Final answer:
Stretching of the bladder causes several reflex actions for micturition, but it does not cause the excitation of sympathetic neurons to relax the internal urethral sphincter, as this activity actually suppresses detrusor muscle contraction. The correct answer to the question is option 2.
Step-by-step explanation:
Stretching of the bladder initiates a complex series of events known as the micturition reflex, which involves both involuntary and voluntary actions to facilitate urination. This reflex involves stretch receptors in the bladder wall that transmit nerve impulses to the sacral region of the spinal cord, activating parasympathetic neurons which cause contraction of the detrusor muscle of the bladder and the relaxation of the internal urethral sphincter. Concurrently, the somatic motor neurons to the external urethral sphincter are inhibited, resulting in its relaxation.
However, it is important to note that stretching of the bladder does not cause excitation of sympathetic neurons that would result in the relaxation of the internal urethral sphincter. Instead, the sympathetic nervous activity suppresses the contraction of the detrusor muscle during the filling of the bladder, thus maintaining continence. As the bladder fills and the need to void urine increases, the individual can initiate the process of urination voluntarily by relaxing the external urethral sphincter and allowing the detrusor muscle to contract.
The correct option that does not result from the stretching of the bladder is option 2) excitation of sympathetic neurons, causing the internal urethral sphincter to relax. This is because sympathetic activity actually works to inhibit the contraction of the detrusor muscle, as opposed to promoting sphincter relaxation during the micturition reflex.