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The detrusor muscle, also detrusor urinae muscle, muscularis propria of the urinary bladder and (less precise) muscularis propria, is smooth muscle found in the wall of the bladder. The detrusor muscle remains relaxed to allow the bladder to store urine , and contracts during urination to release urine.
The walls of the bladder have a series of ridges, thick mucosal folds known as rugae that allow for the expansion of the bladder. The detrusor muscle is the muscular layer of the wall made of smooth muscle fibers arranged in spiral, longitudinal, and circular bundles. [8] The detrusor muscle is able to change its length.
The internal sphincter muscle of urethra: located at the bladder's inferior end and the urethra's proximal end at the junction of the urethra with the urinary bladder. The internal sphincter is a continuation of the detrusor muscle and is made of smooth muscle, therefore it is under involuntary or autonomic control.
[4] The external urethral sphincter is a striated muscle that allows voluntary control over urination. [5] The internal sphincter, formed by the involuntary smooth muscles lining the bladder neck and urethra, receives its nerve supply by the sympathetic division of the autonomic nervous system. [6]
The internal urethral sphincter is a urethral sphincter muscle which constricts the internal urethral orifice.It is located at the junction of the urethra with the urinary bladder and is continuous with the detrusor muscle, [1] [2] but anatomically and functionally fully independent from it. [3]
Female pelvic muscles Male pelvic muscles. The pelvic floor or pelvic diaphragm is an anatomical location in the human body, [1] which has an important role in urinary and anal continence, sexual function and support of the pelvic organs. [2] The pelvic floor includes muscles, both skeletal and smooth, ligaments and fascia.
Should the transitional cell carcinoma grow toward the inner surface of the bladder via finger-like projections, it is known as papillary carcinoma. Otherwise, it is known as flat carcinoma. [11] Either form can transition from non-invasive to invasive by spreading into the muscle layers of the bladder.
The urethra of an adult human female is 3-4 cm long. [4] The female urethra is located between the bladder neck to the external urethral orifice and is behind the symphysis pubis. [4] The urethral wall is composed of an inner epithelial lining, a sub-mucosa layer containing vascular supply, a thin fascial layer, and two layers of smooth muscle. [4]