Internal sphincter muscle of urethra
Encyclopedia
The internal sphincter muscle of urethra is a urethral sphincter
muscle which constricts the internal urethral orifice
. It is the junction of the urethra
with the urinary bladder
. The muscle is made of smooth muscle
, so therefore it is under involuntary control. It is kept tonically contracted by lumbar splanchnic nerves (L1-L2) of the sympathetic nervous system
. During micturition it is relaxed via the parasympathetic nervous system
. This is the primary muscle for preventing the release of urine
.
Urethral sphincter
The term urethral sphincter refers to one of two muscles used to control the exit of urine in the urinary bladder through the urethra. The two muscles are the external urethral sphincter and the internal urethral sphincter...
muscle which constricts the internal urethral orifice
Internal urethral orifice
The internal urethral orifice is the opening of the urinary bladder into the urethra. It is placed at the apex of the trigonum vesicae, in the most dependent part of the bladder, and is usually somewhat crescent-shaped; the mucous membrane immediately behind it presents a slight elevation in males,...
. It is the junction of the urethra
Urethra
In anatomy, the urethra is a tube that connects the urinary bladder to the genitals for the removal of fluids out of the body. In males, the urethra travels through the penis, and carries semen as well as urine...
with the urinary bladder
Urinary bladder
The urinary bladder is the organ that collects urine excreted by the kidneys before disposal by urination. A hollow muscular, and distensible organ, the bladder sits on the pelvic floor...
. The muscle is made of smooth muscle
Smooth muscle
Smooth muscle is an involuntary non-striated muscle. It is divided into two sub-groups; the single-unit and multiunit smooth muscle. Within single-unit smooth muscle tissues, the autonomic nervous system innervates a single cell within a sheet or bundle and the action potential is propagated by...
, so therefore it is under involuntary control. It is kept tonically contracted by lumbar splanchnic nerves (L1-L2) of the sympathetic nervous system
Sympathetic nervous system
The sympathetic nervous system is one of the three parts of the autonomic nervous system, along with the enteric and parasympathetic systems. Its general action is to mobilize the body's nervous system fight-or-flight response...
. During micturition it is relaxed via the parasympathetic nervous system
Parasympathetic nervous system
The parasympathetic nervous system is one of the two main divisions of the autonomic nervous system . The ANS is responsible for regulation of internal organs and glands, which occurs unconsciously...
. This is the primary muscle for preventing the release of urine
Urine
Urine is a typically sterile liquid by-product of the body that is secreted by the kidneys through a process called urination and excreted through the urethra. Cellular metabolism generates numerous by-products, many rich in nitrogen, that require elimination from the bloodstream...
.