Micturition Reflex.ppt
- 2. Micturition • Micturition or urination is the process of emptying urine from the storage organ, namely, the urinary bladder. • The functional anatomy and nerve supply of urinary bladder are essential for the process of micturition. • The detrusor is the smooth or involuntary muscle of the urinary bladder wall. • The urethral muscles consist of the external and internal sphincter.
- 3. Micturition • 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. • The bladder normally accommodates up to 300-400 ml in adults. • When the bladder is distended (expanded) it sends signals to the brain, which is perceived as the 'full bladder' sensation.
- 4. Micturition / Urination • The process of Micturition is regulated by nervous signals, both from the somatic and the autonomic nervous system. • The autonomic nervous system comprises both the sympathetic and the parasympathetic nervous system. • The bladder has two states of function; the storage and emptying phases.
- 5. Micturition / Urination Reflex • The micturition reflex is a reflex pathway by which urination or micturition occurs. • This reflex is induced by the stimulation of stretch receptors present on the wall of the bladder and urethra. • The intra vesical pressure increases when the bladder collects about 300 to 400 mL of urine. • This stretches the wall of the urinary bladder and thus results in stimulation of stretch receptors and the creation of sensory impulses leading to urination. • In healthy adults, this process of micturition is under voluntary control.
- 7. Urinary Reflex Process • When the bladder is full, it sends the sensory signal to the brain for the process of emptying. The bladder emptying phase is called micturition, and • it involves the co-ordinated reflexes of the outer and inner urethral sphincter under somatic and sympathetic regulation, respectively. • At first, the afferent impulses or the sensory impulses from the receptors reach the sacral segments of spinal cord through the sensory fibres of the pelvic nerve (parasympathetic nerve). • The motor impulses created in the spinal cord run through the motor fibres of the pelvic nerve towards the bladder and the internal sphincter. • These motor impulses (efferent impulses) create contraction of the detrusor muscle and also the relaxation of the internal sphincter. Thus, the urine enters the urethra from the bladder.
- 8. Urinary Reflex Process • Once urine reaches the urethra, the stretch receptors present in the urethra are stimulated, and they send afferent impulses to the spinal cord through pelvic nerve fibres. • Now the impulses created from the spinal centres obstruct the pudendal nerve. This leads to the relaxation of the external sphincter, and micturition occurs. • Facilitatory centres for micturition are present in the pons, and some are even in the cerebral cortex. It facilitates micturition through spinal centres. • Inhibitory centres for micturition are present in the cerebral cortex and midbrain. It inhibits the micturition by repressing spinal micturition centres.
- 10. Urination Reflex • The micturition reflex process is self-regenerative. • This is because the initial contraction of the urinary bladder activates the stretch receptors to create an increase in sensory impulses from the urethra as well as the bladder. • These impulses, in turn, create a further increase in reflex contraction of the urinary bladder. • This cycle of events repeats until the force of contraction of the urinary bladder reaches the maximum, leading to the voiding of urine or the micturition process. • During micturition, the urine flow is facilitated by the increase in abdominal pressure. This is due to the voluntary contraction of the muscles in the abdomen.
- 11. Urination Reflex-control Higher Centers for Micturition • Spinal centers for micturition are present in sacral and lumbar segments. But, these spinal centers are regulated by higher centers. • The higher centers, which control micturition are of two types, inhibitory centers and facilitatory centers. Inhibitory centers for micturition • Centers in midbrain and cerebral cortex inhibit the micturition by suppressing spinal micturition centers. Facilitatory centers for micturition • Centers in pons facilitate micturition via spinal centers. Some centers in cerebral cortex also facilitate micturition.
- 12. Micturition Reflex • The micturition reflex process can be summarised as follows – • Filling of the urinary bladder • Stimulation of stretch receptors • Afferent impulses pass through the pelvic nerve and reach the spinal cord • Efferent impulses through the pelvic nerve • Contraction of the detrusor muscle and relaxation of the internal sphincter • The flow of urine into the urethra and stimulation of stretch receptors • Afferent impulses through the pelvic nerve • Inhibition of pudendal nerve • Relaxation of the external sphincter • Voiding of the urine or micturition