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The detrusor muscle, also known as the detrusor urinae muscle, is a smooth muscle found in the wall of the bladder. It is responsible for the contraction of the bladder during urination. The detrusor muscle is under autonomic control, receiving input from both the sympathetic and parasympathetic nervous systems. While the sympathetic nervous system causes relaxation of the detrusor muscle, the parasympathetic nervous system, specifically the pelvic nerve, stimulates its contraction, initiating the process of urination. This interplay between the two systems helps regulate bladder function and maintain urinary control.
| Characteristics | Values |
|---|---|
| Definition | Smooth muscle found in the wall of the bladder |
| Function | Contracts during urination to release urine |
| Control | Autonomic |
| Neurological control | Parasympathetic – pelvic nerve (S2-S4) |
| Neurotransmitter | Acetylcholine |
| Receptors | M2, M3, M4 |
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What You'll Learn
The detrusor muscle is made of smooth muscle cells
The detrusor muscle, also known as the detrusor urinae muscle, muscularis propria of the urinary bladder, or simply muscularis propria, is a smooth muscle found in the wall of the bladder. It is composed of smooth muscle cells that are arranged in three layers: longitudinal, circular, and longitudinal again from the innermost to the outermost layer. This unique arrangement of muscle fibres allows the bladder to stretch and expand in response to the presence of urine.
The primary function of the detrusor muscle is to contract during urination, pushing urine out of the bladder and into the urethra. When the bladder is filling with urine, the detrusor muscle remains relaxed to allow for urine storage. This relaxation is maintained through sympathetic branches from the inferior hypogastric plexus. During urination, the parasympathetic nervous system stimulates the bladder to contract via the pelvic nerve fibres, specifically acting on the postganglionic M3 receptors.
The detrusor muscle fibres arise from the posterior surface of the body of the pubis in both sexes (musculi pubovesicales). In males, these fibres also originate from the adjacent part of the prostate, while in females, they attach to the front of the vagina. As these fibres pass up the inferior surface of the bladder, over its apex, and then descend along its fundus, they intersect with each other at the sides of the bladder, creating an oblique arrangement.
The detrusor muscle plays a crucial role in bladder function, and abnormalities or pathologies in this muscle can lead to urinary retention, incontinence, or a combination of both. In older adults over 60, the detrusor muscle may cause difficulties in completely emptying the bladder, resulting in uncomfortable urinary retention. Understanding the physiology and function of the detrusor muscle is essential for managing and treating bladder-related conditions effectively.
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The detrusor muscle contracts during urination
The detrusor muscle, also known as the detrusor urinae muscle, is a smooth muscle found in the wall of the bladder. The bladder is an organ of the urinary system, situated in the pelvic cavity, that collects and stores urine. The detrusor muscle contracts during urination to release urine.
The detrusor muscle is composed of smooth muscle cells (SMCs) that are organized into three sheets. Two longitudinal smooth muscle sheets surround a circular middle sheet. The muscle fibres are arranged randomly, giving the muscle a trabeculated appearance. During urination, these muscle fibres contract, causing the bladder to expel urine into the urethra.
The detrusor muscle is under autonomic control and is influenced by both the sympathetic and parasympathetic nervous systems. The parasympathetic nervous system, specifically the pelvic nerve (S2-S4), stimulates the detrusor muscle to contract during urination. This contraction is mediated by muscarinic receptors, which facilitate the release of neurotransmitters and induce the detrusor muscle to contract.
In addition to the parasympathetic input, the sympathetic nervous system also plays a role in regulating the detrusor muscle. The hypogastric nerve (T12-L2) causes relaxation of the detrusor muscle, promoting urine retention. This balance between the parasympathetic and sympathetic nervous systems helps maintain normal bladder function.
Distortions in the bladder wall during filling may be due to the activation of postganglionic parasympathetic neurons. These distortions can lead to involuntary contractions and are associated with overactive bladder (OAB). Therapeutic agents, such as muscarinic receptor antagonists, are used to treat OAB, but their exact mechanism of action is still being studied.
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The parasympathetic nervous system is responsible for normal bladder function
The detrusor muscle is a smooth muscle found in the wall of the bladder. It is responsible for the contraction of the bladder during urination, allowing urine to be released. The detrusor muscle is controlled by the autonomic nervous system, which includes both sympathetic and parasympathetic input. While the sympathetic nervous system relaxes the detrusor muscle to promote urine retention, the parasympathetic nervous system is responsible for its normal function.
The parasympathetic nervous system is a key component of the autonomic nervous system, which regulates involuntary bodily functions such as heart rate, digestion, and bladder control. In the context of bladder function, the parasympathetic nervous system, specifically the pelvic nerve (S2-S4), stimulates the contraction of the detrusor muscle, leading to micturition (urination). This contraction is a result of increased signals from the pelvic nerve, which cause the detrusor muscle to expel urine from the bladder into the urethra.
