**Core Concept**
The atonic bladder, also known as a flaccid bladder, is a condition characterized by a loss of bladder muscle tone, leading to incomplete bladder emptying and urinary retention. This condition is often associated with neurological disorders or spinal cord injuries that affect the autonomic nervous system controlling bladder function.

**Why the Correct Answer is Right**
The correct answer is related to the disruption of the parasympathetic nervous system's control over the bladder, which is responsible for promoting bladder contraction and relaxation. The parasympathetic nervous system, specifically the sacral spinal cord, stimulates the detrusor muscle to contract and the internal urethral sphincter to relax, facilitating urination. In the case of an atonic bladder, this parasympathetic input is impaired, leading to a loss of bladder muscle tone.

**Why Each Wrong Option is Incorrect**
* **Option A:** This is not a correct answer, as it does not directly relate to the cause of an atonic bladder. While detrusor overactivity can be associated with overactive bladder, it is not the cause of an atonic bladder.
* **Option B:** This is not a correct answer, as it is actually a characteristic of an overactive bladder, not an atonic bladder. In an overactive bladder, the detrusor muscle contracts involuntarily, leading to frequent urination.
* **Option C:** This is not a correct answer, as it is a type of urinary incontinence characterized by the involuntary leakage of urine during physical activity, not a cause of an atonic bladder.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that atonic bladder is often associated with spinal cord injuries or neurological disorders affecting the autonomic nervous system. This can include conditions such as multiple sclerosis, Parkinson's disease, or spinal cord trauma.

**Correct Answer: B. Detrusor overactivity.**