer of striated muscle found in the inguinal canal and scrotum between the external and internal layers of spermatic fascia, surrounding the testis and spermatic cord. 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 muscle, just superior to the inguinal canal, 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 underneath the testis.

Blood supply

The cremaster muscle is supplied by the cremasteric artery which is a branch of inferior epigastric artery.

Nerve supply

The cremaster muscle is innervated from the genital branch of the genitofemoral nerve. It receives distinctly different innervation and vascular supply in comparison to the internal oblique.

Development

The cremaster develops to its full extent only in males; in females it is represented by only a few muscle loops.

In female humans, the cremaster muscle is smaller and is found on the round ligament.

In rats, it has been shown that cremaster muscles developed from the gubernacular bulb.[1]

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. It does this by increasing or decreasing the exposed surface area of the surrounding tissue, allowing faster or slower dissipation of body heat.

The cremaster muscle is an involuntary muscle and contraction can occur during arousal which can prevent injury to the testicles during sex. Contraction also occurs during ejaculation.[2]

Retraction can also occur 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.

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.[3][4]

Etymology

The name of the cremaster muscle is derived from the Ancient Greek noun κρεμαστήρ (kremastḗr), meaning "suspender"; its plural, κρεμᾰστῆρες (kremastēres), was used by Galen in the sense of "cremaster muscle".[5]

Additional images
  • The scrotum
  • The right testis, exposed by laying open the tunica vaginalis

References
  1. Hrabovszky, Z.; Pilla, N. D.; Yap, T.; Farmer, P. J.; Hutson, J. M.; Carlin, J. B. (2002). "Role of the gubernacular bulb in cremaster muscle development of the rat". The Anatomical Record. 267 (2): 159–165. doi:10.1002/ar.10092. PMID 11997885.
  2. Shafik, A. et al. J. Sexual Medicine 4:1022-1027, 2007
  3. Baty, John A. (5 May 1956). "Cremasteric cramp with testicular retraction". British Medical Journal. 1 (4974): 1014–1015. doi:10.1136/bmj.1.4974.1014. ISSN 0959-8138. PMC 1979762. PMID 13304412.
  4. Mori, Ryan; Sandip Vasavada; Diana Baker; Edmund Sabanegh Jr (July 2011). "Treatment of debilitating cremasteric synkinesia With intracremasteric botulinum-a toxin injections". Urology. Cleveland, OH: Glickman Urological and Kidney Institute. 78 (1): 214–216. doi:10.1016/j.urology.2011.03.011. ISSN 0090-4295. PMID 21601247. Retrieved 11 March 2012.
  5. κρεμαστήρ, in Liddell & Scott (1940), A Greek–English Lexicon, Oxford: Clarendon Press.
  • Anatomy photo:36:07-0102 at the SUNY Downstate Medical Center - "Inguinal Region, Scrotum and Testes: Layers of the Spermatic Cord"
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