Micturition Reflex

Edited By Irshad Anwar | Updated on Jul 02, 2025 06:44 PM IST

The micturition reflex diagram explains how the body controls urine release from the bladder. This is an important process in the waste removal and maintenance of the fluid and electrolyte balance of the body. As part of the Class 11 chapter Excretory Products and Their Elimination, in biology studying this diagram helps students understand how the brain and nerves work together with the bladder during the micturition process.

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What is the Micturition Reflex?
Labelled Diagram of Micturition Reflex
Stages of Micturition
The Micturition Reflex Process
Recommended Video on Micturition

Micturition Reflex - Diagram and Process: Definition, Steps, Phases, Disorders

What is the Micturition Reflex?

The micturition reflex is how the body is controlled to allow urine to be released from the bladder. When the bladder is filled, the increased volume is detected by stretch receptors in the walls and will signal down the spinal cord and the brain that it requires emptying. Along with the decision to urinate, it can also be initiated by the relaxation of the internal and external sphincters of the urethra along with the contraction of the detrusor muscle of the bladder to allow urine out.

Labelled Diagram of Micturition Reflex

Micturition Reflex

Visual Description: It generally includes the bladder, the urethra, the nerves, and the associated muscles that show an interaction in the process of urination.

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Stages of Micturition

Storage Phase: The urine is stored inside the bladder, and the sphincter muscles are contracted not to let it be released.

Voiding Phase: As the levels inside the bladder rise, the nerves get stimulated, and the message is forwarded to the brain. The brain replies that implies the contract of the bladder. The process is to let the urine start flowing through the urethra.

The Micturition Reflex Process

Micturition is the voiding of urine from the urinary bladder.

Filling of the Urinary Bladder

It is a condition where the urinary bladder is filled with urine. When there is a filling of urine in the bladder wall of the urinary bladder is stretched.

Stretch receptors in the urinary bladder sense the rise in its volume and form impulses which are transmitted to the nervous system.

At the point of capacity of the bladder, the stretch receptors send afferent impulses through the pelvic nerve into the spinal.

The stimulus in the stretch receptors produces sensory impulses which are transmitted to the central nervous system.

Afferent Impulses to the Spinal Cord

The sensory impulses as a result of the stretch receptors of the bladder travel via the pelvic nerve and reach the sacral region of the spinal cord.

The impulses that arrive in the bladder enter an integration centre, which is the spinal cord.

Efferent Impulses to the Bladder

Motor efferent impulses are sent from the spinal cord through the pelvic nerve back to the bladder.

The efferent impulses stimulate the detrusor muscle to lead to its contraction.

The Detrusor Muscle Contracts

The contraction of the detrusor muscle increases pressure in the bladder.

This pressure pushes the urine into the urethra and out of the body.

Relaxation of the Internal Urethral Sphincter

There is also an opening of the internal urethral sphincter, which has an involuntary type of control.

The relaxation of the involuntary sphincter will form a passage through which urine can flow from the bladder into the urethra.

Stimulation of Receptors

There shall be a stimulation of the stretch receptors within the urethra when urine flows.

These stretch receptors send further afferent impulses back to the spinal cord, which also serves to reinforce the micturition reflex.

Inhibition of the Pudendal Nerve

Through the relay in the spinal cord, the sensory stimulus can be transmitted further to the brain to issue commands and concomitantly inhibit signals transmitted by the pudendal nerve.

Through this inhibition, it relaxes the external urethral sphincter and releases the urine.

Relaxation of the External Sphincter

Upon relaxation of the external sphincter, the bladder voids urine through the urethra to the external environment.

This can be aided by the voluntary contractions of the musculature of the walls of the abdomen, which increase the intra-abdominal pressure that aids in the micturition.

Self-Regenerative Nature of The Reflex

The micturition reflex is self-renewable in a way that the initial contraction of the bladder causes greater stimulation of the stretch receptors.

This goes on as a continuous process until the bladder has been emptied, and total micturition has been achieved.

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Frequently Asked Questions (FAQs)

1. What is Micturition?

The process by which the urinary bladder voids its urine.

2. What is Neural Control of Micturition?

The control of micturition is neural, and it is mediated by the micturition reflex, involving responses from the bladder to the brain.

3. What are some common disorders found to be associated with micturition and their treatments?

It is found with some frequency that urinary incontinence, urinary retention, and overactive bladder are other common disorders and their treatments primarily include behavioural therapies, medications, and even surgery.

4. What are the most commonly used tests to diagnose micturition problems?

It generally comprises the use of urinalysis, urodynamic studies, ultrasound, and MRI.

