Victor Forge
The pelvic floor muscles, along with the detrusor and urethral sphincter muscles, control the release of urine. The pelvic floor muscles support the bladder, bowel, and uterus, and give people the ability to control the release of urine. The detrusor muscle surrounds the bladder and contracts during urination to release urine. The urethral sphincter muscles envelop the urethra to control the flow of urine when they contract.
| Characteristics | Values |
|---|---|
| Muscle name | Detrusor muscle, Urethral sphincter muscles (internal and external) |
| Muscle type | Smooth muscle |
| Muscle location | Wall of the bladder, urethra |
| Muscle function | Controls the flow of urine by contracting and relaxing |
| Muscle control | Autonomic nervous system, Somatic nervous system |
| Pelvic floor muscles | Support the bladder, bowel, and uterus |
| Pelvic floor muscle function | Control the release of urine, faeces, and flatus |
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What You'll Learn
- The internal urethral sphincter is involuntary and surrounds the bladder opening
- The external urethral sphincter is voluntary and surrounds the urethra outside the bladder
- Urinary incontinence is the loss of bladder control
- Pelvic floor exercises can help control leakage from stress incontinence
- The nervous system, bladder muscle, sphincters and pelvic floor must be synchronised for bladder control
The internal urethral sphincter is involuntary and surrounds the bladder opening
The urethral sphincter is a muscular structure that regulates the outflow of urine from the bladder into the urethra. The internal urethral sphincter is involuntary and surrounds the bladder opening. It is located at the junction of the urethra with the urinary bladder and is continuous with the detrusor muscle. However, it is functionally independent from the detrusor muscle. The internal urethral sphincter is composed of smooth muscle and is controlled by the autonomic nervous system, specifically the sympathetic nervous system. This muscle is responsible for maintaining continence of urine, preventing involuntary urine leakage. It works in conjunction with the external urethral sphincter, which is under voluntary control.
The internal urethral sphincter is tonically contracted through sympathetic fibres travelling via the inferior hypogastric plexus and vesical nervous plexus. Specifically, it is controlled by the hypogastric nerve, primarily through the alpha-1 adrenergic receptor. During urination, signals arising in the pontine micturition centre inhibit the preganglionic neurons of this sympathetic pathway, allowing urine to pass. The internal urethral sphincter relaxes to enable urine to flow from the bladder into the urethra. This relaxation is a result of smooth muscle stretch activating stretch receptors in the bladder wall, triggering the micturition reflex.
The internal urethral sphincter is also associated with penile erection and plays a role in paruresis, a condition where an individual feels unable to urinate when they perceive themselves to be under observation. Additionally, in males, the internal urethral sphincter has the important function of preventing the flow of semen into the bladder during ejaculation. This is achieved through the contraction of the sphincter, which stops the reflux of semen into the bladder.
The pelvic floor muscles also play a crucial role in controlling the release of urine. They support the bladder and work in conjunction with the urethral sphincters to regulate urination. These muscles can be tightened to control the openings of the urethra, and they need to be relaxed for urination to occur. Pelvic floor muscles can be trained to improve bladder control, and their weakness or tightness can impact bladder function.
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The external urethral sphincter is voluntary and surrounds the urethra outside the bladder
The process of urination involves the coordination of various muscles and organs in the body. The bladder, a muscular organ shaped like a pyramid when empty, plays a crucial role in storing and releasing urine. It is surrounded by a smooth muscle called the detrusor muscle, which contracts during urination to expel urine. The detrusor muscle is under the control of the autonomic nervous system, specifically the parasympathetic nervous system, which stimulates the stretch receptors in the bladder wall when it is full of urine. This triggers the micturition reflex, or the urge to urinate.
The urethra, a tube through which urine exits the body, is surrounded by two sphincter muscles: the internal urethral sphincter and the external urethral sphincter. These muscles work together to control the flow of urine. The internal urethral sphincter, located at the opening of the bladder to the urethra, is involuntary and remains contracted to prevent urine leakage. When the bladder is full, it relaxes to allow urine to pass into the urethra.
The external urethral sphincter, on the other hand, is voluntary and surrounds the urethra outside the bladder. This means that it is under conscious control. For urination to occur, this muscle must be relaxed. It is composed of skeletal muscle and is controlled by the somatic nervous system. The external urethral sphincter is responsible for voluntary urine flow from the bladder to the urethra. Any damage to this muscle can lead to urinary incontinence.
In addition to the urethral sphincters, the pelvic floor muscles also play a crucial role in controlling urination. These muscles support the bladder, bowel, and uterus in women, and the bladder and bowel in men. They help to control the release of urine, faeces, and flatus. When contracted, they tighten the openings of the vagina, anus, and urethra, preventing the release of their contents. Relaxing the pelvic floor muscles allows for the passage of urine and faeces. Maintaining strong and healthy pelvic floor muscles is important for bladder control and sexual function in both men and women.
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Urinary incontinence is the loss of bladder control
The pelvic floor muscles are crucial for maintaining bladder control. They support the bladder, bowel, and, in women, the uterus. These muscles work with the deep abdominal, back, and diaphragm muscles to form the 'core', supporting the spine and controlling abdominal pressure. The pelvic floor muscles can be contracted to lift the internal organs of the pelvis and tighten the openings of the vagina, anus, and urethra. Relaxing these muscles allows for the passage of urine and faeces.
