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The detrusor muscle, which forms the walls of the bladder, is responsible for controlling the bladder. The bladder is a hollow muscular organ that lies in front of the pelvis, behind the pubic bone. It has four layers, the outermost of which is continuous with the peritoneum, and the innermost of which is the internal mucosa. The detrusor muscle contracts during urination to push urine out of the bladder and into the urethra, and relaxes to allow the storage of urine. The bladder is under neurological control, with input from both the autonomic and somatic nervous systems. In addition to the detrusor muscle, the urethral sphincter, which has both internal and external components, also plays a crucial role in controlling the flow of urine.
| Characteristics | Values |
|---|---|
| Main muscle controlling bladder | Detrusor muscle |
| Location | Forms the walls of the bladder |
| Composition | Smooth muscle fibres oriented in multiple directions |
| Function | Contracts during urination to push urine out of the bladder and into the urethra; relaxes to allow the storage of urine in the bladder |
| Control | Autonomic nervous system, specifically the parasympathetic nervous system via the pelvic nerve fibres |
| Pathology | Can lead to urinary retention, incontinence, or a combination of both |
| Secondary muscle controlling bladder | Urethral sphincter |
| Location | Deep perineal pouch |
| Composition | Internal urethral sphincter is composed of smooth muscle; external urethral sphincter is composed of skeletal muscle |
| Function | Internal urethral sphincter controls involuntary urine flow from the bladder to the urethra; external urethral sphincter controls voluntary urine flow |
| Pathology | Damage to the urethral sphincter can lead to urinary incontinence |
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What You'll Learn
- The detrusor muscle contracts to push urine out of the bladder
- The internal urethral sphincter controls involuntary urine flow
- The external urethral sphincter controls voluntary urine flow
- Pelvic floor exercises can help control stress incontinence
- The bladder's stretch reflex can cause involuntary urination
The detrusor muscle contracts to push urine out of the bladder
The detrusor muscle is a smooth muscle that makes up the wall of the bladder. It is responsible for the bladder's ability to contract and relax. When the bladder is empty, the detrusor muscle is relaxed, allowing urine to fill the bladder. As the bladder fills, the detrusor muscle stretches to accommodate the increasing volume of urine.
At the same time, the parasympathetic fibres inhibit the internal urethral sphincter, causing it to relax and allowing for the bladder to empty. The internal urethral sphincter is composed of smooth muscle and controls involuntary urine flow from the bladder to the urethra. The external urethral sphincter, on the other hand, is made of skeletal muscle and controls voluntary urine flow.
The detrusor muscle's ability to contract and relax is essential for normal urinary function. If the detrusor muscle malfunctions, it can lead to issues such as urinary retention or incontinence. For example, an overactive detrusor muscle can contract when a person is not ready to urinate, causing a sudden and strong urge to urinate. On the other hand, if the detrusor muscle is underactive and does not contract when it should, it can result in urinary retention, making it difficult to empty the bladder completely.
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The internal urethral sphincter controls involuntary urine flow
The urethral sphincter is a complex of muscles that encircle the urethra and control the flow of urine. It is divided into two types: the internal urethral sphincter and the external urethral sphincter. The internal urethral sphincter is located at the junction of the urethra and the urinary bladder. It is composed of smooth muscle and is under involuntary or autonomic control. This means that the internal sphincter regulates involuntary control of urine flow from the bladder to the urethra.
The internal urethral sphincter is a continuation of the detrusor muscle, which is the primary muscle responsible for contracting during urination to push urine out of the bladder and into the urethra. When the bladder is full, stretch receptors in its muscular wall stimulate a parasympathetic nervous system response, resulting in the contraction of the detrusor muscle and relaxation of the internal urethral sphincter. This allows urine to flow from the bladder into the urethra. The internal urethral sphincter is under involuntary control, and its tonic contraction is maintained by sympathetic supply from the lower thoracic and upper lumbar segments of the spinal cord.
The external urethral sphincter, on the other hand, controls voluntary urine flow. It is located in the deep perineal pouch, at the bladder's distal inferior end in females, and inferior to the prostate in males. Unlike the internal sphincter, the external sphincter is made of skeletal muscle and is under voluntary control of the somatic nervous system. During the voiding phase of micturition, the external sphincter relaxes to allow urine to pass through the urethra. However, it can also voluntarily contract to stop the flow of urine.
Damage to either the internal or external urethral sphincter can lead to urinary incontinence. Incompetence or dysfunction of the urethral sphincter can cause stress urinary incontinence, which is a common problem. This can be due to weak pelvic floor muscles, intrinsic sphincter damage, or damage to the surrounding nerves and tissue. Childbirth, obesity, and age are risk factors for women, while prostate surgery and radiation therapy are risk factors for men.
In males, the internal urethral sphincter has an additional function of preventing the flow of semen into the bladder during ejaculation. Retrograde ejaculation can occur if the internal sphincter fails to adequately contract.
