Urogenital System
Male Internal Urethral Sphincter (Posterior Part)
Sphincter internus urethrae masculinae
Read moreStructure/Morphology
The male internal urethral sphincter is a circular sphincter muscle consisting entirely of smooth muscle.
Key Features/Anatomical Relations
The internal urethral sphincter represents the junction between the urinary bladder (superiorly) and the urethra (inferiorly).
Function
This sphincter is under involuntary control and is tonically contracted due to sympathetic innervation from the lumbar plexus. During urination, the pelvic splanchnic nerves (parasympathetic) cause the internal urethral sphincter to relax allowing urine to pass from the bladder to the urethra.
