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. The PMC coordinates with other brain centers, including the medial frontal cortex, insular cortex, hypothalamus and periaqueductal gray (PAG). The PAG acts as a relay station for ascending bladder information from the spinal cord and incoming signals from higher brain areas.
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Micturition Reflex - Neural Control of Urination Animation Video.
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Physiology of Micturition
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The Urination Process
Transcription
Neural control of urination - micturition reflex. When the bladder is full, stretch receptors in the wall of the bladder send nerve impulses to the sacral region of the spinal cord. By way of a parasympathetic response, signals return to the bladder and stimulate contraction of the muscle of the bladder and relaxation of the internal urethral sphincter. This part of the reflex is involuntary and is predominant in infants and young children. As the central nervous system matures, it acquires voluntary control over the external urethral sphincter. Urination is controlled mainly by the micturition center in the pons. This center receives sensory signals from the bladder and communicates with the cortex about the appropriateness of urinating at the moment. At times when it's not convenient to urinate, the center sends back an inhibitory signal to keep the sphincters closed and prevent voiding. When you wish to urinate, this inhibition is removed; the spinal cord instructs the muscle of the bladder to contract and the sphincters to open to let the urine out.
Regulation
In humans and other mammals, neurons in the PMC send descending excitatory projections to spinally located parasympathetic neurons controlling the detrusor muscle of the bladder and inhibitory interneurons regulating Onuf's nucleus. Additionally, the PMC receives ascending input from the level of the lumbosacral spinal cord. During bladder filling, neurons within the PMC are turned off. However, at a critical level of bladder distention the afferent information arising from mechanoreceptors in the detrusor switches the PMC on and enhances its activity. This activation results in relaxation of the male or female external urethral sphincter and contraction of the bladder. While operating as a spino bulbospinal reflex arc, this pattern of activity is also elicited through the conscious desire to urinate.
References
- Fowler CJ, Griffiths D, de Groat WC. (June 9, 2008) "The neural control of micturition." Nature Reviews Neuroscience (6):453-66
- Kuipers R, Mouton LJ, Holstege G. (January 1, 2006) "Afferent projections to the pontine micturition center in the cat." The Journal of Comparative Neurology 494(1):36-53
- Sasaki M. (December 5, 2005) "Role of Barrington's nucleus in micturition". The Journal of Comparative Neurology 5;493(1):21-6
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This page was last edited on 8 February 2024, at 16:57