5. What's new in the treatment of micturition disorders?

New drugs, minimally invasive surgical procedures, and sequences of ongoing clinical trials for the future appear promising.

6. How does the parasympathetic nervous system influence the micturition reflex?

The parasympathetic nervous system stimulates the contraction of the detrusor muscle and relaxation of the internal urethral sphincter. This action facilitates the emptying of the bladder during urination.

7. What is the role of the sympathetic nervous system in the micturition reflex?

The sympathetic nervous system helps maintain continence by promoting relaxation of the detrusor muscle and contraction of the internal urethral sphincter. This action helps prevent involuntary urination between voiding episodes.

8. What is the role of the pelvic floor muscles in the micturition reflex?

The pelvic floor muscles support the bladder and urethra. They help maintain continence by contracting to prevent urine leakage and relax during urination to allow urine flow. Weakness in these muscles can lead to urinary incontinence.

9. What is the role of neurotransmitters in the micturition reflex?

Neurotransmitters like acetylcholine and norepinephrine play crucial roles in the micturition reflex. Acetylcholine stimulates bladder contraction, while norepinephrine promotes relaxation. The balance of these and other neurotransmitters helps regulate the reflex.

10. How does the cystometrogram (CMG) test help in understanding the micturition reflex?

A cystometrogram measures bladder pressure and volume during filling and emptying. It helps assess the function of the detrusor muscle, bladder capacity, and the presence of involuntary contractions, providing insights into the micturition reflex and potential abnormalities.

11. What is the difference between the storage phase and the voiding phase of the micturition cycle?

The storage phase involves the gradual filling of the bladder with urine while maintaining continence. The voiding phase is when the micturition reflex is activated, leading to the contraction of the detrusor muscle and relaxation of the sphincters to expel urine.

12. What is the significance of the micturition threshold?

The micturition threshold is the point at which the bladder's stretch receptors send strong enough signals to trigger the micturition reflex. When this threshold is reached, the urge to urinate becomes difficult to suppress voluntarily.

13. How does the process of urination differ between infants and adults?

In infants, the micturition reflex is entirely involuntary and occurs when the bladder is full. As children develop, they learn to voluntarily control the external urethral sphincter, allowing them to inhibit the reflex and choose when to urinate.

14. What is urge incontinence and how does it relate to the micturition reflex?

Urge incontinence is the involuntary loss of urine associated with a sudden, strong desire to urinate. It occurs when the micturition reflex is overactive or when there's a failure in the brain's ability to inhibit the reflex, leading to involuntary bladder contractions.

15. How does the spinal cord contribute to the micturition reflex?

The spinal cord acts as a relay station in the micturition reflex. It receives sensory information from the bladder and sends this information to the brain. It also transmits motor signals from the brain to the muscles involved in urination.

16. How does the brain control the micturition reflex?

The brain controls the micturition reflex through the pontine micturition center (PMC) in the brainstem. The PMC receives signals about bladder fullness and coordinates the contraction of the detrusor muscle and relaxation of the urethral sphincter to allow urination. The cerebral cortex can voluntarily inhibit or initiate this reflex.

17. What is the difference between voluntary and involuntary control of urination?

Involuntary control is managed by the autonomic nervous system and occurs automatically when the bladder is full. Voluntary control involves conscious decision-making by the cerebral cortex, allowing us to override the reflex and choose when to urinate.

18. What role does the detrusor muscle play in the micturition reflex?

The detrusor muscle is a smooth muscle in the bladder wall that contracts during urination to expel urine. Its contraction is a crucial step in the micturition reflex, increasing pressure within the bladder to force urine out through the urethra.

19. How do stretch receptors in the bladder wall contribute to the micturition reflex?

Stretch receptors in the bladder wall detect when the bladder is full. As the bladder fills with urine, these receptors are stimulated and send signals to the spinal cord and brain, initiating the micturition reflex when a certain threshold is reached.

20. What is the function of the internal and external urethral sphincters?

The internal urethral sphincter is a smooth muscle that involuntarily controls urine flow, while the external urethral sphincter is a skeletal muscle under voluntary control. Both sphincters work together to prevent urine leakage and allow controlled urination.

21. What is the micturition reflex?

The micturition reflex, also known as the urination reflex, is an involuntary process that controls the emptying of the urinary bladder. It involves a complex coordination of smooth muscle contractions and relaxations, triggered by nerve signals when the bladder reaches a certain level of fullness.

