When the bladder is full of urine, stretch receptors in the bladder wall trigger the micturition reflex. The detrusor muscle that surrounds the bladder contracts. The internal urethral sphincter relaxes, allowing for urine to pass out of the bladder into the urethra. Both of these reactions are involuntary.
How does the micturition reflex affect urination?
This occurs once the bladder is distended to a significant degree. However impulses from the brain can inhibit this secondary action of the micturition reflex. This allows a person to find a suitable setting to urinate.
What are reflexes in the bladder?
Reflexes exist to promote micturition known as the “bladder-bladder reflex.” The bladder afferent nerves connect with sacral spinal cord interneurons ( Fig. 10.1 ). These interneurons synapse with preganglionic efferent parasympathetic nerves to complete this reflex pathway.
How does the brain control the micturition reflex?
In addition, the brain can also directly act on the external urtheral sphincter to maintain its contracted state and prevent urination despite the effects of the micturition reflex. When the situation is suitable, the higher centers can then relax the external urethral sphincter and stimulate the micturition reflex to commence urination.
How does micturition help with urinary incontinence?
During micturition, urinary flow is assisted by additional detrusor contractions and external sphincter relaxation which further lowers resistance to the passage of urine. The abdominal wall and pelvic floor musculature also participates by increasing the force on the bladder to help achieve complete emptying.
How does the bladder respond after being stimulated by the micturition reflex quizlet?
How does the urinary bladder respond to these stimuli? parasympathetic neurons from the spinal cord to the bladder are stimulated, and this causes the smooth muscle of the bladder wall to contract.
What happens in micturition reflex?
The micturition reflex involves a coordinated and sustained contraction of the detrusor muscle (the detrusor reflex) along with simultaneous relaxation of the urethra. Moreover, depending on the size of the bladder, the micturition reflex may also result in urine storage.
How is micturition reflex stimulated?
0:021:38Micturition Reflex - Neural Control of Urination Animation Video. - YouTubeYouTubeStart of suggested clipEnd of suggested clipNeural control of urination micturition reflex when the bladder is full stretch receptors in theMoreNeural control of urination micturition reflex when the bladder is full stretch receptors in the wall of the bladders sends nerve impulses to the sacral region of the spinal.
How does micturition reflex work what is automatic bladder?
3:106:24The Micturition Reflex | Bladder Nerve Supply | Renal Physiology - YouTubeYouTubeStart of suggested clipEnd of suggested clipOnce the mixture is reflex gets strong enough it causes another reflex through the pudendal nerveMoreOnce the mixture is reflex gets strong enough it causes another reflex through the pudendal nerve inhibiting the external sphincter to relax it followed by emptying of the bladder.
What is micturition reflex quizlet?
Definition of micturition. The process of filling the bladder until it reaches a threshold level at which the autonomic micturition reflex results in emptying of the bladder, or if it fails, the conscious desire to urinate. Smooth muscle that lines the bladder.
Why is micturition reflex important?
The act of micturition is an autonomic reflex at the level of the spinal cord. This reflex also helps to complete micturition when the act is voluntarily initiated, or when it follows a period of inhibition by the brain, by relaxing the external sphincter.
What stimulated the bladder?
A sustained bladder contraction is produced by stimulation of the pelvic nerves, and it is generally agreed that reflex activation of this pelvic nerve excitatory tract is responsible for the emptying bladder contraction of normal micturition and for the involuntary bladder contractions seen with various neurologic and ...
Where do impulses from the bladder go?
Impulses from the filling bladder are carried to the spinal cord via the pelvic and hypogastric nerves, whereas the pudendal and hypogastric nerves carry impulses from the neck of the bladder and the urethra.
What is the function of the afferents in the bladder?
In the absence of any other regulation, the afferents from the bladder and urethra to the midbrain and pons and the efferents to the spinal cord would act as an on-off switch, to cause either reflex voiding or storage depending only on the urine volume stored in the bladder. This means that during the filling or storage phase, the voiding reflex is off, but it is switched on to the highest level when the bladder is distended beyond a critical point, activating the tension receptors in the wall.
