The Micturition Reflex | Bladder Nerve Supply | Renal Physiology

Summary

This video provides a concise explanation of the micturition reflex, the process by which the bladder empties when full. It covers the anatomy of the urinary system, including the bladder, urethra, and key muscles involved in bladder control. The video explains the neural control of micturition, highlighting the roles of the pelvic, hypogastric, and pudendal nerves. It also discusses common bladder dysfunctions, such as overflow incontinence, overactive bladder, and detrusor-sphincter dyssynergia. With simple explanations and a clear structure, this video is a quick and effective resource for understanding bladder physiology and its disorders.

Takeaways

• 😀 The micturition reflex is responsible for emptying the bladder when it reaches a certain pressure threshold.
• 😀 The bladder consists of the kidneys, calyces, ureters, bladder body, neck, and urethra. The bladder's structure is crucial in the micturition process.
• 😀 The detrusor muscle in the bladder contracts to increase pressure, which is essential for urination.
• 😀 The internal urethral sphincter is involuntary and maintains continence by preventing urine flow when bladder pressure is lower.
• 😀 The external urethral sphincter is voluntary and is controlled by higher brain centers, allowing for conscious control of urination.
• 😀 The micturition reflex is controlled by three main nerves: the pelvic nerves (sensory and parasympathetic), the hypogastric nerve (sympathetic), and the pudendal nerve (external sphincter control).
• 😀 Parasympathetic fibers in the pelvic nerves contract the detrusor muscle and relax the internal sphincter to initiate urination.
• 😀 Sympathetic fibers via the hypogastric nerve relax the detrusor and contract the internal sphincter, aiding bladder storage.
• 😀 The reflex is self-regenerative, getting stronger and more frequent as the bladder fills. Eventually, it leads to bladder emptying once the reflex is strong enough.
• 😀 Disorders like atonic bladder, automatic bladder, and brain lesions above the pons can interfere with the normal micturition reflex, leading to issues like overflow incontinence, frequent urination, and loss of inhibitory control.

Q & A

What is the micturition reflex?

The micturition reflex is the process by which the bladder empties once it reaches a certain level of filling. The bladder stretches, triggering the reflex, which leads to contraction of the detrusor muscle and relaxation of the internal urethral sphincter, allowing urine to be expelled.

What are the key structures involved in micturition?

The key structures include the kidney, calyces, ureter, bladder, and urethra. The bladder has a body that fills with urine and a neck that leads to the urethra. The detrusor muscle in the bladder wall contracts to increase pressure during urination.

How does the bladder prevent urine from flowing backward into the ureters?

The detrusor muscle compresses the portion of the ureter that passes through the bladder wall, preventing backflow of urine into the ureter when the bladder fills and its pressure increases.

What is the role of the pelvic, hypogastric, and pudendal nerves in micturition?

The pelvic nerves carry sensory and parasympathetic fibers, triggering the detrusor muscle to contract and the internal sphincter to relax. The hypogastric nerve (sympathetic) relaxes the detrusor and contracts the internal sphincter to store urine. The pudendal nerve controls the external sphincter, allowing voluntary control.

What happens during the micturition reflex as the bladder fills?

As the bladder fills, stretch receptors in the posterior urethra detect the increased pressure. Sensory signals are sent to the sacral spinal cord, triggering parasympathetic fibers to contract the detrusor and relax the internal sphincter. The reflex becomes more frequent and intense as the bladder continues to fill.

How does voluntary micturition occur?

Voluntary micturition occurs when the brain overrides the inhibitory effect on the pontine micturition center. The brain signals the release of inhibition, causing contraction of the abdominal muscles to increase bladder pressure, resulting in the reflexive contraction of the detrusor muscle and relaxation of the sphincters.

What is an atonic bladder, and what causes it?

An atonic bladder occurs when the sensory nerves are damaged, preventing the detection of bladder stretch. This disrupts the micturition reflex, leading to overflow incontinence where the bladder fills to capacity and urine leaks out.

What is an automatic bladder, and what causes it?

An automatic bladder results from damage to the spinal cord above the sacral level, while the sacral reflex arc remains intact. Initially, the reflex is suppressed, but as it recovers, it may become exaggerated, leading to frequent urination or an overactive bladder.

What is detrusor-sphincter dyssynergia?

Detrusor-sphincter dyssynergia occurs when both the detrusor muscle and external sphincter contract at the same time, despite a desire to void. This leads to difficulty emptying the bladder, often resulting in a small amount of urine being released.

What happens if there is a brain lesion above the pons in relation to micturition?

A brain lesion above the pons can impair the inhibitory control over the pontine micturition center, causing the bladder to empty too quickly and frequently, even with small volumes of urine. This results in uncontrollable micturition.