Urinary incontinence can occur when the pelvic floor muscles are weakened or damaged, affecting their ability to control the release of urine. Pregnancy and giving birth are common causes of pelvic floor muscle weakness, and obesity can also increase the risk of urine leakage by placing greater stress on the pelvic floor. Certain conditions, such as diabetes mellitus and other neurological issues, can contribute to incontinence as well.
There are several types of urinary incontinence: stress incontinence, urge incontinence, overflow incontinence, and total incontinence. Stress incontinence occurs when urine leaks out during activities that put pressure on the bladder, like coughing or laughing. It is often caused by weakened pelvic floor muscles or damage to the urethral sphincter. Urge incontinence is characterised by a sudden, intense urge to urinate, followed by leakage. It is typically due to overactivity of the detrusor muscle, which surrounds the bladder and controls urination. Overflow incontinence happens when the bladder cannot fully empty, resulting in frequent leaking. This type of incontinence is often caused by obstructions or blockages in the bladder. Lastly, total incontinence occurs when the bladder cannot store any urine, leading to constant urine passage or frequent leaking. It may be caused by birth defects, spinal injuries, or a fistula.
Treatment options for urinary incontinence vary depending on the type and cause. Non-surgical treatments include pelvic floor muscle exercises, reducing alcohol and caffeine intake, maintaining a healthy weight, and addressing any underlying conditions or medications that may contribute to incontinence. In some cases, surgery may be considered, such as sling procedures to reduce bladder pressure or strengthen the muscles that control urination.
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Pelvic floor exercises can help control leakage from stress incontinence
The urinary sphincter is a muscle that encircles the lowest part of the bladder, known as the neck. When contracted, it closes off the urethra, preventing urine from leaving the body. Conversely, when these muscles relax, urine can flow out of the bladder. Urinary incontinence, or the loss of bladder control, can occur when these muscles are damaged or weakened. This can manifest as urine leakage during activities like laughing, sneezing, or coughing.
Pelvic floor muscles play a crucial role in supporting the bladder, bowel, and uterus. Weakened or damaged pelvic floor muscles can lead to bladder leakage, bowel leakage, sexual issues, and even lower back pain. Pelvic floor exercises, such as Kegels, can help strengthen these muscles and improve bladder control. These exercises are suitable for both men and women and can be easily incorporated into a daily routine.
To perform Kegel exercises, identify the muscles used to stop urination and contract them as tightly as possible. Hold this contraction for a few seconds, relax, and then repeat. Gradually increase the duration of the hold to strengthen the pelvic floor muscles. It may take a few months of consistent practice before improvements in bladder control are noticeable.
In addition to Kegels, other exercises such as pilates, squats, and jumping rope can also strengthen the pelvic floor and reduce leakage. Lifestyle changes, such as maintaining a healthy weight, avoiding high-impact exercises, and managing constipation, can further help alleviate stress incontinence symptoms.
While pelvic floor exercises can be highly beneficial, it is important to note that overly tight pelvic floor muscles can also contribute to incontinence. In such cases, stretching exercises, yoga poses, and relaxation techniques may be recommended to ease muscle tension and improve bladder control.
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The nervous system, bladder muscle, sphincters and pelvic floor must be synchronised for bladder control
The process of urination is a complex one, requiring the coordination of multiple muscles and nerves. The bladder, sphincters, and pelvic floor all play a role in maintaining urinary control and must work in harmony.
The bladder is a hollow, muscular organ that stores urine produced by the kidneys. The lowest part of the bladder, known as the bladder neck, is encircled by a muscle called the urinary sphincter. This muscle remains contracted to seal the urethra and retain urine in the bladder. When the bladder is full, nerve signals are sent to the brain, creating the sensation of needing to urinate.
At this point, the nervous system, bladder muscle, sphincters, and pelvic floor must work in synchrony. The pelvic floor muscles, along with the abdominal wall muscles, can be contracted voluntarily to increase pressure on the bladder and prevent accidental urination. The pudendal nerves stimulate the pelvic floor muscles, and these nerves transmit sensory information about bladder fullness to the brain. The somatic nervous system provides voluntary control over the pelvic floor and external sphincter, enabling individuals to perform pelvic floor exercises to strengthen these muscles.
Additionally, the autonomic nervous system, which acts subconsciously, regulates the function of internal organs like the bladder. It consists of the sympathetic nervous system (activated during stress or danger) and the parasympathetic nervous system (activated during rest). These two systems have opposing effects on the bladder. The sympathetic nervous system, through the hypogastric nerves, promotes urine retention by relaxing the detrusor muscle. On the other hand, the parasympathetic nervous system, via the pelvic nerves, stimulates micturition by contracting the detrusor muscle and relaxing the internal sphincter.
When an individual decides to urinate, the external urethral sphincter, a skeletal muscle under voluntary control, relaxes, and the bladder wall muscles contract to push urine out through the urethra. Any damage or weakening of these muscles or nerves can lead to urinary incontinence, the loss of bladder control.
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Frequently asked questions
The urethral sphincter is a muscular structure that regulates the outflow of urine from the bladder.
Yes, there are two types of urethral sphincter muscles: the external urethral sphincter and the internal urethral sphincter.
The external urethral sphincter is a voluntary muscle that must be relaxed for urination to occur.
Damage to the urethral sphincter muscles can cause urinary incontinence, which is the loss of urine control or the inability to hold urine until you reach a bathroom.
