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The detrusor muscle, also known as detrusor urinae muscle, is a smooth muscle that forms part of the bladder wall. The muscle is responsible for the contraction of the bladder during urination, and it relaxes to allow the bladder to store urine. The detrusor muscle is innervated by the autonomic nervous system, receiving input from both the autonomic and somatic branches of the nervous system. During urination, parasympathetic nerves cause contraction of the detrusor muscle, while sympathetic nerves act to relax the muscle and inhibit contraction, allowing the bladder to fill with urine. This complex neurological control of the detrusor muscle ensures the proper storage and release of urine.
| Characteristics | Values |
|---|---|
| Nerve controlling detrusor muscle | Pelvic nerve (parasympathetic) / Hypogastric nerve (sympathetic) |
| Function | Controls contraction of the detrusor muscle during urination |
| Location | Found in the wall of the bladder |
| Type of muscle | Smooth muscle |
| Relaxation | Allows the bladder to store urine |
| Contraction | Releases urine during urination |
| Age considerations | In older adults, the detrusor muscle may cause issues in voiding the bladder |
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What You'll Learn
The detrusor muscle contracts during urination
The detrusor muscle is a smooth muscle that forms the muscular component of the bladder wall. It is innervated by the autonomic nervous system, receiving input from both the autonomic and somatic branches of the nervous system. The autonomic nervous system controls the detrusor muscle through sympathetic and parasympathetic pathways.
During urination, the detrusor muscle contracts to release urine from the bladder. This contraction is mediated by the parasympathetic nervous system, specifically the pelvic nerve (S2-S4). The pelvic nerve acts on postganglionic M3 receptors to stimulate contraction of the detrusor muscle, facilitating micturition.
At rest, the detrusor muscle remains relaxed to allow the bladder to store urine. This relaxation is maintained by the sympathetic nervous system, which inhibits detrusor contraction and promotes urine retention. Sympathetic signals are transmitted through the hypogastric nerve (T12-L2) and act on the bladder outlet and urethral sphincter to prevent involuntary bladder emptying.
The somatic nervous system also plays a role in bladder function through the pudendal nerve (S2-4). This nerve innervates the external urethral sphincter, providing voluntary control over micturition. The coordination between the autonomic and somatic nervous systems ensures the proper storage and release of urine.
In addition to the role of the nervous system, sensory (afferent) nerves in the bladder wall detect stretch and transmit signals to the spinal cord, indicating the need to urinate when the bladder is full. These afferent signals trigger a spinal reflex that initiates detrusor contraction, known as the bladder stretch reflex. However, in adults, this reflex is overridden by higher centres in the brain to allow voluntary control over urination.
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The role of parasympathetic nerves
The detrusor muscle is a smooth muscle found in the wall of the bladder. It remains relaxed to allow the bladder to store urine, and contracts during urination to release urine. The role of parasympathetic nerves in the detrusor muscle is complex and involves various neural pathways.
The parasympathetic nervous system plays a crucial role in stimulating the contraction of the detrusor muscle during urination. Specifically, the pelvic nerve (S2-S4), also known as the pelvic splanchnic nerve, acts on postganglionic M3 receptors to cause contraction of the detrusor muscle. This contraction stimulates micturition, the act of urination. The pelvic nerve is part of the autonomic nervous system's parasympathetic branch, which provides inhibitory input to the detrusor muscle during bladder filling.
During bladder filling, the parasympathetic innervation of the detrusor muscle is inhibited to prevent involuntary bladder emptying. This inhibition is organised by urethral reflexes, specifically the guarding reflex, which is activated by bladder afferent activity conveyed through the pelvic nerves. The lateral pons, or the 'pontine storage centre', may also play a role in facilitating these reflexes or controlling the urethral sphincter.
In addition, the detrusor muscle is also influenced by sympathetic nerves, which work in conjunction with the parasympathetic nervous system to regulate bladder function. During bladder filling, sympathetic nerves inhibit the contraction of the detrusor muscle, allowing the bladder to relax and accommodate urine. This inhibition is mediated by the hypogastric nerve (T12-L2) and the pudendal nerve, which promote urine retention.
Abnormalities in the detrusor muscle or its innervation can result in incontinence or voiding dysfunction. For example, in a condition known as a reflex bladder, the parasympathetic system initiates detrusor contraction in response to bladder wall stretch, leading to involuntary bladder emptying. Understanding the role of parasympathetic nerves in the detrusor muscle is crucial for managing bladder function and treating related disorders.
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The role of sympathetic nerves
The detrusor muscle is a smooth muscle found in the wall of the bladder. It remains relaxed to allow the bladder to store urine and contracts during urination to release urine. The detrusor muscle is innervated by the autonomic nervous system, which receives input from both the autonomic (sympathetic and parasympathetic) and somatic arms of the nervous system.