What is the pontine micturition center?
Pontine Micturition Center. The pontine micturition center (PMC) in the brainstem is activated via afferent signals from the urinary bladder as it is filling. This center sends inhibitory impulses to the spinal reflex arcs to enable bladder voiding. In the absence of any other regulation, the afferents from the bladder and urethra to ...
What is the micturition phase?
The micturition or emptying phase displays a coordinated relaxation of the inner and outer urethral sphincters, under sympathetic and somatic regulation respectively, with strong contractions of the detrusor muscle due to parasympathetic impulses . The distension of the urinary bladder wall causes wall tension to rise very slightly.
What is the detrusor in the bladder?
The detrusor is the smooth or involuntary muscle of the bladder wall. The urethral muscles consist of the external and internal sphincter. The internal sphincter and detrusor muscle are both under autonomic control. The external sphincter, however, is a voluntary muscle under the control of voluntary nerves.
What is the term for the relaxation of the striated sphincter?
Micturition is thus characterized by: relaxation of the striated sphincter (somatic innervation) relaxation of the smooth muscle sphincter and opening of the bladder neck (sympathetic innervation) detrusor contraction (parasympathetic innervation) The distension of the urinary bladder wall causes wall tension to rise very slightly.
What is the guarding reflex?
Urethral reflexes, called ‘the guarding reflex,’ also play a part in inhibiting involuntary bladder emptying during this process. The afferents are all conveyed through the pelvic nerves to initiate a spinal reflex.
How does the bladder control the brain?
The micturition reflex can also trigger a second reflex that inhibits the tonic contraction of the voluntary external urethral sphincter through impulses via the pudendal nerve. This occurs once the bladder is distended to a significant degree. However impulses from the brain can inhibit this secondary action ...
What is the function of the ureters in the bladder?
Filling of the Bladder and the Micturition Reflex. The ureters carry urine from the kidney to the bladder. It penetrates the detrusor muscle of the bladder wall, which can also compress the ureters during urination to prevents urine from the bladder emptying into the ureters (vesicoureteral reflux). As urine collects in the bladder, the pressure ...
Why does the bladder pass out when the situation is acceptable?
The bladder stores urine until the accumulated urine stretches the bladder to a significant degree to trigger the reflexes that will result in urination. With the relaxation of the external urethral sphincter, increase in abdominal pressure and contraction of the detrusor muscle, urine will be passed out when the situation is acceptable. This process seems quite simple but is made of up various phases that contribute to both voluntary and involuntary bladder control.
What muscle contractes and relaxes almost immediately causing sudden peaks and dips known as the micturi?
The detrusor muscle contract s and relaxes almost immediately causing sudden peaks and dips known as the micturition wave. As the bladder fills up further, the frequency and intensity of the micturition reflexes increase substantially. Eventually this leads to period of sustained contraction of the detrusor muscle which leads to ...
How does urine affect the spinal cord?
Stretch receptors in the bladder wall, internal urethral orifice and posterior urethra sends signal back to the spinal cord by the way of the sensory fibers of the pelvic nerve.
Where do motor impulses travel?
Motor impulses travel through the parsympathetic nerve fibers in the pelvic nerves (mainly from S2 and S3 of the sacral spinal cord) and synapse with short postganglionic nerves in the bladder wall. These nerves in turn innervate the detrusor muscle.
Can you prevent urination if you are urging?
Even though a person may voluntary prevent urination despite the urging, eventually the bladder has to be emptied or voluntary control measures will fail. In a suitable setting, a person increases the pressure on the bladder by contracting the abdominal muscles.
What is the function of the bladder?
The bladder is a hollow organ that functions as 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.
What is the process of urination?