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The external urethral sphincter controls voluntary urine flow
The bladder is a complex organ with several muscles and nerves working together to control the flow of urine. The bladder is surrounded by the detrusor muscle, which contracts to excrete urine and relaxes to hold urine. The detrusor muscle is controlled by the autonomic nervous system.
The urethra is the passage through which urine exits the body. The urethral sphincter is a muscular structure that regulates the outflow of urine from the bladder into the urethra. There are two urethral sphincters, the external and internal urethral sphincters. The internal urethral sphincter is composed of smooth muscle and is not under voluntary control. It regulates involuntary control of urinary flow from the bladder to the urethra.
The external urethral sphincter, on the other hand, is under voluntary control. It is made of skeletal muscle and is innervated by the pudendal nerve, which provides voluntary control over micturition. The external urethral sphincter controls voluntary urine flow from the bladder to the urethra. When the external urethral sphincter is relaxed, urine can flow out of the bladder through the urethra. When it contracts, it prevents the release of urine.
Damage or weakening of the external urethral sphincter can lead to urinary incontinence, which is the loss of bladder control. Stress urinary incontinence is a common issue, caused by stress or damage to the sphincters or surrounding muscles. In women, childbirth, obesity, and age can be risk factors, while in men, prostate surgery and radiation therapy can damage the sphincter and cause stress incontinence.
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Pelvic floor exercises can help control stress incontinence
The bladder is a hollow, muscular organ that stores urine. The bladder wall is made up of detrusor muscle, which contracts to release urine and relaxes to store urine. The detrusor muscle is under the control of the autonomic system. The pelvic floor muscles provide support for the bladder, bowel, and core. Weak pelvic floor muscles can lead to bladder leakage.
Pelvic floor exercises, also known as Kegel exercises, can help prevent urine leakage and improve bladder control. These exercises strengthen the pelvic floor muscles, which support the bladder and prevent urine leakage. Kegel exercises are especially beneficial for individuals with stress incontinence, a condition where stress or damage to the sphincters or surrounding muscles causes involuntary urine leakage.
To perform Kegel exercises, individuals can start by identifying their pelvic floor muscles, which can be done by trying to stop the flow of urine while sitting on the toilet. Once the pelvic floor muscles are identified, individuals can perform quick contractions of these muscles before and during actions that can cause incontinence, such as jumping, coughing, or sneezing. This helps reduce urine leakage.
For women, Kegel balls can be inserted into the vagina to help tone the pelvic floor muscles. These devices are held in place by the pelvic floor muscles and can be worn for gradually increasing periods, starting from a few minutes per day. For men, Kegel exercises can help improve incontinence, manage prostate pain, and address issues related to erectile function and ejaculation.
It is important to note that Kegel exercises should be performed correctly and consistently to achieve results. Overdoing these exercises can lead to overly tight pelvic floor muscles, which can also cause incontinence. Seeking guidance from a qualified pelvic floor physical therapist can help individuals ensure proper form and avoid potential issues.
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The bladder's stretch reflex can cause involuntary urination
The bladder is a hollow organ that functions as a reservoir for the storage and periodic elimination of urine. The bladder's walls are made up of three layers of smooth muscle, known as the detrusor muscle. This muscle allows the bladder to contract to excrete urine or relax to hold urine. The primary function of the detrusor muscle is to contract during urination to push the urine out of the bladder and into the urethra. When the bladder is empty, the detrusor muscle relaxes to allow the storage of urine.
The detrusor muscle is under autonomic control. The parasympathetic nervous system stimulates the muscarinic stretch receptors in the bladder through the pelvic nerve fibres. When urine fills the bladder, the M3 receptors located within the bladder become stretched and stimulated, leading to the contraction of the detrusor muscle for urination. This is known as the bladder's stretch reflex.
During the stretch reflex, the parasympathetic fibres also inhibit the internal urethral sphincter, causing it to relax and allowing for bladder emptying. The internal urethral sphincter is a ring of smooth muscle surrounding the bladder neck, which is the outlet from the bladder into the urethra. This sphincter controls involuntary urine flow from the bladder to the urethra. Any damage to this muscle can lead to urinary incontinence.
Involuntary urination can occur when the bladder contracts uncontrollably, a condition known as urge incontinence. This can be caused by detrusor muscle pathology, such as abnormalities or overactivity, or by damage to the internal urethral sphincter. Detrusor muscle pathology can lead to urinary retention, incontinence, or a combination of both. Abnormalities of the detrusor muscle, if left untreated, can lead to deterioration of the upper urinary tracts.
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Frequently asked questions
The detrusor muscle controls the bladder. It is a smooth muscle that makes up the walls of the bladder and allows the bladder to contract to excrete urine or relax to hold urine.
The detrusor muscle is under autonomic control and is composed of smooth muscle. The primary function of the detrusor muscle is to contract during urination to push the urine out of the bladder and into the urethra.
Abnormalities of the detrusor muscle can lead to urinary retention, incontinence, or a combination of both. Urinary incontinence is the loss of bladder control. It can range from releasing a small amount of urine when you laugh or sneeze to having the sudden urge to urinate without having enough time to get to a bathroom.