The sympathetic nervous system plays a crucial role in inhibiting the contraction of the detrusor muscle, allowing the bladder to fill with urine. Specifically, the hypogastric nerve (T12-L2) is responsible for causing relaxation of the detrusor muscle, promoting urine retention. During bladder filling, sympathetic firing inhibits the contraction of the detrusor muscle, preventing involuntary bladder emptying. This is known as the guarding reflex.
The sympathetic nervous system also modulates neurotransmission in bladder ganglia. During urine storage, bladder distension stimulates sympathetic outflow in the hypogastric nerve to the bladder outlet and the pudendal outflow to the external urethral sphincter. These responses occur through spinal reflex pathways and promote continence.
In summary, the sympathetic nervous system, through its inhibitory effect on the detrusor muscle, plays a vital role in maintaining urinary continence and controlling the filling and storage of urine in the bladder. This inhibitory effect is essential for normal bladder function and prevents involuntary bladder contractions and unwanted urine leakage.
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The detrusor muscle is relaxed when the bladder is filling
The detrusor muscle is a smooth muscle that forms the muscular wall of the bladder. It is innervated by the autonomic nervous system, receiving input from both the autonomic and somatic arms of the nervous system. The autonomic nervous system controls involuntary processes, such as the heart rate and digestion, and is further divided into the sympathetic and parasympathetic nervous systems.
The detrusor muscle contracts during urination to release urine. This contraction is caused by parasympathetic nerves, specifically the pelvic nerve (S2-S4), which acts on postganglionic M3 receptors. The pelvic nerve is part of the parasympathetic nervous system, which stimulates micturition.
When the bladder is filling, the detrusor muscle is relaxed to allow the bladder to store urine. This relaxation is maintained by sympathetic branches from the inferior hypogastric plexus, which cause the muscle to relax and promote urine retention. The hypogastric nerve (T12-L2) is part of the sympathetic nervous system, which is responsible for inhibiting detrusor muscle contraction and modulating neurotransmission in bladder ganglia.
In addition to the autonomic nervous system, the somatic nervous system also plays a role in bladder function. The somatic nervous system controls voluntary processes, such as skeletal muscle movement. In the case of bladder function, the somatic nervous system provides voluntary control over micturition through the pudendal nerve (S2-4). This nerve innervates the external urethral sphincter, allowing for the voluntary control of urination.
The complex interaction between the autonomic and somatic nervous systems, as well as the parasympathetic and sympathetic nerves, ensures the proper functioning of the detrusor muscle during bladder filling and urination.
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The detrusor muscle and incontinence
The detrusor muscle is a smooth muscle that forms the wall of the bladder. It contracts during urination to release urine and remains relaxed to allow the bladder to store urine. The detrusor muscle is innervated by the autonomic nervous system, receiving input from both the autonomic (sympathetic and parasympathetic) and somatic arms of the nervous system.
The sympathetic nervous system stimulates the relaxation of the detrusor muscle, promoting urine retention. This occurs via sympathetic branches from the inferior hypogastric plexus. During urination, parasympathetic nerves cause the contraction of the detrusor muscle. The somatic nervous system, via the pudendal nerve, provides voluntary control over urination.
The detrusor muscle can malfunction in two main ways: by being overactive or underactive. An overactive detrusor muscle contracts when not needed, leading to urge incontinence, where urine is lost involuntarily. This can be caused by a sensitized detrusor muscle, in combination with a borderline urethral-vesical pressure differential, resulting in involuntary urine loss without warning. In children, detrusor muscle has less contractility and more passive stiffness compared to adults, which can also lead to incontinence. In older adults, the detrusor muscle may cause issues in voiding the bladder, resulting in uncomfortable urinary retention.
Detrusor muscle pathology can lead to urinary retention, incontinence, or a combination of both. Abnormalities of the detrusor muscle can result in the deterioration of the upper urinary tracts. In women, detrusor overactivity with poor contractility can lead to overflow incontinence, which is common in the aging female population. Treatment of the underlying disease is the most effective approach in such cases, with conservative options like lifestyle modifications, pelvic floor exercises, and bladder training being the first steps.
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Frequently asked questions
The detrusor muscle, or detrusor urinae muscle, is a smooth muscle that forms 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 detrusor muscle is innervated by the autonomic nervous system, which includes both sympathetic and parasympathetic nerves.
The sympathetic nervous system, via the hypogastric nerve (T12-L2), causes relaxation of the detrusor muscle, promoting urine retention.
The parasympathetic nervous system, via the pelvic nerve (S2-S4), causes contraction of the detrusor muscle, stimulating urination.