Micturition, also known as urination, is the process of expelling urine from the bladder. The purpose of urination is to eliminate metabolic products and toxic wastes from the body that have been filtered from the blood by the kidneys. it is a complex mechanism that involves coordination by the sympathetic, parasympathetic and somatic nervous systems, and it is the higher centers within the brain that allow for urination to occur at the right time. Normal muscle tone, absence of physical obstructions and psychological inhibition are other important factors that play a role in this process.
How much urine does the detrusor hold?
A normal healthy adult bladder can hold anywhere from 300-500mL of urine for 2-5 hours.
What are the two components of the urinary tract?
The urinary tract comprises of two mutually dependent components: the upper tract, which contains the kidneys and ureters, and the lower tract consisting of the bladder and urethra. The lower tract is involved in the micturition reflex.
What are bladder reflexes?
These interneurons synapse with preganglionic efferent parasympathetic nerves to complete this reflex pathway. The bladder-bladder reflex is an excitatory one, which becomes activated by the sensing of a full bladder but is inhibited until it is socially appropriate to void. Interneurons activated by bladder afferent fibers also synapse with urethral parasympathetic efferent nerves to form a “bladder-urethral reflex” (Leng and Chancellor, 2005). This is an inhibitory reflex, which relaxes the smooth muscle of the proximal urethra and bladder outlet to open immediately before the onset of bladder contraction.
How does bladder distension affect the bladder?
Normally, bladder distension will cause low-level firing of afferent nerves. This will cause reflex inhibitory response to the bladder via the hypogastric nerve and stimulatory response to the external sphincter from the pudendal nerve. With further distension, myelinated A-delta fiber afferents are activated. Afferents travel up the spinal cord to the pontine micturition center. Here central input, mostly inhibitory, is received from suprapontine centers. If voiding is not desired, the voiding reflex can be interrupted. If voiding is desired, efferent output to the pelvic plexus at S2–S4 via the spinal cord is initiated. Ultimately, the stimulatory message is sent to the bladder via the pelvic nerve. At the same time, inhibitory messages are sent to the hypogastric and pudendal pathways to allow for relaxation of the sphincter mechanisms and coordinated voiding.
What is normal voiding?
This is a coordinated event characterized by relaxation of the striated urethral sphincter, contraction of the detrusor, opening of the vesical neck and urethra, and onset of urine flow ( Fig. 30-2 ). This reflex is integrated in the pontine micturition center, which is located in the rostral brainstem. Also, a sacral micturition center is located at S2–S4, through which the bladder can contract independently of cortical and pontine input. However, the pontine micturition center, through its neural pathways to the sacral micturition center, is responsible for coordinated and voluntary voiding. Both the autonomic and somatic nervous systems play a crucial role in lower urinary tract function. Normal voiding occurs when the bladder responds to threshold tension via its mechanoreceptors. To avoid a random occurrence, central nervous system inhibitory and facilitatory pathways are involved in coordination of urine storage and micturition.
What is the micturition reflex?
The micturition reflex is peripherally mediated by components of the somatic and the autonomic nervous systems. The bladder receives its motor innervation through the parasympathetic pelvic nerves. The principal nuclei innervating the urinary bladder of the cat consist of motor neurons located in the gray matter of the intermediolateral cell column of the sacral spinal cord and motor neurons in the ventral gray matter of the sacral spinal cord in the region of Onuf's nucleus. In humans, sacral nerve blocks have revealed that the detrusor nucleus has a rostral–caudal extension going from the S3 to S4 segment. The precise intramedullary location of detrusor motor neurons and their histological characteristics in the sacral spinal cord have not been described.
What is the term for a detrusor contraction without urethral relaxation?
Detrusor contraction without urethral relaxation is called reflex dyssynergia. 31.
Why do cats lick their mother's bladder?
