BIOL 221 Lecture Notes - Lecture 6: Internal Sphincter Muscle Of Urethra, Urethral Sphincters, Urination
6 Mar 2020
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Document Summary
Micturition, also called urination, is initiated when distension of the bladder by the accumulation of urine (~300 ml) activates stretch receptors. Sensory impulses are sent to the sacral spinal cord where they result in parasympathetic impulses to cause contraction of the bladder and relaxation of the internal urethral sphincter. Simultaneous sensory input to brain allows conscious recognition of need to urinate and initiates conscious control of the external urethral sphincter. Reflexive contractions of bladder cease after about 1 minute if urine is not voided. The cycle begins again after an additional 200-300 ml of urine has accumulated. The maximum capacity is normally about 1000 ml after which a person has to urinate. Micturition (urination) disorders: incontinence, uti (urinary tract infection, urethritis, cystitis, pyelonephritis, renal calculi (kidney stones, anuria. Incontinence is the inability to control micturition voluntarily. It may arise due to damage to the spinal cord or upper motor neurons or damage to the urethral (urinary) sphincters.