22. How does the bladder's elasticity contribute to the micturition reflex?

The bladder's elasticity allows it to expand as it fills with urine without significantly increasing internal pressure. This property helps prevent premature activation of the micturition reflex and allows for the storage of larger volumes of urine.

23. What is the difference between stress incontinence and urge incontinence in relation to the micturition reflex?

Stress incontinence involves urine leakage due to physical stress on the bladder (e.g., coughing, sneezing) and is not directly related to the micturition reflex. Urge incontinence is caused by an overactive micturition reflex, leading to sudden, strong urges to urinate and potential leakage.

24. What is the significance of post-void residual urine in relation to the micturition reflex?

Post-void residual urine is the amount of urine left in the bladder after urination. A large residual volume may indicate an ineffective micturition reflex, possibly due to detrusor muscle weakness, nerve damage, or bladder outlet obstruction.

25. How does the micturition reflex differ in males and females?

The basic micturition reflex is similar in males and females, but anatomical differences can affect its function. Females generally have a shorter urethra, which can lead to a higher risk of urinary tract infections. Males have an additional internal sphincter at the bladder neck, controlled by the sympathetic nervous system.

26. How does caffeine consumption affect the micturition reflex?

Caffeine is a diuretic that increases urine production and can stimulate the bladder, potentially leading to more frequent activation of the micturition reflex. It may also increase the urgency and frequency of urination in some individuals.

27. What is the role of urodynamic testing in evaluating the micturition reflex?

Urodynamic testing assesses bladder function, urine flow, and pressure during filling and emptying. It helps evaluate the effectiveness of the micturition reflex, identify abnormalities in bladder function, and guide treatment decisions for various urinary disorders.

28. What is the role of antidiuretic hormone (ADH) in relation to the micturition reflex?

Antidiuretic hormone (ADH) indirectly affects the micturition reflex by regulating water reabsorption in the kidneys. Higher levels of ADH lead to increased water reabsorption, reducing urine production and the frequency of the micturition reflex.

29. How does the position of the body affect the micturition reflex?

Body position can influence the micturition reflex. Standing or sitting upright increases abdominal pressure, which can enhance the efficiency of bladder emptying. Lying down may delay the sensation of bladder fullness and the urge to urinate.

30. How does aging affect the micturition reflex?

Aging can lead to decreased bladder capacity, reduced muscle tone in the bladder and pelvic floor, and changes in nerve sensitivity. These factors can result in more frequent urination, increased urgency, and a higher risk of incontinence in older adults.

31. How do urinary tract infections (UTIs) affect the micturition reflex?

UTIs can irritate the bladder lining, making it more sensitive to stretching. This can lead to an overactive micturition reflex, causing frequent and urgent needs to urinate, even when the bladder is not full.

32. What is the role of the pudendal nerve in the micturition reflex?

The pudendal nerve innervates the external urethral sphincter and pelvic floor muscles. It plays a crucial role in voluntary control of urination by allowing conscious contraction of these muscles to prevent urination or relaxation to allow it.

33. How does bladder outlet obstruction affect the micturition reflex?

Bladder outlet obstruction, such as that caused by an enlarged prostate, can interfere with the micturition reflex. It may lead to incomplete bladder emptying, increased urinary frequency, and a weakened urine stream as the bladder works harder to overcome the obstruction.

34. What is detrusor-sphincter dyssynergia and how does it affect the micturition reflex?

Detrusor-sphincter dyssynergia is a condition where the detrusor muscle and urethral sphincter contract simultaneously instead of coordinating properly. This disrupts the normal micturition reflex, leading to difficulty in urination and potential bladder damage.

35. How do anticholinergic medications affect the micturition reflex?

Anticholinergic medications block the action of acetylcholine, which is involved in bladder contraction. These drugs can help treat an overactive bladder by reducing involuntary detrusor muscle contractions and increasing bladder capacity.

36. What is the role of baroreceptors in the micturition reflex?

Baroreceptors in the bladder wall detect changes in pressure as the bladder fills. They send signals to the brain about bladder fullness, contributing to the sensation of needing to urinate and helping to trigger the micturition reflex when a certain pressure threshold is reached.

37. How does spinal cord injury affect the micturition reflex?

Spinal cord injuries can disrupt the normal communication between the brain and the bladder, leading to various micturition disorders. Depending on the level and severity of the injury, this can result in an overactive bladder, urinary retention, or a loss of sensation and control over urination.

38. What is the difference between nocturia and enuresis, and how do they relate to the micturition reflex?

Nocturia is the need to wake up at night to urinate, which may be due to an overactive micturition reflex or other factors. Enuresis, or bedwetting, occurs when the micturition reflex activates during sleep without waking the individual, often due to delayed development of reflex control or other underlying issues.