This stimulation is crucial, because separation of the kittens from the mother results in urinary retention. The reason why the mother cat licks the perineum of the kittens is an interesting question that still remains to be answered. This perineal-to-bladder reflex is quite prominent during the first four postnatal weeks, after which it becomes less effective and usually disappears at 7-8 weeks postnatally, the approximate age of weaning. Although during this early postnatal period there is a weak supraspinal bladder reflex present ( Kruse and De Groat, 1990 ), the perineal-to-bladder reflex is so prominent that thoracic cord transections of the spinal cord did not abolish it. Thus, the perineal-to-bladder reflex is a sacral cord reflex. After 7-8 weeks the supraspinal bladder reflexes have replaced the perineal-to-bladder reflex. Transection of the spinal cord in older kittens or adult cats causes reemergence of perineally induced micturition within 1-2 weeks. In humans this spinal cord reflex system is functionally non-existent, except in patients with spinal cord transection rostral to the sacral cord. Thus, although in adult animals and humans pathways exist within the sacral cord that can produce bladder and sphincter contractions, they are usually not well coordinated and often dyssynergic. Bladder dyssynergia means that when the bladder contracts, the sphincter contracts also, preventing micturition.
How do neonates control voiding?
Sometime after the first year of life, the child begins to show some awareness of bladder evacuation and can begin to delay urination for a brief period by contracting the voluntary sphincter. For normal control, the detrusor reflex has to be inhibited by the higher centers above the level of the PMC. By 5 years of age, approximately 90% of children have volitional control of voiding. The remaining 10% have a more infantile or immature pattern, with involuntary detrusor activity that occurs between voluntary voids producing frequency, urgency, and occasionally urge incontinence and nocturnal enuresis. Most of these children gradually have inhibition of the detrusor reflex and resolution of enuresis by the onset of puberty. Treatment is almost always reassurance and observation.
What is the process of micturition?
One may also ask, what is the process of micturition? Micturition (urination) is the process of urine excretion from the urinary bladder. Most of the time, the bladder (detrusor muscle) is used to store urine. As it fills, the rugae distend and a constant pressure in the bladder (intra-vesicular pressure) is maintained. This is known as the stress-relaxation phenomenon.
What is the term for the contraction of the detrusor muscle without urethral relaxation?
Detrusor contraction without urethral relaxation is called reflex dyssynergia.
What is the process of emptying urine from the storage organ?
Micturition or urination is the process of emptying urine from the storage organ, namely, the urinary bladder. The detrusor is the smooth or involuntary muscle of the bladder wall. The process of emptying the urine into the urethra is regulated by nervous signals, both from the somatic and the autonomic nervous system.
Where is the pontine micturition center located?
The Pontine micturition center (PMC, also known as Barrington's nucleus) is a collection of neuronal cell bodies located in the rostral pons in the brainstem involved in the supraspinal regulation of micturition. When activated, the PMC relaxes the urethral sphincter allowing for micturition to occur.
What would happen if the initial level of sympathetic tone were not present?
If the initial level of sympathetic tone were not present, then only vasoconstriction could occur as a result of sympathetic division activity.
What is dual innervation?
Dual innervation means that visceral effectors are innervated by preganglionic axons from both parasympathetic and sympathetic (ANS) divisions.
Where are sympathetic neuron cells located?
-The neuron cell bodies are located in the lateral horns of their spinal cord segments. -The sympathetic trunk ganglia house sympathetic ganglionic neuron cell bodies.
Which system contains both motor and sensory neurons?
The enteric nervous system contains both motor and sensory neurons.
What is the autonomic tone?
Autonomic tone is the continual activity of both parasympathetic and sympathetic divisions of the autonomic nervous system.
What are the two ways to relax the bladder?
1) Relaxation of external & internal urethral sphincters. 2) Contraction of abdominal muscles to help empty bladder. 3) Stimulation of micturition reflex for contraction of bladder wall.
What does it mean when you fill your bladder?
Filling of the urinary bladder stretches the bladder wall, stimula ting the stretch receptors , starting the stretch reflex.