MICTURITION REFLEX
When the urine collects in urinary bladder (about 150 ml), afferent parasympathetic nerves carry sensation from the stretch receptors in Internal Trigone to Sacral Spinal cord [ S2, S3, S4, lateral horn called SACRAL MICTURITION CENTRE]
Then the the efferent motor parasympathetic nerves (from Sacral Micturition Centre) stimulate detrusor smooth muscles of bladder wall generating the urge for micturition.
If you are not willing or not in a proper place the HIGHER CENTRES in the BRAIN (Paracentral Lobule in cerebral cortex, CORTICAL MICTURITION CENTRE) can suppress SACRAL MICTURITION CENTRE and thereby suppress contraction of detrusor muscles.
During filling of bladder at initial stage the sympathetic nerves make the INTERNAL URINARY SPHINCTER (smooth muscles) (at bladder neck, junction of prostatic urethra and lower end of bladder) contracted which helps filling. Once micturition reflex sets in, the internal sphincter is relaxed and urine enters prostatic (in female urethra) urethra.
But EXTERNAL SPHINCTER (Skeletal muscles) remains closed by SOMATIC SPINAL NERVES called PUDENDAL NERVE (coming from Anterior Horn cells of S2, S3, S4). This nerve is under the influence of higher centre (particularly PONTINE MICTURITION CENTRE). When you are comfortable to void urine, the pudendal nerve under the guidance of higher centre, relaxes EXTERNAL SPHINCTER, thus we can void urine.Please see the video:
When the urine collects in urinary bladder (about 150 ml), afferent parasympathetic nerves carry sensation from the stretch receptors in Internal Trigone to Sacral Spinal cord [ S2, S3, S4, lateral horn called SACRAL MICTURITION CENTRE]
Then the the efferent motor parasympathetic nerves (from Sacral Micturition Centre) stimulate detrusor smooth muscles of bladder wall generating the urge for micturition.
If you are not willing or not in a proper place the HIGHER CENTRES in the BRAIN (Paracentral Lobule in cerebral cortex, CORTICAL MICTURITION CENTRE) can suppress SACRAL MICTURITION CENTRE and thereby suppress contraction of detrusor muscles.
During filling of bladder at initial stage the sympathetic nerves make the INTERNAL URINARY SPHINCTER (smooth muscles) (at bladder neck, junction of prostatic urethra and lower end of bladder) contracted which helps filling. Once micturition reflex sets in, the internal sphincter is relaxed and urine enters prostatic (in female urethra) urethra.
But EXTERNAL SPHINCTER (Skeletal muscles) remains closed by SOMATIC SPINAL NERVES called PUDENDAL NERVE (coming from Anterior Horn cells of S2, S3, S4). This nerve is under the influence of higher centre (particularly PONTINE MICTURITION CENTRE). When you are comfortable to void urine, the pudendal nerve under the guidance of higher centre, relaxes EXTERNAL SPHINCTER, thus we can void urine.Please see the video:
No comments:
Post a Comment