39. How does the micturition reflex change during pregnancy?

During pregnancy, increased pressure on the bladder from the growing uterus can lead to more frequent activation of the micturition reflex. Hormonal changes can also affect bladder function, potentially leading to increased urinary frequency and urgency.

40. What is the role of interstitial cells of Cajal in the micturition reflex?

Interstitial cells of Cajal in the bladder wall act as pacemakers, generating spontaneous electrical activity. They play a role in coordinating bladder smooth muscle contractions and may contribute to the initiation and modulation of the micturition reflex.

41. How do diuretic medications affect the micturition reflex?

Diuretic medications increase urine production by the kidneys, leading to more frequent filling of the bladder. This results in more frequent activation of the micturition reflex and increased urinary frequency.

42. What is the relationship between the micturition reflex and bladder training techniques?

Bladder training techniques aim to improve control over the micturition reflex by gradually increasing the intervals between urinations. This helps increase bladder capacity and improve voluntary control over the urge to urinate.

43. How does chronic pelvic pain syndrome affect the micturition reflex?

Chronic pelvic pain syndrome can lead to hypersensitivity of the bladder and surrounding tissues. This may result in an overactive micturition reflex, causing frequent and urgent needs to urinate even when the bladder is not full.

44. What is the role of glycosaminoglycans in the bladder lining and how do they relate to the micturition reflex?

Glycosaminoglycans form a protective layer on the bladder lining, preventing irritants in urine from stimulating underlying nerve endings. Damage to this layer can lead to increased bladder sensitivity and potentially an overactive micturition reflex.

45. How does vesicoureteral reflux affect the micturition reflex?

Vesicoureteral reflux, where urine flows backward from the bladder into the ureters, can interfere with normal bladder filling and emptying. This may lead to incomplete emptying during urination and potentially alter the timing and effectiveness of the micturition reflex.

46. What is the relationship between fluid intake and the micturition reflex?

Fluid intake directly affects urine production and bladder filling rate. Higher fluid intake leads to more frequent activation of the micturition reflex, while lower intake may reduce urinary frequency but can also lead to more concentrated urine, potentially irritating the bladder.

47. How do benign prostatic hyperplasia (BPH) treatments affect the micturition reflex?

BPH treatments aim to reduce prostate size or relax prostatic smooth muscle, alleviating obstruction of the urethra. This can improve urine flow and reduce the frequency and urgency of the micturition reflex by allowing more complete bladder emptying.

48. What is the role of C-fiber afferents in the micturition reflex?

C-fiber afferents are sensory nerve fibers in the bladder wall that are typically silent during normal filling but become active during inflammation or irritation. Their activation can lead to an overactive micturition reflex and increased urinary urgency and frequency.

49. How does bladder augmentation surgery affect the micturition reflex?

Bladder augmentation surgery increases bladder capacity by adding a patch of intestinal tissue to the bladder wall. This can reduce the frequency of the micturition reflex by allowing the bladder to hold more urine before reaching the threshold for activation.

50. What is the relationship between sleep disorders and the micturition reflex?

Sleep disorders can disrupt the normal circadian rhythm of urine production and the sleep-related inhibition of the micturition reflex. This can lead to increased nighttime urination (nocturia) or bedwetting (nocturnal enuresis) in some individuals.

51. How do alpha-blockers affect the micturition reflex in men with benign prostatic hyperplasia?

Alpha-blockers relax the smooth muscle in the prostate and bladder neck, reducing urethral resistance. This can improve urine flow and reduce the frequency and urgency of the micturition reflex by allowing more complete bladder emptying.

52. How does diabetic neuropathy affect the micturition reflex?

Diabetic neuropathy can damage the nerves controlling the bladder, leading to reduced sensation of bladder fullness and impaired control of the micturition reflex. This can result in incomplete bladder emptying, overflow incontinence, or difficulty initiating urination.

53. What is the relationship between pelvic organ prolapse and the micturition reflex?

Pelvic organ prolapse can alter the position and function of the bladder and urethra, potentially interfering with normal bladder emptying and the micturition reflex. This may lead to incomplete emptying, urinary retention, or changes in the sensation of bladder fullness.

54. How do botulinum toxin injections affect the micturition reflex in overactive bladder treatment?

Botulinum toxin injections into the detrusor muscle temporarily paralyze the muscle fibers, reducing involuntary contractions. This can help manage an overactive micturition reflex by increasing bladder capacity and reducing the frequency and urgency of urination.