The normal function of the bladder involves a coordinated interplay between the parasympathetic and sympathetic nervous systems. While the parasympathetic system stimulates contraction of the detrusor muscle, the sympathetic system, via the hypogastric nerve (T12-L2), promotes relaxation of the detrusor muscle, allowing the bladder to store urine. This balance between contraction and relaxation ensures that urine is released during micturition and retained in the bladder at other times.
Additionally, sensory nerves play a crucial role in bladder function. These nerves are located in the bladder wall and detect the stretch of the bladder as it fills with urine. They transmit this information to the spinal cord, which then relays the signal to the parasympathetic nervous system, triggering the contraction of the detrusor muscle and initiating micturition when the bladder is full. This process, known as the bladder stretch reflex, is a primitive spinal reflex that is overridden during toilet training in infancy to give voluntary control over micturition.
Disturbances in the parasympathetic nervous system or its associated receptors can lead to bladder dysfunction. Changes in the receptor systems, such as those observed in pathological states, can impact normal bladder function. Therapeutic agents, such as muscarinic receptor antagonists, are used to treat overactive bladder conditions, although the exact mechanism of their therapeutic effect is still being studied.
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The detrusor muscle is the muscularis propria component of the bladder
The detrusor muscle, also known as the detrusor urinae muscle or the muscularis propria of the urinary bladder, is a smooth muscle found in the wall of the bladder. It is the muscularis propria component of the bladder. The bladder is an organ of the urinary system, situated in the pelvic cavity, and is responsible for collecting and storing urine.
The detrusor muscle is composed of smooth muscle cells (SMC) that are organised in three sheets. Two longitudinal smooth muscle sheets surround a circular smooth muscle sheet in the middle. This interlacing network of multidirectional smooth muscle fibres produces a trabeculated appearance. The detrusor muscle extends over much of the bladder body and base but is distinct from the smooth musculature of the ureter orifices/distal ureters, trigone, and urethra.
The primary function of the detrusor muscle is to contract during voiding events to expel urine from the bladder into the urethra. It remains relaxed to allow the bladder to store urine and contracts during urination to release urine. The parasympathetic nervous system is responsible for maintaining normal bladder function, including contracting the detrusor muscle and relaxing the bladder outlet during micturition. The pelvic nerve (S2-S4) sends signals to cause contraction of the detrusor muscle, stimulating micturition.
Distortions in the bladder wall during filling may be caused by the activation of sporadic populations of low-threshold postganglionic parasympathetic neurons. These distortions can lead to involuntary contractions and are associated with overactive bladder (OAB). In pathological states, changes in receptor systems can result in bladder dysfunction, and muscarinic receptor antagonists are a common therapeutic treatment for OAB.
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The detrusor muscle is controlled by the pelvic nerve
The detrusor muscle, also known as the detrusor urinae muscle, is a smooth muscle found in the wall of the bladder. It is responsible for controlling urination by relaxing to allow the bladder to store urine and contracting to release urine. The detrusor muscle is indeed under parasympathetic control, with the pelvic nerve (S2-S4) stimulating its contraction and initiating the process of micturition.
The pelvic nerve is a parasympathetic nerve that plays a crucial role in the neurological control of the bladder. It receives input from the autonomic and somatic arms of the nervous system, including the sympathetic hypogastric nerve (T12-L2) and the somatic pudendal nerve (S2-4). The pelvic nerve acts on the detrusor muscle by causing it to contract, which leads to the stimulation of micturition, or the release of urine. This contraction is a result of increased signals from the pelvic nerve to the detrusor muscle.
The detrusor muscle is composed of smooth muscle cells (SMCs) that are organized into three sheets. Two longitudinal smooth muscle sheets surround a middle, circular smooth muscle sheet. This unique structure allows the detrusor muscle to contract and relax effectively, controlling the release of urine from the bladder. The muscle fibres of the detrusor muscle arise from the posterior surface of the body of the pubis in both sexes and, in males, from the adjacent part of the prostate.
The function of the detrusor muscle is closely related to the urethral sphincter muscles. While the detrusor muscle contracts during urination to release urine, the urethral sphincter muscles envelop the urethra and control the flow of urine through their contraction. This coordination between the detrusor muscle and the urethral sphincters ensures the smooth and controlled release of urine from the bladder.
Disturbances in the normal functioning of the detrusor muscle can lead to bladder dysfunction. For example, in pathological states, changes in the receptor systems can occur, resulting in an overactive bladder. Additionally, a spinal cord transection can damage the parasympathetic outflow to the bladder, paralysing the detrusor muscle and leading to overflow incontinence.
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Frequently asked questions
The detrusor muscle is an interlacing network of multi-directional smooth muscle fibres that form 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 made of smooth muscle cells (SMC) organised in three sheets. Two longitudinal smooth muscle sheets surround a circular smooth muscle sheet in the middle.
The parasympathetic nervous system is responsible for maintaining normal bladder function. It contracts the detrusor muscle and stimulates micturition.
If the detrusor muscle is paralysed, it will be unable to contract. This can be caused by a spinal cord transection, which damages the parasympathetic outflow to the bladder. The bladder will then fill uncontrollably, leading to overflow incontinence.
